Haritha

Structural Organization In Animals

Introduction To Animal Tissues

A group of cells similar in structure, function, and origin is called tissue. In a tissue, cells may be dissimilar in structure and function, but they are always similar in origin.

• The term “animal tissue” was coined by Bichat.
• Bichat is known as the “father of histology.”
• The term “histology” was coined by Mayer (1819).
• The study of tissues is called histology, Along with cytology (study of cells), histology was placed under the term “microscopic anatomy.”
• Marcello Malpighi is considered to be the founder of microscopic anatomy.

Based On Their Location And Function, Animal Tissues Are Classified Into Four Types:

Epithelial Tissue

Cells of the epithelium are set very close to each other, separated by thin films of extracellular material. Neighboring cells are held together by cell junctions. The epithelial tissue rests on a non-cellular basement membrane, which separates it from the underlying connecting tissue.

The Basement Membrane Is A Non-Cellular Membrane Made Up Of Two Layers: The upper thin layer is called the basal lamina, made up of glycoproteins and mucopolysaccharides and secreted by epithelial cells and the lower thick fibrous layer is called the reticular lamina made of reticular fibers and collagen fibers, which are a part of underlying connective tissue.

• Blood vessels are absent in the epithelial tissue. Materials are exchanged between epithelial cells and ves¬sels of the connective tissues by diffusion across the basement membrane.
• The epithelial tissue is classified into simple and compound epithelium.

Read and Learn More NEET Biology Notes

Specialized Junctions Between Epithelial Cells: To provide mechanical support to tissues, the plasma membrane of the adjacent epithelial cells is modified to form structures called as intercellular junctions.

Fight Junctions (Zonula Occludens): They help to prevent substances from leaking across the tissue. Plasma membranes in the apical parts become tightly packed together or are even fused.

Interdigitations: These are interesting, finger-like processes of the cell membranes of the adjacent cells.

Intercellular Bridges: These are minute projections that arise from adjacent cell membranes. They make contact with one another.

Gap Junctions: they facilitate the cells to communicate with each other by connecting the cytoplasm of adjoining cells, for rapid transfer of ions, small molecules, and sometimes big molecules also.

Intermediate Junctions (Zonula Adherens): These usually occur just below tight junctions. The intercellular space at these places contains a clear, low electron-density fluid. There is a dense plaque-like structure on the cytoplasmic side of each plasma membrane from which fine microfilaments of actin (protein) extend into the cytoplasm. There are no intercellular filaments between the adjacent cell membranes. There is an adhesive material at this point. They probably serve anchoring functions.

Desmosomes (Macula Adherens): They perform cementing to keep the neighboring cells together. These are like zonula adherens but are thicker and stronger and have disc-like junctions. They have intercellular proteins. The plaque-like structures (protein plates) are much thicker. The microfilaments that extend from microfilaments are called tonofibrils. Desmosomes serve anchoring functions.

Hemidesmosomes (single-sided desmosomes) are similar to desmosomes, but the thickening of the cell membrane is seen only on one side. Hemidesmosomes join epithelial cells to the basal lamina (outer layer of basement membrane).

Simple Epithelium

• Simple epithelium is formed of a single layer of cells.
• The adjacent cells are held together by means of a desmosome, resting on the basement membrane.
• Simple epithelium occurs mainly on secretory and absorptive surfaces.
• It helps in nutrition, excretion, and secretion, but not in protecting the underlying tissue.

1. Squamous Epithelium
   • It consists of a layer of thin, flat, scale-like cells with prominent nuclei.
   • The cells have irregular boundaries that fit closely into those of neighboring cells.
   • It forms the inner lining of lung alveoli and blood vessels (endothelium).
   • It is also known as pavement or tessellated epithelium.
2. Cuboidal Epithelium
   • It has cells that are polygonal in outline, but ap-pear cuboidal in vertical section.
   • It lines small salivary and pancreatic ducts and thyroid vesicles.
   • The cells participate in secretion, excretion, and absorption.
   • The cells of cubical epithelium in absorptive surfaces often bear microvilli on their free ends. This gives a brush-like appearance to their free border. They are, therefore, called brush-bordered cubical epithelial cells, for example, in the proximal tubules of kidneys.
   • Microvilli greatly increase the area of the free surface of the cell and thereby enhance absorption.
3. Columnar Epithelium
   • It is characterized by the presence of tall cells that are shaped like polygonal columns.
   • The nucleus is usually located at the base of the cell.
   • Columnar epithelium covers the inner surface of the intestine, stomach, and gall bladder. It also occurs in gastric and intestinal glands.
   • Its function is secretion or absorption.
   • The intestinal mucosa is lined by brush-bordered columnar epithelium which is highly absorptive.
4. Ciliated Epithelium
   • The ciliated epithelium consists of columnar or cubical cells bearing cilia on their free surfaces.
   • The function of the cilia is to move particles, free cells, or mucus in a specific direction over the epithelial surface.
   • Ciliated columnar epithelium lines the inner surfaces of some hollow organs such as fallopian tubes, bronchioles, and small bronchi.
   • The ciliated columnar epithelium lining the ventricles of the brain and spinal canal is called as ependyma.
   • Cilia Is Of Two Types: Kinocilium is motile cilium with 9 + 2 organization whereas stereocilium is non-motile and ciliated columnar epithelium and does not contain basal granule. 9 + 2 organization is also absent. Stereocilia are found in some parts of the male reproductive tracts such as the epididymis and vas deferens.
5. Pseudostratified Epithelium
   • Pseudostratified epithelium covers the inner linings of the trachea and large bronchi.
   • Although made up of a single layer of columnar cells, it appears two-layered, because some cells are shorter than the others and have their nuclei at different levels.
   • The shorter cells lack cilia and secrete mucus which traps particles on the epithelial surface, whereas the longer cells are ciliated.
   • Ciliary movements propel the mucus and the particles toward the larynx.
   • Pseudostratified non-ciliated columnar epithelium tissue is found in the urethra of the male and parotid salivary glands.
   • Squamous cells show some keratinization.

Epithelial Tissue Points To Remember

Special Types Of Epithelium

1. Neuro Sensory Epithelium: In between pillar-shaped supporting cells, modified sensory cells are present. On the free end, sensory hair is present. The base of these cells is attached to the sensory nerve. For example,
   • Gustatory Epithelium: Covers the taste bud of the tongue and receives taste sensation.
   • Olfactory Epithelium: The Schneiderman membrane receives smell sensation.
   • In Stato-acoustic Organ: Lining of the internal ear.
   • In The Retina Of The Eye: Receives optic sensation.
2. Myoepithelium: Around mammary and sweat glands
3. Pigmented Epithelium (Cuboidal): In the retina of eye

Compound Epithelium

• It consists of more than one layer of cells.
• Only the cells of the deepest layer rest on the basement membrane.
• Being multilayered, compound epithelia have little role in secretion or absorption, but they provide protection to underlying tissues against mechanical, chemical, thermal, and osmotic stresses.
• Compound epithelia may be stratified or transitional.

1. Stratified Epithelium
   • The stratified epithelium has many layers of epithelial cells.
   • The deepest layer is formed by cuboidal cells.
   • But the morphology of the superficial layers varies in the different kinds of stratified epithelia.
   • In stratified cuboidal epithelium, the superficial cells are cuboidal.
   • It lines the inner surfaces of larger salivary and pancreatic duct
   • Stratified non-keratinized squamous epithelium covers moist surfaces such as those of the buccal cavity, pharynx, and esophagus.
   • It has several superficial layers of living squamous cells and deeper layers of interlinked polygonal cells,
   • Stratified keratinized squamous epithelium covers the dry surface of skin. It has many superficial layers of horny, scale-like remains of dead squamous cells, and several deeper layers of living polygonal cells.
   • Heavy deposits of the insoluble protein keratin in the dead superficial cells make the epithelium impervious to water and highly resistant to mechanical abrasions.
   • In contrast, non-keratinized stratified epithelium cannot prevent water loss and can afford only moderate protection against abrasions.
2. Transitional Epithelium
   • Transitional epithelium is much thinner and more stretchable than stratified epithelium.
   • It has a single layer of cuboidal cells at the base, two to three middle layers of large polygonal or pear-shaped cells, and a superficial layer of large, broad, rectangular, or oval cells.
   • It lines the inner surface of the urinary bladder and ureters.
   • It allows considerable expansion of these organs to accommodate urine because stretching considerably flattens and broadens the cells of superficial and middle layers.
3. Glandular Epithelia
   • The cells of glandular epithelia are generally columnar or cuboidal.
   • The Glandular Epithelium Can Be Classified Into Two Types: unicellular, consisting of isolated glandular cells (for example, goblet cell of the alimentary canal), and multicellular (for example, salivary glands), consisting of a cluster of cells.
   • A gland with a single unbranched duct is called a simple gland.
   • The secretory part of the gland consists of epithelial cells arranged in the form of tubes (tubules) sacs (acini, alveoli), or a combination of both.
   • The duct is also made up of epithelial cells.
   • A gland with a branched system of ducts is called a compound gland.
   • In these glands, the secretory tubule or acinus may be coiled or branched and open into the single duct of the gland.
   • Compound glands are present in the pancreas and sub-mandibular salivary glands.

Types Of Simple Glands

1. Simple Tubular: Simple tubular glands are present in the intestine (for example, crypts of Lieberkuhn).
   • Simple Alveolar: The terminal part forms the alveolus, for example, mucous glands in the skin of frogs, and poison glands in toads.
   • Simple Coiled Tubular: The terminal part is coiled, for example, sweat glands.
   • Branched Tubular: Gastric glands in the stomach.
   • Branched Alveolar: Example, sebaceous gland.
2. Types Of Compound Glands
   • Compound Tubular Gland: Example, mammary glands of prototherians.
   • Compound Saccular Or Alveolar Gland: Example, salivary glands, (sub-maxillary and sub-lingual).
   • Compound Tubulo Alveolar Or Tubulo Saccular: They are tubular as well as alveolar and are found in mammary glands, pancreas, parotid salivary glands, Cowper’s glands, and Bartholin’s glands.
3. Exocrine And Endocrine Glands: Exocrine glands have a secretory portion that contains the cells for secretion of milk, digestive enzymes, mucus, saliva, ear wax, oil, and ducts, which transport their secretions to the respective sites of action, for example, salivary gland, tear gland, gastric gland, and intestinal glands. Endocrine glands are glands of “internal secretion” whose secretions are usually secreted directly into the blood. Examples are follicle-stimulating hormone from the anterior pituitary or thyroxin from the thyroid. When a gland performs both exocrine and endocrine functions, it is called a mixed gland or heterocrine gland (for example, pancreas, testes, ovaries).
4. Classification Of Glands Based On The Mode Of Secretion
   1. Holocrine Glands: In holocrine glands (for example, the sebaceous gland), the product of secretion is shed with the whole cell leading to its destruction.
   2. Merocrine Glands: When the secretory granules leave the cell by exocytosis (simple diffusion) with no loss of other cellular material, the glands are called merocrine glands (for example, pancreas, salivary glands, intestinal glands, and sweat glands)
   3. Apocrine Glands: In apocrine glands (for example, mammary glands and axillary sweat glands), only the apical portion of the cytoplasm is discharged along with the secretory product.

Connective Tissue

All connective tissues in the body are developed from mesoderm. O. Hartwig called them mesenchyme because they originated from embryonic mesoderm. Only connective tissue constitutes 30% of the total body weight (muscle: 50%, epithelium: 10%, nervous: 10%). On the basis of the matrix type, connective tissue is of three types:

1. Connective Tissue Proper: Soft and fibrous matrix.
2. Connective Tissue Skeleton: Dense and mineralized matrix. Due to the deposition of minerals, it becomes hard.
3. Connective Tissue Vascular: Liquid and fiber-free matrix

Connective Tissue Proper: Connective Tissue Proper is composed of three components:

1. Different types of cells,
2. Fibers, and
3. Matrix.

Cells Of Connective Tissue Proper

• Fibroblast Cells
  • The largest cell of connective tissue proper.
  • Maximum in number.
  • The cell body and nucleus both are oval-shaped.
  • A branched cytoplasmic process arises from these cells so they appear irregular in shape.
  • Rich in rough ER because their main or primary function is to produce fibers. Fibers are composed of protein.
  • They are the chief matrix-producing cells.
  • Old fibroblast cells (fibrocytes) are inactive cells.
  • These are also considered undifferentiated cells of connective tissue because they can be modified into osteoblast and chondrioblast cells to produce bone and cartilage.
  • Fibroblast Cells Function: To produce fibers and to secrete matrix.
• Plasma Cell (Cart Wheel Cell)
  • Less in number.
  • Amoeboid in shape.
  • Chromatin material is arranged like spokes in a wheel, hence is also called cartwheel cells.
  • According to research, these cells are formed by the division of lymphocytes. So they are also called clones of lymphocytes.
  • Plasma Cell (Cart Wheel Cell) Function: Produce, secrete, and transport antibodies.
• Mast Cells/Mastocytes
  • Numerous, amoeboid, and small in size.
  • Structurally and functionally similar to basophils.
  • Two- to three-lobed S-shaped nucleus.
  • The cytoplasm contains basophilic granules which can be stayed with the basic dye methylene blue.
  • Mast Cells/Mastocytes Function: These are important cells of connective tissue proper as they perform certain important functions:
  • Histamine is a protein, a vasodilator, which increases the permeability of blood capillaries. It takes part in allergy and inflammatory reactions.
  • Serotonin, also called 5-hydroxytryptamine, is a protein, a vasoconstrictor, and decreases blood circulation, but increases blood pressure. At the site of cut or injury, serotonin causes a decrease in blood loss.
  • Heparin, a mucopolysaccharide, is a natural anti-coagulant that prevents the clotting of blood in blood vessels by preventing the conversion of prothrombin into thrombin.
• Adipose Cells/Fat Cells: These arc oval-shaped cells that store fat. Fat is collected in the form of fat globules formed by the fusion of small oil droplets. On the basis of the number of fat globules, adipocytes are of two types:
  1. Monolocular Adipocytes/White Fat Tissue Cell
     • In these cells, a single large and central fat globule is present.
     • The nucleus and cytoplasm is peripheral and the cytoplasm is less in amount.
     • Due to the compression of the fat globule, the nucleus becomes flattened in shape.
     • These adipocytes form white fat.
  2. Multilocular adipocytes/brown fat tissue cell
     • In these cells, two to three fat globules are distributed in the cytoplasm around the nucleus.
     • The cytoplasm is more in quantity.
     • The nucleus is rounded and found in the center
     • These adipocytes form brown fat.
• Mesenchymal Cells
  • Less in number. Small-sized with cytoplasmic process having an irregular shape.
  • Oval-shaped nucleus
  • These are undifferentiated cells of connective tissue because they can transform into any cell of connective tissue proper (totipotent in nature).
  • Mesenchymal Cells Function: To form other cells of connective tissue.
• Macrophages/Histiocyte/Plasmatocytes
  • These are the second largest in size and number.
  • These are amoeboid in shape with bean or kidney-shaped nuclei.
  • Cytoplasm quantity is more agranular, but due to the presence of more number of lysosomes, it appears granular.
  • They are phagocytic in nature and destroy bacteria and viruses by phagocytosis. They arise by the fusion of monocytes.
  • Also called as the scavenger cells of connective tissue, because they destroy dead or damaged cells to clean connective tissue.
  • They are named differently in different organs:
    • Lung: Dust cells
    • Liver: Kupffer cells
    • Blood: Monocytes
    • Brain: Microglia cells
    • Thymus gland: Hessels granules
    • Spleen: Reticular cells
• Lymphocytes
  • Less in number and small in size, having an amoeboid shape.
  • A large nucleus is present and cytoplasm is present as a peripheral layer. Cytoplasm quantity is less.
  • They produce, transport, and secrete antibodies.
  • They divide to form the plasma cells of connective tissue properly.

Fibers

• Collagen Fibers (White Fibers)
  • They are shining white fibers composed of collagen protein (tropocollagen).
  • It is present in maximum quantity in vertebrates (only collagen fibers constitute one-third part of connective tissue fibers in human beings).
  • They are wavy and tough fibers and are always arranged in bundles called fascia.
  • On boiling, they convert into gelatin.
  • They can be digested by pepsin enzyme.
• Elastic Fibers (Yellow Fibers)
  • Precursor in color and composed of elastin protein.
  • They are branched fibers but are always arranged singly. Branches of these form a network.
  • In these fibers, maximum elasticity is present.
  • They are highly resistant to chemicals.
  • When boiled they do not dissolve.
  • They can be digested by trypsin enzyme.
• Reticular Fibers
  • Precursor of collagen fibers, delicate with no elasticity.
  • Also known as argyrophilic fibers, since they can be stained with silver salts.
  • They are composed of reticulin protein; highly branched fibers that always form dense networks.
  • These are mainly distributed in lymphoid organs such as the spleen or lymph nodes.

Differences Between Collagen, Elastic, And Reticular Fibers

Matrix: Matrix is composed of mucopolysaccharide which is present in the form of hyaluronic acid.

Types of Connective Tissue Proper

Loose Connective Tissue: It consists of cells scattered within an amorphous mass of proteins that form a ground substance. The gelatinous material is strengthened by a loose scattering of protein fibers such as collagen, and elastin, which makes tissue elastic, and reticulin, which supports the tissue by forming a meshwork.

• Adipose Tissue
  • Adipose tissue is a connective tissue rich beneath the skin, around kidneys in mesentery and bone marrow.
  • Besides fibroblasts, macrophages, collagen fibers, and elastic fibers, the adipose tissue also contains large, spherical, or oval cells called fat cells or adipocytes.
  • The cytoplasm and organelles in adipocytes are pressed by fat globules into a narrow annular layer just beneath the plasma membrane.
  • The adipose tissue synthesizes, stores, and metabolizes fat.
  • There are two kinds of fatty tissues. In the white adipose tissue, there is a single large fat droplet in the cells surrounded by a small amount of the cytoplasm.
  • The brown adipose tissue cell, on the other hand, has many small droplets of fat, suspended in a considerably larger amount of cytoplasm. Whereas brown fat cells contain many mitochondria, white fat cells have comparatively few.
  • The color in the brown fat is due to the high concentration of iron-containing cytochrome pigments.
  • Brown fat is particularly found in newborn babies and hibernating mammals.
  • It accounts for 5-6% of the body weight of the newborn rabbit and also of man.
  • Brown fat has a larger capacity for generating heat.
  • It is because of brown fat that new-boni mammals generally do not shiver in spite of lower temperatures outside.
  • Brown fat cannot be a substitute for food. Adipose tissue may be examined from the fat bodies of frogs or from the skin of rabbits.
  • Adipose Tissue Functions:
    • Prevents heat loss by forming a heat-insulating layer beneath the skin.
    • Forms shock-absorbing cushions around kidneys and eyeballs.
    • Acts as a food reserve.
• Areolar Tissue: Areolar tissue occurs beneath the epithelia of many hollow visceral organs, skin, and in the walls of arteries and veins. It contains different types of cells:
  1. Fibroblasts: They are the principal cells of this tissue. They are irregularly shaped flat cells with long proto¬plasmic processes. Fibroblasts synthesize two kinds of protein collagen and elastin. Fibroblast secretes the major amount of matrix.
  2. Macrophages/Histiocytes/Plasmatocytes: They are phagocytic in nature.
  3. Mast Cells/Mastocytes: They are irregular or ovoid cells and contain basophilic granules which are made of:
     • Histamine: An inflammatory substance produced during allergic reactions.
     • Heparin: Natural anti-coagulant.
     • Serotonin: Vasoconstrictor.
  4. Plasma cells/cartwheel cells synthesize antibodies. The areolar tissue joins different tissues and forms the packing between them and helps to keep the organs in place and in normal shape.

Dense Connective Tissue: Fibers and fibroblasts are compactly packed in dense connective tissues. The orientation of fibers might show a regular or irregular pattern and is called dense regular or dense irregular tissues, respectively.

• In the dense regular connective tissues, the collagen fibers are present in rows between many parallel bundles of fibers, for example, tendons and ligaments.
• Dense irregular connective tissue has fibroblasts and many fibers (mostly collagen) that are oriented in different directions. This tissue is present in the skin, perimysium, perineurium, and around bones as periosteum.
• White Fibrous Tissue: It carries only a few fibroblasts scattered amidst the dense network of thick collagen fiber bundles. It has great tensile strength. The presence of white fibrous tissue at the joints between skull bones makes them immovable.
• Tendon: It is a dense, strong, and fibrous connective tissue with thick parallel bundles of collagen fibers. A few flat, elongated tendon cells lie in single rows between the fiber bundles. The tendon forms the strong inextensible attachment of a skeletal muscle to a bone. Colloidal protein gelatin is obtained by boiling collagen.
• Ligament: Ligaments connect the bones at the joints and hold them in position. A sprain is caused by excessive pulling of ligaments. They are made of bundles of elastic fibers and a few collagen fibers. Many-year-old mummies still have their arteries intact due to well-preserved elastic fibers.

Difference Between Tendon And Ligament

Reticular Tissue: It consists of star-shaped reticular cells whose protoplasmic processes form a network, These cells are phagocytic in function. Matrix and some other types of cells are are also found in the spaces of the network. Reticular tissue is present in the spleen, lymph nodes, bone marrow, etc.

Supportive Connective Tissue

Cartilage: Cartilage is a solid but semi-rigid and flexible connective tis¬sue. Chondrocytes are large, blunt, angular cartilage cells. They occur in clusters of two or three cells in small spaces (lacunae) scattered in the matrix.

1. Hyaline Cartilage: In hyaline cartilage, the matrix is apparently fiberless and glass-like (hyaline), but trans-lucent. It occurs in the larynx, nasal septum, tracheal rings, and costal cartilage. It gives those structures a definite but pliable form. White fibrocartilage carries thick dense bundles of collagen fibers between rows of chondrocytes in lacunae. It occurs in joints between vertebrae. Its collagen fibers make such joints strong but less clastic and only slightly movable.
   • Nucleus Pulposus: In the center of the intervertebral disc, a soft area is present called nucleus pulposus which is supposed to be a remnant of notochord.
2. Elastic Cartilage: It contains a dense network of elastic fibers between scattered chondrocytes. It forms the Eustachian tube, epiglottis, and pinna of the ear. The elastic fibers make those organs considerably elastic and pliable.
3. Calcified Cartilage: Initially, it is like hyaline cartilage but later on it gets hardened like bone due to the dep¬osition of calcium salts, for example, supra scapula of a frog’s pectoral girdle, pubis of the pelvic girdle of the frog.

Bone: It is a solid, rigid connective tissue. The matrix of the bone has the deposition of apatite salts of calcium and phosphorus. For example, hydroxyapatite salts and fluorapatite salts.

• 60-70% of bone is made up of inorganic matter and 30-40% is made up of organic matter.
• If the bone is put in dil. HCI will become decalcified, soft, and flexible. Nothing will happen to the bone if we put the bone in KOH.
• Osteoblasts are bone-forming cells that secrete ossein protein.
• Osteocytes are bin cells, they are metabolic inactive cells present in the lacuna.
• Bone is a solid, rigid, and strong connective tissue. Its matrix is heavily deposited with apatite salts of calcium and phosphorus. Flat irregular spaces called lacunae occur in the solid matrix. Each lacuna lodges a nathone cell or osteocyte. A bone cell has irregular¬shaped and long cytoplasmic processes. These processes extend into minute canals (canaliculi) radiating from each lacuna.
• Compact bone forms the dense outer layers of all bones. It is composed of many parallel, longitudinal column-like structures called Haversian systems, cemented to each other. Haversian canals are connected to each other by Volkmann’s canals. In each Haversian system, several concentric layers (lamellae) of bony matrix encircle a longitudinal central canal (Haversian canal. This canal carries blood vessels and nerves. Lacunae-containing osteocytes occur in a layer between two lamellae.

Spongy Bone: The ends of long bones are composed of an open lattice of bone called spongy bone. The spaces within contain marrow’, where most blood cells are formed. It carries no concentric organization like the Haversian system. It consists of a network of many fine irregular bony plates or trabeculae. Each trabecula consists of many irregularly arranged lamellae with lacunae between them. It has red bone marrow. Spongy bone is also called as cancellous bone and is found in epiphysis, i.e., the ends of long bones.

Differences Between Bone And Cartilage

Differences Between A Dried Bone And Decalcified Bone

Connective Tissue Points To Remember

Types Of Bones

• Cartilage Bones/Endochondrial/Replacing Bones: They are formed by the replacement of cartilage by the bone, for example, hu-merus, femur, vertebrae, ribs, and girdle bones, except clavicle. Chondroblasts are cartilage-eater cells.
• Membrane/investing bone/dermah Examples, skull bones, clavicle, etc. The bones are formed in the dermis of the skin and are invested over the already present cartilage.
• Sesamoid Bones: They are formed by the ossification of the tendons, for example, the patella.
• Visceral Bones: They are those bones that get detached from the skeleton and come to lie in visceral organs, for example,
  • os Cordis: Present in the interventricular septum of the heart of deer.
  • os Falciparum: Palm of mole.
  • os Penis: Penis of rats and carnivores.
  • os Palbebrae: In the eyelids of a crocodile.
  • os Rostralis: Snout of pig.
• Bone China: Porcelain was first made in China during the Tang dynasty. English found a new way of making porcelain with bone ash. Bone china is a form of porcelain made from burned animal bones. Bone ash is mixed with kaolin and white clay. The bone ash increases the porcelain’s translucence.
• Word Roots And Origin Of Periosteum: Greek peri means “around” and osteon means “bone.”

Fluid Connective Tissue (Blood)

• Blood is a fluid connective tissue.
• Its cells are quite distinct from other connective tissue cells both in structure and function.
• The extracellular material in the blood is a fluid devoid of fibers.
• Fluids outside the cells are generally called extracellular fluids (ECF).
• Blood is heavier than water.
• The extracellular material in the blood is a straw-colored, slightly alkaline (pH = 7.4), aqueous fluid called plasma.
• Constituents, having characteristic forms, float in the plasma. They are collectively called the formed elements of blood. They include the blood cells and blood platelets.
• Blood cells are of two types: erythrocytes and leukocytes.
• Blood circulates within blood vessels in higher animals.

Plasma

• Plasma contains three major classes of plasma proteins, viz., serum albumin, serum globulins, and fibrin¬ogen.
• Plasma proteins serve as a source of proteins for tissue cells.
• Tissue cells may utilize plasma proteins to form their cellular proteins.
• Additionally, albumin and globulins retain water in blood plasma by their osmotic effects.
• A fall in plasma proteins leads to the movement of excessive volumes of water from blood to tissues. That is why hands and feet get swollen with accumulated fluid  (edema) in persons suffering from dietary deficiency of proteins.
• Albumins and globulins also transport many substances such as thyroxine and Fe³⁺ in combination with them.
• One class of globulins, called immunoglobulins, acts as antibodies.
• Plasma proteins also maintain the blood pH by neutralizing strong acids and bases. Thus, they act as acid-base buffers.
• It is a slightly alkaline, non-living intercellular substance that constitutes about 60% part of the blood.
• It is a pale yellow but transparent and clear fluid.

Composition of Plasma: Plasma forms 55-60% by the blood volume.

1. Water: Water alone forms about 90% to 92% of the plasma. Solids form about 8% of the plasma.
2. Mineral Salts: These are chlorides, bicarbonates, sulfates, and phosphates of sodium, potassium, calcium, iron, and magnesium. All salts constitute about 0.9% of plasma. Buffer of the blood is sodium bicarbonate.
3. Nutrients: These include glucose, fatty acids, phospholipids, cholesterol, fats, amino acids, nucleosides, etc. Mineral salts have been mentioned above.
4. Plasma Proteins: They constitute about 7-8% of plasma. These mainly include albumin 4.4%, globulin 1.5-2%, prothrombin, and fibrinogen both 0.3%.
5. Defence Proteins: Immunoglobulins which act as antibodies and some other substances, such as lysozyme and properdin (a large protein) are always found in the plasma. They destroy bacteria, viruses, and toxic substances that may enter into the blood from outside.
6. Excretory Substances: These include ammonia, urea, uric acid, creatinine, etc.
7. Dissolved Gases: The water of blood plasma contains oxygen, carbon dioxide, and nitrogen in dissolved form.
8. Anticoagulant: Blood plasma contains a conjugated polysaccharide, heparin, which prevents the coagulation of blood inside blood vessels.
9. Hormones: These are secreted and released in blood by endocrine glands.
10. Vitamins And Enzymes: Different kinds of vitamins and enzymes are present in the blood plasma.

Functions Of Blood Plasma: These can be summarized as under:

1. Transport,
2. Retention of fluid in the blood,
3. Maintenance of blood ph,
4. Body immunity,
5. Prevention of blood loss,
6. Conducting heat to skin for dissipation, and
7. Uniform distribution of heat all over the body.

Blood Glucose

• Glucose is mainly absorbed in the small intestine.
• Glucose is also absorbed in the stomach.
• After absorption, glucose reaches the blood.
• Excess of glucose is converted into glycogen by insulin hormone in the liver and muscles.
• Whenever it is required, glycogen is changed back into glucose by glucagon hormone.
• Usually blood glucose level is about 80-100 mg per 100 mL of blood, 12 hours after a normal meal. But its concentration rises soon after a carbohydrate-rich diet.
• If the blood glucose level exceeds 180 mg per 100 mL, it starts appearing in urine. This condition is called glucosuria.
• Fasting glucose is 70-110 mg/dL. Glucose PP is 110 mg/dL (PP: post-prandial or after breakfast).
• If it is higher, it causes diabetes mellitus (hyperglycemia).
• If it is less, it causes hypoglycemia (less amount of glucose in the blood).

Blood Cholesterol

• Usually, cholesterol is considered a harmful substance. But it is quite useful in limited amount.
• Cholesterol is used in the synthesis of biomembranes, vitamin D, bile salts, and steroid hormones.
• Its normal amount is 80-180 mg in 100 mL of blood plasma.
• Cholesterol comes in the blood plasma either by intestinal absorption of fats by the synthesis from the liver or by both.
• Saturated fats such as ghee and butter increase cholesterol level in the blood.
• Increased blood cholesterol may lead to its deposition in the internal wall of the blood vessels such as arteries and veins which cause high blood pressure and heart problems.

Functions Of Plasma Proteins

1. Prevention Of Blood Loss: Fibrinogen and prothrombin play a role in blood clotting.
2. Retention Of Fluid In The Blood: Albumin helps in osmotic balance.
3. Body Immunity: Certain globulins called immuno-globulins (glycoproteins) act as antibodies in blood and tissue fluid. Antibodies belong to a class of proteins called as immunoglobulins.
4. Maintenance of pH: Plasma proteins serve as acid-base buffers. It means they maintain pH of the blood by neutralizing acids and bases.
5. Transport Of Certain Materials: Thyroxine (hormone) is bound to albumin or specific globulin for transport in the plasma.
6. Distribution Of Heat: Plasma proteins help in the uniform distribution of heat all over the body.
7. Enzymes: Some proteins acting as enzymes also occur in the plasma.

Blood Cells

1. Erythrocytes

• Erythrocytes (red blood corpuscles or RBCs) are the most numerous of the formed elements of blood.
• Their most important characteristic feature is the presence of hemoglobin (Hb), the red oxygen-carrying pigment.
• The total number of erythrocytes per microliter (1μL = 1 mm³ =10^-6 L) of blood is known as the total count of RBC.
• It averages 5 million and 4.5 million in adult men and adult women, respectively.
• The total count would be low in anemia and after profuse bleeding.
• On the contrary, the abnormal rise in the total count of RBC is called polycythemia.
• Anemia is caused due to the deficiency of folic acid, vitamin B₁₂, and hemoglobin.
• The size and shape of erythrocytes vary in different classes of animals.
• In fishes, amphibians, reptiles, and birds, erythrocytes are usually nucleated, oval, and biconvex. But in mammals, they are non-nucleated, biconcave, and circular.
• Only camel and llama possess oval red blood corpuscles.
• Human erythrocytes measure 7-8 μm (1 μm = 10^-6 m) in diameter and 2μm thickness near the rim.
• Old and damaged erythrocytes are phagocytosed and destroyed by macrophages.
• The pigment part (porphyrin) of hemoglobin is then catabolized to the yellow pigment bilirubin which is excreted in the bile.
• The pale yellow color of plasma is largely due to bilirubin.
• If a sample of blood is rendered non-coagulable by adding potassium or sodium oxalate and then centrifuged at a high speed in a graduated centrifuge tube (hematocrit tube), the centrifugal force rapidly sediments the erythrocytes to the bottom of the tube. They become packed into a solid, red. bottom layer while plasma forms a clear, fluid upper layer. On the upper surface of the erythrocyte layer, leukocytes form a thin, buff-colored layer.
• From the graduations on the tube, the relative volume of erythrocytes may be read as a percentage of the total blood volume. This is called the hematocrit value or packed cell volume.
• It normally forms 45% of the blood volume.

RBCs of mammals are circular, biconcave, and non-nucleated, except those of the family Camelidae (camel, which has non-nucleated and oval RBCs). The largest RBCs are found in amphibia. The smallest RBCs are found in mammals.

• In mammals, the smallest RBCs are found in “musk deer,” Tragiilns jammies (1.5 pm).
• In mammals, the largest RBCs are found in elephants. (9.4 pm).
• The graveyard of RBC is the spleen.
• Life span of RBCs in men is 120 days, in frogs 100 days, and in rabbits 80 days.
• The radioactive chromium method (Cr⁵¹) is used for the estimation of the life span of RBC.

Count of RBCs:

In embryo = 8.5 million/mm³

In man = 5-5.5 million/mm³

In woman = 4.5 million/mm³

Daily destruction of RBCs = 1%

ESR (Erythrocyte Sedimentation Rate): It is measured by Wintrobe’s method. It is the rate of the settling down of RBCs. It is also estimated by Westergen’s method.

• ESR is very useful in diagnosing various diseases including tuberculosis.
• ESR in men is 0-5 mm/h and in women 0-7 mm/lt, according to Westergen’s method.

Hemocytometer: It is an instrument for counting the number of both WBCs and RBCs.

Rouleaux: In resting and slow-flowing blood, RBCs aggregate to form rouleaux (RBCs are piled on top of each other). Fibrinogen favors rouleaux formation.

Bone Marrow: It is the main site for the formation of RBC. The volume of bone marrow at the time of birth is 70 mL. In adults, the volume of bone marrow is 4000 mL.

Structure Of RBC Of Man: Biconcave, nonnucleated, and bounded by Donnan’s membrane (plasma membrane of RBC). Hemoglobin is filled in RBC which is a respiratory pigment.

Normal Range Of Hemoglobin

• Infants: 16.5 ± 3.0 g/dL (dL = deciliter)
• Children 3 Months: 11.0 ± 1.5 g/dL
• Childen 10-12 Months: 13.0 ± 1.5 g/dL
• Men: 15.5 ± 2.5 g/dL
• Women: 14.0 ± 2.5 g/dL

Structure Of Hemoglobin: Each molecule of hemoglobin contains four molecules of heme and one molecule of globin. These are attached by coordinate bonds. Heme is a protoporphyrin compound and has four pyrrole groups joined together to form a ring structure. In Hb, Fe is present in (Fe⁺⁺) ferrous form. Heme is 5% and Globin is 95%. Globin is made of four polypeptide chains.

2. Leukocytes

• Leukocytes (white blood corpuscles or WBC) are devoid of hemoglobin and are consequently colorless
• Leukocytes are nucleated blood cells.
• They are of two major classes: granulocytes (with cytoplasmic granules) and agranulocytes (without granules).
• Granulocytes are of three types, viz., neutrophils, eosinophils, and basophils, each with lobed nuclei.
• Agranulocytes are of two types, viz., lymphocytes and monocytes.
• Neutrophils and monocytes protect the body against microbes by phagocytosing them.
• Lymphocytes secrete antibodies in the blood to destroy microbes and their toxins.
• The number of leukocytes per microliter (1 μL = 1 mm³ = 10^-6 L) of blood is called the total count of WBC. It is 6000-8000/mm³ of blood normally.
• It may rise abnormally in acute infections (for example, pneumonia), inflammations (for example, appendicitis), and malignancies (for example, leukemia).
• In some conditions such as folic acid deficiency, the total count falls abnormally (leukopenia).
• The total count of WBCs is also of diagnostic value in many diseases.
• Monocytes have kidney-shaped nuclei.
• The process by which monocytes and neutrophils squeeze out through thin capillary walls is diapedesis.

1. Neutrophils: They are maximum in number, stain equally with both basic and acidic dyes, and have many lobed nuclei, granules are in abundance in the cytoplasm, and help in phagocytosis.
2. Eosinophils: They have a bilobed nucleus. They get stained with acidic stains. Their number increases during allergic reactions (eosinophilia).
3. Basophils: They get stained with basic dyes.  Their nucleus is S-shaped. Coarse granules are few in the cytoplasm. Basophils release heparin and histamine in the blood and have a function similar to the mast cells.
4. Lymphocytes: They have large and rounded nuclei. The cytoplasm forms a thin peripheral film. They have their stem cells in the bone marrow and are differentiated in the bone marrow or in the thymus. Lymphocytes are of two types: B- lymphocytes and T lymphocytes. B-lymphocytes produce antibodies against antigens and they mature in the bone marrow.
5. Monocytes: They are the largest leukocytes (12-15 pm). The nucleus is kidney-shaped. They are produced from bone marrow monoblast cells. They help in phagocytosis.

Differences Between Different Types Of Leukocytes

3. Blood Platelets

• Also called thrombocytes, blood platelets are non-nucleated, round, or oval, biconvex disc-like bodies.
• They are 2-3 pm in diameter and their number normally varies from 0.15 to 0.35 million/mm3 or 150,000-350,000 platelets/mm3.
• They bud off from the cytoplasm of very large megakaryocytes of the bone marrow.
• Their normal life span is about a week.
• When a blood vessel is injured, platelets get clumped at the injured spot and release certain chemicals called platelet factors. These promote blood coagulation.
• Thrombocytopenia is a decrease in the platelet count and purpura is a group of bleeding diseases due to thrombocytopenia.

Blood Coagulation

• When blood oozes out of a cut, it sets into gel within a few minutes. This is called coagulation.
• Coagulation is brought about by the hydrolysis of soluble fibrinogen of plasma to insoluble fibrin. This is catalyzed by an enzyme called thrombin.
• Fibrin precipitates as a network of fibers. This network traps many blood cells, particularly RBCs, to form a red solid mass called the blood clot.
• The clot seals the wound in the vessel to stop the bleeding.
• The straw-colored fluid left after clotting of blood is called serum.
• Serum cannot be coagulated as it lacks fibrinogen.
• Thrombin occurs in normal blood as an inactive globulin called prothrombin.
• It must be activated to thrombin before blood coagulation can occur.
• In the case of injury to a blood vessel, coagulation-promoting substances called thromboplastins are released into the blood from clumped platelets and damaged tissues.
• Thromboplastins help in the formation of the enzyme prothrombinase. This enzyme hydrolyzes prothrombin to thrombin to initiate coagulation.
• Ca²⁺ ions are essential for both activation and action of thrombin.
• Blood normally contains an anticoagulant, heparin, which prevents the activation of prothrombin. Heparin is released from “mast cell” granules.
• Blood also contains antithrombin, which inhibits any thrombin formed accidentally.
• Blood drawn from a blood vessel can be kept coagulated by adding a pinch of oxalate (sodium or potassium oxalate) to it.
• Oxalate precipitates Ca²⁺ and consequently prevents coagulation.
• Chilling of blood also delays coagulation because lesser temperature depresses the action of courage-location-promoting enzymes.

Blood Cells Points To Remember

ABO Blood Clotting Factor

• Karl Landsteiner reported for the first time ABO blood groups in human beings.
• A, B, and O blood groups were discovered by Landsteiner (1900), while the AS blood group was found by de Castello and Steini (1902).
• Agglutinogens (antigens) are present on the surface of red blood corpuscles and agglutinins (antibodies) are found in the blood plasma. Both antigens and antibodies are proteins.
• When two different types of blood are mixed, the red blood corpuscles form a clump.
• The clumping of red blood corpuscles is called agglutination

Clotting Factors

• Thirteen factors help in blood clotting.
• These factors are mainly produced in the liver.
• Vitamin K is required in the synthesis of these clotting factors.
• These factors are represented in Roman numbers.
  • 1: Fibrinogen
  • 2: Prothrombin
  • 3: Thromboplastin
  • 4: Ca⁺² (cofactor in each step of blood clotting)
  • 5: Proaccelerin
  • 6: Accelerin (rejected)
  • 7: Proconvertein
  • 8: AHG (anti-hemophilic globin; absent in hemophilia-A)
  • 9: Christmas factor
  • 10: Stuart factor
  • 11: PTA (plasma thromboplastin antecedent)
  • 12: Hagman factor
  • 13: FSF factors (fibrin-stabilizing factor) (Laki Lorand factor)
• Other natural anticoagulants
  • Hirudin: Found in leech.
  • Anophelin: Found in female Anopheles
  • Lampredin: Found in Petcromyzon (Lamprey)
  • Cumerin: Obtained from plants
  • Warfarin: Obtained from plants
• To collect blood in a bottle in a blood bank, artificial anticoagulants such as sodium citrate, and sodium oxalate. EDTA (ethylenediaminetetraacetic acid), etc., are used. These chemicals act as calcium-binding units and remove Ca⁺² ions from the blood.

Blood Group

• Agglutination is due to the interaction of antigens and antibodies.
• There are two kinds of antigens that are named A and B.
• There are also two kinds of antibodies which are called a and b.
• Antigen A and antibody a are incompatible (antagonistic) cause self-clumping and cannot exist together. The same is the case with antigen B and antibody b. Thus, A and b can exist together and B and a can exist together.
• Corpuscle factors A and B can occur together if their antagonistic plasma factors a and b are not present.
• Plasma factors a and b can occur together if their antagonistic corpuscle factors A and B are absent.

Blood Groups With Corresponding Antigens And Antibodies

Rh Factor

• Another antigen, Rh antigen, similar to one present in Rhesus monkeys (hence Rh), is also observed on the RBC surface of the majority (nearly 80%) of humans.
• In India, the percent ratio of Rh is 97% Rh positive and 3% Rh negative. In the world, it is 80% Rh positive and 20% Rh negative.
• Individuals in which Rh antigen is present are called Rh positive (Rh⁺) and those in whom this antigen is absent are called Rh negative (Rh^–).
• An Rh^– person, if exposed to Rh⁺ blood, will form specific antibodies against the Rh antigens. Therefore, Rh group should also be matched before transfusions.
• A special case of Rh incompatibility (mismatching) has been observed between the Rh^– blood of a pregnant mother and with Rh⁺ blood of the fetus.
• Rh antigens of the fetus do you get exposed to the Rh-blood of the mother in the first pregnancy as the two types of blood are well separated by the placenta. However, during the delivery of the first child, there is a possibility of exposure of the maternal blood to small amounts of the Rh⁺ blood from the fetus.
• In such cases, the mother starts preparing antibodies against Rh antigen in her blood. In the case of her subsequent pregnancies, the Rh antibodies from the mother (Rh^–) can leak into the blood of the fetus (Rh⁺) and destroy the fetal RBCs. This could be fatal to the fetus or could cause severe anemia and jaundice to the baby. This condition is called erythroblastosis foetalis. This can be avoided by administering anti-Rh antibodies to the mother immediately after the delivery of the first child.

Muscular Tissue

Muscles cause movements of limbs and internal organs and also locomotion of the organism. Cells of muscle tissue can shorten forcefully and again return to the relaxed state. This specialized property is called contractility.

• It is based on the organized arrangement of some protein filaments in the cytoplasm of a muscle cell.
• The cell shortens or relaxes according to the relative positions of different intracellular filaments.
• Whenever adequately stimulated, muscle cells respond by contracting. This property of the muscle tissue is responsible for various movements in an animal.
• Muscle cells are usually called muscle fibers because they are thin and elongated.
• In higher animals, some muscles remain associated with the skeleton, but many others form walls of visceral organs, blood vessels, and heart.
• Muscle tissue may be classified into striated, non-striated, and cardiac muscles, according to their structure, location, and functions.

Striated/Skeletal/Voluntary Muscles: Such muscles are attached to bones by tendons. A voluntary muscle is composed of long bundles of striated muscle fib¬ers. Each fiber is a long, unbranched, cylindrical cell. It shows transverse striations in the form of regular alternate dark (A) and light (I) bands.

• At the center of the band is a fine, dense Z band or Z-line (Krause’s membrane). The plasma membrane covering the fiber is called sarcolemma. The cytoplasm inside the fiber is called sarcoplasm.
• The sarcoplasm contains many long, thin, unbranched, cross-striated cylindrical structures called myofibrils. They are arranged along the long axis of the fiber. Dark A bands of neighboring myofibrils are located side by side, and so also are their light I bands. This gives a cross-striated appearance to the entire muscle fiber also.
• A-band has both actin and myosin filaments. The portion of A band, where actin filaments are absent is called H zone. Z line or Krauze’s membrane is a dark membrane that bisects I band or isotropic band.
• Muscle is rich in proteins. Most of these proteins occur as two types of filaments arranged longitudinally in myofibrils. The thick filaments are made up of the protein myosin. Myosin filaments are located inside A bands.
• Thin filaments are more numerous. They are composed of the protein actin. From a fine, dense, dark Z band at the center of each I band, actin filaments extend through I band and encroach between myosin filaments up to a considerable distance into A band.

Each segment of the myofibril from one Z band to the next, functions as a contractile unit and is called a sarcomere. Various parts of a sarcomere have a specific arrangement of actin and myosin filaments as given below.

I Band: Has only actin filaments

A Band: Has both actin and myosin filaments

H Band: Has only myosin filaments

Z Line: A membrane to which actin filaments are attached on both sides.

Differences Between Single-Unit And Multi-Unit Smooth Muscles

Non-Striated or Smooth Muscles: Non-striated fibers do not show cross-striations; instead, they look smooth. Smooth muscles cannot be moved voluntarily. Hence, they are also called involuntary muscles. Functionally, smooth muscles are of two types: single-unit and multi-unit smooth muscles.

• Single-unit smooth muscles are composed of muscle fibers closely joined together. All its fibers contract together as a single unit. They may contract automatically and rhythmically. Such smooth muscles occur on the walls of hollow visceral organs such as the urinary bladder and gastrointestinal tract.
• Multi-unit smooth muscles are composed of more independent muscle fibers, not so closely joined together. Individual fibers of such smooth muscles contract as separate units. These occur at hair roots and in the walls of large blood vessels, for example, erector pili muscles.
• Smooth muscle fibers are elongated spindle-shaped cells. They are packed parallel to each other in branching bundles. Each fiber contains a single, spindle-shaped nucleus at its thick central part. The smooth muscle fiber is generally shorter than a striated muscle fiber. Mitochondria and other organelles are less extensive and protein filaments are not regularly arranged to give rise to striations.

Cardiac Muscle: Cardiac muscle occurs in the heart. It possesses considerable automatic rhythmicity and generates its own wave of excitation. The excitation can also pass directly from one fiber to another in the cardiac muscles. It is not under voluntary control. It shows cross-striations, but striations are much fainter than those of striated muscle.

Between the cardiac muscle fibers, intercalated discs are present. They are specialized regions of the cell membrane of two adjacent fibers. The intercalated discs function as boosters of the contraction wave and permit the wave of contraction to be transmitted from one cardiac fiber to another.

Cardiac muscle cells are short cylindrical cells joined end to end to form rows. They possess abundant cytoplasm with myofibrils (sarcoplasm) and numerous mitochondria and glycogen granules. This is because they need a large amount of energy. Faint but regular, alternately dark and light bands give rise to cross-striations in the cardiac muscle fibers and indicate regular and alternate arrangements of thin and thick filaments in the fiber.

Sarcomeres are also present. Cardiac muscle cells frequently branch to form junctions with neighboring cells. Where two cardiac muscle cells meet end to end, a dense zig-zag junction is formed between them. It is called an intercalated disc. The longest refractory period is present in cardiac muscles.

Differences Between Striated, Non-Striated, And Cardiac Muscles

Nerve Tissue

Ordinary connective tissue is absent inside the central nervous system. The neurons are held together by supportive cells called neuroglia cells. A nerve tissue is made up of neurons and neuroglia cells. A neuron has a large cell body with two or more, thin protoplasmic processes extending from it.

• One of the processes called the axon is long and conducts nerve impulses away from the cell body. Axon ends in a number of small branches on muscle fibers, gland cells, or other neurons. The remaining one or more processes conduct nerve impulses towards the cell body and are called dendrites or dendrons.
• The axon terminals may form intercommunicating junctions, called synapses, with dendrite terminals, cell bodies, or even axons of other neurons. Nerve impulses pass between neurons through the synapse with the help of chemicals, such as acetylcholine, which are termed neurotransmitters.
• The cell body of a neuron is called the soma. It has various shapes.
• Both soma and the processes are covered by a plasma membrane.
• The soma contains abundant granular cytoplasm and a large nucleus.
• To serve the high-energy needs for impulse conduction, neurons have many mitochondria.

• Light microscopy shows many small conical, angular, or rhomboidal and highly basophilic structures in the cytoplasm of soma and dendrites, called Nissl bodies which are absent in the axon and the axon hillock. Nissl bodies are made up ofribosomes, ER, and m-RNA.
• The processes which arise from neurons are called as neuritis. These are of two types: dendrites and axons.
• Dendrites conduct the nerve impulse toward the nerve cell body and are called as afferent processes.
• Axon is a single, usually long process. The part of cyton from where the axon arises is called as axon hillock. The cell membrane of the axon is called axolemma and its cytoplasm is known as axoplasm. The axon divides to form an axon ending, each with a synaptic knob. The synaptic knobs contain mitochondria and se¬cretory vesicles. The vesicles contain neurotransmitters such as nor-adrenaline, adrenaline, acetylcholine, etc.

Synapse

• Nerve signals travel from neuron to neuron all over the body. These associations are called synapses.
• Synapse is a junction between the axon endings of one nerve fiber and the dendrite of the other.
• At a synapse, the membrane of the axon and dendrites are not in physical contact with each other but there is a narrow intercellular gap, 10-20 nm across, separating the axon tip and target cell. This gap is a synaptic cleft. The neurotransmitter is always released from axon endings and not by dendrites, so there is only one-way transmission of nerve impulses.

Types Of Neurons: Based on the number of nerve processes, neurons are of four types

1. Unipolar Neurons: These have only axons but no dendrons and are found only in early embryos.
2. Bipolar Neurons: These have two processes, one axon, and another dendron, and are found in the olfactory epithelium and retina of eye.
3. Multipolar Neurons: These have many processes arising from the cell body; out of them, one (longer) acts as an axon and the remaining as dendrites. Multipolar neurons are most common and are found in the brain and spinal cord.
4. Pseudo-Unipolar Neurons: They are actually bipolar but appear like unipolar. A single process arises first which divides to form dendrite and axon. This is found in the dorsal root ganglion of the spinal cord.

Non-Polar Neurons: Each neuron bears several branched processes which are not differentiated into axons or dendrites. On the basis of function, neurons are of three types:

1. Sensory (Receptor Or Afferent) Neurons: They connect sense organs with the central nervous system (brain and spinal cord).
2. Motor (Effector Or Efferent) Neurons: They connect the central nervous system to the effectors (muscles and glands). They carry motor impulses from the central nervous system to the effectors.
3. Interneurons (Connector, Relaying, Or Adjustor Neurons): They are present in the central nervous system and occur between the sensory and motor neurons for distant transmission of impulses. They are neither sensory nor motor.

The extended axon or dendrite of a neuron is called a nerve fiber. It is generally elongated axon. There are two basic types of nerve fibers:

1. Myelinated/Medullated Nerve Fibers: These are with the myelin sheath. Myelin sheath is formed by the spiral wrapping of the Schwann cell membrane around the axon. Outside the myelin sheath, a neurilemma is present. Myelin sheath is absent at certain points called nodes of Ranvier. In myelinated nerve fibers, the impulse jumps from one node of Ranvier to the other, which is called saltatory conduction of the impulse. The node of Ranvier is without myelin but with neurilemma. Myelinated nerve fibers are found in cranial and spinal nerves.
2. Non-Inyelinated/Non-Medullated Nerve Fibers: These are not covered with myelin sheath and, hence are called non-myelinated or non-medullated nerve fibers. They do not possess nodes of Ranvier but have neurilemma. Myelinated nerve fibers are generally thicker than non-myelinated ones. These fibers are enclosed by Schwann cells that do not form a myelin sheath around these axons and are commonly found in autonomous and somatic neural system.

Nerve: A nerve is a collection of nerve fibers surrounded by connective tissue membranes.

• The membrane of the nerve fiber is a neurilemma; outside this, each nerve fiber is surrounded by a layer of connective tissue called the endoneurium.
• A nerve consists of several bundles of nerve fibers called fasciculi.
• Each fasciculus is surrounded by a layer of connective tissue called the perineurium.
• A dense layer of connective tissue that surrounds the entire nerve made of a number of fasciculi is called epineurium.
• A Nerve Can Be Of The Following Types:
  • Sensory Nerve: It is made up of only sensory nerve fibers surrounded by connective tissue membrane. It carries the impulse from the receptor to the CNS.
  • Motor Nerve: It is made up of motor nerve fibers, which carry the impulse from CNS to the effector organs, i.e., muscles or glands to bring about their movement.
  • Mixed Nerve: It has both sensory and motor nerve fibers. All the spinal nerves in our body are mixed.

Neuroglia Cells/Glial Cells: Neuroglia cells are undifferentiated cells with no Nissl granules. They are of the following types:

1. Astrocytes/Macrocytes: They are large in size with a number of protoplasmic processes. They form a maximum number of glial cells. They help in the repair of nerve tissue and form the blood-brain barrier.
2. Oligodendrocytes: They arc with few protoplasmic processes and form myelin sheath in CNS. There is no neurilemma inside the central nervous system. In the absence of Schwann cells, myelin is formed by the spiral wrapping of nerve fibers by the processes of oligodendrocytes. They are a type of neuroglia cells.
3. Microglial Cells: They are mesodermal in origin. They are smallest in size with few feathery processes and help in phagocytosis.

Nerve Tissue Points To Remember

Cells, tissues, organs, and organ systems split up the work in a way that ensures the survival of the body as a whole and exhibits division of labor. A tissue is defined as a group of cells along with intercellular substances performing one or more functions in the body.

• Epithelial tissues are sheet-like tissues lining the body’s surface and its cavities, ducts, and tubes.
• Epithelia have one free surface facing a body fluid or the outside environment.
• Their cells are structurally and functionally connected at junctions.
• Epithelial tissue is classified into different categories on the basis of the shape and function of cell.
• Diverse types of connective tissues bind together, support, strengthen, protect, and insulate other tissues in the body.
• Soft connective tissues consist of protein fibers as well as a variety of cells arranged in a ground substance.
• Cartilage, bone, blood, and adipose tissues are specialized connective tissues.
• Cartilage and bone are both structural materials.
• Blood is a fluid tissue with transport functions.
• Adipose tissue is a reservoir of stored energy.
• Muscle tissue, which can contract (shorten) in response to stimulation, helps in the movement of the body and specific body parts.
• Skeletal muscle is the muscle tissue attached to bones
• Smooth muscle is a component of internal organs.
• Cardiac muscle makes up the contractile walls of the heart.
• Connective tissue covers all three types of tissues.
• Nervous tissue exerts the greatest control over the response of the body.
• Neurons are the basic units of nervous tissue.

Earthworm (Pheretima Posthuma)

Phylum: Annelida

Class: Oligochaeta

Genus: Pheretima

Species: Posthuma

There are several types of earthworms. The most common genus of earthworms is Pheretima in India and Lumhricus in Europe. Pheretima has 500 species, 13 of which are found in India.

Habitat: Earthworm is a reddish brown terrestrial animal that inhabits the upper layer of moist soil where it lives inside burrows during the daytime.

• Earthworm inhabits those soils that have abundant organic matter.
• An acre of good moist soil can have up to 50,000 animals. Burrow is made by boring and swallowing the soil.
• The burrows are vertical or oblique.
• They are 30-45 cm deep during moist season but may go as deep as 2 m in summer.
• The burrows are lined by debris or mucus secreted by the animals and are wider at the base.
• During winter, the animal drags organic debris into its burrow and plugs the mouth of the burrow.
• This keeps the burrow warm.
• Even the mouth of the burrow is hidden from view by leaves and small stones.
• The area of the burrow can be recognized by fecal pellets called worm castings.

Habit: Earthworm is nocturnal because it is sensitive to higher light intensities.

• It partly creeps out of burrows during the night for search of food.
• It is only during the rainy season that the earthworm comes out of the burrow even during the daytime.
• After heavy rainfall, they can be seen crawling on the ground in large numbers.
• If the burrow is left, the animal does not re-enter the same.
• It digs a new burrow by pushing the body through the soft soil as well as by eating its way through the soil.
• The worm keeps its skin moist through mucus, coelomic oozing, and from the moisture of the soil. The animal respires through the skin.
• The body of an earthworm is long and cylindrical has about 100-120 segments (metameres). The first segment is called as buccal segment or peristomium which bears a very small terminal opening the mouth.

A small projection is also present which hangs over the crescent-shaped mouth and is called prostomium. It serves as a wedge to force open cracks in the soil into which earthworms may crawl. It is sensory in nature.

• The skin of earthworms is brown due to the presence of porphyrin pigment which protects the earthworm from UV radiation.
• In all the body segments, except the first, last, and clitellum, there is a ring of S-shaped setae, embedded in the epidermal pit at the middle of each segment (perichaetine).
• Setae are chitinous structures and are not dissolved in KOH.
• In the intersegmental grooves of 5/6, 6/7, 7/8, and 8/9 segments, four pairs of spermathecal pores are present which are the opening of spermathecae.
• A thick band of glandular tissue clitellum (cingulum) surrounds segments 14-16, forming a thick girdle. Its glands secrete mucus and albumin and also form the cocoon.
• On the ventral surface of the 18th segment, a pair of male genital apertures is present and on the ventral surface of the 14th segment, a median female genital aperture is present.
• On the ventral side of each of the 17th and 19th segments, circular raised pairs of genital papillae are present which help in reproduction.
• The dorsal surface of body is marked by a dark median mid-dorsal line (representing dorsal blood vessels) along the longitudinal axis of the body. The ventral surface is distinguished by the presence of genital openings (pores).

Internal Morphology: The body wall of earthworms is thin, soft, and slimy. From the surface inward, it consists of the cuticle, epidermis, muscular layers, and coelomic epithelium.

Cuticle: It is a thin and clastic non-cellular protective membrane. It is formed of collagen fibers secreted by the underlying epidermis.

Epidermis: This is a single layer of epithelium of tall, columnar cells which arc distinguished into four types as follows:

1. Supporting Cells: Unspecialized epithelial cells that form the major part of the epidermis.
2. Glandullar Cells: These are of two types more numerous and club-shaped mucussecreting goblet cells and fewer, narrower albumen cells. The mucus, se¬creted by these cells, keeps the body wall moist and slimy. It is also used to lubricate and smoothen the walls of burrows.
3. Basal Cells: These are shorter, conical cells wedged in between narrower basal parts of other cells.
4. Sensory Cells: These are narrow, columnar cells occurring, here and there, in small groups. Each sensory cell has small sensory hairs at its free end.

Muscular Layer: Beneath the epidermis is the musculature of the body wall. It consists of a thin outer layer of circular and about twice thicker, inner layer of longitudinal muscle fibers. The circular muscle layer is a continuous sheet around the body, but the longitudinal layer is broken into several longitudinal strips or bands, separated from each other by thin connective tissue partitions. These bands appear elliptical or club-shaped in the transverse section. Numerous granules of porphyrin pigment are found scattered in the circular muscle layer.

Coelomic Epithelium: Next to the longitudinal muscle layer is a thin, membrane-like, mesodermal epithelium of flattened, squamous cells. It is the outer envelope of coelomic cavity and hence called the parietal or somatic layer of coelomic epithelium or peritonium.

Coelom Or Body Cavity: Earthworm has schizocoel type of body cavity. It lies between the body wall and the alimentary canal.

• A layer of peritoneum lines both the surfaces, the outer parietal in contact with the body wall and the inner visceral in contact with the alimentary canal.
• The coelom of the first four segments is continuous or undivided.
• The coelom is divided by septa from the fourth and fifth segments onward.
• The septa lying between segments 5/6, 6/7, 7/8, 8/9 9/10, and 10/11 are thick and muscular.
• One of the two septa, either between the eighth and ninth or between the ninth and 10th segments are absent.
• The first six septa are cone-like and run obliquely backward from the body wall to the gut wall.
• The first nine septa, i.e., up to septum 13/14 are without perforations.
• The remaining septa beginning from the septum 14/15 are perforated by numerous apertures.
• Coelomic fluid is milky white and alkaline. It has a fluid matrix of watery plasma containing proteins, salts, and numerous minute nucleated corpuscles. Corpuscles are of the following four types.
• Phagocytes: They move like Amoeba and engulf harmful germs.
• Leucocytes: These are smaller and fewer. Their function is not fully understood.
• Mucocytes: These are elongated, vase-like corpuscles, one end forms an expanded fan-like structure and the other narrow end contains a nucleus. The function of these cells is not known.
• Eleocytes: They are formed by mitosis of the yellow cells of the visceral peritoneum. They contain glycogen and fat and distribute their food to various tissues.
• The coelomic fluid serves as a hydrostatic skeleton to assist the musculature of the body wall in bringing about the locomotion of the body. It oozes out upon the body surface through dorsal pores, keeping the body wall moist to facilitate respiration and to destroy bacteria and other harmful microorganisms.

Locomotion: The earthworm does not have specialized locomotory organs.

• The locomotion is brought about by the circular and longitudinal muscles of the body wall, aided by the chitinous curved setae embedded in the skin.
• Due to the contraction of the circular muscles of the anterior end, the latter becomes thin, elongated, and extends forward.
• At the same time, the setae of the anterior end hold the ground firmly and prevent the animal from slipping backward.
• Now the circular muscles of the anterior end relax and the longitudinal muscles contract.
  It causes the shortening and thickening of the anterior segments, and thus, the posterior part of the body is pulled ahead.
• The process is repeated and the worm is able to move forward with speed. Earthworms move at the rate of about 15 cm per minute.

Alimentary Canal: The alimentary canal is a straight tube and runs between the first and last segment of the body.

• In the first to third segments, the buccal cavity is present; the pharynx is present in the fourth segment.
• From the fifth to seventh segment, the oesophagus is present.
• Gizzard is present in the eighth segment.
• The ninth to 1 4th segment is a tubular stomach. Calciferous glands are present in the stomach, which produce CaCO₃, to neutralize the humic acid.
• The intestine starts from the 15th segment onward and continues till the last segment.
• A pair of short and conical intestinal caeca projects from the intestine on the 26th segment. They secrete amylolytic enzyme which digests starch. Other enzymes are lipase, cellulase, invertase, etc.
• Surrounding the pharynx there are pharyngeal or salivary glands, made up of masses of chromophil cells, they produce mucin for the lubrication of the food, and also a proteolytic enzyme that can digest some proteins.
• Associated with the intestine arc chloragogen cells which are supposed to be excretory in function.
• The intestine is divided into the pre-typhlosolar region: This runs from the 15th to the 26th segment, it has a small villi.
• Typhlosolar Region: It starts from 27th segment and extends up to 23-25 segments in front of theanus. Typhlosole is a large villus as an internal median fold of the dorsal wall of intestine. This enhances the effective area of absorption after digestion. Post-type solar region: Also known as rectum, it is present in the last 23-25 segments and opens to the outside through a terminal anus.
• Lymph Glands: These are white fluffy bodies that are found arranged on either side of the dorsal vessel from the 26th segment and extend to the successive segments. These glands are believed to produce phagocytes of the coelomic fluid.

Circulatory System

• Earthworms is the first to evolve a closed circulatory system in the evolution of animals.
• The respiratory pigment is hemoglobin which remains dissolved in the plasma, RBC are absent.
• Blood glands are present in the fourth, fifth, and sixth segments. They produce blood cells and hemoglobin.
• There are two main blood vessels: the dorsal vessel is the largest vessel and blood flows forward from the posterior to anterior end. The dorsal vessels have a contractile wall; valves are present. Before the 13th segment, it becomes a distributing vessel and behind the 13th segment, it becomes a collecting vessel. The ventral vessel is the main distributing vessel, blood flows backward from the anterior to a posterior end; valves are absent.
• Latero-oesophageal vessels are paired vessels that extend from the first to 13th segment.
• The supra-oesophageal vessel is unpaired and extends between 9th and 13th segments.

Hearts: There are four pairs of hearts with valves.

1. Two pairs of lateral hearts, one pair in the seventh segment and one pair in the ninth segment.
2. Two pairs of lateral oesophageal hearts in the 12th and 13th segments.
3. There are two pairs of lateral loops in which valves are absent. One pair is in the tenth segment and one pair is in the 11th segment. Blood flows in an upward direction in them.

Earthworm Points To Remember

Earthworm mainly removes nitrogenous waste in the form of urea in soil. But when plenty of water is available, earthworms become ammonotelic. So, earthworm is both ureotelic and ammonotelic.

Excretory System: Excretory organs occur as segmentally arranged coiled tubules called nephridia. They deliver the wastes through a pore to the surface of the body wall or into the digestive tube. Three main types of nephridia

1. Pharyngeal Nephridia: These are situated in the segments 4, 5, and 6. They open in the anterior part of the alimentary canal, i.e., the buccal cavity and pharynx. They are without nephrostome and are enteronephrictype.
2. Integumentary Nephridia: These are scattered in the body wall. They are the smallest, V-shaped, without nephrostome, and are exophoric type. In clitellar segments, they form forests of nephridia.
3. Septal Nephridia: These are the largest, attached to both faces of each intersegmental septum behind the 15th segment. Septal nephridia are the only nephridia with nephrostome or funnel. The terminal duct opens into the septal excretory canal. These canals, in turn, open into two supraintestinal excretory canals.

Septal nephridia are enteronephric. Hence, final excretory products are poured into the intestine. Enteronephric condition is an adaptation for the conservation of water or osmoregulation. The excretory products of earthworms are urea (about 50%), ammonia (about 40%), and traces of creatinine. Earthworms are mainly ureotelic.

Nervous System: The nervous system of earthworms consists of central, peripheral, and sympathetic nervous systems.

Central Nervous System

• The central nervous system consists of a brain ring/cricopharyngeal ring and a ganglionated double ventral nerve cord.
• The circumpharyngeal ring occurs in the third and fourth segments. It has a brain consisting of two suprapharyngeal ganglia, two circumpharyngeal connectives, and a pair of subpharyngeal ganglia.
• The ventral nerve cord arises from subpharyngeal ganglia, which is double, solid, and bears paired ganglia in each segment.

Peripheral Nervous System

• The peripheral nervous system comprises nerves that extend from CNS to supply various parts.
• The nerves are mixed in nature.
• Two pairs of nerves arise from the brain and innervate the prostomium and buccal cavity.
• Nerves from cricopharyngeal connectives supply segments 1 and 2.
• Subpharyngeal ganglia send nerves to the second, third, and fourth segments.
• Each segmental ganglion (actually paired) sends out three pairs of segmental peripheral nerves, one pair from the anterior part and two pairs from posterior part.
• They supply various structures in each segment. All the segmental nerves are mixed in nature, i.e., containing both sensory (afferent) and motor (efferent) nerve fibers.

Sympathetic Nervous System: The sympathetic nervous system consists of various nerve plexes present in the wall of the alimentary canal.

Sense Organs

• A group of specialized cells are found in the skin and lining of the buccal cavity.
• Photoreceptors are located in the prostomium and dorsal epidermis. They perceive light intensity with the help of phagosomes (optic organelle).
• Thigmoreceptors are located in the ventral and lateral epidermis.
• Olfactoreceptors are located in the lining of the buccal cavity.
• Gustatory receptors are located in the lining of the buccal cavity.

Respiratory System

• Earthworm has no special respiratory organs.
• Gaseous exchange takes place simply through the skin, which is thin and highly vascular.
• Effective gaseous exchange takes place only when the skin is moist.
• The skin is kept moist due to damp earth, secretion of the mucus by the epidermal gland cell, and oozing of coelomic fluid through the dorsal pores.

Reproduction

• Earthworms is hermaphrodites.
• There are two pairs of testes present in the 10th and 11th segments. They are surrounded by two testes sacs lying ventrally, one in the 10th and the other in 11th segment.
• There are two pairs of seminal vesicles, one pair in the 11th and the other pair in 12th segment.
• Maturation of sperms occurs in seminal vesicles.
• The testis sac of 10th segment communicates with the seminal vesicles of 11th segment and the testis sac of 11th segment communicates with the seminal vesicles of 12th segment. From each testis sac, the vas deferens carries the sperms up to the 18th segment where they join the prostatic duct from the prostate gland.
• Four pairs of spermathecae are present, one pair in each of the sixth, seventh, eighth, and ninth segments. They receive and store the spermatozoa of another earthworm during copulation.
  One pair of ovaries lies in the 13th segment, which opens through a median aperture on the 14th segment.
• Accessory glands are present on the ventral surface of the 17th and 19th segments, which open through genital papillae. These are a part of the male reproductive system.
• Testes mature earlier (protandrous).
• Development is direct and there is no larval form.

Cockroach (Periplaneta Americana)

Phylum: Arthropoda

Class: Insecta

Genus: Periplaneta

Species: Americana

Morphology: The body is divided into three distinct regions—head, thorax, and abdomen.

• Their size ranges from 1/4 inch to 3 inches (0.6-7.6 cm).
• The head is hypognathus (facing downward) and is formed by the fusion of six segments.
• Anteriorly, the head bears mouth which is provided with appendages collectively called mouth parts which are used in chewing, cutting, and swallowing.
• The mouth parts consist of a pair of mandibles and maxillae, labium forming the lower lip, and a labrum forming upper lip. Within the cavity enclosed by mouthparts, there is a median flexible lobe called hypopharynx which acts like a tongue.
• Thorax consists of three segments—prothorax, mesothorax, and metathorax.
• A pair ofwings arise from mesothorax which are thick and leathery and are called elytra or tegmina. A pair of membranous wings used in flying arise from metathorax. In houseflies and mosquitoes, the metathoracic wings are reduced to halteres for balancing.

Habit And Habitat: Cockroaches are worldwide and found in such places where darkness, warmth, dampness, and plenty of organic debris is available.

• Cockroaches are nocturnal and omnivorous.
• Three species of cockroaches are commonly found in India: Periplanata americana, Blatta orientalis, and Blatta germanica.
• Periplanata americana is the largest and most common species. It is commonly called American cockroach, Bombay canary, or ship cockroach. In both sexes, wings are present which are larger than the body.
• Blatta orientalis is a black or dark brown mediumsized species. The female has rudimentary wings which are not helpful in flight. The male has wings that are short and are not present up to the end of the body.
• Blatta Germania is the smallest of the domestic species of cockroaches. It is pale yellow-brown in color.

External Features (P. Americana)

• The body is narrow, elongated, bilaterally symmetrical, and flattened, measuring about 3-4.5 cm (34-53 mm) in length and 1.5-2 cm in breadth.
• The color is reddish brown with a pale yellow area around the edge of the pronotum and two dark patches over it.

Exoskeleton

• The entire body of the cockroach is covered with a thick, hard, chitinous cuticle, which is secreted by the epidermis, forming the exoskeleton.
• The exoskeleton of each segment consists of four plate-like pieces called sclerites. The dorsal sclerite is called tergum or tergite, the ventral sclerite is called sternum or sternite, and two lateral sclerites are called pleura or pleurites.
• The sclerites of each segment are joined with each other and with those of the adjacent segments by means of soft and flexible articular or arthrodial membranes. This gives the sclerites some freedom of movement upon each other at their edges.
• The stiff, immovable bristles or spines covering the body and its appendages are in fact the outgrowths of the cuticle while the movable hair-like setae occurring at some places are secreted by special trichogen cells of the hypodermis lying below the cuticle.

Segmentation

• Embryologically, the body of a cockroach is formed of 20 segments: six in the head, three in the thorax, and 11 in the abdomen.
• Due to complete or incomplete fusion between some segments during development, the number of distinct segments is reduced in the adult.
• All segments of the head are fused. The thorax consists of three segments. Only 10 segments are retained in the abdomen of the adult. Of these, only the first seven are distinct in females and the first nine in males. The remaining hinders abdominal segments from becoming small and modified into external genitalia that are hidden under the last distinct segment.
• When wings are removed, the three regions—head, thorax, and abdomen—become distinctly visible. A small, soft, and mobile neck or cervical connects the head with the thorax.

Head

• It is small and triangular, and its narrow end is bent downward in a hypognathous position, i.e., at an angle of 90° with the long axis of the body.
• On each lateral side, it bears a large and blackish compound eye.
• At the base of each antenna, on the inner side, a small rounded and light-colored area called fenestra or ocellar spot representing the simple eye is present. The endoskeleton of head is called the tentorium.
• All sclerites of the head are fused, forming a strong head capsule exhibiting only faint lines of fusion.
• Cephalic Appendages: The head appendages include a pair of antennae, mandibles, first maxillae, and second maxillae (fused as single labium or lower lip), one labrum or upper lip, and one hypopharynx.
• Antennae: These are a pair of long, thread-like appendages, extending forward from an antennal socket located dorsally upon the head capsule near the eye. These are mobile and act as tactile, thermal, and olfactory receptor organs. Each is formed of several small segments called podomeres. The first basal podomere, called scape, is the largest. The second, called pedicel, is narrow and elongated. The remaining long, slender, and many-jointed parts of each antenna is called a flagellum.

Mouth Parts: The remaining cephalic appendages are small and located around the mouth. Hence, together these appendages comprise the mouth parts of the cockroach. These help in “biting and chewing” its food.

Labrum (Upper Lip): It is the broad, flattened termi¬nal sclerite of the dorsal side of the head capsule, movably articulated to the clypeus that acts as the upper lip. It has an epipharynx (chemoreceptors) on its inner side.

Mandibles: Thick, hard, and triangular appendages beneath the labrum, one on each lateral side of the mouth, which bear pointed, teeth-like processes called denticles.

First maxillae: Located on each side of the mouth next to mandibles. These serve to hold food particles in between the mandibles for cutting and chewing. They also bear olfactory receptors.

Labium (Lower Lip): The second maxillae are fused together forming a single large structure that covers the mouth from the ventral side, hence called the “lower lip” or labium. It bears tactile and gustatory sensory setae.

Hypopharynx: It is a small, cylindrical mouthpart, sandwiched between the first maxillae and covered by labrum and labium on the dorsal and ventral sides, respectively. It bears several sensory setae on its free end and the opening of a common salivary duct upon its basal part.

Thorax

• The thorax comprises three segments—prothorax, mesothorax, and metathorax.
• The three thoracic segments are covered by relatively thicker and larger tergites called nota.
• The notum of prothorax called pronotum is very large and covers the neck also. Each of the mesonotum and metanotum bears a pair of wings.

Thoracic Appendages: Each thoracic segment bears a pair of walking legs. Each walking leg consists of segments

1. Coxa.
2. A triangular short rod-like trochanter, articulated with coxa and femur
3. A long, spiny femur.
4. A spring-like tibia which represents the longest segment.
5. A long tarsus is divided into five tarsomeres or podomeres. The last tarsomere is called pretarsus forming the claws and bearing an adhesive arolium or pulvillus. Similar but smaller adhesive pads called plantulae are located at each joint of the tarsus.

Abdomen: It is the largest and the broadest; relatively more flattened and softer part behind the thorax. There are 10 tergites. In both males and females, the eighth and ninth tergites are mostly covered by the seventh. The 10th tergum is somewhat bowl-shaped and posteriorly bifurcated into two lobes.

• Ventrally, the abdomen has nine stemites in males and seven in females.
• In females the last stemming (seventh) is larger and boat-shaped and together with indistinct eighth and ninth stemites, it forms a chamber-like structure called gynatrium the posterior part of this chamber is called the oothecal chamber. Behind this chamber, the seventh stemite bifurcates into two prominent oval plates called apical lobes. Female gonopores is located between them.
• In males, the ninth stemite bears a pair of spine-like anal styles.
• In both male and female cockroaches, several small chitinous appendages are located around the gonopore. These help in reproduction and hence are called gonapophyses.
• At several places, certain processes of the exoskeleton extend into the body and form endoskeletal elements that provide attachment to muscles and are hence called apodemes.

Abdominal Appendages

• Abdominal segments lack locomotory appendages. There are certain small structures associated with gonopore, which are different in male and female cockroaches.
• The 10th tergum posteriorly bears a pair of many jointed anal cerci. They bear minute sensory hair sensitive to sound and other vibrations.
• The ninth sternum of males bears, in addition, a pair of small and spine-like, unjointed anal styles.

Digestive System Of Cockroach

The alimentary canal is long and somewhat coiled, di-visible into three main parts, namely, foregut, midgut, and hindgut.

Foregut (stomodeum) is lined by a cuticle and is differentiated into five parts: buccal chamber, pharynx, esophagus, crop, and gizzard. The crop is used for the storage of food.

• The gizzard is muscular and internally provided with six cuticular teeth that crush the food. A stomodeal valve is present between the gizzard and mesenteron.
• The midgut (mesenteron or ventriculus) is short, tubular, and lined with glandular endoderm.
• At the anterior end of the mesenteron, there are six to eight blind glandular hepatic or gastric cecae which secrete digestive enzymes.
• Internally mesenteron is not lined by cuticle but it is covered by a very thin and transparent peritrophic membrane formed of chitin and proteins.
• The peritrophic membrane is secreted by the gizzard which serves to protect the wall of the midgut from abrasion due to the friction of food particles.
• The peritrophic membrane is permeable to digested food and enzymes in the mesenteron.
• The hindgut (proctodeum) is broader than the midgut and comprises the ileum, colon, and rectum.
• The wall of the rectum is provided with six rectal papillae. They help in the absorption of water and salts.
• The cockroach is omnivorous. It feeds on all sorts of organic debris.
• The digestive enzymes of saliva are mainly zymase and amylase.
• Most of the nutrients of food are digested in the crop.
• The absorption of digested food takes place in the mesenteron.

Respiratory System of Cockroach

• The blood of cockroaches is not responsible for the transportation of gases. It serves as a stationary medium for the exchange of gases.
• A complicated system of numerous, shiny, transparent, and branched air tubes or tracheae are found for gaseous exchange in the hemocoel cavity. There are six longitudinal tracheal tubes—two dorsal, two ventral, and two lateral, which are interconnected by transverse commissures. Chitinous rings prevent the collapse of the trachea.
• Atmospheric air enters into and escapes out from this system through 10 pairs of slit-like apertures called stigmata or spiracles located on the lateral sides of the body. Two pairs of these are thoracic and eight pairs are abdominal. The openings of spiracles are regulated by the sphincters.

• Thoracic spiracle, arc somewhat larger. One pair of these is between prothorax and mesothorax and the other between mesothorax and metathorax, upon re¬spective pleurites.
• The first pair of abdominal spiracles is dorsolateral upon the tergite of the first abdominal segment, but the remaining seven pairs are present upon the pleurites of the second to eighth segments.
• Each spiracle is surrounded by a ring-like sclerite called peritreme.

Mechanism Of Respiration

• Several tergo-stemal muscles extend vertically between the tergites and stemites of all abdominal segments.
• Harmonious contractions and relaxations of these at regular intervals cause rhythmic expansion and compression of the abdomen leading to inspiration (with relaxation) and expiration (with contraction) of air.
• At rest, the oxygen requirement is less, and tracheolar ends get filled with tissue fluid.
• The movement of O₂ is along the pressure gradient as the tracheolar ends are losing oxygen to the cells for performing cellular respiration.
• O₂ requirement increases during activity.
• Tracheolar fluid is withdrawn out of Tracheoles.
• Alternate expansion and contraction of the abdominal cavity occurs involving tergo-stemal muscles and abdom¬inal muscles.
• A high level of CO₂ in the abdominal cavity makes tergostemal muscles and abdominal muscles to contract pushing out the air from the tracheal system to the outside through spiracles.
• With relaxation, the abdomen expands, i.e., tracheal trunks and tracheae expand, and as a result, air rushes into tracheae and tracheoles via spiracles, which results in inspiration.

Circulatory System of Cockroach

• Blood vascular system is open and lacunar type. Body cavity contains blood (hemolymph) which bathes viscera in it, therefore known as hemocoel.
• The blood vascular system consists of a tubular heart, a blood vessel called the anterior aorta, and a system of ill-defined blood spaces or sinuses.

Heart: It is a long elongated tube situated in the mid-dorsal line of the thorax and the abdomen immediately beneath the terga.

• The heart consists of 13 chambers.
• The last two posterior chambers are very small.
• The chambers are separated from one another by deep constrictions.
• The opening of each chamber into another is guarded by valves that allow blood from behind to forward.

Blood Sinuses: The large body cavity or hemocoel is divided by two membranous horizontal partitions, into three wide and flattened sinuses—the dorsal pericardial sinus containing the heart, the middle perivisceral sinus containing the gut, and the ventral perineural sinus or sternal sinus containing the nerve cord.

• The partition between the pericardial and perivisceral sinuses is called the dorsal diaphragm and between the perivisceral and perineural sinuses is called ventral diaphragm.
• The sinuses intercommunicate by pores in the respective diaphragms.
• A pair of fan-like, triangular alary muscles in the floor of the pericardial sinus in each segment reinforces the dorsal diaphragm by their broad bases and also con¬nects it by their pointed tips with the tergite of the segment.

Circulation Of Hemolymph

• The pumping force that propels the hemolymph is provided by the pulsations of the heart. The respiratory movements of the abdomen and contraction of alary muscles increase this force.
• From the pericardial sinus, the hemolymph enters into heart through the ostia. When the heart is filled, it contracts from behind forwards. This is its systole phase. Soon the heart becomes relaxed in its diastole phase. Then the next systole follows after a short time interval called diastasis. Thus, the heart pulsates about 50 times/ min.
• During systole, the valve-like ostia closes, preventing the backflow of hemolymph into the pericardial sinus. Therefore, some of its hemolymph is pumped into seg-mental vessels while most of it is poured into the head sinus through the terminally opening anterior aorta.
• From the head sinus, the hemolymph flows backward into the thorax and abdomen. While flowing backward from the head sinus, the hemolymph remains in the ventral part due to the presence of esophagus in the dorsal part. So, it fills into the perineural sinus.
• From the perineural sinus, the hemolymph now flows into the perivisceral sinus through the pores of the ventral diaphragm in the abdominal region.
• Then from the perivisceral sinus, it flows into the pericardial sinus through the pores of the dorsal diaphragm. Then, during the heart’s diastole, it fills in the heart through the ostia.

Excretion In Cockroach: Cockroach is uricotelic. In cockroaches, the following structures help in excretion:

1. Malpighian tubules
2. Fat bodies
3. Nephrocytes
4. Cuticle
5. Uricose glands in some species

1. Malpighian Tubules: Malpighian tubules are attached at the junction of the midgut and hindgut. Excretory products, dissolved in hemolymph and absorbed by Malpighian tubes, are discharged into the hindgut.
2. Fat Bodies: Some fat bodies are also present in hemocoel which have mycetocytes, urate cells, oenocytes, and trophocytes.
3. Nephrocytes: Nephrocytes are present in the lateral wall of the heart and help in the excretion and storage of nitrogenous waste.
4. Uricose Glands: In some species, in males, uricase glands are present on the periphery of mushroom glands. These glands synthesize uric acid. Malpighian tubules are analogous to mammalian kidneys, and bodies are analogous to vertebrate liver.
5. Nervous System of Cockroach: It consists of a series of fused, segmentally arranged ganglia joined by paired longitudinal connectives on the ventral side.
6. Central Nervous System: The central nervous system consists of the brain or supraesophageal ganglion. The brain gives of a pair of short, stout cords, the circumocsophageal connectives, which encircle the esophagus and pass downward and backward over the subesophageal ganglion situated below esophagus.

From the suboesophageal ganglion, a double ventral nerve cord passes backward into the thorax, which bears three ganglia in the thorax and six in the abdomen.

Peripheral Nervous System: The peripheral nervous system consists of nerves, which are given off from the ganglia so as to innervate all the parts of the body.

Sympathetic or Somatogastrlc Visceral Nervous System: The stomatogastric nervous system consists of a frontal ganglion which is situated on the dorsal side of the esophagus in the head. From this ganglion, a median unpaired recurrent nerve reaches the visceral ganglion situated on the crop.

Various nerve branches are given off from the visceral ganglion. The frontal ganglion is joined with the central nervous system by nerves that connect it to circumoesophageal commissures.

Sense Organs of Cockroach: Receptor cells are present on the general body surface.

• Proprioreccptors: They are for hearing or receiving sound vibrations. Auditory receptors are present on the antennae and anal cerci.
• Thigmoreceptors: They are the receptors for touch and arc present on antennae, maxillary palps, and legs.
• Olfactory Receptors: They receive various smells and are present on antennae and palps.
• Gustatory Receptors: They are for the sense of taste and are present on maxillae and labial palps.

Eyes: Cockroach has compound eyes. Each compound eye is formed of about 2000 hexagonal ommatidia. Each ommatidium has a biconvex lens or cornea. Below the lens, there are collagen cells that secrete the lens.

• Below the collagen cells is a transparent crystalline cone surrounded by four vitrellae or cone cell.
• The vitrellae secrete the crystalline cone. All this forms the focusing or dioptrical region.
• Below the cone, there is a refractive body, the rhabdome, surrounded by seven retinular cells.
• Each ommatidium is isolated from the other by an iris pigment sheath and retinal pigment sheath.
• The image formed is an apposition or mosaic vision, composed of as many separate but adjacent images as there are ommatidia.
• In mosaic vision, images are sharp but separate and the eye can use only in bright light.
• In cockroach vision is mosaic and an apposition image is formed (although cockroach is nocturnal).
• If pigmented iris sheath is removed from the compound eye of insects, only a superposition image will be formed.

Reproductive System of Cockroach (Male)

• In cockroaches, the sexes are separate, so it is dioecious.
• The testes of cockroaches are located in the abdominal segments 4, 5, and 6.
• The mushroom gland consists of two types of tubules:
• The long slender tubules, utriculi majors or peripheral tubules, and
• Short tubules, utriculi breviores, make up the major part of the gland. It is present in the sixth to seventh abdominal segments which function as an accessory reproductive gland.
• Small seminal vesicles are also found associated with mushroom glands.
• All sperms of a seminal vesicle are glued together into a large bundle called a spermatophore.
• Spermatophore has a three-layered wall: the inner layer is secreted by utriculi majores; the middle layer is secreted by the ejaculatory duct; and the outer layer is secreted by the phallic gland or conglobate gland.
• There are three asymmetrical chitinous structures called male gonapophyses or phallomeres. Right phallomere, left phallomere (largest), and ventral phallomere (smallest).

Reproductive System of Cockroach (Female)

• Female organs consist of ovaries, oviducts, vagina, genital chamber, spermathecae, colleterial glands, and female gonapophysis (ovipositor processes).
• The ovaries of cockroaches are located in the abdominal segments 2 to 6. Each ovary consists of eight ovarioles.
• Two oviducts from each side open into a common oviduct or vagina which opens into the genital chamber by the female genital pore. A pair of spermathecae (left larger pyriform sac) are present near the female genital pore.

• A pair of colleterial glands also open in the genital chamber.
• The genital pouch or gynatrium is divisible into a genital chamber in front and an oothecal chamber (vestibulum) behind.
• Female genitalia consist of three pairs of chitinous processes hanging from the roof of the oothecal chamber into its cavity.
• The ootheca of cockroaches contains 14 to 16 fertilized eggs. It is formed of a protein secreted by colleterial glands. On average, females produce 9-10 oothecae.
• The nymphs of cockroaches emerge from the ootheca. A nymph resembles an adult in general structure but lacks wings and mature reproductive organs. The next to last nymphal stage has wing pads but only adult cockroaches have wings.
• The instar is a stage in the development of insects (larval instar, nymphal instar). The period between two successive molts in insects is termed stadium.
• In Periplaneta americana, the nymph grows by molting about 13 times to reach the adult form, and in Blatta orientalis, it molts about six times.

Frog (Rana Tigrina)

Phylum: Chordata

Class: Amphibia

Order: Anura

Genus: Rana

Species: tigrina

The most common frog found in India is the Indian bullfrog. It is the largest frog and is named as bullfrog because of its large size and loud call.

• Indian bullfrog is found in freshwater marshes, ditches, ponds, and shallow lakes.
• They undergo aestivation (summer sleep) in summer and hibernation (winter sleep) in winter.
• They are carnivorous (feeding upon other animals, insects, etc.), poikilothermic, i.e., the body temperature changes with the environment.
• They develop protective coloration to camouflage, i.e., to hide in surroundings.
• Frogs belong to the phylum Chordata, subphylum Vertebrata or Craniata, superclass
• Gnathostomata, class Amphibia, and Genus Rana.
• The most common species is known as Rana tigrina (Indian bullfrog).
• The scientific name of the common toad is Bufo melanostictus. Frogs exhibit sexual dimorphism.
• Male and female are distinguishable externally only during breeding season when the males develop nuptial pad in the first digit of the forelimbs.
• Vocal sacs are well developed in males so they produce louder sounds as compared to females which are devoid of vocal sacs.
• The vocal sacs help to produce mating calls.
• The total number of bones in a frog is 153.

External Morphology: Skin is made up of the epidermis and dermis. Mucous glands are present in the dermis and their ducts open at the surface.

• Blood capillaries and pigment cells (chromatophores) are present in the dermis.
• Skin is without scales or any other cover or exoskeleton.
• Body is divisible into head and trunk, neck is absent. The trunk is provided with a pair of fore and hind- limbs. The hind limbs are much larger and muscular than the forelimbs. Forelimbs end in four digits and the hind limbs end in five digits. The digital formula of forelimbs is 02233. The digital formula of hind limbs is 22343.
• Shank or crus is associated with hind limbs.

Sexual Dimorphism

• The male and female frogs exhibit certain differences in their external features, which become more pronounced during breeding season.
• Generally, male frogs are larger than females.
• During the breeding season, however, the females become bloated with large ovaries and numerous ova and appear considerably larger.
• Only the males possess a pair of ventrolateral, wrinkled, pouch-like vocal sacs located a little behind the mouth.
• These sacs become especially large and distensible in the breeding season.
• By inflating these repeatedly with air from the lungs, the males produce a loud croaking sound meant to call the females for copulation (amplexus).
• The sound is actually produced by a pair of vocal cords in the larynx; the sacs only increase its pitch, such as resonators.
• The females produce a low-pitched sound by their vocal cords alone.
• The forelimbs in both male and female frogs bear small particular pads dorsally at the joints of digits, but the males also possess a special nuptial, copulatory, or amplcxusary pad on the ventral side of the first finger of each forelimb.
• Normally, these pads appear merely as rough patches but during breeding season, these become thick and sticky.
• In amplexus, the male strongly grips a female under her armpits by means of these pads.

Internal Morphology: Digestive System

• Since the frogs are carnivorous, their alimentary canal is short in length.
• Tadpole larva is herbivorous, so the alimentary canal is very long and coiled in the form of offspring.
• The mouth is present as a terminal, wide opening.
• It opens into the bucco-pharyngeal cavity, which contains numerous maxillary teeth arranged along the margin of the upper jaw. Vomerine teeth are present under the roofof the buccopharyngeal cavity.
• The lower jaw is toothless.
• Opening of the Eustachian tube, vocal sacs (only in males), gullet, and glottis can be seen clearly in the buccopharyngeal cavity.
• The muscular tongue is bilobed at the tip and free from behind. It is used for capturing the prey.
• The gullet opens into a narrow and short tube-like esophagus, which continues in a large and distended stomach.
• It contains a thick muscular layer, which helps in verting food into chyme.

• It secretes gastric juice containing HCl and proteolytic enzymes. The stomach is followed by a coiled small intestine.
• The intestinal wall has numerous finger-like folds called villi and microvilli, projecting into its lumen to enhance the surface area for absorption of the digested food.
• The first part of the small intestine lying parallel to the stomach is called the duodenum. The intestine continues into a wider rectum, opening into the cloaca.
• The urinary bladder opens into the cloacal chamber through the ureter.
• The gastric and intestinal glands occur in the walls of the stomach and intestine, respectively.
• The other important digestive glands associated with the alimentary canal are the liver and pancreas.
• The liver secretes bile which is temporarily stored in the gall bladder before being released into the duodenum.
• Bile helps in the digestion of food by changing its pH from acidic to alkaline and by emulsifying the fats.
• The liver does not secrete any digestive enzymes. The pancreas is an irregular, elongated gland, situated in a thin mesentery, and lies parallel to the stomach.
• It produces pancreatic juice containing digestive enzymes such as trypsin, amylopsin, etc.

Respiratory System

• Three Types Of Respiration Are Observed: cutaneous, buccopharyngeal, and pulmonary.
• Cutaneous respiration on land is through the body’s surface. During hibernation and aestivation, frog respires only through this method.
• Buccopharyngeal respiration occurs through the lining of the buccal cavity. It occurs only when the frog is out of water. The mucus membrane of the buccal cavity is moist which dissolves oxygen whose diffusion occurs into the blood capillaries.
• Pulmonary Respiration: Lungs in frogs are not efficient respiratory organs because only mixed air enters into them and they mainly function as hydrostatic organs.
• Lungs are a pair of thin-walled, translucent sacs with an inner surface divided into alveoli by septa. Pulmonary respiration has a maximum frequency of 20/min.
• It occurs when more energy is required. The mouth and gullet are kept closed during pulmonary respiration.
• Respiratory movements in pulmonary respiration are because of the buccopharyngeal cavity which acts as a force pump. These movements are carried out by a set of paired muscles—stemohyal and pterohyal muscles.
• Stemohyal muscles are attached to hyoid and coracoid processes and clavicles of the pectoral girdle and, on contraction, depress the buccal floor enlarging the buccopharyngeal cavity.
• Pterohyals are attached in between the hyoid and prootics of the skull and, on contraction, lift the floor of the buccal cavity.
• With the depression of the buccal floor, air enters the buccal cavity through the nares.
• External nerves are then closed by pushing the tuberculum prelingual and the movable pre maxillae.
• It is followed by the raising of the buccal floor by peroneal muscles which reduce the volume and the air is pushed into the lungs where the exchange of gases takes place.
• The buccal floor is again lowered enlarging its volume which draws air into the buccal cavity.
• External nares are opened followed by raising the buccal floor, pushing the air out through external nares.
• The sound-producing organ of a frog is the laryngotracheal chamber. It is supported by one cricoid, two arytenoids, and two pre-arytenoid cartilages. It has a pair of muscle strands (vocal cords) that actually produce sound. The male frog has vocal sacs which act as resonating chambers.

Circulatory System

• The circulatory system in frogs is closed type.
• The heart lies enclosed by a thin, transparent, two-layered sac, pericardium.
• Frog s heart is a three-chambered structure made up of two upper auricles and a single lower ventricle.
• The two additional chambers connected to the heart of the frog are sinus venosus and truncus arteriosus.
• Frogs also possess two well-developed portal systems: the renal portal system and the hepatic portal system. Frog also has two pairs of lymph hearts.

Nervous System

• The nervous system is organized into a central nervous system (brain and spinal cord), a peripheral nervous system (cranial and spinal nerves), and an autonomic nervous system (sympathetic and parasympathetic chains of ganglia).
• There are 10 pairs of cranial nerves.
• The brain is enclosed in a bony structure or brain box (cranium) which has two occipital condyles for attachment with the first vertebra (atlas).
• The brain is divided into forebrain, midbrain, and hindbrain.
• The forebrain includes olfactory lobes, paired cerebral hemispheres, and unpaired diencephalon. The midbrain is characterized by a pair of optic lobes.
• The hindbrain consists of the cerebellum and medulla oblongata.
• Medulla oblongata passes out through the foramen magnum and continues into the spinal cord which is contained in the vertebral column.
• Jacobson’s organ, also called the vomeronasal organ, opens into the nasal chamber and acts as an additional olfactory organ.

Sensory Organs

• Eye
  • The eye is guarded by an immovable upper eyelid, movable low er eyelid, and transparent nictitating membrane.
  • The outer sclerotic ring is cartilaginous and the cornea is the part exposed. In the middle, the highly vascular, pigmented layer is choroid.
  • Iris is yellow-pigmented and perforated by a central aperture, the pupil.
  • The retina is the innermost coat of the eyeball and consists of an inner pigmented layer and an outer receptor layer.
  • Rods and cones are light-sensitive structures found in the retina.
  • Rods have rhodopsin or visual purple meant for night vision while cones have iodopsin responsible for color vision in daylight.
  • The anterior chamber present in the front of the lens is filled with aqueous humor while the chamber behind the lens is a posterior chamber, filled with vitreous humour.
  • The eyeball is moved in the eye orbit by a set of six muscles—two are oblique and four are recti.
  • Besides, there are retractor bulbs and levator bulbs muscles for intrusion or protrusion of the eyeball into the eye orbit, respectively.
• Ears
  • The ear of frog has only a middle and internal ear.
  • The tympanic membrane is present at the body surface.
  • The middle ear has a single bone called columella auris.
  • Its outer end is attached to the eardrum while the inner end is attached to the stapedial plate.
  • The pressure of air in the middle ear is controlled by Eustachian tubes.
  • The membranous labyrinth or internal car consists of a utriculus, sacculus, and semicircular canals. Endolynrph fills the membranous labyrinth.
• Excretory System
  • The main organ of excretion is a pair of kidneys.
  • These compact, dark red, and bean-like structures are situated a little posteriorly in the body cavity on both sides of the vertebral column.
  • The frog excretes urea and thus is a ureotelic animal.
  • Urea is carried by blood into the kidney where it is separated and excreted.
  • Each kidney is composed of several structural and functional units called uriniferous tubules or nephrons.
  • The ureter emerges from the kidney as urinogenital ducts in males.
  • A common ureter opens into the cloaca.
  • A thin-walled urinary bladder is present ventral to rectum which also opens in the cloaca.

Reproductive System: The male reproductive organs consist of a pair of yellowish ovoid testes, which are found to adhere to the upper part of the kidneys by a double fold of peritoneum called mesorchium.

• Vasa efferentia are 10-12 in number and, after arising from the testes, run through the mesorchium and enter the kidneys of their side.
• In kidneys, these open into Bidder’s canal which finally communicates with the urinogenital duct. This duct emerges from the kidneys and finally opens into the cloaca.
• The cloaca is a small, median chamber that is used to pass fecal matter, urine, and sperm to the exterior.
• A pair of ovaries, situated near the kidneys, comprises the female reproductive organs. However, these have no functional connection with the kidneys.
• A pair of oviducts opens into the cloaca, separately
• The release of ovum in females is termed as spawning.
• A mature female can lay 2500-3000 ova at a time.
• Fertilization is external and takes place in water.
• Development involves a larval stage called tadpole.
• Tadpole undergoes metamorphosis to form an adult.

 

Structural Organization In Animals Assertion Reasoning Questions And Answers

In the following questions, an Assertion (A) is followed by a corresponding Reason (R). Mark the correct answer.

1. If both Assertion and Reason are true and the Reason is the correct explanation of the Assertion.
2. If both Assertion and Reason are true, but the Reason is not the correct explanation of the Assertion.
3. If Assertion is true, but Reason is false.
4. If both Assertion and Reason are false.

Question 1. Assertion: Cardiac muscles have striations and fiber is nucleated and involuntary.

Reason: Intercalated discs form the three-dimensional network of cardiac muscle fiber.

Answer: 3. If Assertion is true, but Reason is false.

Question 2. Assertion: Multipolar neurons have several efferent processes.

Reason: Axons are the afferent processes of a neuron.

Answer: 4. If both Assertion and Reason are false.

Question 3. Assertion: Blood circulation is absent in epithelium tissue.

Reason: Blood vessels are unable to pierce the basement membrane.

Answer: 3. If Assertion is true, but Reason is false.

Question 4. Assertion: Reticular fibrous connective tissue is called as embryonic tissue.

Reason: Reticular fibrous connective tissue is mainly found in the embryonic stage.

Answer: 4. If both Assertion and Reason are false.

Question 5. Assertion: Epithelia are highly regenerative.

Reason: When epithelia get damaged, they regenerate more rapidly than other tissues.

Answer: 1. If both Assertion and Reason are true and the Reason is the correct explanation of the Assertion

Question 6. Assertion: Platelets play an important role in blood clotting.

Reason: In the blood oozing from an injury, the platelets disintegrate and release thromboplastin that initiates clotting.

Answer: 1. If both Assertion and Reason are true and the Reason is the correct explanation of the Assertion

Question 7. Assertion: Brown fat produces more energy.

Reason: Brown fat is composed of molecular adiposity

Answer: 3. If Assertion is true, but Reason is false.

Question 8. Assertion: Simple cuboidal epithelium is called as germinal epithelium.

Reason: The cuboidal cells of gonads form gametes.

Answer: 1. If both Assertion and Reason are true and the Reason is the correct explanation of the Assertion

Question 9. Assertion: Heparin is an anticoagulant found in mammals.

Reason: Heparin prevents the conversion of prothrombin to thrombin.

Answer: 1. If both Assertion and Reason are true and the Reason is the correct explanation of the Assertion

Question 10. Assertion: Epithelium cells get their nutrients from adjacent cells.

Reason: In epithelium tissues, large intercellular spaces are present.

Answer: 4. If both Assertion and Reason are false.

1. If both Assertion and Reason are true and the Reason is the correct explanation of the Assertion.
2. If both Assertion and Reason are true, but the Reason is not the correct explanation of the Assertion.
3. If Assertion is tine, but Reason is false.
4. If both Assertion and Reason are false.

Question 11. Assertion: Earthworm is brown or claycolored.

Reason: Because of the presence of pigment porphyrin.

Answer: 1. If both Assertion and Reason are true and the Reason is the correct explanation of the Assertion.

Question 12. Assertion: Chloragogen cells are considered analogous to the liver of vertebrates.

Reason: Because it is concerned with the storage of reserve food, deamination of proteins, formation of urea, etc.

Answer: 1. If both Assertion and Reason are true and the Reason is the correct explanation of the Assertion.

Question 13. Assertion: Earthworms is saprozoic.

Reason: Because it feeds on small insects.

Answer: 3. If Assertion is tine, but Reason is false.

Question 14. Assertion: Earthworm is hermaphrodite.

Reason: Because in earthworms both sexes are separate.

Answer: 3. If Assertion is tine, but Reason is false.

Question 15. Assertion: Earthworms are the enemy of fanner.

Reason: Because they destroy the crop in the field.

Answer: 4. If both Assertion and Reason are false.

Question 15. Assertion: In the body of earthworms, porphyrin pigment is found.

Reason: Because it protects earthworms from chemicals.

Answer: 3. If Assertion is tine, but Reason is false.

Question 16. Assertion: In earthworms, development is direct.

Reason: Because in development larval stage is not found.

Answer: 1. If both Assertion and Reason are true and the Reason is the correct explanation of the Assertion.

Question 17. Assertion: In the anus of earthworms, depressor muscles are found.

Reason: These muscles help in the elimination of excretion from the rectum.

Answer: 1. If both Assertion and Reason are true and the Reason is the correct explanation of the Assertion.

Question 18. Assertion: In cockroaches, inspiration is an active process.

Reason: It is due to the contraction of tergosternai muscle.

Answer: 4. If both Assertion and Reason are false.

Question 19. Assertion: In frogs, sinus venosus is present.

Reason: In mammals and birds, the remnant of sinus venosus has taken part in the formation of SA node.

Answer: 2. If both Assertion and Reason are true, but the Rea¬son is not the correct explanation of the Assertion.

Question 20. Assertion: Septal nephridia take part in osmoregulation.

Reason: They are entcronephric.

Answer: 1. If both Assertion and Reason are true and the Reason is the correct explanation of the Assertion.

Question 21. Assertion: In Periplcineta, only superposition or overlapping images are formed.

Reason: Retinal pigment sheath remains contracted throughout life.

Answer: 4. If both Assertion and Reason are false.

Question 22. Assertion: The pharyngeal gland of earthworms includes chromophil cells, which secrete sativa.

Reason: The salivary amylase of earthworms is essential to digest carbohydrates.

Answer: 3. If Assertion is tine, but Reason is false.

Question 23. Assertion: The head of the cockroach is hypognathus.

Reason: The proximal part of the lower lip of a cockroach is called the pastmentum.

Answer: 2. If both Assertion and Reason are true, but the Reason is not the correct explanation of the Assertion.

Question 24. Assertion: The heart of a cockroach is neurogenic.

Reason: The heartbeat rate in cockroaches is 49 per minute.

Answer: 2. If both Assertion and Reason are true, but the Rea¬son is not the correct explanation of the Assertion.

 

Anatomy Of Flowering Plants Introduction

The branch of botany dealing with the internal organization of plants is called anatomy. N. Grew laid the foundation of plant anatomy. He coined the term tissue. He is known as the father of anatomy.

Tissues

A group of similar or dissimilar cells that perform a common function and have a common origin is called tissue. Tissues are classified into two main groups: meristematic and permanent.

Meristematic Tissues

1. Mesistematic tissues consist of cells that retain the power of division.
2. The protoplasm within the cell is dense, the vacuole is smaller or absent.
3. These cells are isodiametric without intercellular spaces.
4. The nucleus is bigger in size.
5. These cells have thin cellulosic cell walls.
6. These are metabolically active cells with high surface area per unit volume and nucleocytoplasmic ratio.
7. Ergastic substances are absent.
8. Colorless proplastids are present in the cells.

Classification Of Meristems

On The Basis Of Origin And Development

1. Promeristems (Primordial Meristem): Promeristerms are a group of cells that represent the primary stages of meristematic cells. They are found at the apices of embryonic shoots and roots. They give rise to primary meristems.
2. Primary Meristems: They originate from pro meristems. They are found at shoot and root apices, at the apex of leaves, and in intercalary parts. They give rise to primary permanent tissues.
3. Secondary Meristems: They are not present from the beginning of the formation of an organ but develop at a later stage. They give rise to secondary permanent tissues. They develop from primary permanent tissues, for example, interfascicular cambium, cork cambium, and cambium in dicot roots.

On The Basis Of Position

1. Apical Meristem: These cells or tissues are found at the apices of the stem and root. Due to continuous division, the root and stem increase in length. The apical meristem helps the plants to grow in length.
2. Intercalary Meristem: The tissues are intercalated between permanent tissues. These are actually the parts of the apical meristem that get separated from it during the growth of the stem and root in length. The most characteristic example is the stem of grasses and Equisetum. Intercalary meristem is especially responsible for the increase in the length of the stems of grasses.
3. Lateral Meristem: These meristems are present along the lateral side of the stem and root. They divide in a tangential plane, giving rise to secondary permanent tissues on the inner and outer sides and leading to the increase in thickness or girth of the plant body, for example, intrafascicular cambium, inter¬fascicular cambium, and cork cambium.

Read and Learn More NEET Biology Notes

On The Basis Of Plane Of Cell Division

1. Mass Meristem: The cells divide anticlinally in all planes so that a mass of cells is formed. For example, the formation of spores, cortex, pith, endosperm, etc.
2. Plate Meristem: The cells divide anticlinally in two planes, so the plate-like area is increased. For example, the formation of epidemics and lamina of leaves.
3. Rib Or File Meristem: The cells divide anticlinally in one plane, so a row or column of cells is formed. For example, the formation of lateral roots.

On The Basis Of Function

1. Protoderm: They are the outermost meristematic cells. They form the skin or epidermis of the plant and epidermal tissue system.
2. Procambium: They are the innermost meristematic cells. They form the primary xylem, primary phloem, and cambium.
3. Ground Meristem: They form ground or funda¬mental tissues such as hypodermis, cortex, pith, pericycle, etc.

Shoot Apex Organization: Shoot apex is present immediately above the youngest leaf primordia. It consists of meristematic cells. The lateral branches of the stem and leaves are formed by the activity of shoot apex. Many theories have been put forward to explain shoot apex such as

Apical Cell Theory: It was proposed by Hofmeister and Nageli. According to this theory, a single apical cell leads to the development of the entire plant body. This theory is applicable to algae, as well as to most of the bryophytes and pteridophytes.

Histogen Theory: It was proposed by Hanstein. According to this theory, a shoot apex consists of the following halogens:

1. Dermatogen: The outermost layer, it forms the epidermis (skin) and epidermal tissue system.
2. Periblem: It gives rise to the tissues between the epidermis and the stele.
3. Plerome: It is the innermost layer and the central mass of cells that give rise to the central stele.

Tunica Corpus Theory: It was proposed by Schmidt (1924). It is based on the plane of division of the cells. According to this theory, the shoot apex consists of two distinct layers:

1. Tunica: It is mostly single-layered and forms epider¬mis. The cells of tunica are smaller than the corpus and divide mostly by anticlinal divisions.
2. Corpus: It represents the central core with larger cells. The cells divide periclinally. Sometimes tunica is multi-layered, only the outer layer forms epidermis, and the remaining layers with corpus form the cortex of the shoot.

Root Apex Organization: The Root apex consists of a mass of meristematic cells. It is not responsible for the formation of lateral roots. Root cap or calyptrogen is present due to which the root meristem becomes subterminal in position. If the root cap is independent in origin, it arises from dermatogen. Regarding the organization of root apex, the following theories have been put forward

Korper-Kappe Theory: It was proposed b.y Schuepp (1917). This theory is comparable with the tunica corpus theory of shoot apex. Korper means body and kappe means cap.

Quiescent Center Theory: It was proposed by Clowes (1956-5 8). According to this theory, the root apex consists of an inverted cup-like structure, the quiescent center. The cells of this region are with very low mitotic activity (quiescent). They have low amounts of RNA, DNA, and protein. They are surrounded by a layer of actively dividing cells which are responsible for the formation of the different structures of roots.

Permanent Tissue

Permanent tissues are composed of living or dead cells that are derived from the meristematic tissues but have lost their ability to divide. There are of three types: simple tissues, complex tissues, and secretory tissues.

Simple Tissues: They are made up of a single kind of cells performing similar functions. Simple tissues are mainly of three types: parenchyma, collenchyma, and sclerenchyma.

Parenchyma (Grew): These cells are found almost in all parts of plants such as roots, stems, leaves, fruits, and seeds. These cells are isodiametric, spherical, oval, or polygonal with intercellular spaces. These cells are living and with thin cellulosic cell wall.

Types Of Parenchyma

• Prosenchyma: Elongated parenchyma with tapering ends is called prosenchyma.
• Aerenchyma: The parenchyma which encloses the air cavity is called aerenchyma (hydrophytes)
• Chlorenchyma: The parenchyma containing chloroplasts is called chlorenchyma.
• Idioblast: Sometimes parenchyma stores secretory substances (orgastic substances) such as tannins, resins, and gum. They are called idioblasts.

Storage Parenchyma: Examples are fruits, and endosperm.

Collenchyma (Schleiden): Collenchyma has thickenings on the cell wall and in corners of intercellular spaces. They are not found in the roots and monocots. These cells form hypodermis in the stem and petiole. These are living mechanical tissues with high refractive index. The thickening material in the cell wall contains pectocellulose.

Types Of Collenchyma

• Angular Collenchyma: Angular walls thickened, for example, the stem of a marigold and tomato.
• Lamellate Collenchyma: Tangential walls thickened, for example, the stem of a sunflower.
• Lacunate Collenchyma: Lacunate thickening, intercellular spaces are present, for example, stem of cucurbita.
• Functions Of Collenchyma: They provide mechanical support, flexibility, and elasticity to the organs. Due to the peripheral position in stems they resist the bending and pulling action of wind. Collenchyma is especially useful for young plants and herbaceous organs where these act as important supporting tissues.

Sclerenchyma (Mettenius): Sclerenchyma has thickened secondary walls due to the deposition of lignin. At maturity they become dead. These cells have simple pits. They are of two types: Sclereids and sclerenchymatous fibers.

Sclereids: They may be spherical, oval, or cylindrical. They are lignified, and extremely thick-walled. So the lumen of the cells is almost obliterated. They are found in hard parts of the plant.

Types Of Sclereids

1. Brachysclereids (Stone Cells): Grittiness in fruits is due to stone cells, for example, pear, and sapota.
2. Macrosclereids (Rod Cells): Found in the seed coat of leguminous plants.
3. Osteosclereids (Prop Cells): Found in the leaves and seed coat of many monocots and the sub-epidermis of legume seed coats.
4. Astrosclereids (Star Cells): They are common in the stem and leaves of dicots, for example, tea leaves, petiole of lotus, etc.
5. Trichosclereids (Internal Hair): Long, hair-like branched sclereids. They are common in hydrophytes. These are also present in the aerial roots of Monstera.

Sclei Enchymatous Fibers: They are long and tapering at ends. These are thick-walled cells (lignified). These fully developed fiber cells are always dead. The length of fiber varies from 72 to 550 mm in angiosperms and 1 to 12 mm in gymnosperms.

The fibers are present in the hypodermis of monocot stems, in the pericycle of many dicots, in the secondary wood, and in the vascular bundle sheath in monocot stems, for example, jute, flax, hemp, etc. Living fibers are found in tamarix.

Function Of Sclerenchyma: The main function of sclerenchyma is to provide mechanical strength.

Complex Tissues: A group of more than one type of cells having a common origin and working together as a unit is called complex tissue. These are made up of different types of cells: xylem and phloem.

Xylem (Nageli) Or Hadrome (Haberlandt): Xylem is the chief water-conducting element. It consists of the following types of cells

Tracheids: They are elongated cells with pointed chisel-like ends. Their wall is tough, thickened, lignified, and thickened or may be annular, spiral, reticulate, scalariform, or pitted. Cells are dead at maturity and have bordered pits.

In pteridophytes and gymnosperms, wood mainly consists of tracheids (no vessels). In angiosperms, tracheids are associated with vessels. The main function of tracheids is the conduction of water. Tracheids are the most primitive type of conducting elements in the xylem.

Vessels: Vessels are also elongated and tube-like. They are formed from a row of cells placed end to end. The partition walls are either perforated or disappear altogether resulting in an elongated tube. Walls are thickened, and lignified, and may have annular, spiral, reticulate, or scalariform thickening.

Vessels are dead at maturity and without nuclei. In pteridophytes and gymnosperms, vessels are absent (non-porous wood). Sometimes primitive vessels are present in gnetum and ephedra (Gnetales).

Vessels are characteristic of angiosperms (porous wood). Vesselless angiosperm families are Tetracentraceae, Trochodendraceae, and Winteraceae. The main function is the conduction of water. Vessels are an advanced type of conducting element.

On the basis of distribution and size of vessels, porous wood is of two types:

1. Diffuse Porous Wood (Primitive): Vessels of the same size are uniformly distributed throughout the growth, for example, Pyrus, Betula.
2. Ring Porbus Wood (Advanced): Large vessels are formed in early wood when the need of water is great and small vessels are formed in latewood, for example, Quercus, and morus.

Wood Or Xylem Fiber: These cells are elongated and pointed at both ends. Cell wall is highly lignified having simple pits. The air commonly found in the secondary xylem. They may lie

1. Fiber Tracheids: Fiber such ns tracheids with bordered pits.
2. Libriform Fiber: They have extremely thick walls and simple pits. They provide mechanical support.

Wood Or Xylem Parenchyma: They are living parenchymatous cells associated with xylem. They may occur as axial parenchyma or ray parenchyma. When parenchyma is diffused or not associated with vessels, they are called as apotracheal parenchyma and when parenchyma surrounds or is associated with vessels, it is called para tracheal parenchyma.

On The Basis Of Origin Xylem Is Of Two Types:

1. Primary Xylem: It is derived from procambium during the formation of the primary plant body. It is differentiated into protoxylem (formed first and consists of tracheary elements and xylem parenchyma) and metaxylem (formed later and consists of tracheary elements, xylem parenchyma, and fiber). The cells of metaxylem are bigger in size than the protoxylem.
2. Secondary Xylem: It is formed from cambium during secondary growth. It is well differentiated into two systems:
   • Axial Or Vertical System
     • Tracked elements (tracheids and vessels): For conduction of water
     • Xylem or wood fiber: For support
     • Xylem parenchyma: For storage of food
   • Ray Or Horizontal System: Ray parenchyma: For storage of food.

Phloem (Nageli) Or Bast Or Leptome (Haberlandt): The main function of phloem is the transport organic food materials from leaves to stems and roots in down word direction. Phloem consists of the following types of cells

Sieve Element: The sieve elements in angiosperms are sieve tubes which are cylindrical tube like cells with perforated cross walls called sieve plates. Sieve tubes are associated with companion cells, and they are without nuclei. In pteridophytes and gymnosperms, the sieve elements have sieve plates on their lateral walls and companion cells are absent. They are called as sieve cells.

The walls of sieve tube elements are made up of cellulose and pectic substances. The cytoplasm is confined to a thin peripheral layer. P-proteins are proteinaceous structures present in sieve tubes and are believed to be responsible for

1. The movement of materials and
2. The sealing of pores after wounding.

In old sieve tubes, at the end of the growing season, a callose plug (made of callose carbohydrate) is deposited on the sieve plate which inhibits the activity of the sieve tubes. In the spring season, the callose plug gets dissolved.

Companion Cells: They are elongated living parenchymatous thin-walled cells. They are associated laterally to sieve tubes and have dense cytoplasm and nuclei. Companion cells are absent in pteridophytes and gymnosperms. Both sieve tubes and companion cells are related ontogenetically because both develop from the same mother cell. So these are sister cells.

Phloem Or Bast Fiber: They are absent or fewer in phloem and abundantly found in secondary phloem. They are sclerenchymatous fibers associated with phloem. Phloem fibers of plants such as jute, flax, and hemp are rotted in water and extracted for making ropes and coarse textiles.

Phloem Parenchyma: They are parenchymatous living cells with cellulosic cell walls and nuclei. The main function is the storage of food. They are not found in monocotyledonous plants.

Types Of Phloem

On The Basis Of Position

1. External Phloem: It is of normal type and is present outside the xylem, for example, mostly angiosperms and gymnosperms.
2. Internal Or Intraxylary Phloem: It originates from procambium and is the primary phloem which occurs on the innerside of primary xylem in bilateral bundles, for example, members of Apocynaceae, Asclepiadaceae, Convolvtilaceae, Solanaceae etc.
3. Included Or Interxylary Phloem: It originates from cambium and is a secondary phloem that occurs in groups within the secondary xylem, for example, Leptadaenia, Salvadora, Chenopodiwn, Boerhaavia, Amaranthus, etc.

On The Basis Of Origin:

1. Primary Phloem: It develops from procambium and does not have radial differentiation or rays are absent. It is differentiated into protophloem (consists of sieve elements and parenchyma) and metaphloem (develops after protophloem and consists of sieve elements, parenchyma, and fiber). During primary growth, the protophloem elements are crushed by the surrounding tissues and disappear. This process is known as obliteration.
2. Secondary Phloem: It develops from cambium during secondary growth. It shows radial differentiation. It consists of two distinct systems such as
   • Axial or vertical system
     • Sieve Elements: Sieve tube and companion cells. For conduction of food.
     • Bast fiber: For support.
     • Bast Parenchyma: For storage of blood.
   • Ray Or Horizontal System
     • Ray Parenchyma: It is for the storage of food

Secretory Tissues: Secretory tissues perform special functions in plants. For example, secretion of resins, gums, oil, and later. These tissues are of two types laticiferous and glandular tissues.

Laticiferous Tissues: They contain colorless, milky, or yellow-colored juice called latex. These tissues are of two types

1. Latex Cells: They do not fuse and do not form a network. Plants having such tissues are called simple or non-articulated laticifers, for example, Calotropis (Asclep Fabaceae), Nerium, Vinca (Apocyanaceae), Euphorbia (Euphorbiaceae), Ficus (Moraceae).
2. Latex Vessels: They are formed due to the fusion of cells and form a network-like structure. Plants having such tissues are called compound or articulated laticifers, for example, Argemone, Pabaver (Papaveraccae), Sonchus (Compositae), Hevea, and Manihot (Euphorbiaceae).

Glandular Tissues: They include different types of glands which secrete oils, gums, mucilage, tannins, and resins. They may be

1. External Glands: Present as epidermal outgrowths. They are of many types
   • Glandular Hair: With a stalk and head, for example, tobacoo, Plumbago, Boerhaavia.
   • Stinging Hair: Secrete poisonous substances, for example, Urtica.
   • Nectaries: Secrete sugary substance; maybe extra-floral present on the stem, leaves, etc. Examples: Nepenthes, Catheranthus, or floral, for example, Corchorus, Thea, Polygonum, Jatropha.
   • Digestive Glands: Present in insectivorous plants, for example, Drosera, Nepenthes, etc.
2. Internal Glands
   • Oil Glands: Present in the mesophyll of leaves and cortex of stem fruit, for example, orange, lemon, etc.
   • Mucilage-Secreting Glands: Leaves of piper betel.
   • Gum, tannin, and resin-secreting glands or ducts are present in gymnosperms and angiosperms, for example, Pious resin ducts are schizogenous in origin.

Tissue System

The various types of tissues present in the body of a plant perform different functions. Several tissues may collectively perform the same function. A collection of tissues performing the same general function is known as a “tissue system.” According to Sachs (1975), there are three major tissue systems in plants, namely the epidermal tissue system, the ground or fundamental tissue system, and the vascular tissue system.

Epidermal Tissue System: It consists of the epidermis and its associated structure such as hairs, trichomes cuticle, stomata, and bulliform cells. Mostly epidermis is single-layered parenchymatous but multilayered in Ficus, Nerium. The epidermis is mainly protective in nature.

In grasses, motor or bulliform cells are present in the upper epidermis. In grasses and Equisetum, silica is present in the epidermal cells. The epidermal cells containing cystoliths are called lithocysts.

Ground Or Fundamental Tissue System: It extends from the epidermis up to the center excluding vascular tissue. Ground tissues constitute the following parts

1. Cortex: It lies between the epidermis and the pericycle. It is further differentiated into the following parts:
   • Hypodermis: It is collenchymatous in the dicot stem and sclerenchymatous in the monocot stem. It provides strength.
   • General Cortex: It consists of parenchymatous cells. Its main function is the storage of food.
   • Endodermis (Starch Sheath): It is mostly single-layered and is made up of parenchymatous barrel-shaped compactly arranged cells. The inner and radial walls of endodermal cells have Casparian strips. In roots, thick-walled endodermal cells are interrupted by thin-walled cells just outside the protoxylem patches.
     • These thin-walled endodermal cells are called passage cells. The endodermis behaves as water water-tight dam to check the loss of water and air tight dam to check the entry of air in xylem elements.
2. Pericycle: It lies between endodermis and vascular tissue. It is parenchymatous in roots and sclerenchymatous or mixed with parenchyma in the stem. The pericycle cells just opposite the protoxylem are considered as seats for the origin of lateral roots. In dicot roots, the pericycle forms part of the cambium or the whole of the cork cambium.
3. Pith: It occupies the central part in the dicot stem and monocot root. It is mostly made up of parenchymatous cells. In the dicot root, the pith is completely obliterated by the metaxylem elements. In the dicot stem, the pith cells between the vascular bundles become radially elongated and are known as primary medullary rays or pith rays. They help in lateral translocation.

Vascular Tissue System: Vascular bundles found in the steer part constitute the vascular tissue system. Xylem. phloem and cambium are the major part of the vascular bundle. Vascular bundles may be of the following type:

1. Radial: When the xylem and phloem are arranged on different radii alternating with each other, for example, roots.
2. Conjoint: When xylem and phloem combine in the same bundles and are present on the same radius, for example, stem. Conjoint vascular bundles may be of the following types
   • Collateral: The xylem is towards the inner side and the phloem, is towards the outer side.
     • Open: Cambium is present between the xylem and phloem, for example, the dicot stem.
     • Closed: Cambium is absent between the xylem and phloem, for example, monocot stem.
   • Bicollateral: When the xylem has cambium and phloem on both sides, for example, members of Cucurbitaceae, Solanaceae, Apocyanaceae, etc.
3. Concentric: When one vascular tissue surrounds the other. They are of two types
   • Amphicribral Or Hadrocentric: The xylem is surrounded on all sides by phloem, for example, ferns.
   • Amphivasal Or Leptocentric: The phloem is surrounded on all sides by the xylem, for example, Yucca, and Dracaena.

Internal Structures Of Dicot And Monocot Plants

Anatomy Of Root: The three zones that can be distinguished in a root are

1. Epidermis (Epiblema/Rhizodermis): It is single-layered (uniseriate) and consists of tightly placed, thin-walled unscrutinized cells. This epidermis layer is called as epiblema, piliferous layer, or rhizodermis. Epiblema in younger roots bears unicellular root hairs (water-absorbing organs).
2. Cortex: It consists of thin-walled parenchymatous cells with intercellular spaces. In most monocots and some dicots, the cortex layer below the epidermis becomes suberized to form protective tissue called exodermis.
   • The cells of the cortex store food material (for example, carrots). The innermost layer of the cortex develops into endodermis. It is made up of closely packed living cells characterized by the presence of band-like thickening; made of lignin and suberin on their radial and transverse walls.
   • These bands or strips are called Casparian bands or strips. Some cells of endodermis lying opposite to the protoxylem remain thin-walled and are called passage cells which allow radial diffusion of water.
3. Vascular Bundles: Vascular bundles are radial and exarch. The center of the monocot root is occupied by parenchymatous cells called piths.

Some basic differences between a monocot and a dicot root are given.

Differences Between Dicot And Monocot Root

Anatomy Of Stem: The Primary structure of the diet stem consists of the following layers

• Epidermis: It is the outermost layer consisting of a single layer of closely arranged cells with cuticles (cutinized). It bears multicellular hairs.
• Cortex: It is differentiated into hypodermis, general cortex, and endodermis. Hypodennis is collenchymatous. The general cortex bundles consist of the phloem and xylem.
• Vascular Bundles: Vascular bundles are conjoint, collateral, or collateral, open and endarch, and are arranged in a ring (eustele).
• Pith: It is the central portion of the stem consisting of parenchymatous cells with narrow, radially elongated parenchymatous cells extending from the pith toward the periphery called medullary rays. The main function of pith is food storage.

The primary structure of a monocot stem consists of the following layers:

• Epidermis: It is the outermost layer and consists of compactly arranged parenchymatous cells which are usually covered with cuticles.
• Hypodennis: The cells of hypodermis are sclerenchymatous providing mechanical strength to the stem.
• Ground tissue: All the tissues internal to hypodermis represent the ground tissue. It is made up of parenchymatous cells rich in food reserves such as starch.
• Vascular bundles: They lie scattered in the ground tissue. Each vascular bundle is surrounded by a two- or three-layered sclercnchymatous sheath called bundle sheath. The vascular bundles are conjoint, collateral, closed, and endarch (atactostelc). Vessels are arranged in a V-shaped manner. Schizolysigenous water cavity or canal arc present below protoxylem.

Shows the transverse section of the dicot stem and monocot stem. The differences between dicot stem and monocot stem are given.

Anatomy Of Leaf: In the cross-section of a dorsiventral leaf (dicot), the following parts can be made out

Epidermis: The upper and lower surfaces are covered by the epidermis. The cells of the epidermis are parenchymatous and are closely packed together without any intercellular spaces. Mostly the stomata are restricted to the lower surface of the leaf such leaf is called hypostomatic. The outer walls of the epidermal cells are thickened and cutinized (cuticle) which prevents the loss of water.

Mesophyll: Between the two epidermal layers, there are numerous chlorenchyma cells that constitute the mesophyll. In dicots, there are two distinct layers of mesophyll, the palisade (the upper layer consisting of closely arranged column-shaped cells containing abundant chloroplasts) and spongy tissue (the lower layer of irregularly shaped cells containing fewer chloroplasts).

Vascular Bundles: Vascular bundles in the leaf are located in the midrib and the veins. Vascular bundles are conjoint, collateral, and closed. Bundles are surrounded by a compact layer of parenchymatous cells which is called bundle sheath. The xylem (protoxylem) is towards the upper epidermis (adaxial) and the phloem is on the lower side (abaxial). Like the dicot leaf, an isobilateral leaf (monocot) can also be differentiated into the following types of tissues

Secondary Growth

Secondary growth is the increase in girth thickness or diameter of the axis due to the formation of new tissues as a result of the joint activity of vascular cambium and cork cambium in stellar and extrasolar regions, respectively. It occurs in the roots and stems of gymnosperms and dicots. Secondary growth in the dicot stem is completed in the following steps:

Formation Of Vascular Cambium Ring

1. Intrafascicular Cambium: It is primary in origin, present in between the primary phloem and primary xylem.
2. Interfascicular Cambium: It is a true secondary meristem. It originates from the parenchyma cells of the medullary rays region. It lies in between the vascular bundles.
3. Vascular Cambium Ring: Both intrafascicular and interfascicular cambium join together and form cambium ring.

Cambium Cells Are Of Two Types:

1. Fusiform Initials: They form tracheids, vessels, fibers, and axial parenchyma in the secondary xylem and sieve tubes, companion cells, fibers, and axial parenchyma in the secondary phloem.
2. Ray Initials: These are isodiametric and form ray parenchyma and vascular rays.
3. The Periclinal division of the vascular cambium ring helps in the formation of secondary phloem tout side the vascular cambium) and secondary xylem firmer to vascular cambium). The amount of secondary xylem produced is H 10 times greater than secondary phloem.

Fate Of Primary Phloem And Primary Xylem: The primary phloem is crushed to death, known as obliteration. The primary xylem, being dead and lignified, is replaced in the pith region.

Formation Of Secondary Structures

1. Annual Rings: These are formed by the seasonal activity of vascular cambium. Cambium does not stay active uniformly throughout the year. In spring or summer, cambium is more active and forms large-sized xylem elements (vessels) which constitute spring or early wood.
   • In autumn or winter, cambium stays less active and cuts off small-sized xylem elements (vessels) and constitutes autumn wood or latewood. Both autumn and spring wood constitute a growth or annual ring. In one year, only one growth ring is formed. In successive years, numerous growth rings are formed. Thus, by counting the number of annual rings in the main stem at the base, we can determine the age of a tree. This branch of science is known as dendrochronology.
   • Growth rings are distinct or sharply demarcated in the plants of temperate climates, for example, Shimla, Nainital, Mussoorie, etc., due to the presence of contrasting seasonal variations. Growth rings are not distinct or sharply demarcated in the trees of tropical climates (near the equator) for example, Calcutta, Bombay, and Madras, due to the absence of contrast¬ing seasonal variations.
2. Heart Wood And Sapwood: The young elements of the secondary xylem in the peripheral region constitute sapwood or alburnum. It is light in color and physiologically active. The water conduction takes place through sapwood.
   • Sapwood is converted into heartwood or duramen in the central region. It is darker in color—due to the deposition of tannins, gums, and resins, and physiologically inactive (almost dead). It provides mechanical support only
   • During the conversion of sapwood into heartwood, the most important change is the development of tyloses in the heartwood. Tyloses are balloon-like structures, that develop from xylem parenchyma.
   • These tyloses block the passage of xylem vessels, hence so also called tracheal plug. The heart wood is commercially used as wood. When the plant is made hollow, it does not die because the water conduction takes place through sapwood.
   • The heartwood is well developed in Moms alba (mulberry). The heartwood is absent in Populus and salix plants. The wood of Tectona grandis is termite-resistant. As a tree grows older, the thickness of heartwood increases and sapwood remains the same.
   • Heartwood is much more durable and resistant to microorganisms, insects, pests, etc. than sapwood. The wood of dicot trees is called porous or hardwood because it consists of vessels (pores). The wood of gymnosperms does not contain vessels (pores) and is known as soft or non-porous wood. Such wood consists of 90 to 95% tracheids and 5 to 10% of ray cells. Sapwood will decay faster if exposed freely to the air.
3. Formation Of Cork Cambium: Cork cambium or phellogen develops from the outer layer of the cortex. It produces a secondary cortex or phelloderm on the inner side and cork or phellem on the outer side. The cells of phellem are dead, suberized, and impervious to water.
   • Cork cells are airtight and used as bottle stoppers or corks. The bottle cork is prepared from the cork of Quercus suber (oak tree). The cells of the phelloderm are thin-walled, living, and store food. Phellem, phellogen, and phelloderm are collectively called periderm. The periderm is a secondary protective tissue.
   • Due to the pressure of the secondary xylem, the epidermis ruptures arid cortex is largely lost after two or three years of secondary growth. In the cork layer (bark), the lenticels are present which are meant for gaseous exchange.
   • In cork, lenticels have loosely arranged cells called complementary cells with intercellular spaces. For bottle corks, the cork is processed in such a manner so that lenticels come in the vertical direction.

Bark includes all the dead and living tissues outside the vascular cambium. Bark may be of two types:

• Scaly Bark: When develops in strips, for example, Eucalyptus, Psidium.
• Ring Bark: When develops in the form of a sheet or ring, for example, Betula (bhojpatra). The outermost layer of bark is dead and called as rhytidome. The bark of Betula was used as a substitute of paper in ancient times to write manuscripts.

Secondary Growth In Dicot Root: Vascular bundles in the dicot root are radial, exarch, and mostly triarch. Vascular cambium is formed secondary) from conjunctive parenchyma cells lying just below each phloem strand. Thus, the number of cambium strips formed equals the number of phloem strands. The cells of the pericycle lying outside the protoxylem also become meristematic to form part of strips of cambium.

These cambial strips join the first formed cambium strips to form a complete but wavy ring of vascular cambium. This cambium ring produces a secondary xylem on the inner side and a secondary phloem on the outer side.

In roots, the growth rings are not distinct, because there is no seasonal variation under the soil. From the outer layers of the pericycle arises the phellogen which cuts phellem (cork) or the outer side and secondary cortex or phelloderm toward the inner side.

Anatomy Of Flowering Plants Point To Remember

Examples of dicots with scattered vascular bundles are Podophyllum, Peperomia, Piper, and Popover. Examples of cortical vascular bundles are Nyctanthus, Kalanchoe, and Casuarina.

• Examples of medullary bundles are Mivabilis, Bougainvillea, Amaranthus, and Achyranthus. Examples of polystelic conditions are Primula and Dianthera.
• Anomalous or abnormal secondary growth occurs in Bougainvillea, Boerhaavia, Chenopodium, and Aristolchia.
• Some monocots show abnormal secondary growth by meristematic tissue which develops around vascular bundles, for example, Dracaena, Yucca, Agave, etc.  Virgin cork is the first formed periderm.

Wound Cork: It is the secondary meristem; formed below the injured cell, it forms a cork on the outer side and a callus below which heals the wound.

• Abnormal secondary growth in dicot root occurs in beetroot (Beta vulgaris) and sweet potato (Ipomoea batatas) by the formation of numerous accessory rings of cambium which cut more storage—parenchyma in secondary phloem and less secondary xylem.
• Homoxylous wood is the wood of vessels dicots, for example, Ranales (Winteraceae, Tetracentraceae Trochodendraceae).
• Heteroxylous wood is the wood of vessel-bearing dicots.

The latex of some plants is of great commercial importance such as

1. The source of commercial rubber is the latex of Hevea brasiliensis, Ficus elastica, Ciyptostegia, and Manihot glaziovii.
2. The source of chewing or chuckle gum is the latex of Achras sapota.
3. The source of the enzyme papain is the latex of Carica papaya.
4. The source of alkaloid opium is the latex of Popover somnific (poppy).

Polyderm is a special type of protective tissue that occurs in roots and underground stems of the members of Rosaceae and Myrtaceae. Its outermost layer is dead and suberized.

 

Anatomy Of Flowering Plants Assertion Reasoning Questions And Answers

In the following questions, an Assertion (A) is followed by a corresponding Reason (R). Mark the correct answer.

1. If both Assertion and Reason are true and the Reason is the correct explanation of the Assertion.
2. If both Assertion and Reason are true, but the Reason is not the correct explanation of the Assertion.
3. If Assertion is true, but Reason is false.
4. If both Assertion and Reason are false.

Question 1. Assertion: In maize stem, endodermis is present between the general cortex and pericycle.

Reasoning: Eustele is present in maize Stem.

Answer: 4. If both Assertion and Reason are false.

Question 2. Assertion: In the Cucurbita stem, vascular bundles are conjoint, bicollateral, and either open or closed.

Reasoning: The outer and inner cambium are present and only the inner cambium is functional in the Cucurbita stem.

Answer: 4. If both Assertion and Reason are false.

Question 3. Assertion: Fusiform cells are elongated and tapering cells.

Reasoning: These cells form an axial system consisting of vascular rays.

Answer: 3. If Assertion is true, but Reason is false.

Question 4. Assertion: Septa less tracheids are absent in Trochodendron.

Reasoning: Heteroxylous wood is present in Trochodendron.

Answer: 3. If Assertion is true, but Reason is false.

Question 5. Assertion: According to Hanstein, there are three halogens in a monocot root.

Reasoning: In monocot roots, the outermost groups of initials form both root cap and dermatogen.

Answer: 4. If both Assertion and Reason are false.

Question 6. Assertion: The apical meristem is always protected.

Reasoning: A root cap is present above the meristem in roots.

Answer: 2. If both Assertion and Reason are true, but the Reason is not the correct explanation of the Assertion.

Question 7. Assertion: The stem in herbaceous plants do not develop cracks during severe wind and is used to bond under these conditions.

Reasoning: Sclerenchyma is peripheral in position and provides flexibility to the herbaceous stems.

Answer: 3. If Assertion is true, but Reason is false.

Question 8. Assertion: The death of a companion cell leads to the death of a sieve cell also.

Reasoning: Both companion and sieve cells are phloem cells.

Answer: 2. If both Assertion and Reason are true, but the Reason is not the correct explanation of the Assertion.

Question 9. Assertion: Dicot roots are mostly tetrach.

Reasoning: There occur four phloem bundles forming rays.

Answer: 4. If both Assertion and Reason are false.

Question 10. Assertion: Heartwood is not involved in the conduction function.

Reasoning: Tyloses and depositions of tannins, resins, and gums is common in duramen cells.

Answer: 1. If both Assertion and Reason are true and the Reason is the correct explanation of the Assertion.

Question 11. Assertion: Vascular cambium appears wavy in dicot roots.

Reasoning: Vascular cambium is formed by conjunctive tissue in dicot roots which is found located inside the xylem and outside phloem strands.

Answer: 3. If Assertion is true, but Reason is false.

Question 12. Assertion: Velamen is hygroscopic in nature and absorbs environmental moisture.

Reasoning: Velamen is common in orchids which are epiphytes.

Answer: 2. If both Assertion and Reason are true, but the Reason is not the correct explanation of the Assertion.

Morphology Of A Flowering Plant

Morphology deals with the study of forms and features of different plant organs such as roots, stems, leaves, flowers, seeds, fruits, etc. The body of a flowering plant can be divided into two fundamental parts:

1. An Underground Root System And
2. An Aboveground Shoot System. The Root System Grows Downwards Into The Soil Anchors The Plant Firmly In The Soil And Absorbs Water And Various Dissolved Minerals From It. The Shoot Supports Foliage Leaves And Helps In The Conduction Of Water And Mineral Substances From The Soil And Food Material.

Life Span Of A Flowering Plant

The Life Span Of A Flowering Plant Can Be Any Of The Following Forms:

Annual: The life cycle is completed in one season or a few weeks to a few months. Examples are wheat, maize, and Euphorbia prostrata.

Biennials: The life cycle is completed in two seasons: vegetative growth occurs in the first season and food is stored and reproduction occurs in the second season, for example, henbane. Radish, carrot, and turnip are biennials in colder areas and annuals in warmer areas.

Perennials: The plant lives for a few to many years and may bear flowers and fruits every year (polycarpic). Bamboo (Bambusatulda) and agave are monocarpic, i.e., flowering occurs only once in life lifetime.

Habit Of Plants

Herb: Stem is soft, less than 2 m in height.

Shrub: Perennial woody stem with medium height, tiunk is absent for example, Capparis, Rosa, etc.

Trees: Woody stems of great height; the stem is called a trunk. An unbranched stem is called caudex or columnar, for example, a palm. An erect stem with swollen nodes is called a culm, for example, bamboo.

Excurrent: The lateral branches of the trunk do not compete with the stem, for example, Finns, Casuarina, and Eucalyptus.

Deliquescent: The main stem or trunk disappears after some time and the crown is dome-shaped, for example, Dalbergia, Ficus benghalensis.

Read and Learn More NEET Biology Notes

Root

Roots develop from the radicle of the seed. They are non-green, underground, positively geotropic, and negatively phototropic. Roots usually do not bear buds, but buds are present for vegetative propagation in sweet potato (Ipomoea) and Indian redwood (Dalbergia). They do not bear nodes and internodes. They have unicellular root hair. Lateral roots arise endogenously, i.e., from the pericycle.

Types Of Roots: Roots Are Mainly Of Two Types

1. Tap Root: They develop from seed radicles. The primary root grows and gives rise to secondary and tertiary roots forming a tap root system. For example, dicots.
2. Adventitious Roots: They develop from any part of the plant body other than the radicle. For example, monocots. They are usually shallow surface feeders such as fibrous roots of grasses.

Parts Of Root

Root Cap: At the apex of the root, a smooth cap-gaped structure is present which is called as root cap. It is protective. Multiple root cap is found in trial roots of screwpine (Pandanus). In hydrophytes, the root cap is either absent or replaced by a root pocket, for example, Pistia, Lemna, and Eichhomia.

Zone Of Cell Formation Or Division: The cells of this region are in an active state of division and their number increases continuously. No vacuoles or small vacuoles are present. It extends to a few millimeters.

Zone Of Cell Elongation: Maximum growth in the cells occurs in this zone. A large central vacuole is present.

Zone Of Cell Maturation: The cells are differentiated into permanent tissues depending upon the functions they have to perform. Root hairs are also present in this zone. In hydrophytes, root hairs are absent because they absorb water through the general body surface.

Modifications Of Tap Roots

1. Storage/Fleshy Roots
   1. Fusiform: Example, radish (Raphamts sativus).
   2. Conical: Example, carrot (Daucus carota).
   3. Napiform: Example, turnip (Brassica rapa), beetroot (Beta vulgaris).
   4. Respiratory Root (Pneumatophores): Example, Avicennia. Sonneratia.
2. Respiratory Root (Pneumatophores): Example, Avicennia, Sonneratia.
3. Nodulated Roots: Example, Pisum sativum, Cicer arietinum.

Modifications Of Adventitious Roots

1. Storage Roots
   1. Tuberous: Example, sweet potato (Ipomoea batatas)
   2. Fasciculated: Example, Asparagus, Dahlia.
   3. Palmate: Example, orchis.
   4. Nodulose: Example, mango ginger (Curcuma amada)
   5. Beaded Or Moniliform: Example, Portulaca, Momordica.
   6. Annulated: Example, ipecac (Psychortai)
2. Adventitious Roots That Provide Extra Support
   1. Prop Roots: Example, old banyan tree (Ficus benghalensis)
   2. Stilt Roots: Example, sugarcane, maize.
   3. Climbing Roots: Example, Pothos, Piper.
   4. Buttress Roots: Example, Bombax.
3. Adventitious Roots With Special Function
   1. Respiratory Roots: Example, Jussiaea.
   2. Assimilatory Roots: Example, Tinospora, Trapa.
   3. Haustoria: Example, Cuscuta.
   4. Hygroscopic Roots: Example, orchids.
   5. Contractile Roots: Example, saffron (Crocus), Freesia.
   6. Root Thorns: Example, Pothos arinatus, Acanthorhiza.
   7. Foliar/Epiphyllous/Leaf Roots: Example, Btyophyllum, Bignonia, Salvinia.

Stem

Stem is formed by the prolongation of the plumule of the embryo. It is positively phototropic negatively geotropic and hydrotropic. It bears nodes and internodes. The leaf-bearing part of the stem is called the shoot. It has buds. A bud is a condensed immature or embryonic shoot having a growing point surrounded by immature leaves. Cabbage is the largest bud.

According To Nature, Buds Can Be:

• Vegetative: Form leafy shoots.
• Floral: Form flowers.
• Mixed: Form both vegetative and floral characters.

According To Position, Buds Can Be Lateral Or Terminal. Lateral Buds Are Of Four Types:

1. Axillary: Present in the axil of a leaf.
2. Accessory: Additional buds occur either on the side or above the axillary bud.
3. Extra-axillary: Developing on the node but outside the leaf base.
4. Adventitious: Formed from places other than nodes. These can be:
   • Foliar: Example, Biyophyllum, Begonia.
   • Radical: Example, Dalbergia, Ipomoea batata (sweet potato).
   • Cauline: Example, jackfruit.

Types And Modifications Of Stem

Aerial Stems (Epiterranean Stem): It may be reduced, erect, or weak.

1. Reduced: The stem is reduced to a disc, for example, radish, carrot, turnip.
2. Erect Stem: The stem is strong and upright, for example, maize, wheat, and mango. An erect stem with swollen nodes is called a culm (for example, bamboo).
3. Weak Stem: These are thin, soft, and weak and need support. These can be upright or prostrate. These are of the following types.
   • Creepers: The stem creeps on earth and the roots arise at the nodes, for example, grasses, strawberries, and Oxalis.
   • Trailers: The stem creeps on the ground but the roots do not arise at the nodes. They may be of the following types:
     • Prostrate Or Procumbent And Diffuse: Example, Evolvulus, Tribulus.
     • Decumbent: Example, Tridax.
     • Diffuse: Example, Boerhaavia.
   • Lianas (Stem Climber): Woody perennial climbers found in tropical rainforests are lianas. They twine themselves around tall trees to secure sunlight, for example, Hiptage, and Bauhinici vahlii (phanera).
   • Climbers: Plants are with long weak stems and have organs of attachment to climb objects. They may be:
     • Rootlet Climber: Example, Tecoma, Pothos, Piper betel (paan).
     • Hook Climber: In Bougainvillea, Duranta.
     • Tendril Climber: Tendrils are thread-like structures that help in climbing plants.
       • Entire Leaf: Leaf tendrillar, for example, Lathyrus sativus.
       • Leaflet: Leaflet tendrillar for example, Pisum.
       • Twiners: The stem body twines around the support without any special organ of attachment, for example, Cuscuta, Dolichos, and Quisqualis.

Sub-aerial Stems

1. Runner: It is an elongated, prostrate, aerial branch with long internodes and roots that strike at nodes, for example, Oxatis, grasses, Hydrocotyl
2. Sucker: It arises from the axillary bud of the underground part of the stem. The branch creeps below the soil surface grows obliquely upward and produces new shoots. Examples, are Mentha, Chrysanthemum, and Rosa.
3. Offset: Short horizontal branch producing a cluster of leaves above and a cluster of roots below, for example, Pistia, Eichhornia.
4. Stolon: It is a subterranean long lateral branch arising from the base of the stem, for example, Colocasia. It first grows obliquely upward and then bends down to touch the ground surface.

Underground Stems

1. Rhizome: It grows parallel or horizontally to the soil surface. It bears nodes, internodes, buds, and scaly leaves, for example, ginger, banana, turmeric, and ferns. It is of two types:
   • Rootstocks: It is upright or oblique with the tip almost reaching the soil surface, for example, Dryopteris.
   • Straggling: It is horizontal and branched. Branching may be
     • Racemose: The Axis is monopodial, for example, Saccharum, lotus.
     • Uniparous Cymose: Axis is sympodial, for example, Zingiber officinale (ginger), Curcuma domestica (turmeric), and Canna.
2. Tuber: It is the terminal portion of underground stem branches that are swollen on account of accumulation of food, for example, potato, Jerusalem artichoke (Helianthus tuberosus).
3. Corm: It grows vertically to the soil surface. It bears nodes, internodes, buds, and scaly leaves, for example, Colocasia, Gladiolus, Colchicum, Crocus, and Amorphophallus.
4. Bulb: Stem is reduced and disc-shaped. The bud is surrounded by many concentric leaves. The leaf bases are fleshy and edible, for example, onion, lily, and garlic. The bulb may be tunicated or scaly.
   • Tunicated (Layered Or Laminate): The bulb is covered with a dry membranous sheath of scales called a tunic. These bulbs may be again of two types:
     • Simple Tunicated: Onion, Tulipa, and Narcissus.
     • Compound Tunicated Bulb: Garlic.
   • Scaly Or Imbricate Or Naked Bulb: Tunic is absent, for example, lily.

Special Stem Modifications

• Phylloclade: It is a green flattened or rounded succulent stem with leaves either feebly developed or modified into spines, for example, Opuntia, or Casuarina.
• Cladode: Phylloclade with one intemode is called cladode, for example, Asparagus, and Ruscus.
• Thorn: It is the modification of axillary buds, for example, Bougainvillea, Duranta, Carrisa, Alhagi, etc. Thoms of Alhagi possess flowers and in Duranta, thorns bear smalt foliage leaves. Thoms of Carissa are terminal and branched.
• Stem Tendril: Example, Vitis, Passiflora.
• Bulbils: A condensed auxiliary bud (vegetative) is called a bulbil. It helps in vegetative reproduction, for example, Dioscorea, Glabba, Agave, and Oxalis.

Branching Of Stem: Branching is defined as the mode of arrangement of branches on the stem. It is of two types:

1. Lateral Branching: Branches are produced laterally from the main stem. It may be racemose or cymose.
   • Racemose Type: The main stem grows indefi¬nitely by the terminal bud and produces branches later in the acropetal succession, for example, Casuarina, Poly alt hia, etc.
   • Cymose Type: The growth of the main stem is limited and lateral branches produced by the main stem show more vigorous growth. It may be of the following types:
     • Uniparous Cyme: When one lateral branch is produced at a time. It has two distinct types: helicoid (for example, Saraca) and scorpoid (for example, Vine).
     • Biparous Cyme: When two lateral branches develop at a time, for example, Mirabilis, Datura.
     • Multiparous Cyme: When more than two branches develop at a time, for example, Croton, Euphorbia.
2. Dichotomous Branching: When the terminal bud gives out two branches of equal size in a forked manner, for example, Pandanus, or Hyphaene.

Leaf (Phylopopium)

Leaves are lateral, flat, green, and expanded part of plants that arise from nodes on the stem or branches. Usually leaf has a bud in its axil. The chief functions of leaf is photosynthesis and transpiration. All leaves of a plant are collectively called phyllome. The leaves are of the following types:

1. Cotyledonary Leaves: These are embryonic or seed leaves.
2. Cataphylls: These are scale leaves. These may store food also, for example, onions.
3. Hypsophylls or bract leaves.
4. Prophylls: The first formed leaves.
5. Floral Leaves: Include sepals, petals, or perianth.
6. Sporophylls: Bear spores; this is also used for stamens and carpels.
7. Foliage Leaves: The green leaves of the plant are called foliage leaves.

Parts Of A Leaf: A leaf consists of the following three parts: leaf base, petiole, and lamina.

1. Leaf Base (Hypopodium): Leaves are attached to the stem by the leaf base. In some plants, the leaf base becomes swollen and is called pulvinus which is responsible for sleep movement, for example, Cassia, Mimosa, Bean. In some plants, the leaf base expands into a sheath (sheathing leaf base), for example, grasses, and bananas (monocots). When the leaf base partially encloses the stem, it is called auriculate or semi-amplexicaul, for example, prickly poppy, Calotropis procera (Madar).
   • If it completely encloses the stem, it is called amplexicaul, for example, Sonchus, Polygonum.
   • In some plants, minute appendages arising from the leaf base are known as stipules. Leaves with stipules are called stipulate (for example, Rosa, Polygonum) and those without stipules are called exstipulate, for example, Ipomoea.
   • Types Of Stipules: Depending upon duration, they can be:
     • Caducous: Fall off before unfolding of leaf, for example, Michelle Champaca.
     • Deciduous: Fall off soon after unfolding of leaves, for example, Cassia tora and Dillenia indica.
     • Persistent: Remain attached to the leaf throughout life, for example, rose, pea, etc. On The Basis Of Structure And Relation To The Leaf, Stipules Are Classified As:
     • Free Lateral: These are free; and present on both sides of the leaf base, for example, Hibiscus rosasinesis.
     • Scaly: Small dry scales present on both sides of the legal base, for example, Desmodium, etc.
     • Intrapetiolar: These are situated between the petiole and axis, for example, Gardenia.
     • Foliaceous: Large, green-leafy structures, two in number, for example, pea (Pisum) and sweet pea (Lathyrus).
     • Tendrillar: One tendri liar stipule lies on each side of the petiole, for example, Smilax.
2. Petiole (Mesopodium): Petiole in Eichhornia becomes spongy and bulbous. In orange (citrus plants), the petiole becomes winged. Petiole is modified into ten¬drils in Clematis. In Australian acacia, the petiole is modified into a leaf-like sickle-shaped phyllode.
3. Lamina (Epipodium): The broad fiat part of the leaf is the lamina (leaf blade).

Types Of Leaf

• Simple Leaf: Leaf which may be entire or incised and the incisions do not touch the midrib, for example, mango, or banyan.
• Compound Leaf: The leaf blade is incised up to the midrib or petiole and thus divides it into two or more leaflets.

They Are Of Two Types:

1. Pinnately Compound Leaves: Rachis bears several lateral leaflets. These may be of the following types:
   • Unipinnate: They are of two types:
     • Paripinnate: Example, Cassia, Sesbania.
     • Imparipinnate: Example, Rosa, Tephrosia, Azadirachta,
   • Bipinnate: Example, Acacia, Mimosa, Delonix.
   • Tripinnate: Example, Morinaa, Melia, Azadirachta.
   • Decompound: Example, Daucus carota (carrot), Parthenium, Coriandrum.
2. Palmately Compound Leaves: It has no rachis and all the leaflets are joined to a common joint at the tip of the petiole. They may be of the following types:
   1. Unifoliate: Example, Citrus.
   2. Bifoliate: Example, Biginonia grandiflora, Princepia. Balanites, Hardwickia.
   3. Trifoliate Or Ternate: Example, Medicago, Aegle, Oxalis, Dolichos.
   4. Quadrifoliate: Example, Marsilea, Paris quadrifolia.
   5. Multifoliate: Example, Cleome, Bombax.

Venation In Leaves: The arrangement of veins on the lamina is called venation. It is of three types: reticulate, parallel, and furcate.

1. Reticulate Venation: The branches of veins form a network, for example, dicots. However, there are some dicots that show parallel venation, for example, Calophyllum, Eryngium, and Corymbium. It Can Be Of Two Types:
   • Pinnate Or Unicostate: for example, mango, banyan, China rose.
   • Palmate Or Multicostate:
     • Convergent, for example, Ztzyphus, Smilax and
     • Divergent, for example, castor (Ricinus), Luffa, and Vitis (grapevine).
2. Parallel Venation: The veins and veinlets remain parallel to each other, for example, in monocots. Some monocots that show reticulate venation are, for example, Smilax, Dioscorea, and Alocasia. This is Two Types:
   • Pinnate Or Unicostate Parallel Venation: Example Banana {Musa paradisiaca), canna.
   • Palmate Or Multicostate:
     • Convergent, bamboo, grass or
     • Divergent, for example, fan palm.
3. Furcate: The veins branch dichotomously but the finer branches do not form reticulum. It is common in ferns (for example, Adiantum). Among higher plants, it is seen in Cirencester.

Phyllotaxy: It is the mode of arrangement of leaves on the stem or its branches. It is of the following types:

1. Alternate: Single leaf arising at each node, for example, mustard.
2. Opposite: Leaves occurring in pairs at the node. They May Be:
   • Decussate: Leaves that stand at a right angle to the next upper or lower pair, for example, Ocinunn sanctum (sacred basil). Zinnia.
   • Superimposed: Leaves that stand parallel to the next upper or lower pair, for example, Psidium (guava), Eugenia jambolana (Jamun).
3. Whorled: Leaves occurring in more than two at each node, for example, Nerium, Alstonia.

Heterophyily: The occurrence of more than one type of leaves on the same plant is known as heterophyily. It is of three types:

1. Developmental Heterophyily: Leaves of different forms and shapes occur at different periods or places on the same plant, for example, mustard, Sonchus, and Eucalyptus.
2. Habitual Heterophyily: Leaves differ in their shape and incisions due to their habit or nature, for example, Artocarpus, Heterophyllus (jack fruit), and Ficus heterophylla.
3. Environmental Heterophyily: This type is found in aquatic plants where the submerged leaves differ from the floating and aerial leaves, for example, Sagittaria, Ranunculus aquatilis, and Limnophilia heterophylla.

Inflorescence: The arrangement of flowers and mode of distribution of flowers on the shoot system of a plant is called inflorescence.

Racemose (Indefinite) Inflorescence: The main axis of inflorescence does not end in a flower but continues to grow. The development of flowers is acropetal. The opening of flowers is centripetal. It is of the following types:

1. Raceme: Peduncle has bisexual and pedicellate flowers arranged acropetally, for example, larkspur, mustard, and radish.
2. Spike: Peduncle has bisexual and sessile flowers, for example, Achyranthes, and Adhathoda.
3. Corymb: The main axis is short. Lower flowers have longer pedicels than upper ones so that all the flowers are brought more or less to the same level, for example, Iberis, and Capsella.
4. Compound Corymb, for example, cauliflower.
5. Umbel: The main axis is reduced very much and all flowers appear to be arising from the same point. At the base of flowers, clusters of bracts form involucre, for example, hydrocodone, onion. Compound umbel, for example, coriander, carrot, Prunus.
6. Spadix: It is a spike with a fleshy axis and has both male and female flowers. It is surrounded by a large colored bract called a spathe, for example, Musa, palm, Colocasia, and Alocasia (characteristic of innocents).
7. Catkin: It is a pendulous spike that bears unisexual flowers, Morns, birch, oak, and Acalypha.
8. Capitulum Or Head: The main axis becomes flat and called a receptacle which bears many sessile and small florets. Peripheral florets called ray florets are pistillate or neuter and zygomorphic whereas disc florets are bisexual and actinomorphic, for example, sunflower, Zinnia, Cosmos (Asteraceae).
9. Panicle: Peduncle branched and branches have pedicellate flowers, for example, gulmohr, and Rhus.
10. Spikelet: It is a small spike. Flowers are produced in the axis of fertile glumes (bract), for example, wheat, and grasses (Poaceae).

Cymose (Definite) Inflorescence: The main axis ends in a flower. The development of flowers is basipetal and the opening of the flowers is centrifugal. It is of the following types:

1. Monochasial Or Uniparous Cyme: It is of two types:
   • Helicoid Cyme: Example, Atropa, datura, Begonia, Heliotropium.
   • Scorpioid Cyme: Example, Solanum nigrum, Ranunculus.
2. Dichasial Or Biparous Cyme: Example, Dianthus, Clerodendron.
3. Polychasial Or Multiparous Cyme: Example, Hamelia, Calotropis.

Special Inflorescence: These are of the following types:

1. Vertici Ilaster: A cluster of sessile or subsessile flowers borne on a dichasial cyme ending in a monochasial cyme (scorpioid) in the form of a condensed whorl on either side of the node. For example, Ocimum (Tulsi), and Salvia (Lamiaceae).
2. Cyathium: It looks like a single flower. In this cup-shaped involucre encloses a single female flower and a number of male flowers. Each male flower is represented by a single stamen, for example, poinsettia (Euphorbia pulcherrima).
3. Hypanthodium: Fleshy receptacle forming a hollow cavity with an apical opening. The flowers are developed on the inner wall of the hollow cavity. The male flowers are situated at the top near the opening. Below them gall flowers are situated which are sterile and at the bottom are situated female flowers with long styles, for example, Ficus (banyan, fig, guar).
4. Coenanthium: In Dorstenia, the receptacle becomes saucer-shaped and its margins arc slightly. The florets are arranged as similar to hypanthodium.

Flower

Flower is defined as a highly condensed and modified reproductive shoot. The following points can be mentioned to justify that Flower is a modified shoot.

1. Calyx, corolla, androecium, and gynoecium represent four whorls of sterile and fertile leaves borne at different nodes. Sometimes intemode between the calyx and corolla becomes elongated and called as anthophore, for example, Silene, and Dianthus.
   • The intemode between corolla and androecium is known as androphore, for example, Passiflora. The intemode between androecium and gynoecium is called as gynophore, for example, Capparis. When androphores and gynophores both are present in the same flower, they are jointly termed as gynandrophores, for example, Gynandropsis, Cleome. The prolongation of the thalamus beyond the carpel is known as carpophore, for example, Coriandrum, and Foeniculum.
2. In Mussaenda, sepals enlarge to form a leafy structure (foliaceous sepals).
3. Sometimes floral bud is transformed into vegetative buds or bulbils, for example, Agave.

Types Of Floral Characters

• Complete Flower: Calyx, corolla, androecium, and gynoecium are present.
• Incomplete Flower: Flower with one of the four whorls missing.
• Bisexual Flower: Both gynoecium and andoecium are present in the same flower.
• Unisexual Flower: Only androecium (staminate flower) or gynoecium (pistillate flower) are present in the flower.
• Monoecious Plant: When both male and female flowers are present on the same plant. Examples, are Cocos, Ricinus, Zea, Colocasia, and Acalypha.
• Dioecious Plant: When male and female flowers are present on separate plants. Examples are mulberry and papaya.
• Polygamous Plant: When unisexual (male or female), bisexual and neuter flowers are present on the same plant. Example, Polygonum, Mango.
• Monocarpic Plant: The plant that produces flowers and fruits only once in life. For example, pea, mustard, or all seasonal plants.
• Polycarpic Plant: The plant which produces flowers and fruits many times in life. Example, mango, and pear (mostly fruit trees).
• Achlamydeous Flower: Flowers are naked without sepals and petals. Example, Pipelaceae.
• Monochlamydeous Flower: Only one whorl is present (perianth). Examples, are Polygonaceae, and Liliaceae.
• Dichiamydeous Flower: Both whorls are present in a flower Example, most of the flowers.
• Hemicyclic Or Spirocyclic Flowers: Some of the floral parts are in circles and some are spirally arranged. Example, Ranunculaceae.
• Cauliflory: Production of flowers on old stems from dormant buds. Examples, are Artocarpus, and Ficus.

Symmetry Of Flower

• Actinomorphic Flower: When a flower can be divided into two equal halves by many vertical sections passing through the center. Example, Cruciferae, Malvaceae.
• Zygomorphic Flower: When a flower can be divided into two equal halves by only one vertical section passing through the center. For example, pea.

Position Of Floral Parts On Thalamus

• Hypogyny: Ovary is at the top and separable from thalamus. Flowers are hypogynous and the ovary is superior. For example, Malva, Brassica.
• Perigyny: Ovary is hail superior, half inferior. For example, rose.
• Epigyny: Calyx and corolla arise from the upper side of the ovary. The ovary is completely surrounded by and fused with the thalamus. The ovary is inferior and the flower is epigynous. Example, Aster, Luffa.

Bracts: Bracts are specialized leaves that arise from the axil of leaves. They are of the following types:

• Petaloid Bracts: Bracts look like petals (brightly colored). Example, Bougainvillea.
• Spathy Bract: This is a large bract enclosing an inflorescence. Examples are bananas, maize, and palms.
• Foliaceous Bracts: Bracts are leaf-like in appearance. Examples, are Adhatoda, and Gynandropsis.
• Involucre: They are green-colored and in one or more whorls a round or below the entire inflorescence. Examples are sunflower and coriander.
• Glumes: These are small dry, scaly bracts found in spikelet of Gramineae. For example, wheat.

Calyx: The lowermost whorl of a flower is called calyx. It is the non-essential whorl and consists of sepals. Sepals may be free (polysepalous) or fused (gamosepalous). Sepals are modified as follows:

• Pappus: Sepals are modified into persistent hairy structures called pappus which help in the dispersal of fruits. Examples are sunflower and Sonchus (Asteraceae).
• Leafy: In Mussaenda, one sepal is modified into a large leaf-like white structure.
• Spinous: In Trapa, the calyx is persistent and modified into two spines.

Corolla: Corolla is the second whorl of flower and consists of a number of petals which are usually brightly colored. The petals may be gamopetalous (fused) or polypetalous (free). Various forms of petals are:

• Cruciform: Four petals arranged like a cross. For example, members of Brassicaceae.
• Papilionaceous: The number of petals is five with the largest petal standard or vexillum enclosing two lateral wings which are free and in turn enclose the innermost keel (united petals). For example, pea.
• Rosaceous: Five or many small-clawed petals and spread regularly outward. For example, rose.
• Caryophyllaceous: Five free long-clawed with limbs spread at right angles to claws. Example, Diantnus.
• Tubular: Petals are like a tube, for example, disc florets of sunflowers.
• Infundibuliform Or Funnel Shaped: Petals are like a funnel. For example, Datura.
• Bilabiate (Two-Lipped): Upper and lower lips are formed by a fusion of petals. Example, Salvia, Ocimum.
• Ligulate Or Strap Shaped: Gamopetalous petals forming tongue-like structure. For example, ray florets of sunflower.
• Campanulate Or Bell-Shaped: Petals like bell. For example, Physalis.
• Rotate Or Wheel Shaped: Example, brinjal.

Aestivation: The arrangement of floral parts in a floral bud is known as aestivation. It may be of the following types:

• Valvate: When sepals or petals lie very close to each other, without overlapping. For example, mustard.
• Twisted or contorted: When one margin of the sepal or petal overlaps the margin of the next and the other margin is overlapped by the third one. For example, China rose.
• Imbricate: When both margins of one of the petals are covered by others and both margins of another one are external, and of the remaining partly internal, partly external. Example, Cassia, Caesalpinia.
• Quincuncial: When two are inner, two are outer, and one is partly outer and partly inner, Example, Ranunculus.
• Vexillary: The posterior one is the largest and almost covers the two lateral petals and the latter in turn nearly overlaps the two anterior petals. For example, pea (Papilionaceae).

Androecium: It is the third and male whorl of flower in which each stamen consists of filament, anther, and connective. When stamens are free, it is called polyandrous, for example, lily, mustard, and radish. A two-lobed anther is called vitreous (for example, pea) and a one-lobed anther is called monoecious (for example, members of Malvaceae). Attachment of filament to the anther is categorized as:

• Adnate: The filament runs along the back to the anther. For example, Michelia (Champa).
• Basifixed: The Anther is fixed to the filament by its base. For example, Datura.
• Dorsifixed: The Anther is fixed to the filament by its back and the other is immobile. For example, passion flower.
• Versatile: Anther is attached to the filament as in dorsifixed but is able to swing freely. For example, wheat and grasses.

Cohesion Of Stamens: The fusion of stamens among themselves is called cohesion. It is of the following types:

• Monadelphous: Stamens may be united by means of their filaments in one bundle. Examples are China rose, lady’s finger, and cotton (Malvaceae).
• Diadelphous: When the filaments are united into two bundles, the anthers remain free. Examples are peas, beans, and gram (Papilionaceae).
• Polyadelphous: When the filaments are united into more than two bundles but anthers are free. Examples are castor (Euphorbiaceae), and lemon (Rutaceae).
• Syngenesious: When anthers are united but the filaments are free. For example, sunflower (Compositae).
• Synandrous: When anthers as well as filaments of stamens are united throughout their whole length. For example, members of Cucurbitaceae.

Adhesion Of Statements: Fusion with other floral parts is called adhesion. It is of the following types:

• Epipetalous: When stamens are united to the petals. For example, China rose, Solatium, sunflower.
• Episepalous: When stamens are united to sepals. Example, Verbena.
• Epiphyllous (Epipetalous): When stamens are united to perianth (tcpal). For example, members of Liliaceae.
• Gynaiidrous: When stamens are attached to the gynoecium (carpel) either throughout their whole length or by their anthers only. For example, Calotropis (forming gynostegium).

Length And Arrangement Of Stamens

• Didynamous: Four stamens, two outer small and two inner long. Examples, are Ocimum, and Salvia (Labiatae).
• Tetradynamous: Six stamens, two outer small and four inner long. Example, mustard, and radish (Brassicaceae).
• Heterostemony: Stamens are of different lengths. Example, Cassia.
• Obdiplostemonous: Two whorls of stamens, outer whorl lying opposite to the petals (antipetalous) and inner whorl lying opposite to sepals (antisepalous). Examples, are Steilaria, Spergnla, and members of Rutaceae.
• Diplostemonous: Two whorls of stamens, outer whorl Tying opposite to sepals (antisepalous) and inner whorl lying opposite to petals (antipetalous). Example, Cassia.

Gynoecium: It is the female part of the flower comprising carpels bearing ovules. It consists of an ovary, style, and stigma. The gynoecium may be monocarpellary or polycarpellary.

Cohesion Of Carpels

• Apocarpous: Carpels are free (no cohesion). Example, Ranunculaceae.
• Syncarnous: Carpels of more than two and fused. For example, most of the plants.
• Number Of Locules: Ovary has locules or chambers and may be unilocular, bilocular, trilocular, tetralocular, or pentalocular (multilocular).

Placentation: The arrangement of ovules on the placenta within the ovary is called placentation. It is of the following types:

• Marginal: Placenta developing along the junction of two margins of the carpel in a one-chambered ovary. It is the characteristic feature of the family Leguminosae. Example, pea, gram.
• Parietal: Ovary is one-chambered and the placentae bearing the ovules develop on the inner wall of the ovary.

The number of placentae corresponds to the number of carpels. Examples are mustard, radish, and cucumber.

• Axile: The ovary is two to many chambered and placenta-bearing ovules develop from the central axis. Examples are tomato, orange, cotton, China rose, and lily.
• Free Central: Ovary is one-chambered and the placenta bearing the ovules develops all around the central axis. Example, Dianthus, Steilaria.
• Basal: The ovary is unilocular and the placenta develops at the base of the ovary on the thalamus and bears a single ovule. Examples are wheat, maize, aster, Zinnia, and sunflower. It is the most advanced arrangement.
• Superficial: Ovary is multilocular with numerous carpels as in the axile type of placentation, but the placenta develops all around the inner surface of the partition wall. For example, water lily. It is the most primitive.

Fruits

A fertilized and ripened ovary is called a fruit. The fruit consists of seed and pericarp (fruit wall). The pericarp develops from the wall of the ovary and is differentiated into epicarp, mesocarp, and endocarp. Seeds develop from ovules. In some plants, the ovary grows into fruit without fertilization. Such fruits are called parthenocarpic fruits. They are seedless, for example, banana, grapes, pineapple, oranges.

The fruit that develops from ovary is called the true fruit. Most of the fruits are true fruits. If any other floral part takes part in fruit formation, it is called false fruit (pseudocarp), for example, apple, or pear.

Types Of Fruits

1. Simple Fruit: These are developed from the ovary of the single flower with or without accessory parts.
   • Dry Indehiscent Fruits: They do not split or burst. Seeds are liberated only by the destruction of the pericarp.
   • Dry Dehiscent Fruits: These fruits burst automatically and discharge their seeds.
   • Dry Schizocarpic Fruits: They are intermediate between dehiscent and indehiscent fruits. One-seeded indehiscent parts are called mericarps while dehiscent one-seeded are termed cocci.
   • Fleshy Or Succulent Fruits: Pericarp and associated structure become fleshy.
2. Aggregate Fruits: These fruits are formed from polycarpel lary, apocaipous ovary. Each carpel develops into a fruitlet and all fruitlets together form an aggregate fruit. An aggregate of simple fruits borne, by a single flower is otherwise known as etaerio.
3. Multiple Or Composite Fruits: These fruits develop from the entire inflorescence. Sorosis develops from the spike, spadix, or catkin inflorescence. Syconus develops from hypanthium inflorescence.

Seed

Morphologically, a ripened ovule is known as a seed. In other words, seed is A mature, integumented megasporangium. Seeds arc characteristic of spermatophytes (gymnosperms and angiosperms).

Parts Of Seed

Seed Coat: The outer, protective covering of the seed is called the seed coat, which develops from integuments of the ovule. In seeds developing from bitegmic ovules, there are two distinct layers in the seed coat. The outer layer is thick, hard, and leathery (developing from the outer integument) called the testa, whereas the inner layer is thick and papery (developing from the inner in-tegument) called legmen. In seeds developing from unitegmic ovules, there is a single-layered seed coat.

Embryo: The embryo is the most important part of the seed which represents a tiny future plant. The embryo has an embryonal axis or main axis called tigellum, to which one or two cotyledons (seed) are attached, depending upon whether the seed is monocot or dicot. The portion of the embryonal axis or flagellum below the point of attachment of cotyledons is called hypocotyl, which bears a radicle or future root at its tip. Similarly, the portion of the embryonal axis or flagellum above the point of attachment of cotyledons is called epicotyl, which bears plumule.

In some seeds (for example, legumes), the reserve food is stored in cotyledons, whereas in others (for example, cereals), there is a special nutritive tissue called endosperm. The seeds having endosperm are called endospermic or albuminous seeds, for example, cereals, castor, etc., whereas seeds in which the endosperm is fully consumed by the embryo and no endosperm is left are called non-endospermic or exalbuminous seeds, for example, gram, pea, cucumber, tamarind, etc. The reserve food materials in seeds may be carbohydrates (for example, wheat, rice) proteins (legumes) fats (castor, peanut, sunflower), etc. All structures inside the seed coat constitute the kernel.

Monocot Embryo: There is a single cotyledon called scutellum, which is attached to the mid-part of the embryonal axis on its lateral side. On the opposite side of the scutellum is present a tongue-shaped flap-like outgrowth called epiblast (for example, wheat) which represents reduced cotyledon. Further, there is a covering or sheath of the radicle called coleorhiza and a sheath of the plumule called coleoptile.

In Castor Seed (Ricinus Communis): There is a specific outgrowth called caruncle or strophiole, present over the hilum. It is formed by the proliferation of cells of the outer integument at the tip. Caruncle is somewhat spongy and helps in the absorption of water during the germination of seed.

Pcrispermic Seeds: Mostly nucellus is consumed after fertilization due to the absorption of food by the endosperm and embryo. The remains are of nucellus in the seed are called perisperm. Such seeds are called pcrispermic seeds, for example, Piper nigrum (black pepper).

Chalazosperimic Seeds: Chalazosperm is perisperm-like tissue in chalazal region. It is a substitute for endosperm, for example, Cynastrum.

Economic Importance Of Papilionaceae

1. Source of pulses (gram, arhar, mung, etc.)
2. Edible oil (soybean, groundnut)
3. Dye (Indigofera)
4. Fodder (sesbania, Trifolium)
5. Ornamentals (lupin, sweet pea)
6. Medicine (mulethi)

Economic Importance Of Solanaceae

1. Source of food (tomato, brinjal, potato)
2. Spice (chili)
3. Medicine (belladonna, ashwagandha)
4. Fumigalory (tobacco)
5. Ornamentals (petunia)

Economic Importance Of Liliaceae

1. Good ornamentals (tulip, Gloriosa)
2. Source of medicine {Aloe) and vegetables (Asparagus)
3. Colchicine (Colchicum autumnale)

Morphology Of Flowering Plants Points To Remember

Style is generally terminal but may be lateral, for example, Graminae, or mango. Gynobasic style arises from the base of the ovary, for example, Labiatae.

• Examples of endospermic dicot seeds are castor, papaya, and cotton.
• Examples of non-endospermic dicot seeds are gram, bean, pea, cucumber, and tamarind.
• Examples of endospermic monocot seeds are maize, rice, and wheat.

Examples Of Non-endospermic Monocot Seeds: are pothos (money plant), Vallisneria, Alisina, and Amotphophallns.

Defense Mechanisms In Plants

1. Thoms: Lemon, pomegranate, Duranta
2. Spines: Agave, Yucca
3. Prickles: Agave, cotton tree, rose
4. Stinging Hair: Laportea, Urtica clioica
5. Glandular Hair: Jatropha, Boerhavia, Tobacco
6. Stiff Hair: Guaphalium
7. Latex: Ficus, Nerium, Euphorbia
8. Alkaloids: Poppy, Datura
9. Geophilous Habit: Ginger, turmeric. Colocasia, onion
10. Myremecophily: Guava, mango, litchi
11. Mimicry: Cladium, Sansevieria

Anemochory is common in orchids and grasses. The jaculator mechanism in Ruellia and the fountain mechanism in Ecballiurn are related to autochory.

 

Morphology Of Flowering Plants Assertion Reasoning Questions And Answers

In the following questions, an Assertion (A) is followed by a corresponding Reason (R). Mark the correct answer.

1. If both Assertion and Reason are true and the Reason is the correct explanation of the Assertion.
2. If both Assertion and Reason are true, but the Reason is not the correct explanation of the Assertion.
3. If Assertion is true, but Reason is false.
4. If both Assertion and Reason are false.

Question 1.

Assertion: In head inflorescence, florets are arranged centrifugally.

Reason: There are always two types of florets in head.

Answer: 4. If both Assertion and Reason are false.

Question 2.

Assertion: Staminal tube is present in Malvaceae.

Reason: It is due to a monetary condition.

Answer: 1. If both Assertion and Reason are true and the Reason is the correct explanation of the Assertion.

Question 3.

Assertion: The nest of Dischidia is a modified structure of the root.

Reason: Nest roots absorb water and food from humus-rich soil collected in the nest.

Answer: 4. If both Assertion and Reason are false.

Question 4.

Assertion: The lower feathery end of the tigellum is known as a radicle.

Reason: Tigellum bears two nodes on which one or two cotyledons develop.

Answer: 4. If both Assertion and Reason are false.

Question 5.

Assertion: There are five alae in the Pisitm sativum flower.

Reason: Both alae are covered by the largest petal.

Answer: 2. If both Assertion and Reason are true, but the Reason is not the correct explanation of the Assertion.

Question 6.

Assertion: All floral whorls are supposed to be modified leaves.

Reason: A Flower is considered as a modified shoot bearing floral parts on its nodes.

Answer: 1. If both Assertion and Reason are true and the Reason is the correct explanation of the Assertion

Question 7.

Assertion: Young leaves in Poinsettia are brightly colored to attract pollinators and achieve pollination.

Reason: It is only a bright color that can attract pollinators on all plants.

Answer: 3. If Assertion is true, but Reason is false.

Question 8.

Assertion: Schizocarpic fruits arc intermediate between dehiscent and indehiscent fruits.

Reason: These fruits split into single-seeded parts.

Answer: 1. If both Assertion and Reason are true and the Reason is the correct explanation of the Assertion.

Question 9.

Assertion: Leaf in Opuntia functions for the storage of sugars.

Reason: Sugar is transported from leaves in Opuntia and gets stored in the stem.

Answer: 4. If both Assertion and Reason are false.

Question 10.

Assertion: Prop roots develop mostly from horizontal branches of main stem.

Reason: Adventitious roots may perform mechanical supporting functions, working as ropes of a tent.

Answer: 2. If both Assertion and Reason are true, but the Reason is not the correct explanation of the Assertion.

 

Plant Kingdom Systems Of Biological Classification

The following systems of classification have been proposed from time to time. Some early attempts for the classification of plants are as follows:

1. Aristotle: Grouped plants into trees, shrubs, and herbs based on their habit. He divided animals into “Enaima” and “Anaima” on the basis of the presence and absence of RBC, respectively.
2. Charaka (Father of Ayurveda): Listed 200 kinds of animals and 340 kinds of plants in his book “Charak Samhita.”

Artificial System Of Classification: The artificial system of classification is based on a few morphological characters for grouping the organisms. Early systems of classifications given by Aristotle, Theophrastus, Pliny, Bauhin, John Ray, and Linnaeus are artificial systems.

• Theophrastus proposed the first system of artificial classification of plants on the basis of habit of plants into herbs, shrubs, and trees;
• Carolus Linnaeus (1707-1778) proposed the artificial system of classification based exclusively on the nature and number of stamens and carpels. It was called as a sexual system of classification.
• The classification consisted of 24 classes, in which 23 classes were of flowering plants (Phanerogamia) and the 24th class had flowerless plants (Cryptogamia).

The details of his classification were published in Genera Plan/arum (1737). Total 24 classes given by Linnaeus were: Monandria, Diandria, Triandria, Tetrandria, Pentandria, Hexandria, Heptandria, Octandria, Enneandria, Decandria, Dodecandria, Icosandria, Polyandria, Didynamia, Tetradynamia, Monadelphia, Diadelphia, Polyadelohia, Syngenesia, Gynandria, Mcnoecia, Dioecia, Polygamia, and Cryptogamia.

Artificial System Of Classification Drawbacks

1. Because this system was based on few characters, hence diverse animals and plants were placed into a limited number of groups.
2. No natural or phylogenetic relationships were considered.

Natural System Of Classification: The natural system of classification is known as the horizontal system of classification or 2D system. Organisms in this system are classified on the basis of natural affinities.

• This system uses as many taxonomic characters as possible to group organisms. This classification is mainly based on form relationships realizing all information available at the time of collection of plants.
• The classification systems proposed by John Ray, de Jus- siaeu, de Candolle, Bentham, and Hooker were natural.
• George Bentham and J.D. Hooker (1833-1862) gave the most important system of classification of angiosperms and published it in three volumes of “Genera Plantarum.’’
• They described 202 families. In this system, the description of plants was based on their detailed studies and dissections. It is widely acceptable and all British commonwealth countries including India widely follow this system for practical purposes, hence, it is called practical classification.

Read and Learn More NEET Biology Notes

Bentham And Hooker’s Classification: Bentham and Hooker divided plant kingdoms into two subking-doms—Cryptogamia (non-seeded plants) and Phanerogamia (seeded plants). Phanerogamia was further divided into three classes—dicotyledons, gymnosperms, and monocotyledons.

An outline of the classification of Phanerogamia is given below.

Class 1: Dicotyledonae: Pentamerous flower, reticulate venation in leaves, two cotyledons in seed, vascular bundles open (with cambium), secondary growth present, wood formation occurs. It is divided into three sub-classes

1. Sub-class 1 Polypetalae: Petals free and separate. It has three series.
   • Series 1 Thalamiflorae: Flower hypogynous, stamens and pistils many (indefinite), petals free, distinct sepals are free from ovary. It has six orders.
   • Series 2 Disciflorae: Flower hypogynous, calyx consists of free or united sepals, petals free, a prominent cushion-shaped disc is present below the ovary. It has four orders.
   • Series 3 Calyciflorae: Flower perigynous or epigy- nous. Calyx contains united sepals (rarely free); ovary inferior. It has five orders.
2. Sub-class 2 Gamopetalae: Petals united or fused. It is divided into three series.
   • Series 1 Inferae: Flower epigynous, ovary inferior; stamens as many as corolla lobes or fewer. It has three orders.
   • Series 2 Heteromerae: Ovary usually superior; carpels more than two. it has three orders.
   • Series 3 Bicarpellatae: Ovary usually superior, two carpels (rarely one or three). It has four orders.
3. Sub-class 3 Monochlamydeae: Flower incomplete; no distinction between calyx and corolla present which is usually sepaloid and may be absent. It is divided into eight series.
   • Series 1 Curvembryeae: Embryo curved; generally one ovule in the ovary which is one in each locule.
   • Series 2 Multiovulatae: Aquaticae-Plants are aquatic, submerged herbs, syncarpous ovary.
   • Series 3 Multiovulatae Terrestres: Plants are terrestrial, syncarpous ovary.
   • Series 4 Microembryae: Very minute or small embryo.
   • Series 5 Daphnales: Ovary with one carpel and one ovule.
   • Series 6 Achlamydosporeae: Ovary unilocular with one to three ovules. Ovary inferior.
   • Series 7 Uniscxulaes: Flower unisexual.
   • Series 8 Ordines Anomali: Families having plants with anomalous (abnormal) characters.

Class 2 Gymnospermae: Sex organs on cones, perianth absent, ovule naked (not found inside ovary), seeds are also naked, haploid endosperm. It has three families: Gnctaceae, Coni ferae, and Cycadaccae.

Class 3 Monocotyledonae: Parallel venation in leaves, embryo with one cotyledon, flower usually trimerous, wood absent, and no secondary growth. It is divided into seven series.

• Series 1 Microspcrmae: Ovary inferior, seeds minute.
• Series 2 Epigynae: Ovary inferior, seeds larger.
• Series 3 Coronarieae: Ovary superior, perianth colored.
• Series 4 Calycineae: Ovary superior, perianth green.
• Series 5 Nudiflorae: Perianth absent, ovary superior.
• Series 6  Apocarpae: Carpels free (apocarpous).
• Series 7 Glumacae: Flowers arranged in spikelets with bracts, Perianth reduced, bracts large and scaly.

In this classification, class is like division, series is like class, cohort is like order, and order is like family.

Merits Of Bentham And Hooker System Of Classification

1. It is useful for practical value. In India, it is the most used system.
2. Ranales have been given a primitive position and monocots are considered as advanced.

Demerits Of Bentham And Hooker System Of Classification

1. Gymnosperms were placed between dicots and mono-cots.
2. Many important floral characters have been neglected.
3. It is not a phylogenetic system. The idea was to believe on the fixity of species.
4. Some closely related families were separated and placed under different cohorts, and unrelated families have been put nearer.
5. Advanced families such as Orchidaceae have been considered as primitive.

Phylogenetic System Of Classification: The phylogenetic system of classification is also known as the vertical system or 3D system of classification. The term phylogeny was given by Lamarck. Phylogeny is the evolutionary history of an organism.

• According to this system of classification, plants are classified according to their evolutionary and genetic affinities. In this system organisms belonging to the same taxa are believed to have a common ancestor and may be represented in the form of a family tree called a cladogram.
• A.W. Eichler modified Bentham and Hooker’s system by placing gymnosperms in the beginning. He is also known as the pioneer in the phylogenetic system of classification.

Adolph Engler and Karl A.E. Prantl, two German botanists, adopted their system in “Die Naturalichen Pilanzen Familien” (1887-1915). It was a German work that was later translated in English. The work had 23 volumes.

An Outline Of Engler And Prantl System Of Classification

Phylogenetic Merits Of This System: In this system, families are arranged according to the increasing complexity of flowers.

Phylogenetic Demerits Of This System

1. Monocots were considered primitive to dicots.
2. According to this system, primitive forms having naked flowers were kept in the beginning. The more advanced families have distinct perianth, while the highly evolved families have fused perianth.

John Hutchinson presented the phylogenetic classification in his famous book Families of Flowering Plants in 1959. In Hutchinson’s classification,

1. Trees and shrubs are considered to be more primitive than herbs.
2. Dicots have been considered more primitive than monocots.
3. Polypetalous, actinomorphic, and solitary flowers are considered more primitive than gamopetalous, zygomorphic, and inflorescence, respectively.

An outline of Hutchinson’s classification is given. The divisions include orders which again include families. Division does not include classes. Takhtajan stated that “taxonomy without phylogeny is like bone without flesh.”

An Outline Of Hutchinson’s System Of Classification

Branches Of Taxonomy

Classical Taxonomy: It deals with employing all available information to classify organisms on the basis of their origin, evolution, affinities, and variations.

Numerical Taxonomy/Phenetics/Taximetrics/Adansonian Taxonomy

1. It uses statistical methods for evaluating similarities and differences between species. All selected characters are given equal importance. The comparison has been made easier with the availability of sophisticated calculating machines and computers.
2. Dendrogram is the family tree of organisms on the basis of numerical taxonomy.

Biosystematics: It deals with the variations within a species and its general evolution.

Cytotaxonomy/karyotaxonomy: Based on the cytological information on cell, chromosome number, and their structure and behavior during meiosis.

Chemotaxonomy: Based on chemical constituents of plants, for example, betacyanin pigment in beetroots, raphides, and cystolith, sequencing DNA, and the chemical nature of proteins.

Turril Divided Taxonomy Into Three Types:

1. α-taxonomy: It is based on gross morphological features including compilation of monographs and flora.
2. β-taxonomy: It is based on morphology and evidence from genetics, cytology, anatomy, physiology, etc.
3. Ω-taxonomy: It includes all microscopic and biochemical evidence.

Classification Of Plant Kingdom

There are five major groups of Plant Kingdoms or Kingdom Plantae. These are:

1. Thallophyta
2. Bryophyta
3. Pteridophyta
4. Gymnosperms
5. Angiosperms

Thallophyta (Algae)

General Characters Of Algae Are As Follows:

1. Eukaryotic, autotrophic, chlorophyllous, cryptogamic, thallophytes.
2. Aquatic, either freshwater or marine.
3. They are found in many forms: unicellular (for example, Chlamydomonas), colonial (for example, Volvox), palmelloid (for example, Tetraspora), dendroid (for example, Prasinocladus), filamentous unbranched (for example, Spirogyra), or branched (for example, Cladophora), heterotrichous (for example, Fritschiella, Coleochciete, Stigeoclonium), siphonaceous (for example, Vaucheria), parenchymatous (for example, Ulva).
4. Reserve food is mainly starch.
5. Vegetative Reproduction: It takes place by fragmentation.
6. Asexual Reproduction: Zoospores, aplanospores, hypnospores, akinetes, palmella stage, autospores, etc.
7. Sexual Reproduction
   • Sex organs are unicellular or multicellular with all fertile and non-jacketed.
   • The embryonic stage is absent.
   • Sexual Reproduction Three Types:
     1. Isogamous,
     2. Anisogamous, and
     3. Oogamous.
   • Sporic or gametic or zygotic meiosis occurs in life cycle.

R.E. Fritsch classified algae into 11 classes in his book Structure and Reproduction of the Algae mainly on the basis of pigmentation, reserve food, flagellation, thallus structure, modes of reproduction, and life cycles.

Whittaker included only Chlorophyceae (green algae), Phaeophyceae (brown algae), and Rhodophyceae (red algae) in algae under Kingdom Plantae.

Green Algae (Chlorophyceae) General Characters

1. Mostly freshwater (Spirogyra. Ulothrix, Chara, Chla- mydomonas, Volvox, etc.) and some arc marine (Ac- etabularia, Ulva, etc.).
2. Photosynthetic pigments are chlorophyll-a, chloro-phyll-b, and carotenoids.
3. Isokont flagellation.
4. Thylakoids are in the group of 2-20 per lamella.
5. Pyrenoids present.
6. Three types of life cycles occur in green algae:
   1. Haplontic life-cycle, for example, Ulothrix, Spirogyra. Chlamydomonas (zygotic meiosis occurs).
   2. Diplontic life-cycle, for example, Caulerpa (gametic meiosis).
   3. Diplohaplontic life cycle, for example, Ulva, Cladophora. In this type of lifecycle, haploid and diploid phases are well-developed and multicellular. The isomorphic alternation of generation is found.

Chlamydomonas: It is unicellular, motile, pyriform, or pear-shaped. Cell wall is made up of hydroxyproline (glycoprotein). Flagella are isokont, whiplash type. Presence of neuromotor apparatus (basal granules + paradesmos + rhinoplasty + centrosome).

Presence of single cup-shaped chloroplast with a single pyrenoid. Two contractile vacuoles, single eye spot or stigma as photoreceptor organ is present.

Chlamydomonas Reproduction

1. Asexual Reproduction: It is of the following types:
   • By Zoospores: Under favorable conditions.
   • Palmella Stage: It is formed in response to desiccation conditions and toxic salts. Palmella spores are green, non-motile, and are capable of growth and division.
   • By Aplanospore (Thin-Walled Spore) Or Hypno- Spores (Thick-Walled Spore): These are formed under drought conditions. Aplanospore formation occurs in C. caudata.
2. Sexual Reproduction: It is of the following types
   • Isogamy: Fusion of similar gametes, for example, C. debaryana (homothallic) or C. reinhardii (heterothallic).
   • Anisogamy: Fusion between a motile, smaller male gamete and a motile larger morphologically dissimilar female gamete, for example, C. braunii.
   • Hologamy: Fusion of young cells, for example, C. media.
   • Oogamy: Fusion between a motile male gamete and a non-motile female gamete, for example, C. coccifera.

Spirogyra: It is commonly known as summer alga or “hair of princess” “pond silk” “water silk” or “pond scum” (due to mucilage covering found in stagnant water). The cell wall is two-layered; the outer wall of pectose (water soluble which forms mucilage) and the inner wall of cellulose.

• The primordial utricle is present as a thin peripheral cytoplasm due to a large central vacuole. Presence of 1-16 ribbon-shaped, spiral chloroplast. Coiling is sinistral or left-handed. Many pyrenoids are present.
• Spirogyra adnata and S.jogensis remain attached to the substratum by basal cells called holdfast or hapteron.

Spirogyra Spirogyra Reproduction

1. Vegetative Reproduction: By fragmentation
2. Asexual Reproduction: It is generally absent except in the following:
   1. By Parthenospores Or Azygospores: Example, Spirogyra various. If placed in a sugar solution, it develops parthenospores.
   2. By Akinetes: Example, S. Farlow
   3. By Aplanospores.
3. Sexual Reproduction: It occurs by conjugation. It is physiologically anisogamous type. Types of conjugation are:
   • Scalariform Conjugation: The most common type; occurs in heterothallic and homothallic species. A minimum of two filaments are involved, for example, S. tmvensis.
   • Lateral Conjugation: Two adjacent cells of the same filament function as gametangia. It is a primitive type and uncommon.
   • Direct Lateral Conjugation: Example, S.jogensis
   • Indirect Lateral Conjugation: Example, S. affinis.

Economic Importance Of Green Algae

1. Codium and Ulva (Sea lettuce) is used as salad or vegetables in European countries after drying and salting.
2. Chlorella pyrenoidosa (called space alga) is used by exobiologists for food, oxygen, and disposal of CCE and organic waste in prolonged space flight.
3. Cephaleuros virescence is a parasitic green alga that causes red rust of tea disease.

Brown Algae (Phaeophyceae) General characters

1. The members of this group are called brown algae due to their characteristic brown color derived by the presence of an extra brown pigment, fucoxanthin.
2. The brown algae are almost exclusively marine plants found primarily in the coastal zones. These occur mainly in the cooler seas. However, the Sargassum is a well-known warm-water form that occurs in the North Atlantic Ocean region and forms the Sargassum Sea.
3. No unicellular brown algae is known. Except for a few members, most brown algae are macroscopic. Some of these are of massive sizes such as Laminaria (2 – 9 m); Nereocystis (45 m); Macrocystis (60-90 m). Because of their bulky appearance, these are called giant kelps. The body of a typical brown alga (for example, Laminaria) is differentiated into
   • A holdfast,
   • A stipe, and
   • Lamina.
   • In some large brown algae, certain cells are modified into long filaments called trumpet hyphae. These carry food from the lamina to the holdfast.
4. The cell walls of brown algae are generally composed of two layers: an inner cellulosic layer and an outer mucilaginous layer. The cellulosic walls are covered by a colloidal covering called phycocoUoids.
5. Alginic acid is an important component of hydrocolloids and is commercially obtained from kelps. It has hemostatic properties and has been used in emergency transfusions in the treatment of shock. Sodium alginate is used as a stabilizer in food industries; and calcium alginate in plastics. Forms of alginic acid are used in textile, rubber, and paint industries. It is also used for making smooth ice creams.
6. The cells of brown algae contain in addition to other normal structures small colorless vesicles called fu- cosan vesicles. The function of these vesicles is not known.
7. The cells contain pigment fucoxanthin in addition to chlorophyll-a and c. Fucoxanthin dominates over the green color of the chlorophyll, imparting a brown color to the algae.
8. The reserve food material is in the form of laminarin starch and mannitol.

Brown Algae (Phaeophyceae) Asexual Reproduction: Asexual reproduction by fragmentation is quite common. Detached vegetative parts of brown algae have great potential to develop into new individuals. Asexual reproduction also occurs by motile or non-motile spores formed inside large-sized cells called sporangia which may be unicellular (unilocular) or multicellular (multicellular.)

Brown Algae (Phaeophyceae) Sexual Reproduction: Sexual reproduction takes place by the formation of flagellate gametes that are generally formed inside gametangia. In some cases, the female gamete is non-motile. The gametes may be isogametes (both male and female gametes exactly similar), isogametes (both similar, but female, gamete larger than male gamete), and oogamous (female larger non-motile; male motile smaller).

Economic Importance Of Brown Algae

1. Fucus and Laminaria are rich sources of iodine.
2. Laminaria yields a food product rich in carbohydrates called kombu and similarly, A/aria yields a product called sarumen in Japan.
3. Durvillea has antiworm properties.

Red Algae (Rhodophyceae) General Characters

1. They are called so because of their reddish color due to the presence of special pigments: r-phycocyanin and r-phycoerythrin. They are mostly marine.
2. In deeper oceans, these acquire deeper color. Actually, only the blue-green light reaches the deep water. The pigment r-phycoerythrin in red algae does the job of capturing light of available wavelengths for red algae.
3. Red algae show a variety of forms. Their thallus ranges from microscopic, unicellular to neatly hull a meter in length. These may be unicellular, filamentous, ribbons-shaped, or leaf-like. Some of these secrete calcium carbonate over their walls and form coral-line structures. In certain coral reefs, red algae such as Corallina are the main producers.
4. Some red algae are parasitic. For example, llarveyella is parasitic on other red algae. The parasitic forms are colorless.
5. The cell wall contains cellulose and pectic materials together with certain polysaccharides called hydrocolloids, some of which contain sulfur, for example, agar is used widely in preparing solid food media for the growth of bacteria or fungi in the laboratory. Agar has no food value for bacteria or fungi. It is also used by human beings as a thickening and binding agent in various food products. Agar agar is obtained commercially from the red algae Geliclum and Gracilaria.
6. The cell walls of red algae also contain another bio-chemical carrageenin which is also widely used as a thickening and binding agent in food products, especially in puddings.
7. The cells may be uninucleated or multinucleated with one or more plastids that may be with or without pyrenoids. The food reserves lie in the form of floridean starch and a soluble sugar fluoridoside (a galactoside of glycerol).
8. Asexual reproduction takes place with the help of non-motile spores. Reproduction by fragmentation is not common, though some red algae are able to regenerate the full plant from a severed holdfast.
9. Sexual reproduction is highly advanced and oogamous. Flagellated gametes are absent in red algae. The male gametes called spermatia develop in specialized structures called spermatangia while the female cells are called carpogonia. The carpogonium is a flask-shaped body having a neck-like trichogyne.
10. Alternation of haploid and diploid multicellular generations occurs in many algae.

Thallophyta (Algae) Points To Remember

Red snow is caused by hypnospores of Chlamydomonas nivalis. They contain a carotenoid pigment called hematochrome

Bald spot: Receptive, colorless spot of oogonium through which male gamete enters. Chlamydomonas prefers habitats rich in ammonium salts.

Bryophyta

Bryophyta General Characters

1. They are found in moist and shady places, i.e., sporophytes. They are often found to grow during the rainy season forming green carpets or mats on damp soil, rocks, walls, tree trunks, etc.
   • Bryophyta Exceptions
     1. Aquatic Forms
        • Ricciafluitans
        • Ricciocarpus nutans
        • Riella; Funtinalis
     2. Saprophytic Forms:
        • Cryptothallus mirabilis
        • Buxbaumia aphylla
     3. Epiphytic Form:
        • Frullania
2. The dominant phase or plant body is a free-living gametophyte.
3. Vascular tissues are absent.
4. Roots are absent, instead, rhizoids occur. The latter may be unicellular or multicellular.
5. Vegetative reproduction is quite common through fragmentation, tubers, gemmae, buds, adventitious branches, etc. Mitospores are not formed.
6. Sex organs are multicellular and jacketed. They are of two types, male antheridium and female archegonium.
7. An external layer of water is essential for the swimming of male gametes and to reach the archegonia.
8. Fertilization produces an embryo inside the archegonium. The embryo grows into a sporophyte.
9. Sporophytes is parasitic over gametophyte.
10. The sporophyte of bryophytes is also called sporogonium. It produces haploid spores inside its capsule part while attached to the gametophyte.
11. On germination, each spore produces a gametophyte either directly or through a juvenile filamentous stage called protonema.
12. Bryophytes show heteromorphic or heterologous alter-nation of generations in the life cycle.

Classification Of Bryophyta: Shows the classification of Bryophyta.

Life Cycle Of Funaria hygrometrica

• Funaria is a radially symmetric plant that is differentiated into stem or central axis, leaves or phyllodes, and rhizoids. The rhizoids are multicellular, branched with oblique septa. It is monoecious and autogenous (i.e., both sex organs on the same plant but on different branches).
• Antheredia are borne in groups at the tip of the main axis and surrounded by perigonial leaves. Archegonial clusters on lateral branch tip and surrounded by perichaetial leaves. Thus, both male and female gametangia are acrocarpous. Male gametes or sperms are elongated biflagellates with curved bodies. Number of neck canal cells (NCC) in archegonium is 6-10.

Diploid oospore develops into sporophyte. Mature sporogo- nium is differentiated into foot, seta, and capsule. The foot is embedded in a gametophytic plant body meant for the absorption of water, mineral salts, and fixation. Seta is a narrow stalk that lifts the capsule in the air. The capsule is differentiated into three parts: apophysis, theca, and operculum.

Apophysis contains assimilatory tissue; and stomata with a single annular guard cell. Theca contains central sterile columella, a spore sac, air cavity, and assimilatory tissue. The operculum is separated from theca by a one-celled elongated diaphragm. Above the hill lies a few layers of thin-walled cells fonning annulus.

Peristomial teeth are 32, acellular, arranged in two rings of 16 each. The outer peristomial teeth are exostome, and bear transverse thickening of cellulose, showing hygroscopic movement. Endostome or inner peristome teeth are without cellulose thickening, act as sieves, and check the sudden dispersal of spores.

Bryophyta Points To Remember

The smallest bryophyte is Zoopsts.

• The largest bryophyte is Dawsonia,
• The largest archegonium in the plant kingdom is of Funaria.

1. Gemmae in Funaria arc formed at the tips of chloroma branches of protonema.
2. Apospory is present in Funaria. It introduces polyploidy in the race.
3. Sphagnum upon death gets compressed and fossilized over thousands of years to produce a dark spongy mass called peat which is dried, cut, and used as fuel as well as good manure.
4. Dry Sphagnum can absorb 18-26 times its weight of water. In older times, Sphagnum moss was used in the place of absorbent cotton.
5. Polytrichum commune was employed in removing kid¬ney stones.
6. The oldest bryophyte fossils are 350 million years old, for example, Hepaticites, and Ricciopsis.
7. Bryophytes are adapted to land by having a waxy coating on aerial parts.
8. Bryophytes become seldom taller than 20 cm due to the lack of vascular tissue.
9. Elaters in Marchanlia are diploid and have spiral thickenings. They help in spore dispersal.
10. The air sacs in the capsule ofmoss act as shock absorbers.
11. Bryopsida: Common Names
    1. Polytrichum: Hair cap moss
    2. Sphagnum: Peat/bog moss
    3. Andrea: Granite moss
    4. Grimmia: Black moss
    5. Tortula: Twisted moss
    6. Ptilium: Feather moss
    7. Rhodobiyum: Rose moss
    8. Merceya: Copper moss
    9. Climacium: Tree moss
    10. Dicranum: Wind-blown moss

Pteridophyta

Pteridophyta General characters

1. The term pteridophyta was given by E. Haeckel for plants with feather-like fronds.
2. The first group of tracheophytes. The plant body is sporophytic.
3. Vascular tissues are present. They are of two types, xylem, and phloem. In the xylem, true vessels are absent. In phloem, companion cells are absent and sieve cells are present.
4. Meiospores are formed inside sporangia. Sporangia are associated with leaves called sporophylls.
5. Sporangium development is of two types:
   • Leptosporangiate: When sporangium develops from the single superficial cell, for example, Pteris, Diyopteris, and A-chan turn.
   • Eusporangiate: When sporangium develops from a group of cells, for example, Selaginella, or Equisetum.
6. Sex organs are multicellular and jacketed; antheridia are reduced. Archegonia are partially embedded.
7. Sperms arc flagellate. They require an external supply of water for swimming to reach Archegonia.
8. The embryo stage is present.
9. Embryogeny is of two types:
   • Exoscopic Embryogeny: Axis of the embryo is directed towards the archegonial neck, for example, the Equisetum.
   • Endoscopic: Axis of the embryo is directed inward towards the center, for example, Selaginella.
10. Development Of Embryo
    • Holoblastic: When the entire zygote is involved in embryonic development, for example, ferns.
    • Meroblastic: When a part of the zygote is involved in embryonic development, for example, Selaginella.
11. Heteromorphic or heterologous alternation of generations is present in the life cycle.

Steler System: The Steler theory was proposed by Van Teigham and Douliot.

Types Of Steler

1. Protostele: Simplest type, without pith

Haplostele: Example, Rhynia.

Actinostele: Example, Lycopodium serratum.

Plectostele: Example, Lycopodium clavatum.

Mixed Protostele: Example, Lycopodium cemum.

2. Siphonostele: With pith.

Ectophloic Siphonostele: Example, Osmunda, Botrychium.

Amphiphloic Siphonostele: Marxilea.

Solenostele: Stele with one or few leaf gaps. For example, Adiantum caudatum.

Dictyostele: Stele with a large number of overlapping leaf gaps, for example, Dryopteris, Pteris, etc.

Eustele: Conjoint, collateral open vascular bundles, for example, dicot stem, gymnosperm.

Atactostele: Closed vascular bundles scattered in the ground tissue, for example, monocot stem.

Life Cycle Of Selaginella Salient Features

1. The plant body is an evergreen sporophyte. It is differentiated into stems, leaves, and roots. The roots often develop at the tips of special structures called rhinophores.
2. The plant body can multiply vegetatively by fragmentation, bulbils, and tubers. Bulbils and tubers help in perennation as well.
3. Sporangia develop in the axil of fertile leaves or sporophylls at the tips of small branches called spikes. There are two types of sporangia, microsporangia and mega¬sporangia.
4. Each microsporangium produces a large number of small haploid microspores. A megasporangium develops only four haploid megaspores. Growth of the gametophytes is precocious.
5. Microspore produces an endosporic 13-celled male gametophyte. The latter has one urothelial cell eight jacket cells and four androgenic cells. The androgenic cells form 128-256 astrocytes or sperm mother cells. A sperm mother cell gives rise to a biflagellate sperm.
6. Megaspore produces a partially exospheric female gametophyte. The female gametophyte contains an exposed generative apical cushion and a storage tissue. The two are separated by a diaphragm. The apical cushion produces archegonia and rhizoids. Each archegonium has a single female gamete or oosphere. Fertilization requires the help of external water for the swimming of sperm. It produces diploid oospores.
7. The oospore divides to form a suspensor and embryo. The development of the embryo is meroblastic. A suspensor helps in pushing the embryo into food-laden storage tissue. The embryo has a foot for absorbing nourishment, a shoot tip, and a root tip. The latter two elongate and produce an independent sporophytic plant body.
8. Selaginella shows two distinct generations, sporophyte and gametophyte, one producing the other. They are morphologically different. The phenomenon is called hetero-morphic or heterologous alternation of generations.
9. Under dry conditions, the xerophytic species of Selaginella roll on into brown balls. The phenomenon is called cespitose habit. In this state, it may be uprooted. The brown balls become green and unroll again under moist conditions. Because of this characteristic, these plants are known as resurrection plants, for example, S. lepidophylia, and S. bryopteris.
10. The plant body of Selaginella chrysocaulos and S. selaginoides is erect. Its leaves are anisophyllous and arranged in two rows. In S. kraussiana, the plant body is prostrate. Its leaves are anisophyllous or dimorphic and arranged in four rows.
11. The stem in Selaginella is distelic. Rarely, the stem is monostelic.
12. Bower and Goebel named the rhizosphere of Selaginella as an organ suigeneris, i.e., the organ having the characteristics of both, i.e., stem as well as root, but independent in origin.
13. The mucilage oozing out of the neck of archegonium in Selaginella and fern contains malic acid. The neck of archegonium in Selaginella and fern contains only one neck canal cell.
14. Selaginella rupcstris shows a near approach to seed habit.

Ferns General Characters

1. Plant body is a sporophyte. It is differentiated into true stems, leaves, and roots.
2. The stem is an underground rhizome in most of the ferns. Some are called tree ferns, for example, Cyathea, and Celotia.
3. Leaves or their leaflets show furcate venation in which veins branch dichotomously without forming interconnections.
4. The younger parts of the stem, young leaves, petiole, and rachis of mature leaves possess hairs or scales called ramenta. Ramcnta protects them from mechanical injury and desiccation.
5. Young leaves show circinate ptyxis that is they are coiled in the form of a watch spring. This coiling protects the growing point which comes to lie in the center.
6. Sporangia occur on the leaves in clusters called sori (singular-sows). The fertile leaves are known as sporophylls. A sorus is covered by a flap-like outgrowth from its surface (true indusium, for example, Dryopteris) or turned margin of the sporophyll (false indusium, for example, Adiantum).

Life Cycle Of Dryopteris

1. Dryopteris Salient Features: It is found in moist shady places in tropical, subtropical areas. The plant body is perennial, independently living evergreen sporophyte having vascular tissues. It is differentiated into stems, leaves, and roots. Roots are adventitious.
   • Stem is an underground, dark brown rhizome. The large aerial leaves or fronds are incompletely bipinnate compound leaves. The young leaves show circinate ptyxis. Persistent leaf bases of the dead leaves arc found in the older parts of the rhizome.
   • In Dryopteris, a leaflet receives a single midrib which gives rise to lateral veins showing dichotomous divisions. The young leaves, young parts of the rhizome, petiole, and rachis of mature leaves are covered over by brown to black scales called paleae or ramenta.
2. Dryopteris Reproduction: The fern multiplies vegetatively by fragmentation of rhizome and development of adventitious buds. In Dryopteris, the adventitious bud present at the leaf base separates and grows into a new plant. In Adianlum caudatum and a few other species, adventitious buds develop at leaf tips.

When such leaf tips happen to touch the soil, they form new plants the process helps in spreading the fern over a large area. Because of this reason, Adianlum caudatum is also called walking fern and maidenhair fern.

The leaflets of a mature leaf bear sporangia in clusters called sori. The leaflets and leaves having sori or sporangia are called sporophylls. In Adianlum, the sori are borne submarginally at the distal end on the undersurface of the leaflets. The margin of the leaflet is reflexed to cover the sprus. The reflexed margin is known as false indusium.

In Diyopteris, the sori develop in two rows, one on either side of the midrib. Each row contains 4-6 sori except in smaller leaflets which may have 1-2 sori or can be sterile. Each sorus is covered by a membraneous sheath of its own. This covering is carted true indusium. The covered sori of Dryopteris are kidney-shaped in outline. This has given the name of the male shield fern to Dryopteris.

A sorus consists of a parenchymatous cushion or placenta. The placenta bears a number of stalked biconvex sporangia. In each sporangium, there is a single-layered jacket that encloses 12-16 diploid spore mother cells. A marginal row of jacket cells are differentially thickened to form an annulus.

The remaining marginal cells constitute stomium. The diploid spore mother cells divide meiotically to form haploid spores. With the maturity of spores, the indusium shrivels. The exposed sporangia dehisce in the region of the stomium is due to differential contraction of the annulus. The spores are dispersed by air currents.

After failing on suitable soil, each spore germinates and forms a thalloid gametophyte called prothallus. Prothallus is cordate, green, and flat in structure. Prothallus bears antheridia and archegonia at the ventral surface.

Antheridium has a three-celled jacket and about 32 sperm mother cells. The sperms are multiflagellate (multiciliate) and spirally twisted. Flask-shaped archegonium has a single binucleate neck canal cell, a single venter canal cell, and an oosphere. Sperms are attracted to the opened archegonia by malic acid present in their mucilage. Diploid oospore gives rise to an embryo that grows in size to form the fern plant.

Pteridophyta Points To Remember

1. Common names
   1. Spike moss (Selaginella)
   2. Bird’s nest moss (Selaginella rupesiris)
   3. Club moss (Lycopodium)
2. Smallest ptcridophyte – Azolla (an aquatic fern)
3. Largest ptcridophyte = Cyathea (tree term)
4. Apogamy: It is the development of haploid sporophytes from gametophytes without fertilization. It was reported by Farlow in Pier is erotica.
5. Apospory: It is the development of diploid gametophyte from sporophyte without meiosis. It was reported by Druery in Athyrium. Due to apospory, polyploidy is common in ferns.
6. Psilofales such as Rliyniu were the first trachcophytes.
7. Azolla is a water fern used as a biofertilizer.

Gymnosperms

Gymnosperms General Characters

1. All gymnosperms are perennial woody plants forming either bushes or trees. Some of these are very large and live for thousands of years, for example, Sequoia sempervirens.
2. It is the smallest group in plantae with 70 genera and 900 living species. In India, 14 genera and 54 species have been found.
3. Leaves are generally dimorphic, foliage, and scale leaves.
4. Foliage leaves do not have lateral veins. Transfusion tissue (hydrostereom) occurs internally or in lateral transport.
5. Wood is homozygous but Gnetalcs bear vessels in the xylem, for example, Ephedra, Gnetum, and Welwitschia.
6. Types Of Wood
   • Manoxylic: Softwood, vascular tissues with medullary rays, commercially less important, for example, Cycas.
   • Pycnoxylic: Compact wood without or with narrow medullary rays; commercially more important, for example. Pious.
   • Monoxylic: With single persistent cambium rings and bundles, for example, Pious.
   • Polyxylic: With many persistent cambium rings and bundles, for example, Cycas.
7. Flowers absent. There are two types of sporophylls, microsporophylls and megasporophylls.
8. The two types of sporophylls are usually aggregated to form distinct cones or strobilli, pollen cones (male cones), and seed cones (female cones).
9. Seeds do not occur inside a fruit. They are naked or lie exposed on the surface of megasporophylls.
10. Ovules lie exposed on the megasporophyll. Ovules are unitegmic and orthotropous.
11. Pollination is direct as stigma is absent, and the pollen grains directly reach the micropylar ends of ovules. Pollination is usually accomplished by wind (anemophily).
12. The male gametophyte produces only two male gam¬etes or sperms. Generally one of them is functional.
13. External water is not required for the transport of male gametes. Instead, a pollen tube is formed by the male gametophyte to affect fertilization (siphonogamy).
14. Seeds contain a food-laden tissue for the future growth of embryos into seedlings.

Life Cycle Of Pinus: Pinns is a coniferous gymnosperm having pyramidal or excurrent shape like a “Christmas tree.” The sporophytic plant body is divided in stems, leaves, and roots. Stem branches are of two types, long and dwarf. The dwarf branches possess 1-5 needlelike foliage leaves which are surrounded by a sheath of scale leaves.

The number of needles is 1, 2, 3, 4, and 5 in a spur of P monophylla, P. sylvestris, P. roxburghi, P. quciddfolia, and P. wallichiana, respectively. It has a tap root system with long horizontal roots. Mycorrhiza occurs near the soil surface. Mycorrhizal roots lack root hairs and root caps.

• Vegetative reproduction is absent. Pinus is monoecious and develops clusters of shortly stalked male cones subterminally on the lower branches and female cones in the circle of 2-6 on the upper long branches.
• Each male cone has a short stalk, a central axis, and a number of spirally arranged microsporophylls. A microsporophyll bears two oblong, parallel microsporangia on its lower surface.
• In a microsporangium, the diploid microspore mother cells undergo meiosis and form haploid microspores or pollen grains.

At maturity, the pollen grains are released from the male cones and dispersed by air currents. Pollen grain has at this time two prothallial cells, a generative cell, and a tube cell. They are from yellow clouds in the pine forests. A pollen grain has two air sacs or wings to make it light. Male cones are homologous to dwarf branches.

• The female or seed cones develop in groups. 2-6 on the upper long branches of the tree. Each female cone has a long stalk and a central axis on which are a number of spirally arranged paired scales. The lower of the pair is called the bract scale while the upper scale is the ovuliferous scale or megasporophyll. The ovuliferous scale bears two ovules towards the basal region on the upper side.
• Each ovule has a Three-layered integument with a terminal wide, oblique pore or micropyle and a nucellus (megasporangium). In the middle of the nucellus, a megaspore mother cell differentiates. It forms four haploid megaspores by meiosis but only one survives.

The functional megaspore gives rise to the female gametophytes. The female gametophyte bears 1-8 archegonia. An archegonium has a short neck and a broad venter. The neck canal cell is absent. The Venter canal cell is ephemeral. The venter contains a large egg or oospore. Female cones are ho¬mologous to long branches.

• The female cones open in the year of theft formation for pollination. Pollination is anemophilous (by air) and direct. The pollen grains pass into the opened micropyle and rest on the top of the nucellus.
• The micropyle of each ovule contains a mucilage or pollination drop for catching the pollen. Here it germinates and forms a pollen tube but further growth is stopped due to the arrival of winter in the first year, in the spring of the next year, fertilization occurs.
• Fertilization occurs after 13 months from the time of pollination. The pollen tube grows and pierces an archegonium. One male gamete or male nucleus fuses with the oosphere to form a diploid zygote or oospore. The oospore forms an embryo while the ovule matures into a seed.

Part of the upper surface of the ovuliferous scale is peeled off along with the seed to form its wing. A female cone takes 26 months to reach maturity. It then opens to release winged seeds which are dispersed by air. After falling on suitable soil, each seed gives rise to a new plant.

Gymnosperms Points To Remember

The number of cotyledons in Finns ranges from 3 to 18.

1. There are four tiers proembryo basal embryo tier, suspenser tier, rosette tier, and upper tier. The development of sporangium in Pinus is eusporangiate and fertilization is siphonogamous type.
2. Resin is collected by injuring the Pinus.
3. Resin is a semifluid secreted by special tubes. It solidifies on exposure to air. Therefore, it plugs the places of injury. It is an antiseptic and commercially distilled to obtain turpentine and resin. Resin is used in waterproofing, sealing joints, and preparation of writing paper. Turpentine is used as a solvent in paints, polishes, and wax.
4. Seeds of P. gerardiana (chilgoza) are edible after roasting.
5. Smallest gymnosperm = Zamia Largest gymnosperm = Sequoia dendron
6. The three generations in a seed are:
7. Testa, tegmen, and perispenn represent parental sporophyte;
8. Endosperm represents female gametophyte;
9. Plumule, radicle, suspensor, and cotyledons (embryo) represent future sporophytes.
10. Polyembryony: It is the formation of more than one embryo inside a single seed. It was reported by Leu-wenhoek in oranges. Simple polyembryony is due to the fertilization of many eggs, for example, the Pinus ovule has 2-8 archegonia. Cleavage polyembryony is true polyembryony and very common. It is due to the splitting of embryo tissue. Adventive polyembryony is the formation of extra embryos directly from diploid cell (for example, rosette cells) other than embryonal cells.

Cycas

1. It is a dioecious plant.
2. Female cone absent.
3. The stem is unbranched, cylindrical, i.e., caudex.
4. Coralloid roots are present
5. Cycas show fern ancestors in the presence of ramenta, circinate ptyxis, and multicilliated sperms.
6. Vascular bundles are arranged like an inverted omega in the rachis.
7. It has the largest ovule, largest male gamete, and largest egg in the plant kingdom.
8. Fertilization occurs at three stages.
9. Fertilization is siphonogamous and zooidogamous.
10. Seed has two cotyledons.

Angiosperm (Flowering Plants)

These are the most advanced plants, characterized by the presence of flowers, covered ovules, and seeds. These form the largest group of the plant kingdom, containing about 300 families, 8000 genera, and about 300,000 species. These are the highest-evolved plants on this earth.

From the Cretaceous period, the angiosperms eclipsed all other vegetation, and now they are the most dominant plants. They are found almost everywhere in all possible habitats. Angiosperms include all varieties of plants such as hydrophytes, xerophytes, epiphytes, parasites, saprophytes, insectivorous, symbionts, mangroves, etc.

Characteristic Features Of Angiosperms

1. The presence of flowers is the most striking feature of angiosperms. It contains the sex organs of the plant.
2. Ovules are covered and are present inside the ovary.
3. pollen grains are received by the stigma of the carpel, so maturation of pollen grain (male gametophyte) takes place on the stigma.
4. Double fertilization (syngamy and triple fusion) is also characteristic only to angiosperms.
5. Endosperm is formed after fertilization, and it is generally triploid.
6. Vessels and companion cells are present in the xylem and phloem elements, respectively.
7. Fertilized ovules ripen into seeds. The seeds are cov¬ered by fruits. A fruit is technically a ripened ovary7. Fruits not only protect the seeds but also help in their dispersal.
8. The xylem contains vessels.
9. Phloem possesses sieve tubes and companion cells.
10. Spanish moss (Tillandsia) is an epiphytic angiosperm.
11. A gametophyte can be haploid or diploid but always produces gametes.
12. Monocots do not grow in girth though they grow in length and produce new leaves and flowers. Dicots have indefinite growth. New roots, shoots, leaves, bark, and wood are formed year after year.
13. Petals are showy and are meant to attract animal pollinators, especially insects.
14. In most of the plants, pollination is effected by animal insects, worms, birds, bats, and even human beings. Insectaccomplished pollination is termed as entomophily.
15. Angiosperms are divided into two sub-groups, i.e., dicots and monocots.

Dicots: They are angiosperms or flowering plants that are characterized by the presence of two cotyledons in the seed, and generally reticulate venation in leaves (with a few exceptions Calophyllum and Etyngium). Concentric tissues in the stem with open vascular bundles are arranged in a ring: penta or tetramerous flowers.

Monocots: They are angiosperms or flowering plants which are characterized by the presence of a single cotyledon in the seed, generally parallel venation in the leaves (except Smilax, Colocasia, and relatives), scattered closed vascular bundles in the stem, and trimerous flowers, for example, banana, cereals, palms, grasses, bamboo, lilies, orchids, etc.

Differences Between Various Plant Groups

Angiosperm (Flowering Plants)  Points To Remember

Bessey, Oswald Tippo, Cronquist, and Thom also proposed a phylogenetic system of classification.

1. Thallophyta term was given by Endicher.
2. M.O.P. Iyenger is known as the father of Indian psychology.
3. Also known as vascular cryptogams, vascular amphibians, snakes of the plant kingdom, are seedless tracheophytes.
4. Hironymus divided the genus Selaginella in two subgenera, viz., Homeophyllum and Heterophyllum.
5. The term gymnosperm was used by Theophrastus in his book “Enquiry into Plants.”
6. C. revolution is called as sago palm. Sago is obtained from C. revolute.
7. Drug ephedrine is obtained from Ephedra which is used in curing respiratory ailments including asthma.
8. Ginkgo biloba is known as the “maidenhair tree.”

Different Life Cycles And Alternation Of Generation

The life cycle of a plant is called the alternation of generations. In plant life, there are two phases, one diploid sporophyte and one haploid gametophyte, which give rise to each other. In this process syngamy and meiosis are instrumental.

Sporophyte produces spore after meiosis which develops into gametophyte (gamete-producing plant). The gametes undergo fusion/syngamy to form a diploid zygote. The fate of the zygote depends upon the kind of life cycle.

Types Of Life Cycles or Patterns Of Alternation Of Generations: There are three chief kinds of life cycle. They fundamentally differ in the duration of the haploid and diploid phases. They are as follows.

Haplontic: It is characterized by the dominance of haplophasc. The plant body is gametophyte and independent. The sporophyte is dependent on gametophyte and is not a free-living body. The major part of life is enjoyed by gametophytes, for example, the majority of green algae viz, Chlamydomonas, Ulothrix, Spirogyra, etc.

Diplo-haplontic Or Haplo-diplontic: it is characterized by the existence of sporophyte as well as gametophyte. Both of them are photosynthetic and free-living and the two phases, diplophase and haplophse, are nearly equal.

If sporophytes and gametophytes are morphologically different, then the life cycle is termed as diplo-haplontic; heteromorphic, for example, All pteridophytes; all bryophytes; some brown algae, viz., Laminaria and other kelps.

If the two phases are morphologically identical, then the life cycle is termed as diplo-haplontic isomorphic, for example, Green algae, viz., Ulva and claclophora\brown algae, viz., Eclocarpns.

Diplontic: It is characterized by the dominance of diplopia. The plant body is sporophyte which is independent and free living. The gametophytes are extremely reduced and are dependent physically as well as nutritionally on (lie sporophyte. the major purl of life is enjoyed by the sporophyte, for example, all gymnosperms and angiosperms; diatoms; some brown algae, viz., Fuats and Sargussum.

 

Plant Kingdom Assertion Reasoning Questions And Answers

In the following questions, an Assertion (A) is followed by a corresponding Reason (R). Mark the correct answer.

1. If both Assertion and Reason are true and the Reason is the correct explanation of the Assertion.
2. If both Assertion and Reason are true, but the Reason is not the correct explanation of the Assertion.
3. If Assertion is true, but Reason is false.
4. If both Assertion and Reason are false.

Question 1. Assertion: Thallophytes are non-vascular, non-archego- niate. and non-cormophytic plants.

Reason: Thallophytes lack vascular bundles, archegonia, and differentiated plant body.

Answer: 1. If both Assertion and Reason are true and the Reason is the correct explanation of the Assertion.

Question 2. Assertion: Funaria archegonium has a maximum concentration of sucrose at the tip of the neck.

Reason: Male gametes show chemotropic movement.

Answer: 3. If Assertion is true, but Reason is false.

Question 3. Assertion: Pyrenoids may or may not be surrounded by a sheath of starch plates in algae.

Reason: In higher plants, these are replaced by amyloplasts.

Answer: 2. If both Assertion and Reason are true, but the Reason is not the correct explanation of the Assertion.

Question 4. Assertion: Seeds are formed by some species of spike moss.

Reason: All conditions for seed habit are fulfilled by these species of spike moss.

Answer: 4. If both Assertion and Reason are false.

Question 5. Assertion: The resin duct in coniferales is schizogenous in origin.

Reason: The resin duct helps to retain water as well as seals the injured areas of plants.

Answer: 2. If both Assertion and Reason are true, but the Reason is not the correct explanation of the Assertion.

Question 6. Assertion: Chlorella, a green alga, is commonly known as space alga.

Reason: It is used by exobiologists for oxygen and disposal of nitrogen in prolonged space flight.

Answer: 3. If Assertion is true, but Reason is false.

Question 7. Assertion: Bryophytes are not the amphibians of Plant Kingdom.

Reason: An external layer of sucrose instead of water is necessary for the movement of antherozoids.

Answer: 4. If both Assertion and Reason are false.

Question 8. Assertion: Polyploidy is very common in the members of Filicophyta.

Reason: It is due to the development of gametophytes

Answer: 1. If both Assertion and Reason are true and the Reason is the correct explanation of the Assertion.

Question 9. Assertion: The micropyle of Pinus ovule contains pollination.

Reason: The ovule of Pinus is unitegmic and orthotrodirectly from sporophyte without meiospore formation.

Answer: 2. If both Assertion and Reason are true, but the Reason is not the correct explanation of the Assertion.

Question 10. Assertion: Calophyllum leaf has parallel venation and ligation drop for catching the pollen.

Reason: It is the plant of the dicot group of angiosperms.

Answer: 2. If both Assertion and Reason are true, but the Reason is not the correct explanation of the Assertion.

 

Animal Kingdom Introduction

The animal kingdom covers about 35 phyla, of which 11 are considered to be major phyla. In major phyla, 10 are from non-chordates and one is from chordates.

Terminologies Related To Animal Classification

Metazoa

• Animal groups are characterized by mobility and the presence of a sensory or a nervous system. These systems receive stimuli from the environment and animals respond by exhibiting some behavior.
• The only exceptions is of poriferans (pore-bearers) or the sponges. They have no cells that can be termed as nerve cells.
• Like plant life, early animal life also arose in the sea. The animals that live on the sea floor are called benthonic (for example, echinoderms, corals, and deep sea fishes), whereas those that swim about actively in the sea are called nektons.
• The multicellular eukaryotic organisms with the holozoic mode of nutrition are called metazoans. Based on the complexity of the organization, metazoans are further subdivided into two sub-kingdoms, Parazoa and Eumetazoa.

Parazoa: Parazoa include the sponges in which cells are loosely aggregated and do not form tissues or organs.

Eumetazoa: Eumetazoa includes the rest of animals in which cells are organized into structural and functional units called tissues, organs, and organ systems.

Levels Of Organization

1. Cellular Level
   • Though all members of Animalia are multicellular, all of them do not exhibit the same pattern of cell organization. For example, in sponges, the cells are arranged as loose cell aggregates, i.e., they exhibit a cellular level of organization.
   • Some division of labor (activities) occurs among the cells.
2. Tissue Level
   • In coelenterates and ctenophores, the arrangement of cells is more complex.
   • Here, the cells performing the same function are arranged into tissues. Hence, it is called the tissue level of organization.
3. Organ Level
   • A still higher level of organization, i.e., organ level is exhibited by the members of Platyhclminthes and other higher phyla where tissues are grouped together to form organs, each specialized for a particular function.
   • In animals such as annelids, arthropods, mollusks, echinoderms, and chordates, organs are associated to form functional systems, each system concerned with a specific physiological function. This pattern is called the organ system level of the organization. Organ systems in different groups of animals exhibit various patterns of complexities.
   • For example, the digestive system in Platyhclminthes has only a single opening to the outside of the body that serves as both mouth and anus and is hence called incomplete.
   • A complete digestive system has two openings, mouth and anus.

Read and Learn More NEET Biology Notes

Similarly, The Circulatory System May Be Of Two Types: Open Type And Closed Type.

Open Type

• In this type of circulatory system, the blood is pumped out of the heart and the cells and tissues are directly bathed in it. The blood is pumped by the heart into the blood vessels that open into blood spaces (sinuses).
• There is no capillary system (for example, in most arthropods, non-cephalopod mollusks and tunicates). These sinuses are actually the body cavities and are called hemocoel.
• The pressure of the blood is low; it moves slowly between the tissues and, finally, returns to the heart via open-ended blood vessels.

Closed Type

• Many invertebrates and all vertebrates, including humans, have a closed circulatory system. In the closed type, the blood flows inside the body through a series of blood vessels of varying diameters (arteries, veins, and capillaries).
• In this system, the same blood regularly circulates in the body under high pressure and returns back to the heart without leaving the system of tubes.

Symmetry: Based on the basis of their body symmetry, animals can be categorized as follows:

• Radial Symmetry: When any plane passing through the central axis of the body divides the organism into two identical halves, it is called radial symmetry. The animals with radial symmetry are put in the group Radiata, for example, cnidarians (hydra and jellyfish). Biradial symmetry is present in sea anemones, and ctenophores.
• Bilateral Symmetry: The animals with bilateral symmetry arc put in the group Bilateria. The body can be divided into identical right and left halves in only one plane. For example, platyhclminthcs, annelids, arthropods, etc. (platyhel-minthes to chordates).
• Asymmetry: Asymmetric organisms cannot be divided along any plane to produce two equivalent halves. Sponges are mostly asymmetrical.

Germ Layers: Germ lavers give rise to all the tissues and organs of a fully formed individual. On the basis of the number of germ layers, animals can be diploblastic or triploblastic.

• Diploblastic: In diploblastic animals, the body cells are arranged in two layers an outer ectoderm and an inner endoderm with an intervening undifferentiated mesoglea, for example. coelenterates.
• Triploblastic: The body wall in animals is made of three germ layers, i.e…. ectoderm, mesoderm, and endoderm, for example, platyhel-minthes to chordates.

Body Plan: Though diverse in shape and size, animals have a body that fits in one of the three basic plans:

• Cell Aggregate: Cell aggregate type of body plan is present in sponges. They are clusters of cells with a rudimentary division of labor among them. There are no tissues or organs.
• Blind Sac: A blind sac type of body plan is present in Platyhelminthes and Coelenterata where the alimentary canal has only one opening.
• Tube Within Tube: Tube-within-tube type of body plan is present in N’emathelminthes, Annelida, Arthropoda, Mollusca, Echinodermata, and Chordata. The digestive system is a continuous tube with an opening at both ends.

Body Cavity Or Coelom: The presence or absence of a cavity between the body wall and gut wall is very important for classification.

• Eucoelomates: True coelom is a body cavity that arises as a cavity in embryonic mesoderm. In this case, the mesoderm of the embryo provides a cellular lining, called coelomic epithelium or peritoneum, to the cavity. The coelom is filled with coelomic fluid secreted by the peritoneum. True coelom is found in annelids, echinoderms, and chordates. The true coelom is of two types:
  1. Schizococlom: It develops by the splitting up of mesoderm. It is found in annelids, arthropods, and mollusks. The body cavity of arthropods and non-cephalopod mollusks is called hemocoel.
  2. Enterocoelom: The mesoderm arises from the wall of the embryonic gout or enteron as hollow outgrowths or enterococlomic pouches. It occurs in echinoderms and chordates.
• Pseudocoelomntcs: The body cavity is not completely lined with mesoderm. Instead, the mesoderm is present as scattered pouches in between the ectoderm and endoderm. Such a body cavity is called a pseudocolor, for example, in roundworms.
• Acoelomates: The animals in which the coelom is absent are called acoelomates, for example, poriferans, coelenterates, ctenophores, and flatworms. In flatworms, the spaces between various organs are filled with a special tissue called parenchyma.

Segmentation

• In some animals, the body is externally and internally divided into segments with a serial repetition of at least some organs.
• For example, in earthworms, the body shows a pattern called metameric segmentation, and the phenomenon is known as metamerism.
• Metameric segmentation is present in annelids only.

Notochord: Notochord is a mesodermally derived rod-like structure formed on the dorsal side during embryonic development in some animals. Animals with notochord are called chordates and animals which do not have this structure are called non-chordates, for example, porifera to echinoderms.

Phylum Protozoa (Unicellular Protists)

There are about 15,000 species of protozoans known to exist in the world. They are microscopic heterotrophic organisms in which a single cell performs all the vital activities. For this reason, protozoans are also referred to as acellular organisms.

They are aquatic (freshwater and marine) and cosmopolitan in distribution. Some forms are predators and some are parasitic. The protozoan cell body is either naked, for example, Amoeba, or surrounded by a non-rigid pellicle. Cellulose is absent in the pellicle.

• Some protozoans secrete shells of various inorganic compounds as external covers (foraminiferans).
• Different types of locomotory structures are found in protozoans. They may bear flagella (flagellates), cilia (ciliates), or pseudopodia (sarcodines).
• Locomotory structures are absent in the parasitic forms (sporozoa).
• In protozoans, neurofibrils and contractile myofibrils are present underneath the cell surface. Most protozoans are free-living and aquatic.
• They are holozoic and feed largely on bacteria, microscopic algae, and minute animals such as rotifers or on other protozoans including members of their own species.
• Some protozoans are holophytic; they contain chlorophyll and prepare their own food by photosynthesis (for example, Euglena, Amoeba, Paramecium, Elphidium). The parasitic protozoans feed on materials obtained from the hosts (for example, Monocystis, Entamoeba, Plasmodium, Trypanosoma, Giardia, etc.).

The contractile vacuole is found in almost all freshwater protozoans for the maintenance of the osmotic concentration of the cell body. This phenomenon is known as osmoregulation. The contractile vacuole also helps in excretion.

• Many sporozoan parasites are relatively harmless but some are harmful also. For instance, Plasmodium vivax and Plasmodium falciparum cause malaria in humans. Protozoans are generally uninucleate, but all ciliates and many amoeboid types are multinucleate.
• The pattern of reproduction is also specialized in different protozoans. Most sarcodines, flagellates, and ciliates show asexual reproduction by binary fission, multiple fission, or even budding.
• Some ciliates, for example, Paramecium reproduce by sexual means in which two individuals come close to each other and interchange genetic information by a process known as conjugation.
• There is no gamete formation in such a process. In sporozoa, some stages of the life cycle show the formation of gametes, which are morphologically distinct.

Classification Of Phylum Protozoa: Phylum protozoa is divided into four groups: Rhizopoda or Sar- codina, Mastigophora or Flagellata, Sporozoa, and Ciliata.

Group 1 Rhizopoda Or Sarcodina: The locomotion is by pseudopodia; body shape changeable, for example, Amoeba (free-living), Entamoeba (parasitic or commensal), etc. Four types of pseudopodia are: lobopodia {Amoeba), filopodia (Euglypha), reticulopodia (Globigerina), and axopodia (Actinopluys sol).

Group 2 Mastigophora Or Flagellata: The locomotion by one or more thread-like flagella. They are free-living or parasitic. For example,

• Euglena: Connecting link between plants and animals
• Trypanosoma: Parasite causing sleeping sickness
• Leishmania: Parasite causing kala-azar
• Giardia: Parasite causing diarrhea
• Trichomonas: Parasite causing vaginitis in human females
• Trichonympha: Symbiont found in the gut of termite helping in cellulose digestion
• Proterospongia: Colonial with collar cells, a connecting link between Protozoa and Porifera

Two types of flagellates are Phytomastigina (with chloroplast, plantlike, for example, Euglena, Chlamydomonas, etc.) and Zoomastigina (without chloroplast, animallike, for example, Trypano¬soma, Leishmania, etc.).

Group 3 Sporozoa: All parasites have a spore-like stage, no special locomotory organelles, no contractile vacuole (associated with parasitism), and a complex life history. For example,

• Plasmodium: Causes malaria, spread by female Anopheles
• Monocytic: Parasite in the seminal vesicles of earthworm
• Eimeria: Causes coccidiosis in rabbit and chicken
• Babesia: Causes hemoglobinuria fever/tick fever in cattle

Babesia is a protozoan parasite spread by ticks. In India, tick fever is caused mainly by Babesis bigemma. The parasite enters into red blood cells (RBCs) and destroys them.

Group 4 Ciliata: Locomotory organelles are cilia; nuclei two or more in number. Examples are:

• Paramecium: Free-living, slippery animalcule
• Balantidium: Causes balantidial dysentery in man
• Nyctotherus: Rectal ciliate and endo commensal in frog

Phylum Porifera (Sponges)

These are primitive, multicellular, asymmetrical (except Leucosolenia, and Scypha) organisms having a cellular level of organization.

Most of them are marine and remain attached to rocks (sessile). A few live in freshwater, for example, Spongilla. This is the only phylum in the animal kingdom without any nerve cells. Some common examples are Sycon, Euspongia, and Spongilla.

Important Characters Of Phylum Porifera

1. Body Wall: The body wall of a common sponge consists of the following layers:
   • Pinacodcrm (Dermal Layer): It is the outer cellular layer which consists of
     • Flattened pinacocytes and
     • Oval porocytes.
   • Choanoderm (Gas/Ral Layer): It is the inner cellular layer that consists of highly specialized flagellated cells called choanocytes (collar cells). They are the characteristic cells of this phylum responsible for ingestion of food, secretion of mesohyal, and differentiation of sex cells.
   • Mesoltyl Layer (Mesenchyme): Basically, it is a non-cellular layer found between placoderm and choanoderm. It has fine dispersed spongin fibers and numerous spicules. It also contains amoebocytes (amoeba-like cells) of both pinacoderm and choanoderm. Amoebocytes are modified into the following types:
     • Archaeocytes: They may be converted into other types of cells and are also called undifferentiated “totipotent ” cells.
     • Tropliocytes: They provide food to developing cells and are called nurse cells.
     • Thesocytes: They store food granules.
     • Gland Cells: They secrete a slimy substance.
     • Spongioblasts: They secrete spongin fibers of the mesohyl layer.
     • Scleroblasts: They secrete spicules. In calcareous sponges, they are called calcoblasts and in silicious sponges, they are called silicoblasts.
     • Collencytes: They secrete collagen fibers and form connective tissue.
     • Myocytes: They form a circular ring around the osculum and help in closing and opening of the osculum.
     • Germ Cells (sex cells): They form sperms and ova and develop during the breeding season.
     • Chromocytes: They contain pigment granules and excretory substances.
     • Phagocytes: They collect food from choanocytes through their pseudopodia and also engulf excreta and damaged tissues.
2. The central body cavity of a sponge is called a spongocoel or paragastric cavity.
3. The continuous water current flowing through the canal system is very important for the life of a sponge. It brings in food and oxygen and carries away carbon dioxide, nitrogenous wastes, and reproductive bodies. Thus, the canal system helps the sponge in nutrition, respiration, excretion, and reproduction.

Phylum Porifera Skeleton: Almost all sponges possess an internal skeleton. It may consist of calcareous or siliceous spicules of fine spongin fibers or both, located in the mesohyl layer.

Phylum Porifera Digestion: It is intracellular and takes place inside food vacuoles as in protozoans.

Phylum Porifera Circulation: The distribution of food from the ingesting cells to others is brought about by wandering amoeba cytes of the mesohyl layer.

In case of Sycon, pinacoderm is divided into exopinacoderm and endopinacoderm. Exopinacoderm lines the incurrent canal and the spongocoel. Radial canals are lined by flagellated choanocytes.

Phylum Porifera Canal System: The body of a sponge is organized in such a manner as to form a complex system of pores and canals. This system is called the canal system. It is meant for food gathering, respiration, and removal of waste. Three types of canal systems are found in sponges:

Ascon Type: It is the simplest type of canal system which is found in Leucosolenia and few other sponges.

Ingressing water → Canal → Spongocoel → Osculum

Sycon Type: It is more complex than the ascon type. It is found in Sycon and some other sponges.

Leucon Type: It is the most complex canal system which is found in Spongilla and some other sponges.

In Demospongiae, the leuconoid condition is derived from a larval stage, called rhagon. It is a conical organism with a flattened base. The canal system of the rhagon larva does not occur in any adult sponge. Because of its derivation from the rhagon stage in Demospongiae, the leucon type of canal system is also called the rhagon type.

Phylum Porifera Respiration: The exchange of gases occurs by diffusion through cell plasma membranes as in protozoans.

Phylum Porifera Excretion: The removal of metabolic wastes also occurs by diffusion through cell plasma membranes as in protozoans. Ammonia is the chief excretory waste.

Phylum Porifera Reproduction: Both asexual and sexual reproduction occur in sponges. Asexual reproduction occurs, by fragmentation, budding, and gemmules. They are hermaphrodites and show internal fertilization.

Phylum Porifera Development: Zygote undergoes holoblastic cleavage (complete division). The development is indirect and includes a free-swimming larva, the amphiblastula (in Sycon), or parenchymula (in Leucosolenia and other porifers) for dispersal of the species.

Classification Of Phylum Porifera: Based on the type of skeleton, phylum Porifera is divided into three classes: Calcarea or Calcispongiae (Gk. Calcis = lime; spongos = sponge—limy sponge), Hcxactinellida or Hyalo- spongiae, and Demospongiae.

Class 1 Calcarea Or Calcispongiae

• The sponges of this class have a skeleton of calcareous spicules. The spicules are of monaxon, triaxon, and tetraxon types.
• The collared flagellated cells (choanocytes) are large.
• These sponges are exclusively marine and found in shallow water.
• Examples: Leucosolenia, Sycon, Grantia.

Class 2 Hexactinellida Or Hyalospongiae

• The sponges of this class have the skeleton for sili¬ceous spicules which are triaxons with six rays.
• Chonocytes are small.
• They are exclusively marine and are mostly found in deep seas.
• Example: Euplectella (Venus flower basket), Hyalonema (glass rope sponge).
• Euplectella lives in a commensal relationship with certain shrimps. Euplectella is given as a precious marriage gift in Japan, symbolizing the idea that “till death we do part.”

Class 3 Demospongiae

• They may contain a skeleton of sponging fibers or of siliceous spicules with sponging liberals or skeletons may be absent. The spicules are either monaxon or tetraxon (may be eight-rayed but never six-rayed).
• Choanocytes are small.
• They occur in marine as well as in freshwater
• Example: Euspongia (bath sponge)—its skeleton is made only of sponging fibers. Spongilla (freshwater sponge), Cliona (boring sponge)—its larva bores into the shells of mollusks, and Chalina (deadman’s fingers or (mermaid’s gloves).

The characteristics of the three classes of phylum Porifera have been tabulated in Table.

Phylum Porifera Points To Remember

Using Sponges: For centuries, people around the world have used natural sponges with spongin skeletons for cleaning, and bathing by taking advantage of the soft flexible, and highly porous bodies of these sponges.

• An example is Euspongia. The ancient Greeks also used sponges as padding inside helmets.
• Spongin fibers are elongated protein fibers that form a fibrous network.
• Digestion in sponges is intracellular.

Sponge cells, separated by straining pieces of sponge through a fine net, can reaggregate and grow into a sponge. So, a sponge is a republic of cells that identify one another, aggregate and grow together.

• Sponge reproduces asexually by fragmentation. During sexual reproduction, some cells become egg or sperm cells. After fertilization, the zygote develops into a flagellated larva which swims, settles in a new place, and grows into a sponge.
• Proterospongia is a connecting link between protozoa and Porifera.
• In Hyalonema, the root tuft consists of a bundle of long anchoring spicules. These may pass through the columella (body axis) as a gastral cone. It is commonly known as a glass rope sponge.
• Euspongia is commonly found is the Mediterranean Sea. It is commonly known as a bath sponge.
• Amphiblastula is the hollow larva of Sycon, etc., whereas parenchymula is the solid larva of most of the sponges, for example, Leucosolenia.

Phylum Cnidaria (Coelenterata)

The phylum Cnidaria (old name is Coelenterata) includes about 9000 species, mainly marine. They are sessile, free swimming, radially symmetrical invertebrates, and more complex than sponges. Some examples are Aurelia and Adamsia.

The General Characters Of This Phylum Are As Follows:

• Cnidarians exhibit a blind sac body plan and are radially symmetric. They are more advanced than sponges in having true tissues. They are, however, acoelomate.
• The body wall consists of only two cell layers, ectoderm, and endoderm, separated by a jelly-like mesoglea. These animals are, therefore, diploblastic, that is, arising from two embryonic cell layers.

Body Wall In Coelenterates (With Reference To Hydra): They are diploblastic animals, i.e., they are derived from two layers—ectoderm and endoderm. These germ layers form the epidermis and gastrodermis.

• Epidermis: Various epidermal cells are as follows:
• Epithelio-Muscular Cells: Each cell has two functional parts, the outer epithelial part, extending to the body surface and the basal muscular part drawn out into two muscle processes along the longitudinal axis of the body. The muscle processes contain a contractile fibril myoneme.
• Glandulo-Muscular Cells: The epitheliomuscle cells, chiefly in the region of the pedal disc, are specially modified to secrete sticky material for the attachment of the animal to the substratum.
• Interstitial Cells: They are totipotent cells that give rise to all the different cells of the body.
• Sensory Cells: They are scattered throughout the epidermis. They are most numerous on the tentacles, hypostome, and basal disc. They receive and transmit impulses.
• Nerve Cells: They occur for the first time in coelentrates. They are present at the base of epitheliomuscle cells. They conduct impulses in all directions.
• Germ Cells: They remain in restricted regions. They proliferate to form gonads. They are ectodermal in Hydrozoa and endodermal in Scyphozoa and Anthozoa.

Cnidoblasts: Many of the interstitial cells of the epidermis become specialized to form the stinging cells, called the cnidoblasts. They migrate to the tentacles through the mesoglea by means of amoeboid movements. Projecting cnidoblasts act as organs for offense and defense.

Structure Of Cnidoblasts: The cytoplasm of a cnidoblast contains a conspicuous nucleus lying to one side, and a peculiar oval or pyriform sac filled with a poisonous fluid, hypnotoxin. The sac is a part of the stinging apparatus, known as the nematocyst (stinging structure).

Occurrence Of Cnidoblasts (Nematocysts)

• The nematocysts occur scattered mostly singly, throughout the epidermis of the body, but remain absent on the basal disc.
• They are abundant in the epidermis of the oral region and the tentacles where they cluster as wart-like nematocyst batteries.

Differences Between Four Types Of Nematocysts

Gastrodermis: It is the inner layer of the body. The cells are of the following types:

• Endothelio-muscle Or nutritive Muscle Cells: They help in the contraction of the body and nutrition.
• Endothelio-gland Cells: They secrete digestive enzymes in the coelenteron. In the region of the hypostome and mouth are found mucous gland cells. Gland cells are absent in the tentacles and basal disc.
• It also contains interstitial cells, sensory cells, and nerve cells but no cnidoblasts.
• They enclose the gastrovascular cavity (coelenteron), having a single-opening hypostome. Their digestion is intra and extracellular.

Phylum Cnidaria Points To Remember

The green color of Chlorohydra viridissima comes from the alga Chlorella vulgaris (Zoochlorella), which lives inside the gastrodermal cells of Hydra in a symbiotic relationship. Corattium rubrum (red coral) has been used widely in jewelry and is known as red moon.

Hydra

• Chlorohydra Viridissima (Old Name H. Viridis): Green hydra
• Pelmatohydra Oligactis (Old Name H. Fused): Brown hydra
• Hydra Gangetica: White/pinkish hydra
• Hydra Vulgaris: Colorless hydra

Some Important Characters Of Hydra Are:

• Hydra flourishes well in cool, clean, and stagnant water.
• The number of tentacles surrounding the mouth in Hydra is 6-10. The tentacles of Hydra are hollow while
  that of Obelia are solid.
• The food of Hydra is water fleas (Daphnia and Cyclops). Thus, it is carnivorous. It cannot digest starch.
• No free larval stage in the development of Hydra. Hence, development is direct.
• Most species of Hydra are dioecious/unisexual.
• Male Hydra bears one to eight conical testes toward the distal end, whereas female Hydra bears one to two rounded ovaries toward the proximal end of the body.
• Locomotion in Hydra occurs by looping, somersaulting, gliding, walking, floating, etc.

Metagenesis And Polymorphism

• Coelenentrata members show polymorphism most commonly is polyp and medusa forms, as mentioned in the table.
• In the life cycle, there is an alternation of the asexual polyp phase and the sexual medusa phase and it is termed as metagenesis.
• During sexual reproduction, medusae liberate gametes into water. Following fertilization, the zygote forms a ciliated larva called planula, which swims, settles, and grows into a sessile polyp. (Some cnidarians such as Hydra do not have a medusa stage. Hydra has no larval form, no metagenesis).
• Polyps reproduce asexually by budding where as medusa liberates gametes into water during sexual reproduction. Both asexual and sexual forms are free living.

Differences Between Polyp And Medusa Forms

Classification of Phylum Cnidaria: Chiefly on the basis of the dominance of the medusoid or polypoid phase in the life cycle, phylum Cnidaria is divided into three classes as given in Table.

Classification Of Phylum Coelenterata

Phylum Coelenterata Points To Remember

Coral Reefs: A coral reef is a ridge or mound in a shallow, tropical sea, has its upper surface near the surface of water, and supports a variety of animals and plants. It is formed of calcium carbonate produced by some of its inhabitants, chiefly medreporarian corals. Coral reefs form stable marine ecosystems. The coral reefs are of three kinds:

1. Fringing Reefs: The coral reefs lying close to the shores of some volcanic island or part of some continent are called fringing reefs. Hawaiian islands are an ideal example of permanent flanging reefs.
2. Barrier Reefs: They are like the fringing reefs but are located some distance from the shore. The stretch of water of the lagoon separates the barrier reefs from the land. Australia’s Great Barrier Reef is an example of such a reef which is about 900 nautical miles long and 90 miles from sea shore.
3. Atoll Reefs: An atoll reef is also called a coral island or lagoon island which is a circular or horseshoe-shaped reef that encircles a lagoon but not an island. It may be complete or broken by a number of channels of which only a few are navigable. The Lakshadweep and Maldives islands in the Indian Ocean are composed of atoll reefs.

Phylum Ctenophora (Sea Walnut Or Comb JelLies)

Ctenophores are exclusively marine, solitary, free swimming or pelagic, very active animals with transparent and flat or oval body shapes and have the following important characteristics:

• Body soft, delicate, transparent, and gelatinous without segmentation.
• Polyp phase is absent in their life cycle, shape is typically spherical, pear-shaped or cylindrical, flat in some.
• They are radially symmetrical, and diploblastic, have a tissue level of organization, and are devoid of cnidoblast cells.
• Tentacles may be present or absent. When present, the number of tentacles is 2. They are solid and possess adhesive cells called colloblasts (lasso cells). Digestion is both extracellular and intracellular. Bioluminescence (the property of a living organism to emit light) is well-marked in ctenophores.
• Animals move by cilia, which join together to form comb plates. There are eight median combplates forming locomotor organs, hence organisms are called comb jellies or sea walnuts.
• The gastrovascular cavity is branched and opens to the exterior by stomodaeum.

They are diploblastic animals, but the mesoglea is different from that of cnidaria; it contains amoebocytes and smooth muscle cells and is comparable to a loose layer of cells. From this viewpoint, ctenophores may be considered as triploblastic.

• Skeletal, circulatory, respiratory, and excretory systems are absent. The nervous system is a diffuse type.
• The presence of a special sense organ statocyst at the opposite end of the mouth (aboral end) is characteristic of the members of this phylum.
• All are hermaphrodite. Testes and ovaries are formed side by side from the endoderm of digestive canals.
• Asexual reproduction does not occur. They reproduce only by sexual means. Fertilization is external. Development is indirect and an immature ciliated stage called cydippid larva is found in some forms.
• Examples: Hormiphora (sea walnut), Pleurobrachia, Ctenoplana, and Cestum (Venus girdle).

Phylum Platyhelminthes (Flat Worms)

Phylum Platyhelminthes contains about 13,000 species, mostly parasites that live in other animals including man. The important characters of this phylum are:

• The flatworms are mostly parasites but some are free-living, for example, Planaria.
• They are acoelomate, triploblastic, bilaterally symmetrical, and dorsoventrally flattened animals.
• They have an organ system level of organization.
• The body is not segmented except in class Cestoda (false segmentation).

Body is covered with a cellular, syncytial, single-layered, partly ciliated epidermis, while in parasitic trematodes and cestodes, the epidermis is lacking and the body is covered with a cuticle.

• The exoskeleton and endoskeleton are completely absent. However, hooks, spines, suckers (in parasitic form), teeth, or thorns may be present which act as adhesive organs.
• The space between the body wall, alimentary canal, and other organs is filled with a peculiar connective tissue called the parenchyma. It helps in the transportation of food materials.

The digestive system is totally absent in tapeworms, so they absorb food directly through the body’s surface. In Trematoda and Turbellaria, it consists of mouth, pharynx, and blind intestine (anus absent).

• Respiratory and circulatory systems are absent.
• The excretory system consists of single or paired protonephridium with flame cells.
• The nervous system is primitive. The main nervous system consists of a pair of cerebral ganglia or brain and one to three pairs of longitudinal nerve cords connected to each other by transverse commissures. This type of nervous system is called a ladder-like nervous system, for example, Planaria.
• Sense organs are of common occurrence in Turbellaria but these are greatly reduced in parasitic forms.
• Sexes are united, i.e., hermaphrodite, with very few exceptions such as Schistosoma (blood fluke).
• Asexual reproduction by fission occurs in many freshwater forms such as turbellarians.
• In the majority of forms, eggs are devoid of yolk but provided with special yolk cells and are covered by eggshells.

Cross-fertilization in trematodes and Turbellcria and self-fertilization in cestodes is very common. Fertilization is internal. Development is indirect with many larval stages.

• The life cycle is complicated and involves one or more hosts.
• Regeneration. It is well-marked in some flatworms such as Planaria.

Classification Of Phylum Platyhelminthes: Phylum Platyhelminthes is divided into three classes as given in.

Classification Of Phylum Platyhelminthes

• Turbellaria
  • Free-living freshwater or marine known as planarians or Eddy worms.
  • The body is unsegmented and the leaf is covered by a delicate ciliated epidermis. Rod-shaped rhabdites in the epidermis.
  • The mouth is often ventral and the anus is absent. The alimentary canal is present (branched).
  • Reproduction is asexual as well as sexual and shows good power of regeneration; no larva.
  • Suckers absent.
  • Example, Dugesia(Planaria).
• Trematoda
  • Endoparasite, known as flukes, or flatworms.
  • Body unsegmented and leaf-like, covered by tegument (fine spines), no epidermis in adult.
  • The mouth on the anterior side and anus is absent. The alimentary canal is branched.
  • Life history includes larval stages and involves more than one host.
  • Suckers are present for attachment in the host.
  • For example, Fasciola (sheep liver flukes)
  • Causes liver rot disease. Primary host: Sheep and goat Secondary host: Snail (Planorbis, Lymnaea, Bulinus) Shows polyembryony, life-cycle involves miracidium (free-swimming larva), sporocyst, redia, cercaria, and metacercaria larval form.
• Cestoda
  • Endoparasite, an intestinal parasite, known as tapeworm.
  • Body ribbon-like, covered by tegument. No epidermis in adults.
  • Mouth and anus absent (food from body surface). Alimentary canal absent.
  • Life history includes larval stages and involves more than one host. Each proglottid has one or two sets of male and female reproductive organs.
  • Scolex has suckers and hooks for attachment. The body is divided into scolex, neck, and strobilla of few to numerous proglottids. No true segments.
  • For example, Taenia solium (pork tapeworm)
  • Primary host = Man (cysticercus in the infective stage).
  • Secondary host = Pig (concosphere is the infective stage).
  • Shows multiplication in the larva stage, namely, oncosphere, hexacanth, bladderworm, and cysticercus. Causes disease taemiasis or cysticercosis.

Phylum Nemathelminthes (Aschelminthes)

The phylum Nemathelminthes includes bilaterally symmetrical, triploblastic, pseudocoelomate animals with organ system grade of organization. They are circular in cross-section.

• They are free-living, aquatic or terrestrial, or parasitic (on plants or animals).
• The excretory system involves an excretory cell (a large giant H-shaped cell) called a renette cell (multinucleated).
• They have a tube-within-tube type of body plan that evolved along the protostome evolutionary line.
• Sexes separate and show sexual dimorphism, internal fertilization, and direct or indirect development.

Classification Of Phylum Nemathelminthes: On the basis of caudal receptors or phasmids, Aschelminthes can be divided into two classes; Aphasmidia and Phasmidia. The characteristic differences between the two classes are given in Table.

Differences Between Classes Aphasmidia And Phasmidia

Phylum Annelida

The phylum includes over 9000 species of metamerically segmented animals with a true coelom called the schizocoelom.

General Characters Of Phylum Annelida

• The organisms are triploblastic, bilaterally symmetrical, coelomates with organ system level of body organization, and metamerically segmented.
• The body wall has an epidermis of columnar epithelium coated externally by moist albuminous cuticle and with circular and longitudinal muscle fibers.
• Chitinous setae, aiding in locomotion, may or may not be present on fleshy parapodia; absent in leech.
• Annelids are the first animals to have a true schizocoelic coelom. The coelom is divided by septa into compartments.
• The coelomic fluid acts as a hydrostatic skeleton.
• The digestive system is complete and digestion is extracellular.
• Respiration occurs by moist skin (cutaneous respiration) or through gills (branchial respiration).

The blood vascular system is usually closed. Respiratory pigments, either hemoglobin or erythrocruorin. are dissolved in blood plasma. Free amoeboid blood corpuscles are present, but there are no RBCs. In leech, there is no true blood vascular system.

• Nephridia are excretory organs. Ammonia is the chief excretory waste.
• The nervous system consists of a nerve ring and a solid, double, mid-ventral nerve cord with ganglia and lateral nerves in each segment.
• Sensory organs include tactile organs, taste buds, statocysts, photoreceptor cells, and eyes with lenses.
• The sexes may be separate (for example, Nereis) or united (for example, earthworm, leech).
• Development is mostly direct (for example, earthworm). There is indirect development in Nereis. Larva, when present, is trochophore.

Classification Of Phylum Annelida

Class 1 Archiannelida: All members are marine and small, segmentation is mainly internal, and no parapodia or setae. The trochophore larva stage is present. Examples are Dinophilus and Polygorclius.

Class 2 Polychaeta

• Almost all members are marine and occur in great abundance near the seashore. The head is distinct with eyes, palps, and tentacles.
• Locomotory structures are parapodia with setae; a clitellum is never developed.
• Sexes separate, trochophore larva is present which undergoes metamorphosis to reach the adult stage during development.
• The sexual stage of Nereis is called heteronereis. It has its body differentiated into anterior atoke and posterior epitoke. The epitoke is provided with foliaceous parapodia and gonads.

Class 3 Oligochaeta

• Commonly called “earthworms.” Mostly terrestrial, some are found in fresh water too.
• A well-marked head is absent. Parapodia are absent.
• A clitellum is generally present main function being cocoon formation.
• Hermaphrodites, fertilization external, development direct, no larval stage, and therefore, no metamorphosis. Chloragogen cells in earthworms help in excretion.
• Septal and pharyngeal nephridia will help in the conservation of water.
• Examples: Tubifex, Megascolex (South Indian earthworm). Lumbricus is a European earthworm, not found in India.

Class 4 Hirudinea

• Commonly called “leeches,” ectoparasites, and body with a fixed number of segments, i.e., 33.
• Each segment is subdivided into annuli; parapodia and setae are absent; body with two suckers.
• Suctorial mouth, sanguivorous (feeding on blood).
• Coelom is reduced by botryoidal tissue; a connective tissue supposed to be excretory.
• Circulation open type with hemocoelic system.
• A temporary clitellum is present. They are mostly aquatic. Leeches secrete anticoagulant “hirudin” from salivary glands which do not allow blood clotting of the host.
• Locomotion is by looping and swimming.
• They are hermaphrodites; with no larval stage or metamorphosis. Fertilization is internal but embryos develop inside a well-formed cocoon.
• Examples: Hirudo, Hirudinaria, Pontobdella.

Class 5 Echiurida: These annelids are without external and internal segmentation. Setae are rare; usually, they have long prostomium. Examples are Bonellia and Echiuris.

Nereis

• Inhabits in sea shore between tide mark; burrower, nocturnal, carnivorous, gregarious, fertilization in the sea.
• Parapodia in each segment except first and last.
• During breeding, the body divides into two parts. Anterior asexual partatoke and posterior sexual portion epitoke. This change is known as epitoky.

Phylum Arthropoda

Phylum Arthropoda is the largest phylum in the animal kingdom, including 900,000 species. The largest class is Insecta with 750,000 species. The general characters of this phylum are:

• They are triploblastic, coelomate, and bilaterally symmetrical animals. The body cavity is full of hemolymph (blood) and it is known as hemocoel. The true coelom is restricted to gonads.
• The body is covered by a chitinous cuticle, which forms the exoskeleton which is shed at intervals, i.e., it undergoes molting/ecdysis.
• They have a segmented body, each segment bearing a pair of jointed appendages covered by a jointed exoskeleton. The chitinous exoskeleton is secreted by the underlying epidermis.
• The body is divided into the head, thorax, and abdomen. In some cases, the head and thorax is fused to form a cephalothorax. In insects, the thoracic segments have legs and wings; the abdomen has no legs in insects.
• Respiratory organs are the gills, book gills, book lungs, or tracheal system.

Excretion takes place through green glands or Mal-pighian tubules since nephridia are absent.

• Sensory structures in arthropods are antennae for perceiving odor, eyes, statocysts or balance organs, and sound receptors (in chirping crickets and cicadas). Eyes are simple or compound. In honey bees, butterflies, moths, and some other insects, the gustatory receptors are present on their feet.
• The heart is dorsal and the circulatory system is open.
• The central nervous system consists of paired pre-oral ganglia connected by commissures to a solid double ventral nerve cord.
• In Inland arthropods, fertilization is always internal.
• Arthropods are mostly dioecious, and oviparous. In some arthropods such as the scorpion, the eggs hatch within the female body. They bring forth the young ones alive. They are viviparous. Development is direct or indirect.

Advancement Over Annelida

1. Distinct head in all species.
2. Jointed appendages serve a variety of functions.
3. Jointed exoskeleton for protection and muscle attachment.
4. Striped muscles are arranged in bundles for moving particular body parts.
5. Special respiratory organs such as gills, trachea, book lungs, etc., in the majority of cases.
6. Well-developed sense organs such as compound eyes, statocysts, auditory organs, taste receptors, etc.
7. Endocrine glands and pheromone secretion for communication.

Classification Of Phylum Arthropoda: The phylum Arthropoda is divided into five classes.

Class 1 Crustacea

• The body is divisible into cephalothorax (head + thorax) and abdomen.
• Dorsally, the cephalothorax is covered by a thick exo-skeletal carapace.
• There are present two pairs of antennae and a pair of stalked compound eyes and biramous appendages.
• Respiration is earned out either by the body surface or by gills.
• Excretion takes place usually by antennary glands (green glands).
• Sexes are usually separate. Sexual dimorphism is also seen.
• Development is usually indirect.
• Examples: Palaemon (prawn), Macrobrachium (prawn), Astacus (crayfish), Palinurus (lobster), Cancer (crab), Lucifer (shrimp), Eupagurus (hermit crab), Oniscus (woodlouse, terrestrial), Daplwia (water-flea), Cyclops, and Balanus (barnacle). Tiny crustaceans such as Daphnia and Cyclops act as zooplanktons which form important links in the food chain in water.

Class 2 Chilopoda

• The body is long, segmented, and divisible into head and trunk.
• Each trunk segment bears a pair of legs. The first pair of legs is modified into poison claws.
• There is a single pair of antennae and ocelli.
• Many legs are present.
• Respiration occurs by tracheae.
• Excretion takes place by Malpighian tubules.
• Development is direct
• Examples: Scolopendro.

Class 3 Diplopoda

• The body is divided into the head, thorax, and abdomen.
• There is a single pair of antennae and ocelli.
• Except for the first thoracic segment (if does not have legs), each thoracic segment bears a pair of legs; however, each abdominal segment has two pairs of legs.
• Respiration occurs by tracheae.
• Excretion takes place by Malpighian tubules.
• Development is generally direct, for example, Julus.

Class 4 Insecta (Hexapoda)

• The body is divided into the head, thorax, and abdomen.
• There is a pair of antennae and a pair of compound eyes.
• The thorax consists of three segments with three pairs of legs and usually two pairs of wings. For example, mesothoracic wings which are thick and leathery are called tegmina, and metathoracic wings are membranous (in cockroaches). Wings may be absent in the same insects.
• The abdomen may consist of 10 segments.
• Respiration usually takes place by tracheae (no respiratory pigments).
• The heart is tubular and divided into chambers.
• Malpighian tubules are the excretory organs. Uric acid is the chief excretory waste.
• Sexes are separate.

Development may be direct or indirect, for example, silverfish, cockroaches, bedbugs, locusts, termites, butterflies, rat fleas, beetles, wasps, aphids, glowworms, etc. A maggot is the larva of a housefly.

Insects communicate with each other by ectohormones called pheromones. Pheromones are chemicals secreted outside the body and perceived as smell by other individuals of the same species. They help in communication amongst the organisms of the same species.

Class 5 Arachnida

• The body is usually divisible into cephalothorax and abdomen.
• The cephalothorax bears simple eyes and six pairs of appendages (one pair of chelicerae, one pair of pedi- palp, and four pairs of legs).
• Antennae are absent.
• Respiratory organs are book lungs or tracheae or both.
• Excretion takes place by Malpighian tubules coxal glands or both.
• Development is generally direct.
• Examples: Tick, mite, Aranaeus (garden spider), Palamneus (scorpion), Buthus (scorpion).
• Spiders spin webs by means of proteinaceous secretions of abdominal glands known as “spinnerets.”
• There are two more classes in the phylum Arthropoda. These classes are Onychophora and Merostomata.
• Peripatus is an important example of the class Onychophora which has the characters of phylum Annelida and Arthropoda. Hence, it is called a “connecting link.” Umulus, (king crab or horseshoe crab) is an example of the class Merostomata which respires with book gills.
• The king crab is called a “living fossil.” A living fossil is a living animal of ancient origin with many primitive characteristics.

Phylum Arthropoda Points To Remember

1. Peripatus is considered as a connecting link between Annelida and Arthropoda as it has unjointed legs and breathes by the trachea.
2. Larvae of different arthropods:
   • Bombyx (silkworm)—Caterpillar/silkworm.
   • Beetles—honey bee grub
   • Musca (housefly)-Maggot
   • Culex, Anopheles-Wriggler
   • Pennaeus (marine prawn), Mysis, Nauplius—Protozoea
   • Cancer (Crab)—Megalopa, metanauplius, zoea
3. Terga are dorsal plates whereas sterna are ventral plates of exoskeleton.
4. Arthrodial membranes join different sclerites.
5. Halters are drumstick-shaped, second pair of reduced wings of houseflies and mosquitoes which help in balancing.
6. The eggs of Culex are cigar-shaped; they are laid vertically on the surface of water in clusters; airfloats are absent; whereas in Anopheles, eggs are boat-shaped, laid singly and horizontally; they have airfloat.
7. The larva of Culex is the bottom feeder whereas the larva of Anopheles is a surface feeder.
8. The adult of Culex lies parallel to the surface and both ends of the body are deflexed whereas m Anopheles, the body is inclined at an angle of 45° to the surface. So, they can be distinguished with the help of sitting posture.
9. In spiders, spinnerets are present anterior to the terminal anus. They produce silken thread.
10. Von Frisch described the process of communication of food sources in honey bees.
11. Insecticides sprayed over the mosquitoes desensitize their nervous system as well as the chemoreceptors and mechanoreceptors of the antennae.
12. Johnston’s organs are present on the antennae of mosquitoes.
13. The life cycle is generally accompanied by metamorphosis. Larvae and adults may show different feeding habits and occupy different habitats.
14. Insects such as bees, wasps, beetles, moths, and butterflies are good pollinators for important crops.
15. Ants, termites, and locusts are eaten by Chinese and Indians; the eggs of aquatic bugs are used as food by Mexicans; ox-warbles are eaten by Red Indians.
16. Dragonflies feed on the larvae of mosquitoes
17. Glow womb (firefly) shows bioluminescence.
18. Adult Ctrier and Anopheles can be distinguished with the help of sitting posture.

The insects may be divided into five groups on the basis of their mode of development.

Ametabola Insects: Metamorphosis absent. The young ones resemble adults.

Eggs → Young → Adult

Example: Lepisma (silverfish)

Paurometabola Insects: Gradual metamorphosis.

Eggs → Nymph → Adult

Examples: Cockroaches, grasshoppers, locusts, etc.

Hemimetabola Insects: Incomplete metamorphosis. Habitat of young ones is different from adults.

Eggs → Naiads → Adult

Example: Dragonflies (naiads aquatic but adults aerial)

Holometabola Insects: Complete metamorphosis.

Eggs → Larva → Pupa → Adult

Examples: House flies, butterflies, mosquitoes, etc.

Hypermetabola Insects: Various forms of larvae.

Eggs → Larva (1) → Larva (2) → Pupa → Adult

Example: Blister beetle.

Phylum Mollusca

Phylum Mollusca is the second largest phylum in the animal kingdom which includes over 60,000 species. The general characters of this phylum are as follows: Molluscs are terrestrial, aquatic (freshwater or marine) triploblastic, bilaterally symmetrical, schizocoelici, and unsegmented animals.

• Most mollusks secrete a shell of calcium carbonate that protects and supports their soft tissues.
  The body is organized into three general regions: head, foot, and visceral hump.
• The visceral hump contains the digestive tract and other visceral organs.
• The body is covered by a soft and spongy skin fold called a mantle which secretes the shell.
• The space between the hump and the mantle is called the mantle cavity in which feather-like gills are present.
• Molluscs typically employ a feeding organ called radnla which is armed with rows of chitinous teeth. The radula protrudes from the mouth and works back and forth to rasp the food into fine particles.
• The circulatory system is mainly of open type but some reduced sinuses are present. The respiratory pigment is hemocyanin.
• Respiration occurs by feather-like gills, pulmonary sacs, or both, or through the general body surface.
• Excretion occurs by the paired organ of Bojanus. Another excretory organ called Keber’s organ (pericardial gland) is also present in Unio along with the paired organ of Bojanus. It pours the waste into the pericardium from where the waste is carried to the organ of Bojanus that opens out through the mantle cavity.

Sense organs include eyes, statocysts, and osphradia (chemoreceptors to test the chemical nature of water).

• Reproduction sexual, adults can be dioecious (unisexual) or monoecious (bisexual or hermaphrodite). Fertilization is generally external; development is direct or through free larval forms such as trochophore, veliger (in Pila), glochidium (in Unio)—an ectoparasite on fishes. Pila produces two types of sperms:
  • Eupyrene: Motile and functional sperms, 25 pm long, thread-like with a single cilium.
  • Oligopyrcne: Non-motile and non-functional sperms, 32.5 pm long, spindle-shaped with 4-5 cilia.

Classification Of Phylum Mollusca: The classification of Mollusca is mainly on the basis of shell and foot.

Class 1 Monoplacophora

• The flattened, bilateral, and oval body has some annelidan characters. For example, some internal organs exhibit metameric segmentation. There are also present nephridia. However, these animals are mollusks because they have the characteristics of the phylum Mollusca.
• Their body is enclosed in a mantle which secretes a dome-shaped outer shell.
• A broad and flat muscular foot is present for locomotion. Sexes are separate.
• Example: Neopilina galathea, the most primitive mollusk, has the characters of annelids. A “living fossil” and a connecting link between annelids and mollusks. It is the only mollusk that has a segmented body and is covered with a shell.

Class 2 Polyplacophora/Amphineurs

• They are all marine.
• They are bilaterally symmetrical with elongated bodies having mouth and anus at opposite ends.
• The head lacks eyes and tentacles.
• The ventral surface has a flat foot.
• The shell may consist of one to eight plates.
• Examples: Chiton (coat of mail shell), Chaetopleura (chiton)

Class 3 Scaphopoda

• They are marine and burrow in mud and sand.
• They are bilaterally symmetrical with tubular shell openings at both ends.
• The Head has many prehensile tentacles.
• The foot is conical and used for digging.

Class 4 Gastropoda

• Gastropoda is the largest class of mollusca comprising limpets, slugs, snails, etc. A characteristic feature that distinguishes all gastropods from other mollusks is torsion.
• They are terrestrial, freshwater, and marine forms.
• The shell is made of one piece enclosing the visceral mass.
• The hand is distinct and has eyes and tentacles.
• The foot is flat and muscular.
• The buccal cavity has an odontophore with a radula bearing chitinous teeth.
• There is present a veliger larva during development.

The early embryo is symmetrical with an anterior mouth and posterior anus but during development, the body twists, bringing the anus near the mouth, showing torsion so that it becomes asymmetrical. Thus, in the adult forms, the mouth and anus are both anterior.

Examples: Pila (apple snail), Aplysia (sea hare), Doris (sea lemon), Patella, Umax (grey slug, slowest invertebrate terrestrial), Achatina (land snail).

Class 5 Pelecypoda (Bivalvia)

• Pelecypods include clams, mussels, oysters, scallops, and related bivalve mollusks.
• The body is laterally compressed and enclosed in a bivalve.
• No head, tentacles, eyes, jaws, or radula.
• Food is often hatchet-shaped and extends between mantle lobes.
• Mostly filter feeders. Usually dioecious, veliger, or glochidium larvae are present during development.
• Mostly marine, few freshwater forms.
• Examples: Unio (freshwater mussel), Mytilus (sea mussel), Teredo (shipworm), Pecten (scallop), Spon-dylus (edible oyster), Pinctada (pearl oyster), Solen (razor clam), Ostrea (pearl oyster), Lamellidens (mussel).

Class 6 Cephalopoda (Siphonopoda)

• Cephalopods are exclusively marine.
• Cephalopoda contains the most specialized molluscs including squids, octopods, cuttlefish, and nautiloids (living fossils).
• They are the most active mollusks, the foot is located on the head, modified in the form of oral arms.
• Nautilus has an external shell but in others, the shell has been reduced and enclosed within the body or lost entirely.
• The head is distinct and large with well-developed eyes.
• It is surrounded by a ring of tentacles.
• Part of the foot forms a funnel-shaped siphon.
• Locomotion is by expelling water in jets through siphons (jet propulsion).
• Ink glands are present in some squids for offense and defense.
• When the squid is attached, it emits a cloud of inky fluid through its siphon.
• This “smoke screen” interferes with the visual and chemoreceptors of the predator and thereby helps the squid to escape.
• Examples: Sepia (Cuttlefish), Loligo (squid or sea arrow), Octopus (devilfish), Nautilus, Spirula (spiral shell), Architeuthis (giant squid), etc.

Phylum Mollusca Points To Remember

Architeuthis (giant Atlantic squid) is the largest and heaviest among invertebrates, 55 feet in length. Nautilus is the only cephalopod with an external shell, so ink glands are absent. The color change in cephalopods occurs due to chromatophores.

Phylum Echinopermata

Echinoderms are exclusively present in marine water and there are no parasitic forms. Similarities with chordates are as follows:

• They have a tube-within-tube type of body plan which has evolved along the deuterostome evolutionary line.
• They possess a true coelom called enterocoelom.
• They have mesodermal skeletons made of calcareous plates or ossicles.

All these characters make echinoderms closer to chordates. The other characters are:

• The symmetry is bilateral in larvae, but pentamerous radial in adults.
• Many echinoderms bear a number of calcareous spines on their body surfaces called tubercles. Between the spines, there are pincer-like structures called pedicellariae to keep the surface clean. Pedicellariae are made of three calcareous plates. Two calcareous valve-like structures in the form of aws rest upon a basal calcareous plate.
• Between the spines, there are finger-like processes called dermal branchiae which help in respiration. The mouth is on the ventral/oral side and the anus is on the dorsal or aboral side.
• There is no distinct anterior and posterior end, i.e., no cephalization.

Hemal and peripheral systems: Instead of a blood vascular system, there are present hemal and peripheral systems that are of coelomic origin. Thus, the so-called circulatory system is open type. The so-called blood is often without a respiratory pigment. There is no heart.

• Respiratory Organs: Gaseous exchange occurs by dermal branchiae or papulae in starfishes, peristominal gills in sea urchins, genital bursae in brittle stars, and cloacal respiratory trees in holothurians. The exchange of gases also takes place through tube feet.
• Excretory Organs: Specialized excretory organs are absent. Nitrogenous wastes are diffused out via gills or dermal branchiae. Ammonia is the chief excretory matter.
• Sexes are separate. Reproduction is sexual. Fertilization is usually external. Development is indirect with free-swimming larvae.

Classification Of Phylum Echinodermata: Phylum Echinodermata is divided into five classes.

Class 1 Asteroidea (Gk: Aster = star, eidos = form)

• The body is flat and star-like.
• Five anns are usually present which are not sharply marked off from the central disc.
• Autonomy: The ability of starfish to break off a part of its body, followed by regeneration.
• The oral surface has mouth and ambulacral grooves.
• The aboral surface bears the anus and madreporite.
• Respiration by dermal branchiae and tube feet.
• Spines are short.
• Pedicellariae are present.
• Larvae of starfish are pleura, bipinnaria, and brachiolaria.
• Examples: Asterias (starfish), pentaceros (starfish), and Astropecten (starfish).

Class 2 Ophiurodea (Gk: Ophis = snacks, oura = tail, eidos = form)

• The body is flat and star-like.
• Arms are sharply marked off from the central disc.
• The oral surface has a mouth and madreporite.
• Anus and ambulacral grooves are absent.
• Spines are short.
• Pedicellariae are absent.
• Larva is ophiopluteus.
• Examples: Ophiothrix (brittle star), Ophioderma (brittle star), Ophiocoma (brittle star), and Ophiura (brittle star).

Class 3 Echinoidea (Gk: Echino = hedgehog, eidos = form)

• The body is globular or disc-like.
• Arms and ambulacral grooves are absent.
• The oral surface has a mouth.
• A biting and chewing apparatus with teeth called Aristo¬tle’s lantern is present.
• The aboral surface bears the anus and madreporite.
• Spines may be small or large.
• Pedicellariae are present.
• Larva is echinopluteus.
• Examples: Echinus (sea-urchin), Clypeaster (cake urchin), Echinarachinus (sand dollar), and Echinocordium (heart urchin).

Class 4 Holothuroidea (Gk: Holothurion = sea cucumber, eidos = form)

• The body is elongated and cylindrical.
• Arms are absent.
• The oral end has a mouth surrounded by tentacles.
• The aboral end has an anus.
• Madreporite is internal.
• Ambulacral grooves, spines, and pedicellaria are absent.
• Larva is auricularia.
• Examples: Holothuria (sea cucumber), and Cucumaria (sea cucumber).

Class 5 Crrinoidea (Gk: Crinon = lily, eidos = form)

• The body has a central disc which is attached to the substratum
• Arms are breached with pinnules
• The oral surface has a mouth and anus.
• Ambulacral grooves are present.
• Spines, Pedicellariae, and madreporite are absent.
• They are commonly called feather stars or sea lilies.
• Larva is doliolaria.
• Examples: Antedon (sea lily; feather star).

Phylum Echinopermata Points To Remember

The starfish uses the suction-cup-like ends of the tube feet of one arm to hold on to rocks, as it moves the other anus. It can open bivalves (mollusks) by attaching two anus to either side of a bivalve and pulling them apart.

• The bivalve opens out; the stomach of starfish is then everted through its mouth and introduced into the open mollusc which is partly digested before being ingested.
• Echinodenns predate on coral polyps also.

Phylum Hemichordata Or Stomochordata

Hemichordata was earlier considered as a sub-phylum under chordata. But now it is placed as a separate phylum under non-chordata.

The phylum consists of a small group of worms-like marine animals with an organ system level of organization. Its characteristics are:

• In hemichordata or stomochordata, true notochord is absent. Gill slits are present but they are dorso lateral in position. They are worm-like, bilaterally symmetrical, Triploblastic, and entero-coelomate animals.
• Stomochord is a hollow outgrowth arising from the roof of the buccal cavity, also called a buccal diverticulum. It is present in the proboscis.
• Dorsal heart, ventral hollow nerve cord, and no respiratory pigments. The circulatory system is open. Respiration occurs by the gills.
• Development is mostly indirect through a free-swimming tomaria larva, for example, Balanoglossus (acorn, tongue worm), or Glossobalanus. Sexes are separate. Fertilization is external.
• Believed to be a connecting link between non-chordates and chordates.
• Due to the absence of true notochord in hemichordata, many taxonomists do not consider these animals as chordates.
• Excretory organ is proboscis gland.
• The body is cylindrical and is composed of an anterior proboscis, a collar, and a long trunk.
• Examples: Balanoglossus, Saccoglossus

Phylum Chordata

The Most Important Characteristics Of Phylum Chordata Are:

• They possess a notochord either throughout life or during early embryonic development.
• Dorsal hollow nerve cord.
• Paired gill slits on the lateral sides of the pharynx.
• Post anal tail.
• Closed circulatory system.

Sub-Phylum Protochordata Or Acraniata

Sub-Phylum 1 Urochordata

• They are exclusively marine.
• This sub-phylum is also called Tunicata because the adult body is enclosed within a leathery test or tunic formed of a cellulose-like organic substance termed tunicin.
• The larva (Ascidian tadpole) undergoes retrogressive metamorphosis, i.e., change from a better-developed larva to less developed adult, for example, Herdmania (sea squirt).
• Vanadocytes are present except in Herdmania. Vanadium gives a green color to blood. Excretion occurs by the neural gland, hence excretion is glandular.
• Examples: Salpa, Doliolum, Ascidia.

Phylum Chordata Can Also Be Divided As:

Sub-Phylum 2 Cephalochordata

• The notochord extends up to the anterior end of the body. Hence, this sub-phylum is named so.
• The tail is present throughout life, for example, Brcmchiostoma (Amphioxus).
• AmphioxusiBrcmchiostoma has both ends pointed like a lance. Hence, it is commonly called a lancelet.

Sub-Phylum Vertebrata Or Craniata

• These are advanced chordates that have a cranium (cartilage or bony brain box) around the brain.
• Notochord is present only in the embryonic stages. It is replaced by a cartilaginous or bony vertebral column (backbone) in the adult forms. They have paired appendages as fins and limbs.
• A closed circulatory system is present; a muscular and ventral heart with two, three, or four chambers; a lymphatic system is present; erythrocytes and hemoglobin are present.
• A pair of kidneys is present for excretion and osmoregulation; endocrine glands are well-developed; members are generally unisexual and have a single pair of gonads.

Phylum Chordata Division 1 Agnatha (Jawless Vertebrates)

• They are the most primitive of all craniates.
• The mouth does not possess jaws, hence named Agnatha.
• The vertebral column is represented only by small imperfect neural arches over the notochord.
• They do not have exoskeletons and paired appendages.
• They have a single nostril. The internal ear has one or two semicircular canals.
• They are cold-blooded.
• It includes two classes: Ostracodermi and Cyclostoinata.

Class 1 Ostracodermi

• Ostracoderms are all extinct now and are called fossil agnatha.
• These were shell skinned with an exoskeleton of bony plates, for example, Cephalaspis.
• They were the first jawless fishes (originated in the Ordovician period in the Palaeozoic era).

Class 2 Cyclostomata: Its general characters are as follows:

• All living members of the class Cyclostomata are ectoparasites on some fishes. The body is devoid of scales and paired fins. The head and brain are poorly developed. They are also called jawless fishes.
• Cyclostomes have an elongated body bearing 6-15 pairs of gill slits in their gill pouch for respiration and have a sucking and circular mouth.
• Single-sex organ discharges gametes in the well-developed coelom.
• The cranium and vertebral column are cartilaginous with persistent notochord.
• The stomach is absent.
• A single dorsal nostril leads into a closed nasal sac. A functional pineal eye is present just behind it.
• Circulation is of closed type.
• Kidneys are mesonephric.

Differences Between Lamprey And Hagfish

Phylum Chordata Division 2 Gnathostomata (Jawed Vertebrates)

• It includes advanced vertebrates.
• The embryonic notochord is usually replaced in adults by a vertebral column.
• Paired fins or limbs are present.
• The mouth has jaws, hence it is named gnathostomata.
• Paired nostrils are present.
• The internal ear has three semicircular canals. Girdles are present.
• Gnathostomata is divided into two superclasses: Pisces and Tetrapoda.

Super Class 1 Pisces: Pisces includes true fishes. All are aquatic. The body bears fins. They are cold-blooded. The characteristics are as follows:

• Monocondylic skull; slimy glands present on skin.
• Vertebrae are amphicoelous types.
• Neck absent, no upper or lower eyelids, no tympanum (only internal ear is present). Each eye has a well-developed nictitating membrane.
• Heart two-chambered (S-shaped); venous heart with sinus venosus and conus arteriosus.
• Both renal portal and hepatic portal systems are found. A hypophyseal portal system is also present.
• Respiration occurs typically by gills.
• Scales are mesodermal or dermal and embedded in the skin.
• Kidneys are mesonephric and ammonotelic (sharks: ureotelic).
• Lateral line sense organs are present.

Super class Pisces is divided into three classes: Placodermi, Chondrichthyes, and Osteichthyes.

Class 1 Placodermi (Extinct): It includes the earliest fossil fishes that lived in freshwater. The body had an external protective armor of bony scales or plates. Primitive jaws with teeth were present. The skeleton was bony. Fins were mostly formed of large spines, for example, Climatius (spiny shark).

• They appeared in the Silurian period, flourished in the Devonian and Carboniferous periods, and became extinct in the Permian period.
• The name placodermi means “armored fish” or “plate skinned.”
• Both paired and unpaired fins were present. Caudal fin heterocercal.
• Autostylic jaw suspension; gill slits are covered by operculum.

Class 2 Chondrichthyes: This class includes cartilaginous fish, for example, Scoliodon (dogfish), Torpedo (electric ray), etc.

Sharks are fast-swimming predators, whereas the rays and skates are stout, bottom-living scavengers and mollusk feeders.

Class 3 Osteichthyes: It includes bony fishes, for example, Labeo, Hippocampus, Exocoetus, Catla, Clarias, Betta, Pterophyllum, etc.

Differences Between Cartilaginous And Bony Fishes

Some Important Fishes Of Super Class Pisces

Torpedo (Electric Ray): A torpedo is a bottom-dwelling, carnivorous fish. It stuns or kills the prey and enemies with electric shock from its electric organs. The latter are modified muscles. The skin is scaleless.

Pristis (Sawfish): The head bears a series of strong tooth-like denticles along the margin. It uses these denticles for offense and defense. It is viviparous.

Exocoetus (Flying Fish): It does not fly but often leaps into the air up to about 6 m high. The pectoral fins are modified into wing-like structures, with the help of which the fish glides.

Hippocampus (Sea Horse): The neck and head of the fish are horse and the tail is prehensile. The male bears a brood pouch in which the female lays eggs and the latter remain there till they hatch.

Labeo (Rohu): Labeo rohita and Labeo calbasu are the common freshwater edible carp. It is covered by large overlapping scales.

Clarias (Cat Fish/Magur): Indian catfish (Clarias batrachus) live in ponds. It is carnivorous, flic head bears sensory threads called barbels. The body is smooth and without scales. Other freshwater catfishes of India are Mystus seengala (slinghara), Rita lita, and Wallago attu (Malli).

Latimeria Chalumnae (Coelacanth): It was first caught in 1938 off the east coast of South Africa. It swims by curious rotating movements of its pectoral fins. All its fins except the anterior dorsal are lobed. It is the oldest living fish and has survived till today without undergoing any change in it. It is therefore described as a living fossil.

Endothermic Fishes: Although most fishes are ectothermic, a few species such as blue fish tuna, and swordfish are able to maintain a body temperature higher than the temperature of the water that surrounds them. Genetic studies of these endotherms have revealed that the ability to maintain high body temperature gives these fishes an adaptive advantage by allowing them to hunt in much colder waters than their competitors.

Fish taken out of water dies of suffocation due to the lack of oxygen. This is because the gill filaments stick together when taken out of water, thereby reducing the surface area.

Freshwater Species

1. Labeo rohita (Rohu)
2. Labeo calbasu (Calbasu)
3. Catla caila (Catla/cat fish)
4. Gyprinus carpio (Carp)

Marine Species

1. Harpoon (Bombay duck)
2. Anguilla (Eel)
3. Sardinella (Salmon)
4. Hilsa (Hilsa)

Some air-breathing fishes used their paired fins to move on land and gave rise to the first land vertebrates. A living fossil of this group is Latimeria, a lobe-finned fish.

Some Important Body Parts Of Super Class Pisces Fins

1. Paired Pectoral And Pelvic Fins: Act as balancers and brakes; provide lift and counteract pitching and rolling.
2. Anterior Dorsal Fin: Counteracts rolling and yawing.
3. Posterior Dorsal And Anal Fins: Counteract yawing and rolling.
4. Caudal Fin: Propels the body and provides lift.

Scales

1. Cosmoid: Absent in living fishes; consists of four distinct layers: outermost ganoine, followed by cosmine, spongy bone, and innermost compact bone. For example, extinct fishes.
2. Placoid: Backwardly directed spine arising from a basal plate, for example, Chondrichthyes.
3. Ganoid Or Rhomboid: Scales are thick, diamond- or rhomboid-shaped plates, for example, primitive bony fishes such as Acipencer, etc.
4. Cycloid: Thin, flexible, circular in outline, marked with concentric lines of growth which can be used for determining age, for example, lungfishes, Amia, etc.
5. Ctenoid: Bear numerous small comb-like spines, for example, higher bony fishes such as perch, etc.
6. Air Bladder: It is associated with respiration, liydrostasis, sound production, and audition.

Parental Care

• Nest building, for example, Gasterosteus, Amia (bowfin), Protoptehis, and Lepidosiren (the nest is built by the males of these fishes).
• Shelter in mouth, for example, males of catfish, Arias.
• Brood pouch, for example, male Hippocampus.

Common Food Fishes Of India

False Fishes In Animal Kingdom

Super Class 2 Tetrapoda: All gnathostomes excluding fishes are included in this super class.

• Typically ail tetrapods (Gk. Tetra = four + podos = foot) possess two pairs of limbs.
• Skin is adapted to withstand exposure to air,
• They have lungs for aerial respiration. Their sensory organs are adapted for reception in air such as vision, hearing, smelling, etc.
• Tetrapoda is divided into four classes: Amphibia, Rep- tilia, Aves, and Mammalia.

Class Amphibia: Vertebrates with dual-life (Gk. Amphi = two or both; bios = life). The general characteristics of members of this class are as follows:

• There are about 3000 species of amphibians out of which 2600 species arc in the order Anura.
• They are present in the warmer regions of the world except for newts and salamanders, which are present in cooler regions.
• They occur only in fresh water and moist land. Amphibians are not found in seawater.
• They are poikilothermal animals. They are amphibious in nature, i.e., they can live on land as well as in water. They are mostly found in warm countries. They are ectothermic (cold-blooded). The body is divisible into a head and trunk. The tail may be present in some forms.
• The skin is smooth or rough, having cutaneous glands which keep it moist. They are usually without scales, but if scales are present, they are hidden beneath the skin (for example, Caecilians).
• Two pairs of limbs are used for locomotion.
• The gills are present at least in the larval stage; some adult forms also carry them in addition to lungs (for example, Necturns).
• The alimentary canal and urinary and reproductive tracts open into a common chamber called cloaca which opens to the exterior.

Classification of Class Amphibia

The skull is cacodylic, i.e., with two occipital condyles for articulation with the vertebral column. The respiratory organs are the lungs, buccopharyngeal cavity, skin, and gills.

• The heart is three-chambered, having two auricles and one ventricle. In the heart, there are present sinus venosus and truncus arteriosus. Both the hepatic portal and renal portal systems are well-developed.
• Kidneys are mesonephric. The urinary bladder is present in frogs. Larvae and tailed amphibians (for example, salamanders) are ammonotelic. Frogs and toads are ureotelic.
• The ear consists of the internal and middle ear. The tympanum (outer membrane) covers the middle ear. The middle ear has a single ear ossicle called columella auris.
• Ten pairs of cranial nerves are present. Sexes are separate; fertilization is external; and oviparous; and development indirect.
• They return to the water for breeding. Male lacks copulatory organs. Indirect development occurs. A fish-like stage, the tadpole, is present.
• Male frogs can croak louder than females because of the presence of vocal sacs.
• Examples: Bufo (toad), Rana (frog), Hyla (tree frog), Salamandra (salamander), Ichthyophis (limbless amphibia).
• Living amphibians are divided into three orders:

Class Reptilia: Their name refers to their creeping or crawling mode of locomotion.

• Reptiles are cold-blooded or poikilothermic animals.
• There are only about 6000 species of reptiles now living. But fossils show that 200 million years ago, the reptiles were the most dominant animals on earth.
• Herpetology is the study of reptiles.
• The largest reptiles today are the “komodo dragon” Varanus komodoensis of Indonesia (a lizard) 3 m in length, crocodiles (up to 7 m), pythons (up to 10 m), and giant tortoises weighing up to 600 kg.
• They are covered by dry and cornified skin having epi-dermal scales or scutes. Snakes and lizards shed their scales as “skin cast.” Scales prevent the loss of body water and so reptiles do not require a moist environment like amphibians.
• Respiration is only through the lungs, which is improved by the development of ribs.
• Limbs when present are in two pairs; pentadactyl; digits have horny claws.
• The mouth is terminal with conical teeth which arc pleurodont in lizards and snakes and the thecodont in crocodiles. Teeth are absent and replaced by home beaks in turtles.
• The endoskeleton is bony; the skull is monocondylic (with one occipital condyle).
• Heart is usually three-chambered or partially four-chambered. The interventricular septum is incomplete.
• The heart is completely four-chambered in crocodiles. Two systemic arches are present. Erythrocytes are oval and nucleated.
• Kidneys are metanephric. Excretion is uricotelic. The urinary bladder is absent in snakes and crocodiles.

Cranial nerves are in 12 pairs. Jacobson’s organ (vomeronasal organ) present in the roof of the buccal cavity, and concerned with smell, is well-developed in snakes and lizards. They do not have external ear openings. Tympanum represents ears.

Sexes are separate. Males usually have a muscular copulatory organ. Fertilization is internal. Most are oviparous and development is direct. Some are viviparous. No metamorphosis.

Examples: Chelone (turtle), Testudo (tortoise), Chameleon (tree lizard), Calotes (garden lizard), Crocodilus (crocodile), Alligator (alligator), Iiemidactylus (wall lizard), poisonous snakes—Naja (cobra), Bangarus (krail), Vipera (viper), etc.

Classification Of Reptiles Is Based On The Temporal Fossa Of Skull. The Class Reptilia Is First Divided Into Five Sub Classes:

1. Anapsida,
2. Euryapsida,
3. Parapsida,
4. Synapsida, and
5. Diapsida.

Out Of The Five Sub-Classes, The Living Reptiles Are Found Only In Two Sub-Classes:

1. Anapsida and
2. Diapsida.

 

1. Anapsida: Primitive reptiles with a solid skull roof. No temporal openings/fossae.
   • Order: Chelonia
     • Commonly called turtles (marine), tortoises (terrestrial), and terrapins (edible freshwater).
     • The body is encased in two shell plates, a dorsal carapace, and a ventral plastron.
     • Limbs clawed, webbed, or paddle-like.
     • Sternum is absent.
     • Jaws with home sheath, no teeth.
     • Certain aquatic turtles perform cloacal respiration, but all other reptiles respire with lungs.
     • Cloacal respiration is reported.
2. Diapsida
   • Order: Rhynchocephalia
     • All are extinct except a living species Sphenodon punctatum.
     • Sphenodon is the “Tuatara” of New Zealand. It is a living fossil and going to become extinct.
     • Sphenodon is a protected animal under the law of the New Zealand government.
     • An interesting feature of Sphenodon is the presence of the pineal parietal or third eye.
     • Sphenodon is referred to as a living fossil because it has retained many primitive characteristics of fossil or stem reptiles.
   • Order: Squamata
     • Divided into two sub-orders: Lacertilia (lizards) and Ophidia (snakes).
     • Saurology is the study of lizards.
     • Serpentology or ophiology is the study of snakes.
     • Lizards have four well-developed pentadactyl limbs with claws. For example, Ccdotes (garden lizard).
     • The tail of most lizards is easily broken off when threatened or seized by a predator. This ability is known as autotomy. Autotomy is the voluntary breaking of the tail to confuse the enemy.
     • A new tail is soon regenerated which, however, does not possess vertebrae.
     • Most lizards are oviparous, two viviparous lizards are Phrynosoma (homed toad) and Chameleon (tree lizard).
     • Draco is a lizard that glides with the help of patagium and is hence called a flying dragon.
   • Order: crocodile

Heloderma (Gila monster) is the only poisonous lizard in the world. It is also called a “beaded lizard” because its scales resemble beads.

There are two species of heloderms, H. suspectum, and H. horridum. Both are found in America. Heloderma rarely bites humans, but its bite is fatal. Its poison is neurotoxic.

• Limbs are absent in lizards such as Ophio-saunis, Angitis, and Rhineura, also called glass snakes.
• A limbless lizard can be distinguished from snakes by the presence of movable eyelids and external ear openings.
• Barkudia is a limbless lizard from South India.
• The glass snake Ophiosaurus derives its name from its ability to break off its tail when seized.
• Lizards are mostly omnivorous, but a herbivorous lizard is Iguana from South and Central America.
• The largest living lizard in the world is the ferocious dragon, Varanus koinodoensis, found in the Malaya Archipelago, The Length is 2.5 m, weighing over 100 kg.

Difference Between Tortoise And Turtle

Identification Of Poisonous And Non-Poisonous Snake

Differences Between Crocodile, Alligator, And Gavialis

Class Axes (Birds): The study of birds is known as ornithology. The general characters are as follows:

• Birds are feathered bipeds, air-breathing, truly flying vertebrates (other being bats from class Mammalia). Jawbones are prolonged into a toothless beak or bill.
• Limbs are two pairs. Forelimbs are modified as wings for flying. Hindlimbs or legs are large, each foot usually bears four, clawed toes. Hindlimbs generally have scales.
• The exoskeleton consists of feathers, scales, and claws, which are epidermal derivatives. Skin without glands; the only cutaneous gland is the uropygial gland or preen gland/oil gland at the base of the tail.
• The esophagus is dilated into a crop for quick feeding and storage. Crop secretes “pigeon milk” during the breeding season. The stomach is divided into a glandular proventriculus and a muscular gizzard.
• The junction of the small intestine and rectum is marked by a pair of rectal cecae. The Cloaca of birds is three-chambered: anterior coprodaeu’m, middle erodium, and a large posterior proctodaeum. There is no gall bladder in birds like pigeons.
• Respiration is due to compact, spongy, non-distensible lungs continuous with thin-walled air sacs. Air sacs reduce body weight, and help in double respiration and internal cooling.
• The larynx is present without vocal cords. A sound box or syrinx-producing voice lies at or near the junction (furcula) of the trachea and bronchi.

The heart is completely four-chambered as in mammals. Sinus venosus absent. Only the right aortic (systemic) arch persists in adults. The renal portal system is vestigial. Erythrocytes are minute, oval, and nucleated.

• The blood of the birds may be called the richest blood in the animal kingdom. It has more RBCs per cubic mm of blood than in any other animal.
• Kidneys are metanephric and three-lobed. Ureters open into cloaca. The urinary bladder is absent. Excretion is uricotelic.
• Cranial nerves are of 12 pairs.
• Olfactory organs are poor. The middle ear contains a single ossicle. Eyes possess a nictitating membrane. Pecten is a comb-like structure found in the eyes near the blind spot. Pecten helps in the nutrition of the eyeball. Pecten is found in all birds except Kiwi.
• Sexes separate. Some birds show sexual dimorphism (for example, parrots and peacocks). The male bird has a pair of abdominal testes and a pair of sperm ducts. A copulatory organ is absent in all birds except in ratitae, geese, ducks, etc. Females are oviparous with a single (left) functional ovary and oviduct (Mullerian duct). Development is direct.

Different Parts Of The Oviduct Secrete The Following:

• Ostium—Dense albumin
• Magnum—White albumin
• Uterus—Calcareous shell

Eggs of birds are cleidoic (with calcareous shell), macrolecithal (amount of yolk), and mesolecithal (distribution of yolk). Extraembryonic membranes are present (amniota).

• Feathers are found only in birds. Feathers are made up of the protein keratin and are waterproof due to the oily secretion of preen glands. The arrangement of feathers on the body of birds is called tylosis. The featherless areas are called as apteria. Four types of feathers are quill feathers, contour feathers, filoplumes, and down feathers.
• In the absence of down feathers, the birds will not be able to keep their body warm. Quill feathers in the wings are called remiges. Quill feathers in the tail are called rectrices. Filoplumes and down feathers help in the insulation of the body.
• Birds are the first vertebrates to have warm blood. Body temperature is regulated (homoiothermous). Ala spuria (bastard wing): Feathers on first digit (thumb).

Examples: Corpus (crow), Columba (pigeon), Psittacula (parrot), Struthio (ostrich), Pavo (peacock), Aptenodytes (penguin), Neophron (vulture).

Classification Of Class Aves: Class Aves is divided into two subclasses Archaeomithes and Neomithes.

Subclass 1 Archaeomithes

• All extinct Jurassic period birds of the Mesozoic era.
• Wings primitive with little power of flight.
• Tail long, lizard-like with two lateral rows of rectrices.
• Hand with clawed fingers.
• Skull with teeth in both jaws, for example, Archaeopteryx.

Subclass 2 Neomithes

• Modem as well as extinct, post-Jurassic period birds.
• Wings are well-developed and adapted for flight (with few exceptions).
• Tail short and reduced.
• Teeth are absent except in some fossil birds.
• Sternum with keel or carina.

There are four superorders in this subclass:

1. Super-order 1 Odontognathae: For example, Hesperornis (with teeth) is extinct.
2. Super-order 2 Palaeognathae (Ratitae): Example, flightless running birds.
3. Super-order 3 Impennae
   • For example, penguins (Aptenodytes): Penguins are found in Antarctica (south pole). They have paddle-like wings and cannot fly. Penguins are marine and lay eggs in ice.
4. Super-order 4 Neognathae (Carinatae): Example, modem flying birds such as Columba (pigeon), Psittacula (parrot), Neophron (vulture), and Pavo (peacock).

List Of Flightless Birds

Differences Between Super Orders Ratitae And Carinatae

Class Mammalia: They are terrestrial, warm-blooded (endothermic), or homeothermic animals so that their body temperature remains constant in spite of the changes in the temperature of the environment. The general characteristics of this class are as follows:

• The skin is covered with epidermal hair which acts as an insulating layer and allows high body temperature to be maintained. The hair may be partly lost as a second adaptation. In some aquatic mammals where hair is negligible, there is a subcutaneous layer of heat which provides insulation of heat and makes the warmblooded condition possible.
• The skin has two kinds of glands, sudorific glands which produce sweat; evaporation of sweat controls the body temperature; second kind of glands is sebaceous glands which produce an oily secretion that makes the hair water-resistant.
• Modified sweat glands (sudoriferous) form mammary glands that produce milk in females for the nourishment of the young for some time after birth. Because they possess mammae (breasts) and mammary glands, they are called mammals. It is the most unique character of mammals.

There is an external ear or pinna with an external auditory meatus. This is in addition to the middle and internal ear.

• In higher mammals, the anus is separated from the urinogenital aperture; consequently, the urinary and genital ducts have no connection with the digestive tube.
• In males, testes have come to lie outside the body cavity in scrotal sacs (except in elephants, aquatic mammals, and prototherian mammals).
• Teeth are embedded in sockets of the jaw bone and are said to be thecodont. There are only two sets of teeth in a lifetime, one deciduous or milk set and another permanent set. This condition is spoken of as diphyodont. There are four different types of teeth, hence mammals are heterodont.
• A muscular diaphragm divides the coelom into a thoracic and an abdominal cavity; the thoracic cavity has a pericardial cavity containing the heart and two pleural cavities containing the lungs. The remaining viscera lie in the abdominal or peritoneal cavity.

The heart is four-chambered with two auricles and two ventricles so that oxygenated blood lies in the left half and deoxygenated blood in the right half. This condition is also found in birds. Only the left aortic arch is present. Erythrocytes are round, biconcave, and non-nucleated (except in camel where they are oval and non-nucleated).

• Cerebral hemispheres and cerebellum are large-sized and highly developed with a great increase in the cortex. The two cerebral hemispheres are joined by a transverse band of nerve fibers called corpus callosum. There are four solid optic lobes called corpora quadrigeminal in the mid-brain. Twelve pairs of cranial nerves are present.
• The middle ear has three ear ossicles called malleus, incus, and stapes; the internal ear has a spirally coiled cochlea which acts as an efficient organ of hearing.
• The neck generally has seven cervical vertebrae.
• Examples: Oviparous—Ornithorhynchus (platypus); viviparous—Macropus (kangaroo), Pteropus (flying fox), Camelus (camel), Macaca (monkey), Rattus (Rat). Cains (Dog), Fells (cat), Elephas (elephant), Equus (horse), Delphinus (common dolphin), Balae- noptera (blue whale), Panthera tigris (tiger), Panthera leo (lion), etc.

Difference Between The Three Groups Of Mammals

Classification Chart

Class Mammalian Is Divided Into Three Sub-Classes: Prototheria, Metatheria, and Eutheria.

1. Sub-Class 1 Profotheria Or Monotremata: They are primitive mammals that show many characteristics of their reptilian descent. Their reptilian characteristics are that they lay large yolky eggs, urogenital organs open into a cloaca and large T-shaped interclavicles.
   • Their mammalian characteristics are the presence of hair and mammary glands—the latter are modified sweat glands: the presence of a diaphragm; the four-chambered heart has only the left aortic arch; and seven cervical vertebrae.
   • Examples: Tachyglossus (spiny ant-eater) and Ornithorhynchus (duckbill mole), both in Australia and Tasmania.
2. Sub-class 2 Metatheria Or Marsupialia: These Australian mammals are viviparous but the young are born in an immature state and develop in a pouch or marsupium on the abdomen of the mother where they are fed on milk produced by true mammary glands having teats.
   • Anus and urinogenital apertures are separate but have common sphincter muscles. They have two uteri and two vaginae, in males, the scrotal sacs are in front of the penis which is often bifid.
   • Examples: Macropus (kangaroo), Phascolarctos (kola bear), Didelphys (opossum), Parameles, and Dendrolagus (wallaby).
3. Sub-class 3 Eutheria Or Placentalia: They have an allantoic placenta that nourishes the embryo. The placenta establishes a connection between the uterus of the mother and the developing embryo.
   • They are viviparous and the young are like small adults, born after a long period of gestation. The anus and urogenital apertures are separate. The brain is highly developed and has a corpus callosum. The uteri generally and vaginae always are united into one.

Order 1 Edentate: They have no front teeth, though simple molars may be present. The snout is long and an elongated tongue is used for eating insects. Digits bear claws are used for hanging from trees.

Examples: Bradypus (sloth), and Dasypus (armadillo) (both of American origin). The sloth moves swiftly hanging upside down from trees. Yet, on the ground, it can only drag itself along at a speed of about 5 km/h. Armadillo has bony plates and shows polyembryony.

Order 2 Pholidota: Exoskeleton of epidermal scales, hair scanty, teeth absent, tongue long, sternum has rods of cartilage, limbs short with five-clawed digits.

Examples: Munis (pangolin or the scaly anteater). Pangolins use their prehensile tails while climbing from branch to branch. 1 hey arc found in the sub-Himalayan forests. Munis is also called bajra kit as it eats pebbles.

Order 3 Insectivore: Small terrestrial and nocturnal mammals living on insects and worms. Teeth are small and pointed. The brain is small and the skull is constricted in the middle.

Examples: Erinaceus (hedgehog), Talpa (mole) of the In¬dian subcontinent.

Order 4 Lagornorpha: They have sharp incisors for gnawing, and a large upper pair of incisors has a smaller pair behind it. Canines are absent. The cheek teeth bite with the lower set inside the upper.

The lower jaw has a wide range of movements due to the articular surface of the squamosal being broad and flat. Hindlimbs are long and used for jumping; the tail is short. They are herbivorous and include rabbits and hares.

Examples: Oiyctolagus (rabbit), Lepus (hare).

Order 5 Rodentia: The upper jaw has only a single pair of incisors with enamel on the anterior surface only. Hence, they become chisel-shaped by wedr and tear. The dentaries of the lower jaw are not joined and can be drawn apart. The cheek teeth bite with the upper set inside the lower. The forelimb often has a prehensile hand for holding food to the mouth. They have a very large number of species with a worldwide distribution.

Examples: Castor (beaver), Funambidus (squirrel), Mus (mouse), Rattus (rat), Hystrix (porcupine). The harvest mouse is the only European mammal to have a prehensile tail. Hystrix is the largest spiny mammal.

Order 6 Chiroptera: They are the only mammals that can fly. Forelimbs are long in which the metacarpals and phalanges of the second to fifth digits are elongated to support a fold of skin called patagium to form a wing that joins the hindlimbs and the tail.

The first digit is small, free, and clawed. Sternum has a keel for attachment of muscles of flight. Hindlimbs are weak and rotated outwards with the knees backward. They hang upside-down by their hindlimbs.

Examples: Pteropus (flying fox), Vespertilio (bat).

Order 7 Artiodactyla: They walk on the tips of their digits (unguligrade) and have an even number of dig¬its. The third and fourth digits are long and equal, end in hooves; the other digits are reduced or lost. Upper ends are absent, and lower ones bite against hardened gums.

The stomach is complicated with several chambers where bacteria digest cellulose. The frontals may grow out to form horns. They are generally large sizes and herbivorous.

Examples: Camelus (camel), Bos (cow and buffalo), Ovis (sheep), Capra (goat), Sits (pig), Giraffe (giraffe).

Order 8 Perissodactyla: They walk on the tips of their digits but have an odd number of toes. The third digit is the longest having a hoof, the other digits are generally lost or reduced.

Incisors are present in both jaws, but canines are found only in males. The stomach is simple, there is no gall bladder. They are large-sized and herbivorous; bacteria digest cellulose in a long cecum.

Examples: Equus cabalus (horse), Equus asinus (ass), Rhinoceros unicornis (one-homed Indian rhinoceros).

Order 9 Proboscides: They are an isolated group of large-sized animals with thick skin (called pachyderms) and scanty hair. They have massive pentadactyl limbs with united digits having nails. The skull has thick bones with air spaces. Testes are internal.

The nose and upper lip form a long trunk or proboscis used for transporting food and water to the mouth. Two upper incisors are elongated to form tusks of solid ivory. Canines and premolars are absent. There are three molars in each jaw, but only one is functional at a time.

Examples: Elephas maximus (Indian elephant)—tusks in males only. Loxodonta (African elephant)—tusks are present in both the sexes.

Order 10 Cetacea: Aquatic mammals breathe by lungs and have blubber or subcutaneous layer of the fat present which helps in heat conservation; skin glands absent; forelimbs are modified into paddle-like flippers; no Hindlimbs: no external ears; testes abdominal.

Balaenoptera (blue whale) is the largest animal ever lived. It is a filter feeder and feeds upon microscopic phytoplanktons. Physeter is a sperm whale with a single nostril; Delphinus (common dolphin).

Order 11 Sirenia: Herbivorous aquatic mammals, blubber present, intra-abdominal testes. They have homodont teeth and tusks.

Examples: Halicore, Manatee (sea cow).

Order 12 Carnivore: Canines and carnassials are well developed. The last upper premolar and the first lower molar are modified as shearing teeth or carnassials for cutting the bone and flesh, for example, Panthera tigris (tiger). Acinonyx jubatus (cheetah), Can is (dog), Eel is (cat), Panthera leo (Lion).

Order 13 Primates: Primates include loris, lemurs, tarsiers, Macaca (monkeys), apes, and man. They have plantigrade locomotion. Large, convoluted cerebral hemispheres are present.

Salient Features Of Different Phyla In The Animal Kingdom

Animal Phyla With Example

Comparison Among The Various Classes Of Vertebrata

Phylum Chordata Points To Remember

Stonefish is the most poisonous fish. Gambusia fish (larvivorous) was introduced into several tropical regions to control malaria.

Catadromous fishes live in fresh water and go down to sea for breeding, for example, Anguilla (European Anadromous fishes live in seawater and move to rivers for breeding, for example, Hilsa, Salmon, etc. When fishes migrate from sea to rivers, it is called anadromous migration.

1. Hilsa is the only Indian fish that migrates from sea to rivers for breeding.
2. The most primitive fish (fossil) is Climatius (placodermi).
3. Anabas (climbing perch). It has accessory respiratory organs for breathing atmospheric air which enables the fish to take long overland excursions in search of earthworms.
4. Pomfret is the most widely eaten fish in India.
5. Dipnoi has an incompletely divided three-chambered heart.
6. The urinary bladder is absent in fish.
7. Some elasmobranchs retain urea in the blood to maintain hypertonicity.
8. Ampulla of Lorenzini is a thermoreceptor.
9. Electric organs of electric ray are modified muscles.
10. Bioluminescent fishes: Anamalops, Porichthycs, etc.; sound-producing fishes: Molct, Batistes.
11. Poisonous glands are found in sting ray, eagle ray, Chimaera, Diodon, and Tetrodon.
12. Fish byproducts are fish meals and fertilizers; fish flour, fish proteins, fish oil, steaming, fish glue, leather, artificial pearls, etc.
13. Weberian ossicles were discovered by Waber (1820). These connect the air bladder with the internal ear.
14. The commercial name of the integument of Scoliodon is “shagreen.”
15. Typical trunk vertebrae of fish are amphicoclous, centrum peculiar as is supported by four wedge-shaped calcified fibrocartilages forming a “Maltese cross” and leaving an uncalcified area.
16. The study of fish is called ichthyology.
17. The study of skates, rays, and sharks is called torpedology.
18. Crossopterygians (Rhipidistia, Osteolepis genus) gave rise to amphibia.
19. Parental care is well-developed in the Hippocampus.
20. Isinglass is a gelatinous product obtained from the air bladders of certain fishes such as carp, salmons, catfishes, etc. It is used for making cements, and jellies, and for clarification of wines and beers.

Types of vertebrae

• Petromyzon, though marine, goes to fresh water for spawning, i.e., anadromous. After spawning within a few days, they die.
• Larva ammocoete hatches out of eggs in about 14-21 days. The larval period may long from three to seven years.
• Ammocoete is the connecting link between Amphioxus and the cyclostomes.
• Lingual cartilage is also a part of the skeleton, that lies in the tongue region and supports it (lingual = related to the tongue).
• Typhlosole is a fold of epithelium in the intestine. It prevents the rapid flow of food in the intestine and increases the absorptive surface area.

Types Of Caudal Fin

• Diphycercal Or Protocercal: The most primitive kind of tail fin. The tail is symmetrical, both externally and internally as in protocercal, but it is secondarily symmetrical.
• Heterocercal/Hypocercal Tail: Epicaudal and hypocaudal lobes are of unequal sizes.
• Homocercal: Identical lobes. Externally symmetrical and internally asymmetrical.

Some frogs have developed in amazing ways to prevent their eggs from drying out. The female Surinam toad of South America carries her eggs in the pits/pockets of skin on her back. As many as 60 young ones pass through the tadpole stage while embedded in her back and then emerge as small frogs.

In frogs, external ears are absent, only the tympanum is seen externally. Frogs have a tympanic membrane on the surface of both sides of their head. The tympanic membrane of a human is called the eardrums and each is protected inside the ear canal.

Word Roots And Origins

• Caudata: From Latin, Caudata meaning “tail.”
• Nictitating: From Latin, nictare meaning to “wink.”

Seymouria is a connecting link between amphibia and reptiles.

Paedogenesis: Development of gonads and/or production of young ones by immature or larval forms, for example, salamander (Ambyostoma).

• Total neoteny is shown by Necturus, Siren, and Proteus.
• Toads are used in Chinese medicines. The skin of the toad secretes a substance that increases blood pressure when injected into humans.
• The skin of a tadpole also secretes an enzyme, diastase.
• The upper jaw of a frog is derived from quadrate cartilage whereas the lower jaw is derived from Meckel’s cartilage.
• The first toe is called hallux.
• Jaw suspension is autostylic; urostyle is the last component of the vertebral column.
• The shape of the second to seventh vertebrae is procoelous (typical); the eighth vertebra: is amphicoelous; the ninth vertebra: is acoelous.
• Amphiinna has the largest RBCs among vertebrates.
• At the time of metamorphosis, tadpoles do not feed.
• Blind worms (limbless amphibians) are unusual amphibians as only one species lives in water. All the others burrow underground and are rarely seen on the surface. Many do not even need water to breed. The carboniferous period is known as the age of amphibians.
• The arrow poison frogs secrete a powerful poison from the skin which can cause instant death.
• The most poisonous frog—The golden dart poison frog—is from South America. One adult frog contains enough poison to kill 200 people.

Types Of Feathers

1. Quills: They are large feathers found in wings and tails.
   • It has a central axis called the shaft.
   • The small proximal part of the shaft is hollow; translucent, and cylindrical and is termed as calamus. The longdistal, solid, and opaque part of the stem is known as rachis.
   • An umbilical groove extends all along the ventral side of the rachis.
   • A small hole on the proximal end of the calamus is known as the inferior umbilicus; the hole on the distal end of the calamus is known as the superior umbilicus.
   • Each vane is composed of parallel filaments, the barbs. Each bears barbules.
   • The distal barbules of each barb bear small hooklets.
   • Emu birds have an after shaft as long as the main shaft.
2. Coverts: They are small feathers found in the wings and tail. They fill up the gaps left between the bases of the quills. They have short calamus in comparison to quills.
3. Contours: Small feathers that cover the body and give it its shape. They resemble the quills, but their barbs are not so strongly joined and can be separated easily.
4. Filopluntes: Occur beneath contour feathers; very small in size; consist of long rachis bearing at the tip a few weak free barbs with barbules.
5. Down Feathers/Nestling Downs: They cover the newly hatched bird. They consist of a short calamus, and reduced rachis bearing flexible barbs with short barbules. They are found beneath contours.
6. Bristles: Short calamus, a long rachis bearing a few vestigial barbs at its base. Bristles occur near the mouth in flycatchers. The first digit of the hand (thumb or pollex) bears a tuft of small feathers known as a bastard wing or ala spuria or false wing.

• Benadryl is used as an antidote to counteract the effect of hemotoxin.
• Seymouria is considered as the connecting link between amphibians and reptiles.
• The Mesozoic era is known as the “age of reptiles.”
• The loreal pit of a viper is a thermoreceptor organ.
• Reptiles without urinary bladder are snakes, crocodiles, and alligators.
• Many sea snakes are viviparous. Pit vipers are also mostly viviparous.
• The oldest living animal in any Indian zoo is the Aldabra giant tortoise.
• Rattle snake’s tail emits a frightening sound that scares away the enemy.
• The king cobra of India is the only snake in the world that builds a nest.
• The largest snake is a python; the smallest snake is a thread snake.
• The largest lizard is the Komodo dragon; the smallest lizard is two species of dwarf gecko

The longest dinosaur is Dipldocus; the smallest dinosaur is Compsognathus.

1. The heaviest dinosaur is Brontosaurus.
2. Largest living reptiles are (1) python, (2) crocodile, and (3) Komodo dragon.
3. Hemidactylus or wall lizard (gecko) is a swift runner on smooth vertical surfaces due to the presence of vacuum pads.
4. Draco is a flying lizard but it does not fly.
5. Heloderma is a poisonous lizard (Gila monster).
6. Ophiosaurus is known as “glass snake,” “blind worm,” or “slow worm,” limbless lizard.

Anguis is also known as a blind worm and is limbless. The most poisonous snake in the world is the peninsular tiger snake.

Poisonous Sea Snake: Hydrophis

• Biggest flesh eater dinosaur is Tyrannosaurus
• Homed Dinosaur: Stegosaurus
• The monitor lizard (Varanus) is the largest living lizard. Varanus is commonly called “Goye” or “monitor”; semiaquatic; slightly laterally compressed tail.
• A carapace is a hard shield-like structure present on the dorsal surface of a tortoise or turtle.
• Reptiles arose in the lower carboniferous time, from labyrinthodont amphibia.
• Phrynosoma is found in deserts; called “homed toad,” skin hygroscopic; takes water in the form of dew; exudes red blood-like stream from eyes, whenever, terrified.

Iguana is 5-6 feet long; body and tail laterally compressed; arboreal in habit; herbivorous found in tropical America.

• Sphenodon is the only living genus of Rhynchoce- phalia. It is commonly called Tuatara. It is found only in New Zealand. It is called a living fossil as it resembles with Hanaesaurus of the Jurassic age.
• The largest living carnivorous reptile is the Crocodihts.
• Thermomorpha is a group of reptiles that are considered to be the ancestors of mammals.
• Hedonic glands present in males secrete a sticky substance that hardens structures such as the spine and helps to hold the mate firmly.
• In Uromastyx, the cloaca possesses a pair of copulatory organs called hemipenes.
• Russel’s viper is the largest Indian viper.
• Hafkine Institute of Bombay is the main center where antivenom is produced.
• The limbs of the Chameleon show syndactyly (fusion of digits) as an adaptation to arboreal life to form opposable fingers to hold the twigs.

How many vertebrae do giraffes have in their neck? Most of the vertebrates, including giraffes and camel, have seven cervical (neck) vertebrae. At almost 6 m (20 ft) tall, the giraffe is the tallest of all vertebrates and its seven cervical vertebrae are greatly elongated. Exception: three-toed sloth (Bradypus) with nine cervical vertebrae and Manatee with six neck vertebrae.

Armadillos: The nine-banded armadillo (Dasypus) is one of the few mammalian species whose range is expanding. In the late 1800s, they lived only as far north as central Texas. Leprosy bacteria is cultured in the armadillos (Dasypus).

• Humans remain plantigrade at rest or during locomotion; use only their toes for running. Thus, is called sub-plantigrade.
• The color of human skin is yellow to orange due to carotene pigment in the cells of the stratum corneum and subdermal fat cells. Melanin is found in melanocytes.
• In humans, sweat glands are absent at lip borders, clitoris, glans penis, and nail beds, under the surface of the prepuce.
• Sweat or sudoriferous glands secrete sweat. Sweat comprises 95% water and 5% metabolic waste.
• Spiny anteaters, scaly ant eaters, moles, cetaceans, sirenians, and some edentates do not possess sweat glands.
• Tusks of elephants are two incisors of the upper jaw that constantly grow throughout life.
• Primates such as monkeys, man, apes, etc., acquired three-dimensional vision clues to their most evolved motor understanding of visual sensation.
• Deer, amongst vertebrates, proportionately to their body size, possess the largest eyes.

Carnassial Teeth: Special shearing teeth in carnivores for cracking bones—fourth premolar of the upper jaw and first molar of the lower jaw.

Milk-Producing Male Mammal: Spiny ant eater/ Echidna.

Monotreme: With a single aperture of cloaca for urinogenital and digestive tracts.

Largest Land Animal: Loxodonta africana (African elephant), height 3.5 m and weight 7 tonnes.

Tallest Land animal/mammal: Giraffe, up to 6 m.

• Mouse and Rat have first molar bigger than combined second and third molars.
• Stripes of no two zebras are alike.

Fastest Mammal: Acinonyxjubatus (Cheetah) (extinct from India but present in Africa). Speed up to 100 km/h.

Slowest Terrestrial Mammal: Three-toed sloth (Bradypus), Tridactylus, 100-150 m/h.

Slowest Aquatic Mammal: Sea otter, 10 km/h.

Longest Gestation Period In Mammal: 609 days/20 months in E/epbas maximus.

Shortest Gestation Period In Mammal: Opossum, 12- 13 days.

• Panthera tigris is the national animal of India (declared in 1973).
• Today marsupials are found mainly in Australia except a few marsupials such as the American opossum are found outside that continent.
• Plantigrade mammals are those whose palms and soles touch the ground when moving from one place to another, for example, bears and certain insectivores.
• Rabbit is a digitigrade because it moves on digits.

Unguligrade mammals are those whose only the tips of one or two fingers and toes remain in contact with the ground both at rest and locomotion. These are fastest fastest-running terrestrial mammals, for example, horses, deer, cows, donkeys, etc.

• Hides are prepared from the dermis of animal skin.
• Seals and whales have scanty hairs because heat insulation is done by blubber.
• The horns of rhinoceros, scales of scaly anteaters, and spines of porcupines are derivatives of hairs.
• The retina of owls contains only rods (suitable for nocturnal habit). Also, the same occurs in shrews, hedgehogs, rodents, bats, etc.
• The retina of fowls contains only cones (suitable for diurnal habit). Squirrels also have only cones.
• Whales, mice, shrews, and also some other mammals, but not rabbits and man, possess a Harderian gland like that of a frog.

The scrotum of mammals contains testes in most of the mammals; it acts as a thermostatic chamber. Testes lie outside the abdominal cavity because sperm cannot develop in body temperature.

• Thus, these become close, if the temperature falls more than 2°C or comes apart from the body if the temperature rises more than 2°C of the body temperature.
• In insectivores, Chiroptera, and Rodentia, the scrotum is formed only during breeding season. It later moves to the abdominal cavity, for example, bat, or otter.
• Insectivores. edentates, proboscidians (elephants), and cetaceans (whales) always have their testes inside the body cavity.

Biological Classification Introduction

Since the dawn of civilization, there have been many attempts to classify living organisms. Previously, it was done not using any scientific criteria, but on the basis of the need to use organisms for our own use, i.e., for food, shelter, and clothing, Aristotle was the earliest scientist who made an attempt scientifically to classify and use of characters of plants and animals for dividing them into various groups.

Systems Of Classification Of Living Organisms

There are proposed five systems of classification.

Two Kingdom Classification: Linnaeus gave this system and divided all organisms into two kingdoms, viz., Plantae and Animalia.

• Shortcomings Of This System: Tunicatcs have cellulose and branching patterns like plants. Slime molds are amoeba-like structures but like fungi in reproduction.

Three Kingdom Classification: It was proposed by E. Haeckel. He separated out all unicellular organisms into a separate kingdom Protista (fungi, protozoans, algae, bacteria, and slime molds were included in Protista). Thus, he proposed three kingdoms, viz., Protista, Plantae, and Animalia.

• The protists are believed to have evolved from prokaryotic moncrans and the precursors from which higher eukaryotic kingdoms—Plantae, Fungi, and Animalia have evolved. The protists exhibit the following features:
  1. These have a typical eukaryotic cell organization- and possess a nucleus, mitochondria, endoplasmic reticulum, Golgi bodies, and in some organisms, plastids.
  2. Locomotion takes place with the help of pseudo-podia, cilia, or flagella. The flagella or cilia have 9 + 2 internal microtubular structures.
  3. These exhibit diverse lifestyles some are photosynthetic, some are predatory or parasitic, while some are saprobes, living on decaying organic matter.

Read and Learn More NEET Biology Notes

Four Kingdom Classification: Copeland (1956) gave four kingdom classifications and included Monera in them. Copeland originally called the kingdom Monera as mychota. It was called Monera by Daugherty and Allen. Kingdom Monera includes all the prokaryotic organisms, i.e., eubacteria (including cyanobacteria, formerly known as blue-green algae) and archaebacteria.

• Actinomycetes (filamentous bacteria) are also included in this kingdom. Hence, according to Copeland, there are four kingdoms, namely, Monera, Protista, Plantae, and Animalia. The monerans are characterized by the following features:
• All moneran cells are microscopic (1 mm to a few millimeters), do not contain an organized nucleus, and are membrane-bound organelles.
• Except for a few monerans (for example, Mycoplasma), the moneran cells are surrounded by a rigid cell wall.
• Chemosynthesis, as a mode of nutrition, is found only in certain members of the kingdom Monera.
• Some monerans are autotrophs. These prepare their own food by reducing CO₂, using either light energy (photoautotrophs), or energy derived from chemical reactions (chemoautotrophs). Many monerans are heterotrophs (parasites or saprotrophs). The saprotrophs obtain their food by decomposing dead organic matter and absorbing it in solution form as their wall prevents the ingestion of complex organic material. Some of these live symbiotically with other forms of life.
• These are cosmopolitan in distribution. Their representatives are found in all kinds of habitats, which can possibly support life. Some monerans (archaebacteria) can flourish under extreme environmental conditions such as the absence of oxygen, high salt concentration, high temperature, or acidic pH.
• Many monerans are important decomposers and mineralizers. Some of them are important nitrogen-fixers.

Five Kingdom Classification: It was developed by Whittaker. The five kingdoms proposed by Whittaker are Monera, Protista, Fungi, Plantae, and Animalia. It is a phylogenetic system that was based on the following criteria:

1. Complexity Of Cell Structure: Prokaryotic vs eukaryotic organization of cells.

2. Mode Of Nutrition: Autotrophic (holophytic) or heterotrophic [absorptive (saprozoic or parasitic) or ingestive (holozoic)]. The mode of nutrition is a major criterion of classification in this system.

3. Complexity Of Body Organization: Unicellularity vs multicellularity. The five kingdoms include various organisms as mentioned below:

4. Major Ecological Role: Producers vs consumers vs decomposers

5. Cell Wall Decomposition: Cellulose vs chitin vs murine.

The Five Kingdoms Include Various Organisms As Mentioned Below:

1. Kingdom Monera includes prokaryotic, autotrophic, and heterotrophic organisms.
2. Kingdom Protista includes eukaryotic, unicellular, autotrophic, and heterotrophic organisms.
3. Kingdom Fungi include eukaryotic, multicellular, heterotrophic organisms exhibiting absorptive (assimilative) types of nutrition; and sporeproducing.
4. Kingdom Plantae or Metaphyta includes all chlorophyllous, multicellular, photosynthetic organisms (plants) that occur on land, on sea shores, in lakes as well as in streams, and on their non-green relatives. Their photoautotrophic nutrition is also termed holophytic nutrition. These include red, brown, and green algae, liverworts, mosses, ferns, and seed plants with or without flowers.
5. Kingdom Animalia includes all multicellular holozoic or phagotrophic or ingestive eukaryotes. These are also known as Metazoa and include a wide variety of animal life such as sponges; cnidarians (Hydra and jellyfishes); worms, snails, and other mollusks; arthropods; insects; fishes; amphibians; reptiles; birds; and mammals.

Six Kingdom Classification: It was given by Carl Woese. The six kingdoms are Eubacteria and Archaebacteria. Protista, Fungi, Plantae, and Animalia. He separated archaebacteria from eubacteria on the basis of major differences such as the absence of peptidoglycan in the cell walls of the former and the occurrence of branched chain lipids (a monolayer) instead of a phospholipid bilayer in the membrane. Based on the sequence of 16S ribosomal RNA genes, Woese found that the six kingdoms naturally cluster into three main categories. He called these categories as domains. These domains are Bacteria, archaea, and Eukarya. All three domains have evolved from a common ancestor, the progenitor.

Kingdom Monera

It is the kingdom of prokaryotes that includes Eubacteria, Archaebacteria, Actinomycetes, Mycoplasma, Spirochaetes, Rickettsiae, Chlamydiae, Cyanobacteria, etc.

• These are unicellular/colonial/multicellular prokaryotic organisms without nuclear membrane, nucleolus, chromatin, and histone proteins.
• The nucleoid or genophore incipient nucleus or pro-chromosome is composed of naked DNA, RNA, and non-histone proteins.
• Membrane-bound organelles are absent.
• Cyclosis is absent and ribosomes are of 70S type.
• The cell wall is made of peptidoglycan (exceptions are archaebacteria and mycoplasmas).
• Respiratory enzymes are found associated with the plasma membrane.
• Reproduction is by the asexual method.
• Cell division is the amitotic type and lacks spindle formation.

Let us discuss various monerans.

Archaebacteria: They form a primitive group of bacteria and are the oldest of the “living fossils.” Some important characteristics of archaebacteria are distinct from eubacteria and are as follows:

• The cell wall lacks muramic acid and peptidoglycan.
• The lipids contain phytanyl side groups (branched lipids). Branched-chain lipids decrease membrane fluidity and increase tolerance to extremes of heat as well as low pH.
• Ribosomal proteins are unusually acidic.

Archaebacteria Are Of The Following Types:

• Methanogens: Methanobacteria are obligate anaerobic forms of Gram-negative bacteria that produce methane gas from CO₂  or formic acid. These bacteria are found in the rumen (first part of the stomach) of cattle and in marshy areas.
• In biogas plants, they produce methane gas. The cell wall contains protein (for example, Methanospirilium, Metlumococcus) or noncellulosic polysaccharides (for example, Methanosarcina) or pseudoinurein (for example, Methanobacterium) in which Ar-acetyltalosaminuronic acid is present instead of NAM.
• Halophiles: Halophilic bacteria are Gram-negative obligate anaerobic forms associated with coccoid forms of bacteria. Their habitats are tidal pools, salt ponds, brines, salted fish, salted hides, etc. Halobacteria can grow well in culture medium containing as high as 25-35% of NaCl. In the presence of sunlight, they develop a purple pigment (bacteriorhodopsin) in the membrane to use sunlight. They trap light with the help of purple pigment and synthesize ATP, but do not use the latter for synthesizing organic food.
• Thermoacidophiles: They are aerobic from of Gram-negative bacteria found in hot sulfur springs. At a temperature of about 80°C, they oxidize sulfur to sulfuric acid. This happens in a highly acidic medium (pH = 2). Under anaerobic conditions, they reduce sulfur to hydrogen sulfide, and under aerobic conditions, they oxidize sulfur to sulfur dioxide. They are facultative anaerobes and are chemosynthetic in nature, for example, Thermoplasma and Thermoproteus.

Eubacteria

Eubacteria History: Antoni van Leeuwenhoek discovered bacteria from stored rain water and teeth scum and called them “wild animalcules.” He is known as the discoverer of the microbial world or the wonder world of microbes. He used the term “darkens.”

• Ehrenberg gave the term “bacteria.”
• Nageli placed bacteria in schizomycetes, called “fission fungi.”
• Louis Pasteur proposed the germ theory of disease. He discovered bacteria causing chicken cholera and invented the antirabies vaccine. He gave the term “microorganism.” He is known as the father of modern microbiology and sterilization techniques.
• Robert Koch developed “Koch’s postulates.”
• Joseph Lister developed the technique of aseptic cul¬ture.
• D.A. Bergey gave the classification of bacteria in the “Manual of Determinative Bacteriology.”
• Sedillot used the term microbe for animalcules.

Eubacteria Habitat: These are cosmopolitan in distribution. They are present in water, soil, air, and in plant and animal bodies.

Eubacteria Size: It ranges from 0.1-1.5 m in diameter and 2-10 m in length.

• The smallest rod-shaped bacterium Dialisterpneumosintes (0.15-0.3 m long) present in the nasopharynx of man during the early stage of influenza.
• Spirillum Laidlaw, Epulopscium fishelsoni (600 m X 80 m), and Thiomargarita rainibiensis (750 m) are among the largest unicellular bacteria.
• The filamentous bacterium Beggiatoa mirabilis is the lamest bacterium (16-45 g diameter and up to several centimeters long).

Eubacteria Shape: Cohn classified eubacteria into four types based on their shapes:

1. Coccus (pl. cocci): Spherical or nearly spherical, small, and always non-flagellated.
   • Micrococci: Occur singly, for example, Micrococcus hi tens, M. roseus.
   • Diplococci: Found in pairs, for example, Diplococcus pneumoniae.
   • Streptococci: Cells remain attached to form a chain, for example, Streptococcus lactis, Leptotricha buccal is.
   • Staphylococci: Irregular bundles of cells or grape-like clusters, for example, Staphylococcus aureus.
   • Sarcinae: Three-dimensional geometrical figures such as cubes, for example, Sarcina.
2. Bacillus (pi. bacilli): Rod-shaped/cigarette-like with rounded or blunt ends. Most common shape. Motile/non-motile. They may occur as:
   • Monobacillus: Occurs singly
   • Diplobacillus: Occurs in the group of two
   • Streptobacilli: Found in a chain, for example, Streptobacillus
   • When the cells of the chain have a much larger area of contact with each other, these are said to have formed trichomes for example, Beggiatoa.
   • If the cells are lined side by side like matchsticks and at angles to one another, the arrangement is said to be palisade-like, for example, Corynebacterium diphtheriae.
   • In many bacteria (for example, Streptomyces), cells are arranged to form unicellular long, branched filaments called hyphae.
3. Vibrio (Singular Vibrion): Bacteria with less than one complete twist or turn, and these resemble a comma (,) in appearance, for example, Vibrio cholerae.
4. Spirilla (Singular Spirillum): Coiled tonus or bacteria exhibiting twists with one or more turns giving a spiral appearance, for example. Spirillum minus.
   • Other Uncommon Shapes:
   • The stalked bacterium, for example, Caulnbacter.
   • The budding bacterium, for example, Rhoclomicrobium.
   • Pleomorphic Occurs in more than one form, for example, Rhizobium, Corynebacteriurn, Azolobacter, and Mycobacterium.

Flagella: Instead of the “9 + 2” arrangement of tubulin-containing microtubules, there is simply a single filament of a globular protein called flagellin.

1. Parts Of Flagellum
   • Basal Body: It is the most complex portion of flagellum and has four rings (L, P, S, and M) in Gram-negative and two rings (S and M) in Gram-positive bacteria.
   • Hook: It is made up of different protein subunits.
   • Filament: The longest and most obvious portion of the flagellum. Protein molecules are arranged in a spiral manner. It is 20 nm wide and 1-70 nm long and consists of eight vertical rows of flagellin.
2. Flagellar Arrangement: 

Pllus And Fimbriae: They are small outgrowths of the plasma membrane. They help in sharing conjugation.

Gram Staining Technique: It was introduced by Christian Gram in 1884. Gram-negative bacteria become colorless on treatment with declining agents due to thin cell wails and more lipids in the cell wall.

Differences Between Gram Positive And Gram Negative Bacteria

Glycocalyx: The cell envelope consists of the outermost glycocalyx, the middle ono the cell wall, and the innermost cell membrane.

• Glycocalyx protects cells and also helps in adhesion. It is represented by either a slime layer or a capsule.
• The slime layer is composed of dextrin and levan, while the capsule is made of polysaccharides and D-glutamic acid.
• The slime layer protects the cells from loss of water and nutrients.
• Capsule provides gummy and sticky characters to the cell.

Cell Wall: It is made of peptidoglycan mucin or mucopcptide.

• The Glycan portion forms the backbone of peptidoglycan which is composed of alternating units of NAM (N- acctyl muramic acid) and NAG (A-acetyl glucosamine) joined together by 1,4-linkage.
• The tetrapeptide chain is attached to NAM.
• Teichoic acids are acidic polymers consisting of a carbohydrate (for example, glucose), phosphate, and an alcohol. It performs several functions such as binding metals, acting as receptor sites for some viruses, and maintaining cells at low pH to prevent degradation of cell walls by self-produced enzymes.
• Porins function as channels for the entry and exit of hydrophilic low molecular-weight substances.
• The outer layer of the cell wall in Gram-negative bacteria contains lipopolysaccharides that act as the main surface antigen in the cell wall.

Mesosonie (chondroid; Fitz James): Particularly in Gram-positive bacteria, the plasma membrane shows infoldings into the cell. Various types of mesosomes are:

• Central Mesosome: It holds the nucleoid, and helps in the separation of nucleoid and septa formation.
• Peripheral Mesosome: Help in storing respiratory enzymes such as succinic dehydrogenase, and cytochrome oxidase.

Plasmid (Ledcrbcrg And Hayes): In addition to the normal chromosomal DNA, some extrachromosomal genetic elements are often found in bacteria. These elements are called plasmids. In fact, these are circular pieces of DNA that have extra genes. These are capable of autonomous replication in the cytoplasm of the bacterial wall. Plasmid is circular, supercoiled double-stranded naked DNA. It is also called minichromosomes. Various types of plasmids arc as follows:

• Sex-plasmid: It carries the sex fertility factor responsible for the transfer of genetic material during conjugation.
• R-plasmid: Confers resistance to antibiotics, having resistance transfer factor (RTF).
• Col-plasmid: Produces special proteins colicins (bacteriocin) to kill other bacteria.
• Degradative Plasmid: Decompose hydrocarbons in petroleum.
• Ti-plasmid And Ri-plasmid: Tumor-inducing and rhizogene plasmids, respectively. These are large plasmids with about 200 kbp.

Plasmid (Ledcrbcrg And Hayes) Respiration: Depending upon the mode of respiration and their capability to perform alternate modes of respiration, bacteria are of the following types:

• Obligate Aerobes: Can perform only aerobic respiration, for example, Bacillus subtilis.
• Obligate Anaerobes: Can perform only anaerobic respiration, for example, Clostridium botulinum.
• Facultative Aerobes: Anaerobic forms but can live in the presence of O₂, for example, Chlorobium.
• Facultative Anaerobes: Aerobic forms but can live an-aerobically also, for example, Pseudomonas.
• Aerotolerant Anaerobes: Bacteria continue to perform anaerobic respiration even in the presence of O₂, for example, lactic acid bacteria.
• Anaerotolerant Aerobes: Aerobic bacteria continue to perform aerobic respiration even in the absence of free O₂ by using O₂ of oxidized salts, for example, denitrifying bacteria.

Plasmid (Ledcrbcrg And Hayes) Reproduction:

Plasmid (Ledcrbcrg And Hayes) Reproduction By Binary Fission

• It is the common method of reproduction under favorable conditions.
• The bacterial chromosome divides (replicates) during binary fission, resulting in the formation of two “circular” chromosomes. Since at one stage, the replicating chromosome appears like the Greek letter, this mode of replication is called the theta model. This mechanism of replication was suggested by Caim (1963) and is also known as Cairn’s model.
• Bacterial population multiplies by 2n (n = number of generations)

Plasmid (Ledcrbcrg And Hayes) Reproduction By Endosporeformation

• Discovered by Cohn in hay bacteria (Bacillus subtilis).
• Endospores are thick-walled, highly dehydrated, and resistant spores formed under adverse conditions. Their wall is differentiated into 3-4 layers. The structure of the endospore is depicted.
• Endospores are, commonly formed in genera such as Bacillus and Clostridium. One endospore is formed per bacterial cell; so they are more a means of perennation than reproduction. Cortex and cytoplasm contain Ca²⁺ and an anticoagulant, dipicolinic acid, which prevents the protoplasm from coagulating at high temperatures.

Plasmid (Ledcrbcrg And Hayes) Reproduction  Genetic Recombination Or Parasexuality: Three methods are known by which genetic recombination is achieved by bacteria. These are called parasexual because they do not involve syngamy and meiosis (true sexual reproduction). In the order of their discovery, these arc transformation, conjugation, and transduction.

Plasmid (Ledcrbcrg And Hayes) Reproduction  Transformation: The donor and recipient do not come into contact. In this process, a bacterium picks up small DNA fragments of its dead relatives from the surrounding medium with the help of membrane receptors.

• The “competence” of a bacterium to pair up DNA and get transformed is present usually at the end of its active growth period. The process was discovered by Griffith. In 1928 while working with the bacteria Diplococcus (Pneumococcus) pneumoniae which causes pneumonia.

Plasmid (Ledcrbcrg And Hayes) Reproduction  Conjugation: Involves DNA transfer between cells in direct contact and larger fractions of the donor DNA may be exchanged as compared to other means of genetic recombination. The process was first described by Laderberg and Tatum (1946) in Escherichia coli. It may involve the replication and transfer of the F plasmid (fertility factor) from donor (F⁺) to recipient (F^–), thus also making the former a donor.

• Sometimes, the foreign plasmid integrates with the bacterial genome and such bacteria are termed as super male. When F is crossed with super male, the frequency of recombination is increased by 1000 times and that is why the super male is called Hfr or high frequency of recombination.

Plasmid (Ledcrbcrg And Hayes) Reproduction Transduction: A small double-stranded piece of DNA is transferred from donor to recipient by a bacteriophage. This mode of genetic recombination in bacteria was first demonstrated by Zinder and Lederberg in 1952 with Salmonella typhimurium. Following Are The Types Of Transduction:

1. Generalized Transduction: Transducing bacteriophage can transfer any gene of the donor bacterium, for example, T₄ bacteriophages.
2. Restricted (Specialized) Transduction: Transducing bacteriophages can carry only a specific region of the bacterial DNA to a recipient, for example, bacteriophages.
3. Abortive Transduction: DNA fragments from the donor bacterium is not integrated in the genome of the recipient bacterium and is lost after one or few generations.

Plasmid (Ledcrbcrg And Hayes) Reproduction Economic Importance

1. Beneficial Activities:
   • Sewage Disposal: E. coil, Clostridium, Pseudomonas, Streptococcus.
   • Free Living Nitrogen Fixers: Beijerinckia, Clostridium
   • Symbiotic Nitrogen Fixers: Rhizobium, Frankia, Xanthomonas.
   • Ammonifying Bacteria: Bacillus mycoides, B. ramosus.
   • Lactic Acid Production: Lactobacillus bulgaricus or L. delbrueckii convert ammoniated sugar solution into lactic acid.
   • Vinegar Production: Acetobacter aceti, A. schizenbachi.
   • Retting Of Fibers: Clostridium perfringens, Pseudomonas fluorescence.
   • Curing Of Leaves: Curing of tea leaves by Micrococcus candisans and tobacco leaves by Bacillus megatherium.
   • Vitamins: Riboflavin is prepared from Clostridium butyricum. Cobalamin (B12) is produced from B. megatherium.
   • Single Cell Protein: Rhodopseudomonas capsulatci, Methylophilus methylotropus (source of protein).
   • Pollution Control: Pseudomonas putida degrades petroleum wastes. Flavobacterium can decompose 2,4-D. DDT can be decomposed by Acetobacter aerogens. Ganges water contains Bdellovibrio bacteriovorus which maintains the purity of its water. Poly- P-hydroxybutyrate is used to produce biodegradable plastic.
2. Harmful Activities:
   • Spoilage Of Domestic Articles: Attack on domestic articles and resulting in their Spirochaete cytophaga and Cellulomonas.
   • Denitrification: Thiobacillus denit rificans, Pseudomonas aeruginosa, Micrococcus denitrificans.
   • Desulfunification: Desulphovibrio desulphur icons.
   • Spoilage Of Alcoholic Beverages: Acetobacter Aceti.
   • Diseases: About 90% of human diseases are bacterial.

Antibiotics Produced By Various Bacteria

Human diseases caused by various bacteria

Plant Diseases Caused By Bacteria

Cyanobacteria (BGA)

• Cyanobacteria are included into separate classes: Cyanophyceae or Myxophyceae (myxo = slime), according to phycologists.
• They are Gram-negative, oxygenic, photosynthetic monerans.
• They contain chlorophyll-a, carotene, a bit of myxo-xanthin, and phycobilin or phycobiliproteins. There are three types of phycobiliproteins: c-phycocyanin, c-phycoerythrin, and allophycocyanin.
• The cell wall is four-layered and the cell membrane lacks sterol with a 2:1 protein and phospholipid ratio.
• The lamellasome connects the nucleoid to the cell membrane.
• The reserve food material is cyanophycin protein, cynophycean starch or oc-granules, and p-granules (fat droplets).
• These are nonflagellate and movement (if it occurs) is by special gliding motion.

Sometimes, the same species, when grown under different wavelengths of light, exhibit variations in pigment composition. It is believed that by doing so, the alga is able to absorb the maximum available light for photosynthesis.

• This capacity to change color with a complementary effect toward light is known as the Gaidukov phenomenon (first given by Gaidukov) or complementary chromatic adaptation, for example, Trichodesmium erythreum causes red sea.
• Blue-green algae are the only monerans that are capable of performing oxygenic photosynthesis and in this respect are similar to the higher plants. Many of them are efficient nitrogen fixers. The existence of the processes of oxygenic photosynthesis and N₂ fixation in some organisms is surprising since N₂ fixation is an anaerobic process and the enzyme nitrogenase is inactivated by the presence of O₂ even in low concentrations.
• Usually, but not always, N₂-fixing cyanobacteria are filamentous and produce a specialized type of cell, called heterocyst, within which N₂ fixation occurs.
• The heterocysts are distinct and thick-walled cells with pale-yellow homogenous contents. These may be terminal or intercalary. Under the light microscope, a heterocyst appears to be surrounded by a thick layer two-layered wall.

The outer thick layer is persistent, made up of pectin or cellulose only: one or two pores also perforate the heterocyst wall. The wall is thickened near the pores. A prominent granule called a polar granule is present at the pore of the heterocyst.

• Through the pores of heterocysts, protoplasmic connections are established with the neighboring cells. The heterocysts lack photosystem 2 and thus do not evolve oxygen.
• Some blue-green algae such as Anabaena, and Nostoc form a thick layer on the soil surface during the rainy season. These can be used for reclaiming usar soils.
• Many species of blue-green algae belonging to genera Anabciena, Anlosira, Nostoc, Scytonema, etc., are known to be able to fix atmospheric nitrogen. Anabaena, Tolypothrix, and Aulosira play an important role in enriching (up to 20%) rice fields with nitrogen.
• Nostoc commune is used as a food called “Yuyucho” in China and Japan.
• The excessive growth of BGA in water produces water blooms.

Mycoplasma: E. Nocard and E.R. Roux (1898), French scientists, discovered a new type of organism from the pleural fluids of cattle suffering from bovine pleuro-pneumonia. This new type was pleomorphic and was called PPLO (pleuro-pneumonia-like organisms). This organism was later given the name Astero-coccus mycoides by Bon-el et al. (1910) and later the name Mycoplasma by Nowak (1929).

Mycoplasma Characters:

1. Unicellular,
2. Prokaryotic,
3. Non-motile,
4. Highly pleomorphic,
5. Filterable through bacterial filters,
6. Lack of cell wall,
7. Are resistant to antibiotics such as penicillin which acts on cell walls,
8. Are inhibited by tetracycline and similar antibiotics which act on metabolic pathways,
9. Reproduce by the form on of elementary bodies,
10. Tonn “fried egg” colonies in culture, and
11. DNA is linear, double-stranded extending almost throughout the cell.

Mycoplasmas are also called jokers of the plant kingdom owing to their ability to have varying shapes; PPLO or MLO (molicute-like organisms) or MLBs (mycoplasma-like bodies). These are bacteria without cell walls, mesosomes, and flagella, and are pleomorphic.

Mycoplasma gallisepticum (0.3 to 0.5 m) is the smallest prokaryote. They are either saprophytic or cause diseases such as pleuropneumonia in domestic animals and potato witch’s broom, aster yellows, little leaf of brinjal, etc., in plants.

Kingdom Protista

They are solitary, unicellular eukaryotic organisms. Few may be colonial.

• They are mostly aquatic organisms.
• A well-defined nucleus is present. Protists can be uni-nucleate, binucleate, or multinucleate.
• The cytoplasm contains, besides ribosomes, a variety of membrane-bound organelles. Many have centrioles also.
• Cell wall, if present, contains cellulose.
• Locomotion can occur through flagella, cilia, and pseudopodia. Ciliary mode is the fastest averaging to 2 mm/s.
• Flagella and cilia, when present, have 9 + 2 patterns of microtubular strands.
• The nutritive modes are variable: photosynthetic (holophytic), ingestive (holozoic, phagotrophic), and absorptive (saprobic, parasitic). The photosynthetic protists act as chief producers of food in the oceans and in freshwater.
• Some protistans are parasitic. Some live symbiotically as in the guts of other animals while a few act as decomposers.
• Reproduction is through asexual and sexual processes. Sexual reproduction involves meiosis and syngamy. Meiosis is zygotic in some and gametic in others.
• Reserve food can be starch, paramylum, chrysolaminarin, glycogen, and fat.

Photosynthetic Protists: Diatoms (Chrysophytes)

Salient Features Of Diatoms

• Basically unicellular and aflagellate except in the reproductive state.
• They possess beautiful colors and shapes.
• They may be marine, freshwater forms, or ones dwelling in moist terrestrial habitats.
• A transparent, siliceous, bivalved frustule covers the body. It has two valves, the upper epitheca and the lower hypotheca. The frustule is variously sculptured. It may possess bilateral symmetry (centric as in Melosira) or radial symmetry (centric as in Melosira).
• Large central sap vacuole present. Primordial utricle condition exists.
• Nutrition: holophytic or photosynthetic. Plastids contain chlorophyll-a and chlorophyll-c, carotene, and a variety of xanthophylls (diatoxanthin, etc.). The reserve food is oils and leucosin. Proteinaceous volutin granules are also present.
• Movement is brought about by mucilage propulsion.
• Diatoms synthesize about half the total organic matter synthesized in the biosphere. Oils extracted from fish are actually contributed by diatoms.
• Siliceous frustules of diatoms form diatomaceous earth diatomite or kieselguhr which is employed for a variety of purposes such as filtration, soundproofing, industrial catalysts, etc.
• They serve as sewage pollution indicators.

Reproduction In Diatoms

1. Asexual Reproduction: By binary fission, each daughter cell receives the epitheca from the parent cell because of which the size goes on reducing in successive generations. Extrusion of protoplasm may serve to restore normal cell size. Resting spores called statospores may be formed by centric diatoms.
2. Sexual Reproduction: It ranges from isogamy to oogamy. The zygote grows in size and forms a rejuvenescent cell called an auxospore.
3. The life cycle is diploidic.

Dinoflagellates – Salient Features Of Dinoflagellates

• These are basically unicellular (rarely palmelloid or filamentous), and biflagellate (rarely nonmotile) with heterokont conditions.
• They are mostly marine; some are freshwater species also.
• Cells are generally covered by a rigid coat (theca/lorica) of sculptured plates of cellulose and pectin Due to the presence of sculptured plates these are also called armored dinoflagellates.
• It is absent and replaced by pellicle/penpals in endosymbiotic dinoflagellates called zooxanthellae
• The longitudinal flagellum is narrow and smooth and lies in the longitudinal groove (sulcus).

The transverse flagellum is ribbon-like and lies in the transverse groove (cingulum/annulus/girdle):

• Both flagella are oriented at right angles to each other and produce spinning movement.
• Therefore, these protists are also called “Whirling whips ”
• Holophytic or photosynthetic (rarely holozoic).
• Pigments are chlorophyll-a, c, carotene, and xanthophylls (such as peridinin).
• A non-contractile vacuole, called a pustule, is present.
• Reserve food: carbohydrates and oil.
• Gymnodinium and Gonyanlax cause red tides.
• Gonyaulax calendula produces saxitoxin (a neurotoxin) that accumulates in marine shellfish. When these shellfish are eaten by humans, it causes paralytic shellfish poisoning (PSP) that may be fatal.
• Bioluminescent dinoflagellates: Noctiluca, Pyrodinium, Pyrocystis.
• Some dinoflagellates possess trichocysts and cnidoblasts (nematocysts).
• The nucleus in dinoflagellates is called a mesokaryon (Dodge et. al). It is large and possesses permanently condensed chromosomes that lack association with histones.
• The life cycle is haplontic (for example, Ceratium) or diplontic (for example, Noctiluca)

Reproduction In Diatoms

1. Diatoms Asexual Reproduction: Through cell division and encystment.
2. Diatoms Sexual Reproduction: It is reported in some organisms such as Ceratium. It may be isogamotts or anisogamous.

Euglenoids

• Unicellular and flagellate protists (rarely non-motile). May be in fresh waters and damp soils.
• The body of Euglena is spindle-shaped with a blunt anterior end and a pointed posterior end
• An elastic and flexible pellicle (periplast) composed primarily of elastic protein is present. The pellicle is composed of obliquely running parallel strips called myonemes (in epiplasm) underlying a delicate plasma membrane. The cell wall is absent.
• Two different flagella (heterokont) arise from blepharoplasty and arc united at their roots where the paraflagellar body occurs. The latter is photosensitive. The long flagellum is stichoncmatic (the tinsel type with a row of mastigoncmes). The other flagellum is very short. Euglenoids are also capable of wriggling movements by expansion and contraction of their body (metabolic).

• An orange-red eye spot occurs attached to the membrane of the reservoir. It comprises the pigment astaxanthin and is a photoreceptive structure.
• It can be holophytic, holozoic (Peranema), saprobic (Rhabdomonas), or mixotrophic (Euglena).
• In holophytic forms, usually elongated or discoid plastids are present. They may possess pyrenoids (proteinaceous bodies). The photosynthetic pigments constitute chlorophylls a and b, carotene, and xanthophylls.
• The food reserve is paramylum bodies which store a 1,3-glucan called paramylon, which does not stain with iodine.
• A contractile vacuole occurs just below the reservoir and evacuates its contents into the latter. It is osmoregulatory in function.

Euglenoids Asexual Reproduction: It occurs by longitudinal binary fission. The nuclear membrane and nucleolus persist during division.

Euglenoids Palmella Stage: It is reported in some euglenoids at the advent of unfavorable conditions.

Euglenoids Sexual Reproduction: Not yet reported

Consumer-Decomposer Protists

• They were formerly included amongst metazoa or fungi.
• Slime molds are included in the division of gymnomycota by mycologists. Because of their protistan nature, they are also called protistan fungi.
• They do not have chlorophyll.
• They are surrounded by the plasma membrane only (somatic parts are without cell walls). However, the spores do not always have cell walls.
• At one stage of the life cycle, they have an amoeboid structure.
• They have phagotrophic or saprotrophic nutrition.
• There are of two types:
  • Acellular slime molds (plasmodia, slime molds) and
  • Cellular slime molds (communal).

Acellular Slime Molds Salient Features

• Some Of The Common Acellular Slime Molds Are Physeuglena: structure arella and Physarum.
• Somatic bodies are free-living multinucleate, naked diploid protoplasmic masses called plasmodia.
• Acellular slime molds are holocarpic and polycentric.
• The sporangium usually contains a network of fine threads called capillitium.
• Acellular slime molds are present as slime masses on decaying leaves and lumber (disused article of timber wood for building).
• They move with the help of pseudopodia like amoebae.
• Sexual reproduction is an isogamous type.

Cellular Slime Mold Salient features

• Complete absence of flagellated cells in their life cycle.
• Presence of wall-less uninucleate myxamoebae.
• Formation of pseudoplasmodium by the aggregation of myxamoebae. The myxamoebae secrete acrasin (cAMP) and show chemotactic movements. They aggregate to form a pseudoplasmodium. These are holocarpic and monocentric. Capillitia are lacking in the sporangium.
• Presence of naked sporangia (without sporangial cover)
• Presence of cellulosic wall around spores

Cellular Slime Mold Anisogamous Sexual Reproduction: During sexual reproduction. one of the myxamoebae in the duster becomes larger by engulfing other myxamoebae. Karvogamy occurs inside the large myxamoeba. now called the macrocyst. Maerocvst later undergoes meiosis to release haploid myxamoebae.

Cellular Slime Mold Sexual Reproduction Examples: Dictyostelium. Polysphondylium

Cellular Slime Mold  Protozoan Protists: These protists have been discussed in the phylum Protozoa in the kingdom Animalia.

Kingdom Fungi

These are eukaryotic, heterotrophic, non-flowering, thalloid, mostly multicellular, decomposers, mineralizers of organic wastes, and help in the recycling of matter in the biosphere. The study of fungi is called mycology’. The term fungus was given by Gaspard Bauhin. Some important mycologists and their contributions/popularly known as

Pier Antonio Micheli: Father or founder of mycology

E.M. Fries: Father of systematic mycology

H.A de Barry: Father of modem mycology

E.J. Butler: Father of Indian mycology

K.C. Menta: Famous for studying rust disease in wheat

Bessey: Defined fungi as chlorophyll-less. nonvascular Plants

Fungi General Characters: Fungi are mostly terrestrial and occur in soil. They may be aquatic, parasitic, saprotrophic, or symbiont (Lichen and Myconhiza). Saprophytic fungi are called vegetable vultures.

On the basis of habitat, fungi are classified as coprophilous (on dung), corticolous (on bark), epixylic (on wood), xerophilous (on burnt wood), lignicolous (on lignified wood), keratinophilic (on hairs, horns).

Fungi Somatic Structure: In most of fungi, the thallus consists of a mass of fine, tubular branching thread-like structures called hyphae which are usually woven into a network called mycelium.

Mycelium Is Of The Following Types:

1. Primary Mycelium: Uninucleate, septate, for example, ascomycetes.
2. Secondary Mycelium: Dikaryotic mycelium, for example, basidiomycetes.
3. Coenocytic Mycelium: Multinucleate, aseptate, for example, oomycetes, zygomycetes.

Modifications Of Mycelium

• Prosenchyma: Loosely arranged long elongated hyphae.
• Pseudoparenchyma: Densely arranged hyphae giving a false appearance of parenchyma.
• Sclerotium: Tough and hard perennating structure formed by a compact mass of hyphae, for example, Claviceps.
• Rhizomorph: Dense mass of hyphae, running parallel. The hyphae lose their individuality; and subterranean nature; the growing tip looks like a root, for example, Agaricus.
• Appressorium: Terminal swollen structure of germ tube for penetration and attachment.
• Haustoria: Terminal swollen structure of germ tube for absorption of food.
• Snares Or Hyphal Traps: Helps in capturing nematodes in preda¬ceous fungi such as Dactylaria and Arthrobotrys.

Fungi Cellular Structure

• The cell wall is made of fungus cellulose/chitin, a polymer of TV-acetyl glucosamine (except oomycetes where cellulose occurs).
• Presence of unicistemal Golgi bodies.
• Karyochorisis type of mitosis occurs, it is mitosis with intranuclear spindle fibers formation.
• Reserve food material is glycogen and oil.
• Hyphae can be septate or aseptate. There are three types of septa in septate hyphae:
  • Complete septum,
  • Septum with simple pore (ascomycetes), and
  • Dolipore septum (basidiomycetes).

Fungi Nutrition: It is heterotrophic and absorptive.

Fungi Asexual Reproduction: It occurs by following asexual spores.

1. Zoospore: Many fungi, especially aquatic fungi, produce this type of spore. It may be uniflagellate or biflagellate. The flagella are always heterokont type, i.e., of unequal length. Example. Saprolcgnia.
2. Conidiosporcs Or Conidia: These are single-celled, double-celled, or many-celled structures borne on the sides of the hyphal structures called conidiophores. These are borne singly in chains.
3. Chlamydospores: These are usually formed during unfavorable conditions and are thick-walled, single-celled spores that are highly resistant to adverse conditions, for example, Mucor.
4. Sporangiospore: Noil-motile, multinucleate spore produced inside the sporangium, for example. Rhizopus.
5. Oidia: Non-motile, thin-walled spores develop under the condition of excess sugar. The budding condition of oidia is called the tomla stage, for example, Mucor, and Rhizopus.

Fungi Sexual Reproduction: It involves plasmogamy, karyogamy, and meiosis. As a result of sexual reproduction, sexual spores are produced. However, these are fewer in number than the asexual spores. There are several types of sexual spores:

• Ascospores: Usually, but not always, single-celled haploid spores are produced in a sac called an ascus (plural asci).
• Basidiospores: Haploid spores produced exogenously by special structures called basidia (singular basidium)
• Zygospores: Thick-walled diploid spores produced by tire fusion of entire gametangia.
• Oospores: Formed within a special female structure, the oogonium as a result of fertilization of female oospheres by male gametes.

Plasmogamy is brought about by any one of the following methods:

• Gametic Fusion Or Copulation: It may be isogamy, anisogamy, or oogamy, for example, Phytophthora.
• Gametangial Contact: Fusion of female and amoeboid male gamete by fertilization tube, for example. Albugo, Pythium.
• Gametangial Copulation: By fusion of gametangia, for example, Rhizopus, and Mucor.
• Spermatization: Fusion between spennatia and receptive hyphae, for example, Puccinia.
• Somatogamy: Fusion of somatic cells, for example, Agaricus.
  • The site of meiosis is zygospore/zygote/oospore, for example, oomycetes, or zygomycetes.
  • Site of meiosis is ascus, for example. ascomycetes.
  • Basidium, for example, basidiomycetes.

Classification Of Fungi: Humycota (true fungi) are classified into five classes:

1. Oomycetes/Phycomycetes
2. Zygomycetes
3. Ascomycetes
4. Basidiomycctcs
5. Deutcromycetes

Fungi Oomycetes/Phycomycetes

• Common Name: Algal fungi
• Mycelium: Coenocylic
• Cell Wall: Cellulosic
• Asexual Spores: Zoosporcs/conidiosporangia
• Sexual Reproduction: Gametic fusion and gametangial contact
• Sexual Spore: Oospore
• Aquatic phycomycetes are called water molds, for example, Saprolegnia, Plasmodiophora, etc.
• Saprolegnia grows on dead bodies of insects, houseflies, tadpoles, and gills of fish causing salmon disease of gills in fishes. It shows diamagnetism, i.e., the formation of two types of zoospores-primary and secondary zoospores.

Common examples of oomycetes and diseases caused by them are as follows:

• Synchytrium Endobioticum: Black wart disease of potato.
• Phytophthora Infestens: Late blight disease of potato. The great Irish famine (1845-47) was caused by this fungus.
• Albugo Candida: White rust of crucifers.
• Pythium Debaiyanum: Damping off disease (seedlings).
• Sclerospora Graminicola: Downy mildew of cereals

Fungi Zygomycetes

• Common Name: Conjugation fungi.
• Cell Wall: Chitinous
• Mycelium: Coenocytic
• Sexual Reproduction: Gametangial copulation
• Sexual Spore: Zygospore Motile stage is absent.

Life Cycle Of Rhizopus: Rhizopus grows on carbohydrate-rich medium. It is a saprophyte with an absorptive mode of nutrition.

The mycelium contains two types of vegetative hyphae, which arise from definite points called apparent nodes or holdfasts. The two types of hyphae are stoloniferous and rhizoidal in the asexual phase the mycelium produces a third type of hyphae called sporangiophore.

A dome-shaped partition or columella separates the spore-bearing part from the rest of the sporangiophore. During sexual reproduction, a fourth type of hyphae arises. They are called as zygospores.

Life Cycle Of Rhizopus Asexual Reproduction: Mycelium can multiply asexually by means of three types of mitospores: sporangiospores, chlamydospores, and oidia. Oidia formation occurs when the hyphae get submerged in sugary fermentation. Chlamydospores are produced under unfavorable conditions while sporangiospores are formed in favorable environments.

Life Cycle Of Rhizopus Sexual Reproduction: Most of the species of Rhizopus are heterothallic, but a few (for example, R. sexualis) are homothallic. The phenomenon of heterothallism was discovered by Blakeslee in R. stolonifer. Heterothallism results in greater variations and it is a device to prevent inbreeding.

• Sexual Reproduction occurs by conjugation. In heterothallic species, mycelia are morphologically similar but genetically different. They are designated as plus (+) and minus (-). The presence of both types of mycelia stimulates (through trisporic acid) each other to produce special subaerial hyphae called zy- gophores.
• The two types of zygophores come in contact and produce gametangia at the tips of club-shaped branches. The common wall between the gametangia dissolves. Their protoplasts function as gametes. They fuse to form a diploid zygote- spore. The wall of the mature zygospore is five-layered (two in exosporium and three in endosporium).

Zygomycetes: Zygospore germinates under favorable conditions. Its diploid nuclei divide meiotically to produce haploid nuclei. Only one haploid nucleus remains functional. It multiplies repeatedly to produce multinucleate conditions.

Importance Of Zygomycetes

• Ramysin antibiotic is produced by Mucor Armenians.
• The growth of Mucor arrhizus removes heavy metal contamination of water.
• Fumaric acid is obtained from R. stolonifer and citric acid is obtained from Mucor.
• Rhizopus species produces soft rot or leak disease in sweet potatoes, apple, and strawberries.
• Ahsidia corymhifera causes bronchomycosis.

Ascomycetes (Sac Fungi)

• Plant body is unicellular (for example, yeast) or mycelial (for example, Penicillium, Aspergillus).
• Mycelium is branched, septate, generally monokaryotic (for example, Penicillium) or dikaryotic (shorter phase).
• The simple septal pore is present in mycelia, which may get partially plugged by membrane-bound bodies and a crystalline structure called worn bodies.
• Asexual reproduction takes place by the formation of conidia.
• Sexual reproduction occurs by (1) gametangial contact (for example, Pyronemd), (2) conjugation (for example, yeast),
• somatization (for example, Ascoholus), (4) homogamy (for example, Peziza), or (5) autogamy.
• Each ascus lias four to eight ascospores arranged either in linear order (for example, Neurospora) or unorderly (for example, yeast).
• Asci are aggregated into fructifications called ascocarps. It is surrounded by a peridium of vegetative hyphae and internal contents collectively called centrum.

Yeast

• Unicellular with a size 3-15 m x 2-10m. Under conditions of rapid growth, they form temporary chains or pseudomycelia.
• The cell wall contains mannan, glucan, lipid, protein, and chitin.
• The cells are spherical to cylindrical in outline.
• These are facultative aerobes.
• A birth scar and a bud scar are present on opposite sides in budding yeast.
• True yeasts do not develop ascocarps.
• Yeast in which ascus formation is not reported are called false yeast, for example, Candida, Cryptococcus, Mycodernta, Geotrichum.

Types Of Yeast

1. Saccharomyces: They are budding yeast and show a diplohaplontic life cycle. There are four ascospores produced per ascus.
2. Schizosaccharomyces: They are fission yeast, and the harmonic life cycle produces eight ascospores per ascus.
3. Saccharomvcoides: They are global yeast and show a diplontic life cycle. There are four ascospores produced per ascus.

Importance Of Yeast

• Saccharomyces cerevisiae – Brewer’s/beer yeast or Baker’s yeast
• S. ellipsoids — Wine yeast
• Toru/opsis utilis and Endomyces vermalis are rich in proteins. Rhodotorula is rich in vitamin A and Ashbya gossypii is rich in vitamin.
• Yeasts are used in curing cocoa beans.

Diseases Caused By Yeast

• Candidiasis/Moniliasis: Candida albicans
• Blastomycosis: Blastomyces dermatitis
• Histoplasmosis: Histopiasma capsules
• Cryptococcosis: Cryptococcus neoformans
• Some yeasts reduce the yield of the silk industry by attacking silkworms.
• Species of Nematospora attack cotton, tomato, and beans.

Penicillium

• Facultative parasite and saprophytic fungi.
• Mycelium is branched septate with simple septal pores and each cell is uni or multinucleate depending upon the species.
• Asexual Reproduction: By conidia. Conidiophores are often branched. The ultimate branches or metulae of conidiophore possess bottle-shaped sterigmata. Each sterigmata produces a chain of conidia. The conidia in the chain are arranged in basipetal order. Each conidium is uninucleate, non-motile, two-layered, dispersed by air, and germinates to form new mycelium.
• Sexual Reproduction: It produces dikaryophase and ascocarp. The ascocarp is a cleistothecium type. Each ascus has eight ascospores. Ascospore germinates to form new mycelium.

Importance Of Penicillium

• Penicillin (the wonder drug, the first antibiotic): Flemming discovered penicillin from Penicillium notation. Nowadays, it is obtained commercially from P. chrysogenum.
• Griseofulvin and brefeldin are obtained from P. griseofulvin and P. brefeldin, respectively.
• Ripening of Camembert and Roquefort types of cheese is carried out by P. camemberti and P. roqueforti, respectively.

Some More Ascomycetes And Their Importance

• Aspergillus flavus: It produces a carcinogenic toxic called aflatoxin.
• A. oryzae: Source of diastase enzyme
• Claviceps Purpurea: Ergot of rye disease. Source of LSD (lysergic acid diethylamide)
• Erysiplte Graminicola: Powdery mildew of cereals.
• Morchella (morel): Ascocarp is edible, for example, Morchella esculent.
• Tuber (truffle): Ascocarp is edible, for example, Tuber aestivum.

Basidiomycetes (Club Fungi)

• They are decomposers of wood. They decompose cellulose and lignin. These are the most commonly seen fungi.
• Primary mycelium is monokaryotic (n) and short-lived. Secondary mycelium is bikaryotic (n + n) and long-lived.
• Septa bear dolipore except for rusts and smuts.

Clamp connections are present. They are meant for proper distribution of dikaryon at the time of cell division.

Basidiospores are four in number and are produced exogenously at the tip of sterigmata. In Agaricus bisporus, only two basidiospores are formed from each basidium.

Life Cycle Of Mushroom

• Agaricus (Psqffiota) campestris is the common field mushroom that has edible basidiocarp. The fungus is saprotrophic.
• The vegetative or assimilative part of mycelium is subterranean. It is found in moist humus-rich soil of open fields, grasslands, and piles of straw. The mycelium multiplies by fragmentation. Occasionally, oidia and chlamydospores are also formed.
• Mushrooms contain two types of mycelia, primary and secondary. Primary mycelium is short-lived. It consists of septate hyphae having monokaryotic cells or cells with a single nucleus. Sex organs do not differentiate.
• The mycelia are heterothallic, that is, there are two mating types, (+) and H. The hyphae of two matting types come in contact and show somatogamy or fusion between their cells. However, only plasmogamy occurs at this time. It gives rise to a dikaryotic cell that grows, divides, and produces a long-lived and extensive dikary¬otic or secondary mycelium.
• The hyphae of secondary mycelium show clamp connections and dolipore septa. Its cells possess two haploid nuclei (n + n) instead of the single diploid nucleus (2n) in diplophase or a single haploid nucleus (n) in haplophase.
• Under favorable conditions, hyphae of secondary mycelium collect at places and give rise to rounded or pyriform compact masses of hyphae called buttons. The buttons enlarge and produce aerial basidiocarps.

The basidiocarps of Agaricus are cream-colored to pinkish brown. In contrast, the secondary mycelium, from which mushrooms develop, is known as spawn. The basidiocarps or mushrooms often lie in rings. The latter are spoken as fairy rings.

• Each basidiocarp or mushroom consists of two parts, stipe and pileus. The stipe or stalk is fleshy. It is slightly swollen at the base. The pileus is an umbrella-like cap of the mushroom. In the button stage, the pileus is connected to the stipe, by a membrane called a veil or velum. It ruptures during the growth of pileus.
• However, its remains can be seen on the upper part of the stipe as the annulus. The pileus is circular in outline. The upper surface is more or less convex. The undersurface is flat or concave. It bears 300-600 radiating rows of vertical plates named gills (lamellae).
• The two sides of the vertically placed basidiocarp are lined by thousands of club-shaped basidia along with sterile paraphyses (singular paraphysis). The two together constitute the fertile layer or hymenium of the gill.

Hymenium is subtended by compact subhymenium. The center consists of interwoven hyphae. It is called trauma. Each basidium functions as the site for both karyogamy and meiosis.

• The two nuclei fuse to form a short-lived diploid synkaryon. The latter then divides meiotically giving rise to four haploid nuclei, two of (+) strain and two of (-) strain.
• The free end of the basidium now develops four peg-like outgrowths called sterigmata. Each sterigma forms an ovoid pinkish-purple meiospore at its tip, the same is termed as basidiospore
• A droplet is collected at the base of each basidiospore which creates tension for breaking and throwing the same. The air current carries away the discharged basidiospores. Basidiospores are of two strains, (+) and (-). After falling on a suitable substratum, each basidiospore germinates to produce monokaryotic primary mycelium.
• The fruiting bodies (basidiocarps) of Agaricus arise in concentric rings (called fairy rings/final flowers) from the mycelium present in the soil. Since the ring of underground mycelium spreads centrifugally, the diameter of the fairy ring also increases every year.

Puccinia (Puccinia Graminis Tritici)

• It causes black rust of wheat.
• Heteroecious Fungus: Completing life cycle on two host plants, i.e., primary host (wheat) and secondary host of alternate host (barberry).
• The life cycle is macrocyclic and polymorphic.
• Five types of spores are formed.
• Uredospore: Unicellular, dikaryon (n + n), on wheat
• Teleutospore: Bicelled, dikaryon (n + n), on wheat
• Basidiospore: Unicellular, monokaryotic, formed in soil.
• Pycniospore: Unicellular, monokaryotic, formed on the upper surface of barberry
• Aeciospore: Unicellular, dikaryon, formed on the lower surface at the same barberry leaf.

Some More Basidiomycetes And Their Importance

• Rust Fungi: These fungi cause rust disease.
  1. Puccinia Striformis: It causes yellow/stripe rust of wheat.
  2. Puccinia Recondita: It causes leaf/brown rust of wheat.
  3. Puccinia Hordei: It causes brown/leaf rust of barley.
  4. Puccinia Graminis-Tritici: It causes the black rust of wheat.
• Smut Fungi: These fungi cause smut diseases. Few examples are given below
  1. Ustilago Tritici: It causes loose smut of wheat.
  2. Ustilago Avenae: It causes loose smut of oat.
  3. Ustilago Jensenii: It causes covered smut of barley.
  4. Ustilago Rnaydis: It causes smut of com.
  5. Ustilago Scitaminae: It causes whip smut of sugarcane.
• Toad Stools (Poisonous Mushrooms)
  • Amanita caesarea (Caesarea’s mushroom)
  • A. phalloides (death cup): Emperor Claudius Caesar was murdered by his wife by giving extract of this fungus which stops mRNA synthesis.
  • Bracket Or Shelf Fungi: Example, Fames applant us, Polyporus, Ganoderma.
  • Puffballs: Basidiocarp sends puffs of spores on ripening, for example, Lycoperdon.
  • Stinkhorn: Example, Phallus impudicus (dead man’s finger). It gives a stinking odor and attracts flies.

Deuteromycetes (Fungi Imperfect)

• It includes all those fungi in which the sexual or perfect stage is either absent or not reported.
• Asexual reproduction commonly occurs by means of conidia.
• In any case, it is not possible for us, at present, to place these in any subdivision. Therefore, an artificial division is made.

Common Deuteromycetes And Diseases Caused By Them

Common Fungicides And Their Composition

• Bordeaux Mixture (CuSO₄ · Ca(OH)₂ – H₂O): First fungicide discovered by RMA Millardet. Commonly known as the holy water of plant pathology
• Burgandy Mixture: A mixture of CuSO₄ + Na₂CO₃ + H₂O; was discovered by mass or soda Bordeaux.
• Chestnut Mixture: Ammonium carbonate + Copper sulfate

Mycorrhiza

• It is a mutualistic symbiotic association of a fungus with the roots of a higher plant.
• Mycorrhizae can be divided into two groups: ectomycorrhiza and endomycorrhiza.
• In ectomycorrhiza, hyphae penetrate between the outermost cell layers of the host. The hyphae in intercellular space form a network called the Hartig net. Fungus partner is commonly basidiomycetes.
• In endomycorrhiza, most of the fungus is within the root and may be intercellular as well as intracellular. Fungus partners is commonly zygomycetes. In VAM (vesicular arbuscular mycorrhizae), the hyphae develop vesicles and arbuscules within the cortex of the root. VAM helps in phosphate absorption from soil.
• Fungus obtains shelter and food from roots. It helps the root in the dissolution and absorption of inorganic nutrients locked in the organic matter.

Kingdom Plantae

It includes all eukaryotic, chlorophyll-containing organisms commonly called as plants.

• The plant cells have eukaryotic structures with prominent chloroplasts, and cells are mainly made up of cellulose.
• The mode of nutrition is autotrophic but few members are partially heterotrophic such as insectivorous plants or parasites. The common examples of insectivorous plants are bladderwort and Venus fly trap, whereas a common example of a parasite is Cuscuta.
• They show distinct alternation of generation.
• Kingdom Plantae includes algae, bryophytes, pteridophytes, gymnosperms, and angiosperms.

Kingdom Animalia

It includes heterotrophic eukaryotic organisms that are multicellular.

• The cells lack cell walls.
• They directly or indirectly depend on plants for food.
• The food is atoned as a reserve in the form of glycogen or fat.
• The mode of nutrition is holozoic: by ingestion of food.
• Sexual reproduction is by copulation between males and females followed by embryological development.
• In that chapter, we shall also explain the unicellular protozoans which are placed normally in Kingdom Protista.

Virus

General Structure Of Virus A Virus Has Following Parts:

• Envelope: It has smaller subunits, known as telomeres. For example, herpes virus, HIV, etc.
• Capsid: Protein coat made up of subunits called capsomeres.
• Nucleoid: Viruses contain either DNA or RNA.

On the basis of the type of genetic material, viruses are classified as:

1. Deoxy Viruses:
   • Contain double-stranded DNA (ds DNA), for example, pox virus, and cauliflower mosaic virus.
   • Contain single-stranded DNA (ss DNA), for example, x 174.
2. Riboviruses:
   • Contain ds RNA, for example, reovirus, wound tumor virus.
   • Contain ss RNA, for example, TMV, HIV, and influenza vims.

Structure Of Some Viruses

1. Tobacco mosaic virus (TMV) is elongated rod-like, 300 (one, ISO in diameter with a molecular weight, of 39.4 x 106. 2130 capsomercs are arranged helically to form the capsid. 40 capsid tires present in three turns and 130 turns in complete virus capsid. UNA strand is helical ssRNA and consists of 6400 nucleotides. Thus, the ratio of nucleotides and capsomeres =3:1.
2. Pox virus/variola is the causal agent of smallpox. These are among the largest of animal viruses and are rectangular (brick-shaped), 300 x 230 nm in size. The genome is dumbbell-shaped with a central core of dsDNA. The core has two enzymes: RNA polymerase and ATP phosphohydrolase.
3. AIDS virus consists of ssRNA. It has two copies of ssRNA. The outer cover has five-layer, the outermost glycoprotein, followed by a double lipid layer, and the innermost has two protein layers
4. T₄ bacteriophage has a tadpole-like structure with a polyhedral head connected to a helical tail. J lic head consists of nucleic acid surrounded by a protein coat or capsid. Nucleic acid is double-stranded f)NA. The tail is proteinaceous tube-like, core surrounded by a sheath. At one end, lube is jointed to the head by a thin collar. At the other end, it has a hexagonal base plate with six small tail pins and six tail fibers which help in the attachment of the phage to the host cell.

Reproduction In Virus: Reproduction is of two main types: phagic and pinocytic.

1. Phagic Reproduction: It is further of two types:
   • Lytic Cycle: Occurs in virulent phages, for example, T4 bacteriophages.
   • Lysogenic Cycle: Occurs in temperate viruses such as phage.
2. Pinocytic Reproduction: An example, occurs in TMV.

Diseases Caused by Virus in Man

Cryptogram of Virus: The International Committee of Virus Nomenclature has given a system of naming virus. The system consists of two parts. The first part is the common name of the virus and the second part has the coded information about the virus. This is called as cryptogram.

1. Cryptogram Of TMV: R/1: 2/5: E/E: S/A
2. Cryptogram Of Pox Virus: D/2, 160/5-7.5,X/*,V/0
3. Cryptogram Of Poliovirus: R/1, 2.5/30, S/S, V/O
4. Cryptogram Of T4 Bacteriophage: D/2, 130/40, X/X, B/O

In a cryptogram,

1. The first pair represents the type of nucleic acid/number of strands in nucleic acid.
2. The second pair represents the molecular weight of nucleic acid/amount of nucleic acid expressed as a percentage.
3. The third pair denotes the shape of the virus/shape of nucleo-protein.
4. The fourth pair denotes the type of host/carrier used in the transmission of virus.

Viroids And Prions: Viroids were discovered by T.O. Diener. It has RNA without a protein coat. Viroids cause potato spindle tuber disease (PSTD), Chrysanthemum stunt, citrus exocortis, cucumber pale fruit, etc.

Prions are proteinaceous infectious particles. It causes

1. Kuru (laughing death) disease
2. Mad cow disease (C-Jakob)
3. Alzheimer’s disease in human beings
4. Scrapie disease in sheep

Lichens

They are composite organisms that are formed by a fungus partner (mycobiont) and an algal partner (phycobiont). Mycobiont is dominant forming 95-99% of total thallus and is responsible for reproduction. It belongs mostly to the ascomycete group (ascolichens, for example, Graphis, Cladonia, Parmelia, Usnea). Their fruiting body is perithecium or apothecium and is sometimes similar to basidiomycetes (basidiolichens, for example, Cora, and Corella).

• In 75% of lichens, phycobiont is mostly chlorophyceae (for example, Chlorella, Palmella, Protococcus, Trebouxia) or can be cyano-phyceae (for example, Chlorococcus, Nostoc, Scytonema, etc.).
• Lichens are called terricolous (growing in soil saxicolous (on stones/rocks), corticolous (on bark), and lignicolous (on wood).
• Soredia are the most efficient means of asexual reproduction. Soredia are composed of algal cells clasped and surrounded by fungal hyphae.
• There are three types of lichens on the basis of external morphology:
  1. Crustose Lichens: These form a thin crust closely adhered to the substratum, partly or wholly embedded into it, for example, Strigula, Graphis, Rhizocarpon.
  2. Foliose Lichens: These have flat, leaf-like, well-branched, or lobed thallus attached to the substratum usually with the help of rhizoid-like structures called rhizines, for example, Peltigcra, Parmelia.
  3. Fruticose Lichens: These are more or less bushy, usually much branched, and pendant to upright, for example, Bryonia, Usnea, Cladonia, etc.

Special Structures In The Thallus Of Lichen Are:

• Cyphellae: Help in the exchange of gases, present in lower context.
• Cephalodia: Helps to retain moisture and its algal partner fixes nitrogen also.

Breathing Pores: For aeration, present in the upper cortex of the thallus.

Economic Importance Of Lichen

• Pioneers Of Vegetation: They initiate weathering of rocks into soil particles.
• As Food And Fodder: Reindeer moss {Cladonia rangiferina) of the Arctic region is eaten by reindeer and cattle. Iceland moss (Cetraria islandica) is used as food by man in Iceland. Species of Parmelia are used as curry powder in India.
• In Cosmetics And Perfume: Some species of Evernia and Ramalina yield essential oils which are used in the manufacture of soap. Dye orchil or cudbear are obtained from the species of Roccella and Lecanora. Litmus is derived from Roccella.
• In Medicine: Lobaria pulmonaria is used for lung troubles, Usnea barbata for strengthening hair, and for uterine ailments. Xanhoria parietina is used in jaundice and Parmelia saxatilis for epilepsy. Peltigera canina is used against hydrophobia. Usnic acid is obtained from Usnea.

Indicators Of Air Pollution: Lichens are very sensitive to SO₂ and die at higher levels of SO₂.

 

Biological Classification Assertion Reasoning Questions And Answers

In the following questions, an Assertion (A) is followed by a corresponding Reason (R). Mark the correct answer.

1. If both Assertion and Reason are true and the Rea¬son is the correct explanation of the Assertion.
2. If both Assertion and Reason are true, but the Rea¬son is not the correct explanation of the Assertion.
3. If Assertion is true, but Reason is false.
4. If both Assertion and Reason are false.

Question 1.

Assertion: Cellular slime molds have the character of both plants and animals.

Reason: The reproductive phase is animal-like and the vegetative phase is plant-like.

Answer: 3. If both Assertion and Reason are false.

Question 2.

Assertion: An outer membrane is present in Rhizohlum.

Reason: The outer membrane contains lipopolysaccharides.

Answer: 2. If both Assertion and Reason are true, but the Rea¬son is not the correct explanation of the Assertion.

Question 3.

Assertion: Lichens do not grow in polluted areas having SO₂.

Reason: Lichens secrete carbonic acid and oxalic acid on barren rocks.

Answer: 2. If both Assertion and Reason are true, but the Reason is not the correct explanation of the Assertion.

Question 4.

Assertion: The secondary mycelium of Agaric us is hi nucleated.

Reason: Secondary mycelium is formed by the somatogamy of primary mycelium.

Answer: 1. If both Assertion and Reason are true and the Rea¬son is the correct explanation of the Assertion.

Question 5.

Assertion: Cyphcllae help to retain moisture in lichens.

Reason: They contain a large number of hyaline cells.

Answer: 4. If both Assertion and Reason are false.

Question 6.

Assertion: Unicellular eukaryotes are included in monera.

Reason: Unicellular eukaryotes have 70S cytoribosomes.

Answer: 4. If both Assertion and Reason are false.

Question 7.

Assertion: Lamellasomc connects nucleoid to cell membrane.

Reason: Lamellasome is present in oxyphotobacteria.

Answer: 2. If both Assertion and Reason are true, but the Reason is not the correct explanation of the Assertion.

Question 8.

Assertion: Pseudomonas fluorescense is a cephslotrichous bacteria.

Reason: It is helpful in the retting of fibers.

Answer: 2. If both Assertion and Reason are true, but the Rea¬son is not the correct explanation of the Assertion.

Question 9.

Assertion: MLO is Gram-negative, pleomorphic monerans.

Reason: They are wall-less having acetylglucosamine as-sociated with cell membrane which is rich in cholesterol.

Answer: 2. If both Assertion and Reason are true, but the Rea¬son is not the correct explanation of the Assertion.

Question 10.

Assertion: Gram-positive bacteria detect and respond to chemicals by lipopolysaccharides.

Reason: They have high amounts of porins and lipids which act as antigens.

Answer: 4. If both Assertion and Reason are false.

Question 11.

Assertion: Holophytic protistans are important phytoplankton and contribute 80% of the total photosynthesis.

Reason: They lack chemosynthetic nutrition and utilize non-sulfur organic compounds as the source of carbon assimilation.

Answer: 3. If both Assertion and Reason are false.

Question 12.

Assertion: Sexual spores in pink mold are meiospores produced endogenously.

Reason: They develop a flask-shaped fruiting body in the sexual life cycle.

Answer: 2. If both Assertion and Reason are true, but the Rea¬son is not the correct explanation of the Assertion.

Question 13.

Assertion: Azotodesmic lichens are biofertilizers enriching nitrogen contents in soil.

Reason: This ability is due to the presence of heterocystous blue-green algae as a phycobiont component.

Answer: 1. If both Assertion and Reason are true and the Rea¬son is the correct explanation of the Assertion.