NEET Biology

Sexual Reproduction In Flowering Plants Introduction

R. Camerarius was the first to describe sexual reproduction in plants. The sexual reproductive organ in angiosperms is flower. The male sex organs are known as stamen or microsporophyll and the female sex organs are known as pistil or carpel.

Stamen Or Microsporophyll: Male Sex Organ

The fertile portion of stamen is called anther. Each anther is usually made up of two lobes connected by a connective. A typical anther consists of two lobes or four microsporangia; such an anther is called bithecous. In the members of Malvaceae, arther consists of one lobe or two micro-sporangia; such an an er is called monothecous and is bisporangiate. In Arceutho- bi, the smallest dicot parasite, anther consists of only one microsporangium (monosporangiate).

Development of Anther

A young anther consists of homogeneous mass of meristematic cells called primary sporogenous cells surrounded by anther wall. Primary sporogenous cells form microspore mother cells (2n) inside the microsporangium.

The anther wall consists of the following layers:

• Epidermis: It is single layered and protective in function.
• Endothecium: The cells of this layer have a-cellulosic fibrous bands arising from inner tangential wall which help in the dehiscence of anther. Fibrous bands are ab- sent in hydrophytes.
• Middle layer: The cells of this layer are ephemeral and are three-layered.
• Tapetum: This is the innermost layer of anther wall which surrounds the sporogenous tissue. Tapetal cells are nutritive. They are multinucleate and polyploid. The tapetum has two types of cells:
  • Secretory or glandular: These cells secrete sporopollenin, pollen kit, and compatibility proteins. The Ubisch bodies are present in these cells, which help in the ornamentation of exine, as they have a chemical called sporopollenin deposited on them.
  • Amoeboid or plasmodial or invasive: Cells undergo breakdown and entire protoplast moves in the center and nourishes microspores.

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Microsporogenesis

The formation and differentiation of microspores (pollen grains) is called microsporogenesis. In the cavity of microsporangium, the microspore mother cells divide meiotically to produce microspore tetrads or pollen tetrads.

Cytokinesis may occur either after each meiotic division (successive type) leading to the formation of isobilateral tetrad of microspores (e.g., monocots) or after both meiotic (1 and 2) divisions (simultaneous type) leading to the formation of tetrahedral tetrad of microspores (e.g., dicots). Successive type of cytokinesis is advanced type.

Tetrads are of five types: (a) tetrahedral, (b) isobilateral, (c) T-shaped, (d) linear, and (e) decussate.

 

In Aristolochia elegans, all five types of tetrads are present.

Some Exceptions to Remember

• After formation, the microspores are separated from the tetrad. But in Elodea, Drosera, and Typha, the microspores do not separate from each other. Thus, com- pound pollen grains are formed.
• In Asclepiadaceae (Calotropis) and Orchidaceae, all microspores in a sporangium adhere together in a single mass known as pollinium.
• In Calotropis, the pollinia of adjacent anthers of different stamens are attached by thread-like caudicles to a sticky disc called corpusculum. The whole structure is called translator.
• In Cyperaceae, out of four microspores formed, three are degenerate. So, ultimately one microspore mother cell (2M) produces only one microspore or pollen grain.
• Sometimes, more than four pollen grains are produced from one microspore mother cell. It is called polyspory. For example, Cuscuta reflexa.

Structure of Microspore or Pollen Grain

The cell wall of microspore (sporodern) consists of two layers. The outer layer is exine and the inner layer is intine. Exine is made up of sporopollenin and intine is pectocellulosic in nature. Sporopollenin, a fatty substance, is resistant to physical and biological decomposition. So pollen wall is preserved for long periods in fossil deposits. Pollen kit is a sticky layer found on the outside of mature pollen grains of many insect pollinated species. The material of pollen kit is contributed by the tapetal cells. It acts as an insect attractant.

Exine has proteins for enzymatic and compatibility reactions. It is two-layered:

• Ektexine: Highly sculptured and is differentiated into tectum, baculum, and foot layer
• Endexine: Not sculptured

Some weak points are present on the exine. These are called germ pores.

Pollen grains can be monocolpate (having one germ pore called germinal furrow, e.g., monocots), bicolpate (two germ pores), and tricolpate (three germ pores, e.g., dicots).

The study of pollen grains is called palynology (term given by Hyde and Williams).

Male Gametophyte

Microspore is the first cell of male gametophyte. Its germination starts in situ (in the mother place). It can be best defined as partially developed male gametophyte.

Microspore divides mitotically into large tube cell and small generative cell. At this two-celled stage (in some cases at three-celled stage), pollination takes place. Further development of male gametophyte takes place on the stigma.

Pollen grain expands by absorbing liquid from the moist surface of stigma. Stigma provides boron, sugar, amino acids, etc. The exine bursts and the intine comes out in the form of pollen tube.

Pollen grains are either monosiphonous (with one pollen tube) or polysiphonous (with more than one pollen tubes). For example, members of Cucurbitaceae and Malvaceae. Pollen tube was first observed by G. B. Amici (1824) in Portulaca.

The generative nucleus divides mitotically to form two male gametes called sperms. The male gametes are non-motile and amoeboid. They are slightly unequal in size.

The function of the pollen tube is to carry sperm. In the pollen tube, the tube nucleus enters first (it is a vestigial structure) and soon disintegrates. The growth of the pollen tube is apical and the entire cytoplasm of pollen grain is confined to the tip of the pollen tube.

Carpel Or Megasporophyll: Female Sex Organ

A carpel consists of ovary, style, and stigma. Ovary contains ovules.

Structure of Ovule or Integumented Megasporangium

Ovule is an outgrowth of placenta. Each ovule is attached to its placenta by a stalk known as funicle. The point of attachment of the funicle with the main body of the ovule is called bilum. Sometimes funicle gets fused with the body of the ovule along one side and forms a ridge known as raphe. The basal region of the ovule is known as chalaza.

 

The main body of an ovule is called nucellus (called mega- sporangium) which consists of mass of parenchymatous tissue. On the basis of the development of nucellus, ovules are of two types:

• Crassinucellate: The nucellus is well developed, e.g., polypetalae.
• Tenuinucellate: The nucellus is poorly developed, e.g., gamopetalae.

The nucellus is invested all around by one or two ring-like coverings called integuments except at the apex where a small passage is formed known as microplyle. On the basis of the number of integuments, ovules are of the following types:

• Unitegmic: These are ovules with one integument, e.g., members of gamopetalae and gymnosperms.
• Bitegmic: These are ovules with two integuments, e.g., members of polypetalae and monocots.
• Ategmic: These are ovules without integument, e.g., Santalum, Loranthus (parasites), and Viscum.

The third integument in the form of aril develops from the base of ovule or funicle in many plants, e.g., litchi and Inga dulce. In litchi and Inga dulce, aril is fleshy and edible.

Types of Ovules

• Orthotropous: The micropyle, chalaza, and funicle are in straight line. This is the most primitive type of ovule. For example, piper, polygonum, and cycas.
• Anatropous: The ovule turns at 180° angle. Thus, it is inverted ovule. Micropyle lies close to hilum or at the side of hilum. For example, it is found in 82% angiosperm families.
• Hemianatropous: The ovule turns at 90° angle upon the funicle or the body of ovule and is at right angle to the funicle. For example, Ranunculus.
• Campylotropous: The ovule is curved more or less at right angle to the funicle. The micropylar end is bent down slightly, for example, in the members of Leguminosae and Cruciferae.
• Amphitropous: The ovule as well as embryo sac is curved like horseshoe. For example, Lemna, poppy, and Alisma.
• Circinotropous: The ovule turns at more than 360° angle and, so, the funicle becomes coiled around the ovule. For example, Opuntia (Cactacea).

 

Megasporogenesis

Any cell of nucellus towards the micropylar end is differentiated from the other cells. This cell is called the megaspore mother cell (MMC). It divides meiotically to produce linear megaspore tetrad. In majority of angiosperms, the chalazal megaspore is functional and the other three megaspores degenerate.

Female Gametophyte of Embryo Sac

P. Maheshwari classified embryo sac, on the basis of number of megaspore nuclei participating in its formation, into the following:

• Monosporic embryo sac: Only one megaspore nucleus forms embryo sac. For example, Polygonum and Oenothera.
• Bisporic embryo sac: Two megaspore nuclei take part in the development of embryo sac. For example, Allium and Endymion.
• Tetrasporic embryo sac: All four megaspore nuclei take part in the development of embryo sac. For example, Adoxa, Plumbago, Drusa, Fritillaria, Penaea, Plumbagella, and Peperomia.

Development of Monosporic Embryo Sac (Polygonum Type)

The normal type of embryo sac development has been studied in Polygonum by E. A. Strasburger. Since this embryo sac develops from one megaspore, it is monosporic embryo sac. It develops from chalazal functional megaspore (fourth from micropyle). The nucleus of functional megaspore divides by three mitotic divisions to form eight nuclei.

• Three cells at the micropylar end form egg apparatus. One is egg cell (n) and two are synergids (n) or cooperative cells.
• Three cells at the chalazal end form antipodals (n) or vegetative cells of gametophyte.
• Two nuclei (one from each pole) in the center are called polar nuclei (n).

As the embryo sac matures, these polar nuclei get fused to form a secondary nucleus (2n) or definitive nucleus. An embryo sac is seven-celled and eight-nucleated structure.

Pollination

The transfer of pollen grains from the anther of a flower to the stigma of the same or different flower of the same species is called pollination. It is of two types:

• Self-pollination or autogamy: When pollen grains are transferred from the anther to the stigma of the same flower, the process is called self-pollination or autogamy.
  • Bisexuality: The flower should be bisexual or hermaphrodite. For example, Cartharanthus.
  • Homogamy: Male and female reproductive parts in a bisexual flower mature at the same time. For example, Mirabilis.
  • Cleistogamy: Sometimes bisexual flowers remain closed and never open. Such flowers are known as cleistogamous. For example, Commelina benghalensis, Viola, Oxalis, and Arachis.
  • Bud pollination: Self-pollination occurs in the bud stage before the opening of flowers. For ex- ample, Pisum, wheat, and rice.
• Cross-pollination or allogamy: When pollen grains are transferred from the anther to the stigma of the flower of another plant of the same or different species, the process is called cross-pollination or allogamy. It is of two types:
  • Geitonogamy: Pollination taking place between two flowers of the same plant (genetically self- pollination but ecologically cross-pollination)
  • Xenogamy: Pollination taking place between two flowers of different plants (genetically and ecologically cross-pollination)

Contrivances for Cross-Pollination

• Unisexuality or dicliny: It is the formation of unisexual flowers. In unisexual flowers, allogamy becomes obligatory. Unisexuality can be seen in monoecious plants, e.g., maize and Vallisneria.
• Dichogamy: In bisexual flowers, the two sexes mature at different timing. When anthers mature first, it is called protandry. For example, sunflower and cotton. When gynoecium matures first, it is called protogyny. For example, Vallisneria.
• Heterostyly: Flowers are dimorphic with regard to the length of style and, thus, facilitate cross-pollination. For example, Primula (primrose) jasminum.
• Herkogamy: It is the presence of natural and physical barrier between androecium and gynoecium. For example, Gloriosa and Salvia.
• Self-sterility or incompatibility: Due to physiological or genetic reasons, the pollen fails to germinate on its own stigma. For example, tobacco.

Agencies for Cross-Pollination

• Entomophily (pollination by insects): 80% of in- sects’ pollination occurs by bees (chief pollination). All flowers pollinated by bees are brightly colored, have a sweet smell, and produce nectar. Entomophil- ous flowers produce a small amount of pollen which has a spinous and sticky exine due to the presence of pollen kit. The stigmas of such flowers are long, rough, and sticky. Salvia is an excellent example of insect pollination, which occurs by lever or turn-pipe mechanism. Calotropis exhibits translator mechanism. Aristolochia shows pitfall or flytrap mechanism. Moth-pollinated plants are white flowered and fragrant. Pollination in orchid (Ophrys speculum) occurs by wasp (pseudocopulation mechanism). In Ficus carica, pollination occurs by an insect Blastophaga (trapdoor mechanism). Yucca is pollinated by Pronuba yuccasella (obligate relation between two).
• Anemophily (pollination by wind): It is a non-directional and wasteful process. Windpollinated flowers produce a large number of pollen grains to compensate for the wastage. Female flowers have large feathery brush like stigmas to catch the pollen grains. Anemophilous flowers are small and inconspicuous with long and versatile stamens. Pollen grains are dry and powdery and are produced in large numbers. For example, sugarcane, maize, wheat, bamboo, Pinus (winged pollen), and papaya.
• Hydrophily (pollination by water): All aquatic plants are not hydrophilous.
  Some hydrophytes are anemophilous, such as Potamogeton and Myriophyllum, or entomophilous, such as Alisma and lotus. Hydrophilous plants may be pollinated inside the water (hypohydrophily) as in Zostera and Ceratophyllum or outside the water (epihydrophily) as in Vallisneria (tape grass and ribbon weed).
• Ornithophily (pollination by birds): Flowers are brightly colored but are odorless and produce plenty of nectar and large quantities of pollen. For example, Bombax, Callistemon, Strelitzia, and Erythrina.
• Chiropterophily (pollination by bats): Bats pollinate the flowers of tropical regions. For example, Anthocephalus, Kigelia, and Adansonia.
• Malacophily (pollination by snails): For example, arum lillies, Arisaema, and Lemna.
• Ophiophily (pollination by snakes): For example, Santalum and Michelia.

Entry of Pollen Tube into Ovule

A pollen tube mostly enters into an ovule through the micropyle; it is called porogamy, as seen in most of the flowering plants. In some plants, such as Casuarina, the pollen tube enters the ovule through chalaza; it is called chalazogamy. Sometimes it enters through integuments; it is called mesogamy. For example, Cucurbita.

Double Fertilization

Pollen tube enters one of the synergids and bursts releasing two male gametes. One male gamete fuses with the egg to form dip- loid zygote. The fusion is called syngamy or generative fertili- zation. It was discovered by Strasburger.

Male gamete (n)+ Egg (n) → Zygote (2n)

The other male gamete fuses with the secondary nucleus (2n after the fusion of polar nuclei) to form primary endosperm nucleus (3n). This fusion is also called triple fusion because three nuclei take part in this. It is also known as vegetative fertilization or pseudofertilization or trophomixis.

Male gamete (n)+ Secondary nucleus (2n) → Primary endosperm nucleus (3)

Both syngamy and triple fusion are called double fertilization. As the fusion in the embryo sac occurs twice, this is called double fertilization. Triple fusion and double fertilization were discovered by S. G. Nawaschin and Guignard in Lilium and Fritillaria, respectively. Double fertilization occurs in angiosperms only. In all, five nuclei are involved in double fertilization.

Endosperm

An endosperm is a product of triple fusion and develops from the central cell of embryo sac. It is generally a triploid tis- sue. This endosperm is the nutritive tissue for the developing embryo. It is absent in families such as Orchidaceae and Podostemaceae, and trapaceae.

Nature of Endosperm

• Cells are isodiametic and polyploid.
• Starch endosperm in cereals.
• Proteinaceous endoperm (aleurone layer) in cereals.
• Oily endosperm in castor and coconut.
• Cellulosic endosperm in ivory palm (hard endosperm).
• Hemicellulosic endosperm in date palm.

Types of Endosperms

• Nuclear endosperm: Primary endosperm nucleus of the central cell divides without wall formation (free nuclear division). It is the most common type of endosperm. For example, cotton, maize, Capsella, and coconut (milk).
• Cellular endosperm: Primary endosperm nucleus divides many times and each division is followed by wall formation. For example, Petunia, Utricularia, and coconut (copra).
• Helobial endosperm: It is intermediate between nuclear and cellular types. For example, members of order Helobiales (monocot).

Embryo

The study of the development of embryo is called embryogeny.

Development of Embryo in Dicots

The normal type of dicot embryo development has been studied in shepherd’s purse (Capsella bursa-pastoris) which belongs to family Cruciferae. This is called as crucifer or onagrad type of embryo development.

The development of embryo is endoscopic. The zygot (oospore) divides into two unequal cells a larger sus- pensor cell towards micropyle and a smaller embryonal cell (or terminal cell) towards the antipodal region. The suspensor cell undergoes transverse divisions forming 6-10 celled long sus- pensor. The first cell of the suspensor (towards embryo cell) is known as hypophysis. It forms the radicle tip.

The embryonal cell divides twice vertically and once trans- versely to produce a two-tiered eight-celled embryo. The epibasal tier forms two cotyledons and a plumule while the hypobasal tier produces only hypocotyl and most of the radicle. For this, the octant embryo undergoes periclinal divisions producing protoderm, procambium, and ground meristem. It is initially globular, but with the growth of cotyledons, it becomes heart-shaped and then assumes the typical shape. For example, Capsella bursapastoris. In orchids, Orobanche, and Utricularia, the embryo does not show the distinction of plumble, cotyle- dons, and radicle.

 

Development of Embryo in Monocot

The normal type of monocot embryo development has been studied in Luzula forsteri and is called Sagittariatype.

The early developments of dicot and monocot embryos are similar up to the octant stage. Later on differentiation starts. Suspensor is single celled.

The zygote of oospore divides transversely producing a vesicular suspensor cell towards the micropylar end and an embryo cell towards the chalazal end. The embryo cell divides transversely again into a terminal and a middle cell. The terminal cell divides vertically and transversely into globular embryo. It forms a massive cotyledon and a plumule.

The growth of cotyledon pushes the plumule to one side. The remains of the second cotyledon occur in some grasses. It is called epiblast. The single cotyledon of monocots is called scutellum. It is shield-shaped and appears terminal. The middle cell gives rise to hypocotyl and radicle. It may add a few cells to the suspensor. Both radicle and plumule develop covering sheaths called coleorrhiza and coleptile, respectively.

Incompatibility

Incompatibility is the inability of certain gametes, even from genetically similar plant species, to fuse with each other. This is also called intraspecific incompatibility, self-sterility, and self- incompatibility. It involves many complex mechanisms associated with the interaction of pollen and stigmatic tissues. It is of two types:

• Sporophytic incompatibility: It is the incompatibility due to the genotype of sporophytic/stigmatic tissues.
• Gametophytic incompatibility: It is the incompatibility due to the genotype of the pollen. This may be due to the prevention of pollen germination, deorientation of pollen tube, or even failure of nuclear fusion. It is controlled by genes with multiple alleles (S-allele). A plant carries two such alleles, e.g., S₁, S₂, S₂, S₃, S₁, S₃, S₂, S₄, S₃, S₅, etc. A pollen carries only one allele. If it happens to be one of the two alleles of pistil, the pollen fails to form pollen tube.

Apomixis and Polyembryony

Apomixis is the formation of new individuals directly through asexual reproduction without involving the formation and fusion of gametes. It is of two types: (a) agamospermy and (b) vegetative propagation.

Agamospermy

In this type of asexual reproduction, the embryo is formed by a process in which normal meiosis and syngamy have been eliminated. This type of apomixis occurs within the seed.

Types of Agamospermy

• Adventitive embryony (sporophytic budding): The embryo arises from diploid sporophytic cells such as nucellus or integuments (other than egg). Examples are Citrus and Opuntia.
• Recurrent agamospermy: In this method, a diploid embryo sac is formed from MMC which has a diploid egg or oosphere. The diploid egg grows parthenogenetically into diploid embryo. Examples are apple, pear, and Allium.
  Diploid embryo sac can develop directly either from the diploid MMC (diplospory) or the diploid nucellai cell (apospory).
• Non-recurrent agamospermy: The embryo develops parthenogenetically from the haploid egg. Example is banana.

Polyembryony is the phenomenon of having more than one embryo. There may be more than one egg cell in an embryo sac or more than one embryo sac in an ovule. All the eggs may get fertilized. Synergids and antipodal cells may also form embryos. The occurrence of polyembryony due to the fertilization of more than one egg is called simple polyembryony.

The formation of extra embryos through sporophytic budding is called adventive polyembryony. Polyembryony is quite common in onion, groundnut, mango, lemon, and orange. In some of these cases, a stimulus of pollination may be required. Citrus seed has 2-40 embryos-one normal and the rest adventitive mostly nucellar.

 

Assertion-Reasoning Questions

In the following questions, a statement of Assertion (A) is followed by a statement of Reason (R).

1. If both Assertion and Reason are true and the reason is the correct explanation of the assertion, then mark (1).
2. If both Assertion and Reason are true but the reason is not the correct explanation of the assertion, then mark (2).
3. If Assertion is true but Reason is false, then mark (3).
4. If both Assertion and Reason are false, then mark (4).

Question 1. Assertion: All the pollen grains of a microsporangium are held together and form rollinium.

Reason: Pollinium is very suitable for anemophily.

Answer. 3. If Assertion is true but Reason is false, them mark (3).

Question 2. Assertion: An endosperm represents the triploid condition.

Reason: It is formed due to the fusion of triploid nuclei.

Answer. 3. If Assertion is true but Reason is false, them mark (3).

Question 3. Assertion: Allele of pollens happens to be one of the two alleles of pistil; the pollen fails to form pollen tube.

Reason: The incompatibility is due to the genotype of the pollen.

Answer. 1. If both Assertion and Reason are true and the reason is the correct explanation of the assertion, then mark (1).

Question 4. Assertion: The pollen grains of dicot are tricolpate.

Reason: It has three distinct lens shaped apertures,

Answer. 1. If both Assertion and Reason are true and the reason is the correct explanation of the assertion, then mark (1).

Question 5. Assertion: The main body of an ovule is called nucellus.

Reason: The nucellus is well-developed in polypetalac.

Answer. 2. If both Assertion and Reason are true but the reason is not the correct explanation of the assertion, then mark (2).

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.

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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.

 

Reproduction In Organisms Introduction

Every organism can live only for a certain period of time. The period from the birth to the natural death represents its life span.

Life spans of organisms are not necessarily correlated with their sizes. The sizes of crows and parrots are not very different, yet their life spans show a wide difference. Similarly, a mango tree has a much shorter life span as compared to a peepal tree. Whatever be the life span, the death of every individual organ- ism is certain, i.e., no individual is immortal, except single- celled organisms.

Reproduction is defined as a biological process in which an organism gives rise to young ones (offsprings) similar to itself. The offspring grows, matures, and, in turn, produces new off- spring. Reproduction enables the continuity of the species, generation after generation.

Based upon whether there is participation of one organism or two, reproduction is of two types: asexual and sexual. When an offspring is produced by a single parent without the involvement of gametes, the reproduction is called asexual reproduction. When two parents (opposite sex) participate in the reproductive process and also involve the fusion of male and female gametes, it is called sexual reproduction.

Vegetative Reproduction

In vegetative reproduction, new plants or individuals are produced from the vegetative parts of plants. Newly formed in- dividuals are genetically identical to the parent plant. It is common in flowering plants.

Vegetative reproduction is of two types: natural vegetative reproduction and artificial vegetative reproduction.

Natural Vegetative Reproduction

Natural vegetative reproduction takes place by the following means:

• By roots: A portion of root breaks and gives rise to new plant as seen in Dalbergia sissoo, Populus, Psidium, Murraya, Albizia, sweet potato, tapioca, yam, Dahlia, and Asparagus.
• By underground stem: A portion of underground stem bearing bud forms a new plant as seen in rhizome (e.g., banana, turmeric, ginger, Aspidium, and Adian- tum), corm (e.g., Gladiolus, Colocasia, Freesia, and Crocus), bulb (e.g., garlic, Narcissus, and onion), and tuber (e.g., potato and artichoke).

Read and Learn More NEET Biology Notes

• By creeping stem: Examples are runners (e.g., grass), stolons (e.g., strawberry, Vallisneria), and offset (e.g., Eichhornia).
• By aerial shoots: Examples are Opuntia and sugarcane.
• By leaves: Examples are walking fern (Adiantum), Bryophyllum, Begonia, Streptocarpus, and Saint- paulia.
• By bulbils: These are fleshy buds which produce new plants. Examples are Agave, Oxalis, Ananas, Di- oscorea, lily, and Chlorophytum.
• By turions: These are fleshy buds in aquatic plants. Examples are Potamogeton and Utricularia.

Artificial Vegetative Reproduction

Artificial vegetative reproduction takes place by the following ways:

• Cutting: Senseviera is propagated by leaf cuttings. Stem cutting is employed in case of rose, Duranta, and Bougainvillea. Root cuttings are used in blackberry and raspberry.
• Layering: A lower branch is bent down and a ring of the bark is removed. This part is covered by soft soil. Roots develop in 2-3 months. This branch is cut off and grown independently. It is common in lemon and grapes. It is of four types:
  • Tip layering: The tip of the current season’s shoot is bent in the sloping hole. For example, blackberry and raspberry.
  • Serpentine layering: Basal branch is pegged in the soil at several places. For example, Clematis.
  • Mound layering: Basal part of a lower branch is bent down and the tip is kept outside the soil. For example, currant and gooseberry.
  • Air layering: In air layering (gootee), a ring of bark is removed from an aerial shoot. It is covered by grafting clay (water, clay, cow dung, and hay) with small quantity of root-promoting hormone and is wrapped in polythene. After 1-3 months, roots appear and the shoot is removed to be used for planting. For example, litchi and pomegranate.
• Micropropagation: Micropropagation is the raising of new plants from a small plant tissue with the help of tissue culture technique. Tissue culture is the technique of maintaining and growing cells, tissues, etc., and their differentiation on artificial medium under aseptic conditions inside suitable containers.
• Grafting: In grafting, a new plant is developed by the association of stock and scion. Scion grows and retains all its qualities. It is useful in Citrus, mango, rose, apple, pear, Lathyrus, orange, etc.
  The shoot (scion or graft) of one plant is joined to the stump (root system or stock) of a related plant through different unions such as tongue grafting (whip or slice grafting), wedge grafting, crown grafting, and side. grafting. In crown grafting, several scions are joined to a single stock. In approach grafting, the shoots of two independently growing plants are brought together. It involves the removal of a slice of bark. A small tongue- like cut is given before joining together by grafting wax. The cut must be at least 2.5-5 cm away from the removal area of the bark. After union, the stock is cut above the graft while the scion plant is cut below the graft. In bud grafting, the scion is a bud with a small piece of bark, e.g., rose, apple, peach, etc.
  Grafting is used for quick multiplication and proper growth of better varieties with weak roots, e.g., mango, apple, pear, rubber, orange, etc.

Asexual Reproduction

In the asexual method of reproduction, a single individual (parent) is capable of producing offsprings.

Asexual reproduction is common among single-celled organisms and in plants and animals with relatively simple organizations. In protists and monerans, the organism or the parent cell divides into two to give rise to a new individual.

Members of the kingdom fungi and simple plants such as algae reproduce through special asexual reproductive structures. The most common of these structures are conidia and zoospores.

In Penicillium, the conidia are produced exogenously at the tips of conidiophores by constriction. The conidiophores may be unbranched (monoverticillate) or branched (biverticillate). The branches of conidiophores are known as metulae. Each metula bears 2-6 flask shaped structures called sterigmata (phialides). Each sterigma produces a chain of pigmented conidia. Each conidium is multinucleated. The conidia in the chain are arranged in basipetal manner.

 

In Chlamydomonas, under favorable condition, asexual re- production takes place by zoospores formation. The protoplast of cell divides to form 8-16 zoospores. They are pyramid shaped and anteriorly bifiagellate resembling the parent cell. The parent cell wall breaks and the zoospores are liberated in water. They enlarge and behave as an adult individual.

Sexual Reproduction

Sexual reproduction involves the formation and fusion of the male and female gametes, produced either by the same individual or by different individuals of opposite sex. The gametes fuse to form a zygote which develops to form a new organism. Sexual reproduction results in offsprings that are not identical to the parents or amongst themselves.

All organisms have to reach a certain stage of growth and maturity in their life, before they can reproduce sexually. This period of growth is called the juvenile phase. It is known as vegetative phase in plants.

The end of juvenile/vegetative phase, which marks the be- ginning of reproductive phase, can be seen easily in higher plants when they come to flowering.

Plants that are annual and biennial show clear-cut vegeta- tive, reproductive, and senescent phases, but in the perennial species, it is very difficult to clearly define these phases. Bam- boo species flower only once in their lifetime generally after 50-100 years. Strobilanthus kunthiana (neelakuranji) flowers once in 12 years.

Events in Sexual Reproduction

After the attainment of maturity, all sexually reproducing organisms exhibit events and processes that have remarkable fundamental similarity, even though the structures associated with sexual reproduction are indeed very different. These sequential events may be grouped into three distinct stages: (a) pre-fertilization, (b) fertilization, and (c) post-fertilization events.

• Pre-fertilization events: Two main pre-fertilization events are gametogenesis and gamete transfer.
  • Gametogenesis: It refers to the process of formation of gametes-male and female. Gametes are haploid cells. In some algae, both gametes are structurally and functionally similar. It is not possible to categorize them into male and female gametes. They are, hence, called isogametes or homogametes. However, in a majority of sexually reproducing organisms, the gametes produced are of two morphologically distinct types (hetero- gametes). In such organisms, the male gamete is called the antherozoid or sperm and the female gamete is called the egg or ovum.
    The male and female reproductive structures may be found in the same plant (bisexual) or in different plants (unisexual). In several fungi and some plants, terms such as homothallic and monoecious are used to denote bisexual condition while heterothellic and dioecious are used to describe unisexual condition.
    In flowering plants, the unisexual male flower is called staminate (bearing stamens) while the female flower is called pistillate (bearing pistils). In some flowering plants, both male and female flowers may be present on the same individual (monoecious) or on separate individuals (dioe- cious). Some examples of monoecious plants are Acalypha, cucurbits, and coconuts and those of dioecious plants are mulberry, papaya, and date palm.

 

Several organisms belonging to monera, fungi, algae, and bryophytes have haploid plant body; but organisms belonging to pteridophytes, gymnosperms, and angiosperms, and most of the animals including human beings have diploid parental body. In diploid organisms, specialized cells called meiocytes (gamete mother cell) un- dergo meiosis. At the end of meiosis, only one set of chromosomes gets incorporated into each gamete.

Sexual reproduction in Chara and Marchantia: Chara is green algae. It is oogamous. The sex or- gans are highly specialized. While some workers preferred to call the male sex organ as antheridium and the female one as oogonium, others did not fa- vor this terminology. They called the male sex or- gan as globule and the female one as nucule; this terminology is largely followed in Chara. The sex organs are borne on the adaxial face of the short lateral branch almost on each node.

The nucule occupies a higher position than the globule. While most of the species of Chara are monoecious, Catreus wallichii is dioecious. The globule matures prior to the nucule (protandrous). Each antheridium produces band-shaped, spirallycoiled biflagellate antherozoids. The oogonium contains a single egg. The egg is laiden with starch and oil globules.

In Marchantia, the archegonia are borne on spe- cial branches called archegoniophores or the fe- male receptacles. The archegonia may be stalked or sessile. The archegoniophore, or carpocepha- lum, has rows of archegonia protected by invo- lucre or perichaetium. In some plants, a perianth also protects an archegonial group. The arche- gonia are flask-shaped structures distinguishable into a long neck and globular, swollen venter.

A multicelled stalk is also present in the archegonia of mosses, but in others, it is very short. The neck is one-cell thick. It is generally made up of six vertical rows of cells but in Jungermamnniales, it is composed of four or five vertical rows only. The neck is capped by four cover cells and contains varying number of neck canal cells inside.

• • Gamete transfer: After the formation of male and female gametes, they must be physically brought together to facilitate fusion (fertilization). Exceptions are a few fungi and algae in which both types of gametes are motile. There is a need of a medium through which the male gametes move. In several simple plants such as algae, bryophytes, and pteridophytes, water is the medium through which gamete transfer takes place a large number of male gametes, however, fail to reach the female gametes. To compensate this loss of male gametes, the number of male gametes produced is several thousand times the number of female gametes produced.
    In seed plants, pollen grains are the carriers of male gametes and ovule bears the egg. Pollen grains are produced in anthers and, therefore, have to be transferred to the stigma before it can lead to fertilization.
• Fertilization events: The most important event of sexual reproduction is the fusion of gametes. This process is called syngamy. It results in the formation of a diploid zygote.
  In most aquatic organisms, such as in majority of algae and fishes as well as amphibians, syngamy occurs in the external medium (water). This type of gametic fusion is called external fertilization. In a majority of plants, such as bryophytes, pteridophytes, gymnosperms, and angiosperms, syngamy occurs inside the body of the organism. Hence, this process is called in- ternal fertilization.
• Post-fertilization events: In sexual reproduction, the events that take place after the formation of zygote are called post-fertilization events.
  The process of development of embryo from the zygote is called embryogenesis. In animals, the zygote starts developing soon after its formation. In flowering plants, after fertilization, ovary develops into fruit and ovules mature into seeds. Inside the mature seed is the progenitor of the next generation-the embryo.

 

 

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.

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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.

• The Living World Notes
• Biological Classification Notes
• Plant Kingdom Notes
• Animal Kingdom Notes
• Morphology of Flowering Plants Notes
• Anatomy of Flowering Plants Notes
• Structural Organization in Animals Notes
• Cell: The Unit of Life Notes
• Biomolecules Notes

• Cell Cycle and Cell Division Notes
• Transport in Plant Notes
• Mineral Nutrition Notes
• Photosynthesis in Higher Plants Notes
• Respiration in Plants Notes
• Plant Growth and Development Notes
• Digestion and Absorption Notes
• Breathing and Exchange of Gases Notes
• Body Fluids and Circulation Notes
• Excretory Products and Their Elimination Notes
• Locomotion and Movement Notes
• Neural Control and Coordination Notes
• Chemical Coordination and Integration Notes
• Reproduction in Organisms Notes
• Sexual Reproduction in Flowering Plants Notes
• Human Reproduction Notes
• Reproductive Health Notes
• Principles of Inheritance and Variation Notes
• Molecular Basis of Inheritance Notes
• Evolution Notes
• Human Health and Disease Notes
• Strategies For Enhancement in Food Production Notes
• Microbes in Human Welfare Notes
• Biotechnology: Principles and Processes Notes
• Biotechnology and Its Applications Notes
• Organisms and Populations Notes
• Ecosystem Notes
• Biodiversity and Conservation Notes
• Environmental Issues Notes

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.