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NEET Biology Notes For Major Abiotic Factors

NEET Biology Notes For Temperature

Ecologically, it is the most relevant factor as temperature variation affects the enzyme kinetics, basal metabolic activities, and physiological functions of organisms. So, thermal tolerance de- cides to a large extent the geographical distribution of different species.

NEET Biology Notes For Stenothermal

Such organisms live in areas where the temperature is uniform throughout the year. These organisms cannot tolerate temperature variation.

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NEET Biology Notes For Eurythermal

Such organisms can tolerate large changes in temperature. These organisms are classified into four temperature groups on the basis of their occurrence in different climatic zones.

• Megatherms: High temperature throughout the year as found in a tropical zone.
• Mesotherms: They are adapted to winters and high summer temperatures. These organisms live in subtropical zone.
• Microtherms: They live in temperate areas where the winter temperature is low but the summer temperature is moderate.
• Hekistotherms: These organisms are adapted to a brief period of summer below 10°C and a long snowy winter period. This condition occurs in arctic or alpine zone.

Some effects of temperature are defined as under:

• Bergman’s rule: Warm-blooded animals (birds and mammals) have a larger body size in cold climate than in hotter areas..
• Allen’s rule: Extremities (legs, ears, tail, and mouth) of warm-blooded animals become smaller in colder areas as compared to the animals of warmer areas.
• Renton’s rule: In a colder climate, birds possess narrow and acuminate wings as compared to broader wings of birds found in warmer areas.
• Jordan’s rule: As the temperature is lowered, some fishes possess a larger size with a larger number of vertebrae.

NEET Biology Notes For Thermoperiodicity

Thermoperiodicity or thermoperiodism is the response of living organisms to regular changes of temperature. It is of two types: diurnal and seasonal.

• Diurnal thermoperiodicity: It is the response of organisms to daily changes of temperature. Generally, the day-time temperature is higher while the night-time temperature is lower.
• Seasonal thermoperiodicity: It is the response of organisms to seasonal changes in temperature. Along with photoperiodicity, it controls the growth of plants.

NEET Biology Notes For Thermal Stratification in Lakes

The occurrence of different temperatures in different horizontal layers as in a forest or a deep water body is called thermal stratification. A deep-water body, such as a lake, has three temperature strata: epilimnion, metalimnion, and hypolimnion.

• Epilimnion: It is the upper stratum in the water body. Epilimnion is warmer during summer and cooler during winter.
• Metalimnion: It is a short transitional zone between epilimnion and hypolimnion. The middle part of metalimnion is called thermocline. It is the area of maximum temperature changes.
• Hypolimnion: It is the lower stratum of a water body with lesser temperature fluctuations.

class 12 organisms and population notes

NEET Biology Notes For Water

Water is an important component of protoplasm, which is a general solvent. Water is also present over more than 71% surface of the earth as oceans, lakes, rivers, ice caps, and glaciers. The seawater has a high percentage of salt content (3.5%). Water present on land is called fresh water. Its salt content is low-less than 0.5%. The salt concentration (measured as salinity in parts per thousand) is less than 5% in inland water, 30-35% in the sea, and more than 100% in some hypersaline lagoons.

The regular movement of water among various regions and components of biosphere, viz., aquatic systems, air, and land, constitutes a water cycle. Water comes over land and water bodies as precipitation or rainfall. The total global rainfall is 4.46 G. Precipitation comes from water vapors present in the air. At any time, the atmosphere contains only 0.13 G of water vapors (1 G or genogram

Animals found in coastal water are called neritic and those found in open water are termed pelagic. Pelagic organisms are plankton (if microscopic), neuston (if macroscopic and found on the surface), and nekton (if actively swimming). Organisms found at the bottom of water bodies are called benthos.

NEET Biology Notes For Light

Light has a wide range of spectrum. The electromagnetic spectrum is a complete range of oscillating waves that travel together through space at a speed of 3 x 105 km/s. At 83 km above the surface of the earth, solar radiation carries an energy equivalent to 2 cal/cm2/min. This value is called solar constant.

Shortwave radiations are cosmic rays (with a wavelength less than 10-5 nm), gamma rays (103-105 nm), X-rays (10-1–10-2 nm), and UV rays (100-400 nm).

All shortwave radiation is extremely harmful. Most of them are trapped in the ionosphere and mesosphere. UV rays are also harmful.

UV-C and half of UV-B radiations are absorbed by the ozone layer of the stratosphere. A large amount of the rest is dissipated by the particles of troposphere; only a small amount reaches the earth.

Light affects photosynthesis, growth, reproduction, movement, stratification, photoperiodism, and phenology in plants, whereas it affects migration, reproduction, development, pigmentation, locomotion, and the period of activity in animals.

NEET Biology Notes For Light Zonation Of Lakes

• Littoral zone: It is exposed to wave action and is highly productive.

• Limnetic zone: It is an open water body.
• Euphotic zone: This zone receives maximum light above the light compensation point.
• Disphotic zone: This zone receives diffused light at or below the light compensation point. It is also known as the twilight zone.
• Profundal (dark, abyssal) zone: It has no light.
• Benthic zone: It lies at the bottom of the sea.

NEET Biology Notes For Soil

Soil Composition

Soil consists of four components: two solid and two nonsolid. The solid components are mineral particles and organic matter. The nonsolid components are air and water. A fifth component of variable nature is soil organisms.

Chief characteristics of soil are studied with the help of a soil profile. The type of soil profile depends upon the climate and vegetation of the area. The smallest three-dimensional volume of the soil required to study the profile is called pedon. Most soils possess three-four horizons and a number of subhorizons. A soil horizon is a horizontal layer approximately parallel to the soil surface that possesses distinctive properties which are unlike the ones present in adjoining regions. In general, a profile consists of O, A, B, C, and R horizons.

• Weathering: It is the breaking of rocks into fine particles as present on the soil. Weathering occurs by the following methods:
  • Physical weathering: It is caused by alternate heating and cooling, alternate wetting and drying, and action of frost, snow, rain, and wind.
  • Chemical weathering: Oxidation, reduction, carbonation, and solubilization are performed to break the rock.
  • Biological weathering: It is caused by lichens, mosses, and other organisms.
• Humification: It is addition of organic matter or humus to a weathered rock. Humification is essential to starting biological activity and nutritional cycling. Humus is a dark-colored amorphous substance. It is slightly acidic and colloidal and is a reservoir of nutrients. The main functions of humus are biogeochemical cycling, preventing soil from compaction, helping in the formation of soil crumbs, and improving the aeration and water-holding capacity of the soil. It also makes the soil spongy, therefore, rendering it easy for penetration by roots.
• Eluviation and illuviation: The two processes bring about transport and deposition of materials in the soil. Eluviation is washing down of materials from the upper strata of soil and helping in enriching the different layers of soil with minerals. Illuviation is deposition of minerals in the lower strata of soil.
• Mineral matter: It consists of inorganic substances present as particles of different sizes and composition.
  • Gravel: It is made of fine pebbles with a size of 2-10 mm.
  • Sand: It consists of grains of quartz or silicon dioxide (SiO2). Size varies from 0.02-2.0 mm. Sand is chemically inert. It allows quick percolation of rain or irrigation water. Aeration is good.
  • Silt: It is formed of fine grains of quartz. The size is 0.002-0.02 mm. It is chemically inert.
  • Clay: It is made of Al, Fe, and Si. The size is less than 0.002 mm. Clay particles are chemically active and have fine interspaces that can hold abundant water, but aeration is poor.
  • Soil air: It is the air present in macropores with a size between 20 and 50 μm. A good soil should have 25% air by volume. Soil air is required for the respiration of roots and several microorganisms. Soil air is richer in CO2 and poorer in O2.
  • Soil porosity: It is the percentage of interspaces present per unit dry weight of soil. The value of soil porosity is 30% in sandy soil, 45% in loam soil, and 50% in clay soil. There are two types of soil pores: micropores and macropores. Micropores are small sized interspaces having a diameter of 20 μm or less. These hold water by capillarity. Macropores are interspaces with a size of more than 20 μm.
    Residual soils develop in situ. Transported soils are brought from other places through gravity (colluvial), running water (deposited on flood plains and called alluvial), wind (colian or acolian), and glacier (glacial soil).

Soil Types:

• Red soils: These are acidic laterite soils which are deficient in lime, magnesium, phosphorus, and potassium but rich in organic matter, iron, and aluminum. These soils support tea, coffee, rubber, cardamom, areca nut, and paddy plantation.
• Black soils: Also called black cotton soils, locally known as regular, these soils have dark brown or black color from organic matter, clay/hydrated iron, aluminum silicate, and undifferentiated B-horizon (A-C soil).
• Terai/Bhabar soils: These soils are mostly colluvial and highly productive.

Soil Texture:

There are three main types of soil textures.

• Sandy soils: These soils contain about 80% or more of sand, the remaining being silt and clay. Sandy soils are porous and loose. Their water-holding capacity is poor and there is little chemical nutrition.
• Clay soils: These are soils having 40-50% clay, the rest being silt. Sand is little. Clay soils have abundant capillary pores; therefore, their water-holding capacity is high. Inorganic nutrients are available in good quantity. However, aeration is poor.
• Loam soils: These soils contain 20% clay, 40% sand, and 40% silt. These have good mineral nutrition, aeration, and hydration. Therefore, loam soils are the best for plant growth.

Soil pH:

Soil pH determines the type of soil microorganisms, the solubility of different minerals, and the type of plants which will grow on it. In alkaline soils (pH above 7), there is reduced availability of Zn, Mn, Cu, and Fe. In acidic soils, there is an abundance of Fe, Mn, and Al but deficiency of Ca, Mg, and K. Certain soils possess excess of salts, especially of Na and Mg. These are called saline soils. Salinity increases with excessive irrigation. Another category of infertile soil is alkali soil.

NEET Biology Notes For Topography

Topography, i.e., surface configuration of an area (physical features like hills, plains, or slopes), also influences the distribution of organisms. For example, the center and edge of a pond or a stream, the top side and underside of a rock, and the north and south face of a ridge or a mountain are usually inhabited by different species of organisms,

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NEET Biology Notes For Fungi Zygomycetes

• Common Name: Conjugation fungi.
• Cell Wall: Chitinous
• Mycelium: Coenocytic
• Sexual Reproduction: Gametangial copulation
• Sexual Spore: Zygospore Motile stage is absent.

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NEET Biology Notes For 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.

1. 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.
2. 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).

NEET Biology Notes For 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.

NEET Biology Notes For 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.

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NEET Biology Notes For 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

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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

NEET Biology Notes For 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).

NEET Biology Notes For 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.

NEET Biology Notes For 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.

NEET Biology Notes For 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.

NEET Biology Notes For Fungi Asexual Reproduction

Fungi Asexual Reproduction 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.

NEET Biology Notes For Classification Of Fungi

Humycota (true fungi) are classified into five classes:

1. Oomycetes/Phycomycetes
2. Zygomycetes
3. Ascomycetes
4. Basidiomycctcs
5. Deutcromycetes

NEET Biology Notes For 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

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NEET Biology Notes For 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.

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NEET Biology Notes For 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.

NEET Biology Notes For 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.

botany notes

NEET Biology Notes For 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)

NEET Biology Notes For 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.

NEET Biology Notes For Kingdom Monera

Kingdom Monera 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.

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NEET Biology Notes For 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.

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NEET Biology Notes For 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.

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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.

NEET Biology Notes For 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

1. Cryptogram of Virus

The International Committee of Virus Nomenclature has developed a system for naming viruses. The system consists of two parts: the common name and the coded information about the virus. This is called a 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 nucleoprotein.
4. The fourth pair denotes the type of host/carrier used in the transmission of the virus.

2. 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

NEET Biology Notes PDF Free Download

NEET Biology Notes For 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.

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NEET Biology Notes For 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.

NEET Biology Notes For 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.

NEET Biology Notes For 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.