Botany वनस्पतिशास्त्र

Quick summary

Microorganisms (microbes) are living things too small to be seen clearly without a microscope – viruses, bacteria, cyanobacteria, many algae, fungi and protozoa. This topic covers what microorganisms are, how they were discovered, how they were classified over time (two kingdoms to five kingdoms to three domains) and why they matter to botany.

Key points

• Microbiology is the study of microorganisms. Microbes are found in soil, water, air, inside plants and animals, and even in hot springs and salt pans.
• Antonie van Leeuwenhoek (1670s) first saw bacteria ("animalcules") with his simple microscope. Louis Pasteur disproved spontaneous generation and gave pasteurisation. Robert Koch proved that a specific microbe causes a specific disease (Koch's postulates).
• Two-kingdom system (Linnaeus, 1758): Plantae and Animalia. Bacteria and fungi were wrongly placed in plants.
• Three-kingdom system (Haeckel, 1866): added Protista for simple organisms.
• Five-kingdom system (R. H. Whittaker, 1969): Monera, Protista, Fungi, Plantae, Animalia. Based on cell type, body organisation, mode of nutrition and phylogeny.
• Three-domain system (Carl Woese, 1990): based on 16S rRNA sequences. Domains: Bacteria, Archaea and Eukarya.
• Archaea look like bacteria but differ in cell wall (no peptidoglycan), membrane lipids (ether-linked) and rRNA. Examples: methanogens, halophiles, thermoacidophiles.
• Mycoplasma (PPLO) are the smallest free-living cells; they have no cell wall, so they are resistant to penicillin. They cause little-leaf of brinjal.
• Actinomycetes are filamentous, Gram-positive bacteria; Streptomyces gives antibiotics such as streptomycin.
• Viruses are not cells; they are kept outside all kingdoms in Whittaker's system.

Important terms

• Prokaryote – cell without a true nucleus or membrane-bound organelles (bacteria, archaea).
• Eukaryote – cell with a true nucleus and membrane-bound organelles.
• 16S rRNA – RNA of the small ribosome subunit; used to compare and classify prokaryotes.
• Extremophile – organism living in extreme heat, salt or acidity.
• Mycoplasma – wall-less, pleomorphic prokaryote.

Key facts

5 important questions

Q1. What are archaebacteria? Give two examples.

Archaebacteria (Archaea) are prokaryotes that live in extreme habitats. Their wall lacks peptidoglycan and their membrane lipids are ether-linked. Examples: methanogens (Methanobacterium) and halophiles (Halobacterium).

Q2. What is Mycoplasma?

Mycoplasma are the smallest known free-living prokaryotes. They have no cell wall, so their shape changes (pleomorphic). They cause diseases such as little leaf of brinjal and are not affected by penicillin.

Q3. Explain Whittaker's five-kingdom classification.

• Proposed in 1969; criteria: cell type, body organisation, nutrition, reproduction, phylogeny.
• Monera – prokaryotes (bacteria, cyanobacteria).
• Protista – unicellular eukaryotes (diatoms, Euglena, protozoa).
• Fungi – heterotrophic, absorptive, chitin wall.
• Plantae – multicellular autotrophs with cellulose wall.
• Animalia – multicellular heterotrophs without cell wall.
• Merits and demerits (viruses and lichens not placed).

Q4. Describe Carl Woese's three-domain system.

• Based on 16S rRNA sequence comparison (1990).
• Domain Bacteria: true bacteria and cyanobacteria.
• Domain Archaea: methanogens, halophiles, thermoacidophiles.
• Domain Eukarya: protists, fungi, plants, animals.
• Shows archaea are closer to eukaryotes than to bacteria in some features; give the comparison table.

Q5. Write a note on the contributions of Leeuwenhoek, Pasteur and Koch.

• Leeuwenhoek: first saw microbes with a simple microscope.
• Pasteur: swan-neck flask experiment, pasteurisation, vaccines for anthrax and rabies.
• Koch: isolated causes of anthrax and tuberculosis; Koch's postulates; pure culture on solid media.

Exam tip

Learn the classification table with scientist and year, and the Bacteria–Archaea–Eukarya comparison. Short notes on Mycoplasma and Archaea are often asked.

Quick summary

Viruses are very small infectious particles that can multiply only inside a living host cell. They are made of nucleic acid (DNA or RNA) covered by a protein coat. They show both living and non-living characters, so they are called a link between living and non-living things. This topic covers their structure, types, multiplication and the diseases they cause in plants.

Key points

• The word virus means "poison" in Latin. Viruses (विषाणू) pass through bacteria-proof filters.
• D. J. Ivanowsky (1892) showed that the agent of tobacco mosaic disease passes through bacterial filters.
• M. W. Beijerinck (1898) called the infectious fluid "contagium vivum fluidum" (living infectious fluid).
• W. M. Stanley (1935) crystallised Tobacco Mosaic Virus (TMV) and received the Nobel Prize in 1946.
• A complete virus particle is called a virion. It has a nucleic acid core and a protein coat called the capsid, made of sub-units called capsomeres.
• A virus has either DNA or RNA, never both. Most plant viruses have single-stranded RNA (e.g. TMV).
• Some animal viruses (e.g. influenza, HIV) have an outer lipid envelope.
• Viruses have no cell wall, no ribosomes and no own metabolism. They are obligate intracellular parasites.
• Living characters: they multiply inside a host, have genetic material, and can mutate.
• Non-living characters: they can be crystallised, have no respiration or metabolism, and are inactive outside a host.
• Shapes: rod-shaped (TMV), spherical/polyhedral (poliovirus, adenovirus), complex/tadpole-like (T4 bacteriophage).
• Viruses that attack bacteria are called bacteriophages.

Important terms

• Virion – a complete, infective virus particle outside the host.
• Capsid – the protein coat around the nucleic acid.
• Capsomere – a protein sub-unit of the capsid.
• Bacteriophage – a virus that infects bacteria (e.g. T4 phage of Escherichia coli).
• Viroid – a small, naked circular RNA without protein coat; causes potato spindle tuber disease (discovered by T. O. Diener, 1971).
• Prion – an infectious protein particle without nucleic acid.
• Lytic cycle – virus multiplies and bursts (lyses) the host cell.
• Lysogenic cycle – viral DNA joins the host DNA (as a prophage) and is copied with it without killing the cell.

Key facts

• Common plant viral diseases: tobacco mosaic, yellow vein mosaic of bhindi (lady's finger), leaf curl of papaya and tomato, bunchy top of banana.
• Viruses spread in plants through insects (aphids, whiteflies), grafting, seeds and contact.

5 important questions

Q1. What is a virion?

A virion is a complete virus particle that can infect a host. It has a nucleic acid core (DNA or RNA) covered by a protein capsid. Some virions also have an outer envelope.

Q2. Why are viruses called a link between living and non-living?

Inside a host they multiply and mutate like living things. Outside a host they are inactive, can be crystallised and show no metabolism, like non-living matter.

Q3. Describe the structure of TMV with a labelled diagram.

• Rod-shaped, helical virus.
• Central single-stranded RNA coiled in a helix.
• Protein coat (capsid) of many identical capsomeres arranged spirally around the RNA.
• Hollow central canal along the length.
• Diagram labels: RNA strand, capsomeres, capsid, central hollow core.

Q4. Explain the lytic cycle of a bacteriophage.

1. Attachment (adsorption) of tail fibres to the bacterial cell wall.
2. Penetration: tail sheath contracts and viral DNA is injected; the empty coat stays outside.
3. Synthesis: viral DNA takes control and makes new viral DNA and proteins.
4. Assembly (maturation) of new phage particles.
5. Release: the host cell bursts (lysis) and new phages are set free.

Q5. Give the general characters of viruses.

• Ultramicroscopic; seen only with an electron microscope.
• Obligate parasites; multiply only inside living cells.
• Contain either DNA or RNA.
• No cell wall, cytoplasm or enzymes for metabolism.
• Can be crystallised; host-specific.
• Cause diseases in plants, animals and humans.

Exam tip

Always draw TMV and T4 phage with clear labels. Remember the scientists and years: Ivanowsky 1892, Beijerinck 1898, Stanley 1935.

Quick summary

Bacteria are single-celled prokaryotic organisms found almost everywhere: in soil, water, air and inside other organisms. They have no true nucleus and no membrane-bound organelles. This topic covers their discovery, shapes, cell structure, nutrition, reproduction and importance.

Key points

• Antonie van Leeuwenhoek first saw bacteria (1676) with his simple microscope. He is called the father of microbiology. Robert Koch is called the father of bacteriology.
• Bacteria (जीवाणू) are prokaryotes: DNA lies free in the cytoplasm in a region called the nucleoid.
• Shapes: coccus (spherical), bacillus (rod), spirillum (spiral), vibrio (comma-shaped).
• Cocci may occur as diplococcus (pairs), streptococcus (chains), staphylococcus (grape-like bunches).
• Cell wall is made of peptidoglycan (murein). This makes it different from the cellulose wall of plants.
• On the basis of Gram staining (Christian Gram, 1884), bacteria are Gram-positive (stain violet, thick peptidoglycan) or Gram-negative (stain pink/red, thin peptidoglycan with outer membrane).
• Ribosomes are of the 70S type.
• Many bacteria have small circular extra DNA called plasmids.
• Flagella help in movement; pili/fimbriae help in attachment and conjugation.
• Reproduction: mainly asexual by binary fission; some form endospores to survive bad conditions.
• Genetic recombination occurs by conjugation, transformation and transduction (no true sexual reproduction).

Important terms

• Nucleoid – region holding the single circular DNA.
• Plasmid – small, circular, self-replicating extra-chromosomal DNA.
• Capsule / slime layer – sticky layer outside the cell wall; gives protection.
• Mesosome – infolding of plasma membrane; thought to help in respiration and cell division.
• Endospore – thick-walled resting spore formed inside the cell.
• Conjugation – transfer of DNA from donor to recipient cell through a sex pilus.
• Transformation – uptake of free DNA from surroundings (Griffith, 1928).
• Transduction – transfer of DNA by a bacteriophage.

Key facts

• Nutrition types: autotrophic (photosynthetic, e.g. green sulphur bacteria; chemosynthetic, e.g. Nitrosomonas, Nitrobacter) and heterotrophic (saprophytic, parasitic, symbiotic).
• Useful bacteria: Rhizobium (nitrogen fixation in root nodules of legumes), Lactobacillus (curd), Streptomyces (antibiotics like streptomycin), Azotobacter (free-living nitrogen fixer).
• Harmful bacteria: Xanthomonas citri (citrus canker), Xanthomonas oryzae (bacterial blight of rice), Mycobacterium tuberculosis (TB), Vibrio cholerae (cholera).

5 important questions

Q1. Differentiate between Gram-positive and Gram-negative bacteria.

Gram-positive bacteria have a thick peptidoglycan wall and retain crystal violet, appearing purple. Gram-negative bacteria have a thin peptidoglycan layer with an outer lipid membrane and appear pink after counterstaining with safranin.

Q2. What is a plasmid?

A plasmid is a small, circular, double-stranded DNA found in bacteria outside the main chromosome. It replicates on its own and may carry genes for antibiotic resistance. Plasmids are used as vectors in genetic engineering.

Q3. Describe the ultrastructure of a bacterial cell with a labelled diagram.

• Outer capsule/slime layer, then cell wall (peptidoglycan), then plasma membrane.
• Mesosome formed by infolding of membrane.
• Cytoplasm with 70S ribosomes, food granules, plasmids.
• Nucleoid with circular DNA, no nuclear membrane.
• Flagellum and pili on surface.
• Labels: capsule, cell wall, plasma membrane, mesosome, nucleoid, ribosome, plasmid, flagellum, pili.

Q4. Explain reproduction in bacteria.

1. Binary fission: DNA replicates, cell elongates, a cross wall forms, two daughter cells result.
2. Endospore formation in bad conditions (e.g. Bacillus, Clostridium).
3. Recombination: conjugation (Lederberg and Tatum, 1946), transformation (Griffith), transduction (Zinder and Lederberg, 1952).

Q5. Give the economic importance of bacteria.

• Nitrogen fixation and soil fertility (Rhizobium, Azotobacter).
• Decomposition of dead matter; recycling of nutrients.
• Dairy (curd, cheese), vinegar, retting of fibres (jute, hemp).
• Antibiotics, vitamins, enzymes; genetic engineering (E. coli).
• Harmful: plant diseases, human diseases, food spoilage.

Exam tip

Draw a neat labelled bacterial cell. Name one example for every type of nutrition; examiners like specific names.

Quick summary

Cyanobacteria (blue-green algae) are photosynthetic prokaryotes. They were earlier studied with algae as Myxophyceae, but their cell structure is bacterial. This topic covers their general characters, cell structure, the type studies Nostoc and Oscillatoria, and their importance in nitrogen fixation and agriculture.

Key points

• Cyanobacteria are prokaryotes: no true nucleus, no chloroplast, no mitochondria; 70S ribosomes.
• They are among the oldest organisms on Earth; fossil stromatolites are about 3.5 billion years old. They made the early atmosphere rich in oxygen.
• Pigments: chlorophyll a, c-phycocyanin (blue), c-phycoerythrin (red) and carotenoids. Phycobilins sit in phycobilisomes on the thylakoids.
• Stored food: cyanophycean starch and cyanophycin granules (protein).
• Cell has an outer coloured chromoplasm and inner colourless centroplasm (with DNA).
• Cells often have a mucilage sheath; no flagella at any stage.
• Gas vacuoles help planktonic forms float.
• Heterocysts – large, thick-walled, pale cells that fix atmospheric nitrogen using nitrogenase; they lack photosystem II, so no oxygen is produced inside.
• Akinetes – thick-walled resting spores that survive bad seasons.
• Reproduction is only vegetative and asexual: fission, fragmentation, hormogonia, akinetes. No sexual reproduction.

Important terms

• Hormogonium – short piece of trichome cut off between dead or separation cells; grows into a new filament.
• Trichome – row of cells of a filament without the sheath.
• Separation disc (necridium) – dead biconcave cell that breaks a trichome into hormogonia.
• Water bloom – dense surface growth of cyanobacteria in nutrient-rich water.
• Biofertiliser – living organism that adds nutrients to soil, e.g. Anabaena, Nostoc.

Key facts

• Uses: nitrogen fixation in paddy fields (Anabaena, Nostoc, Tolypothrix); Anabaena azollae in the water fern Azolla; Spirulina as protein-rich food; reclamation of usar (alkaline) soils.
• Harmful: toxic water blooms (Microcystis), bad smell and taste in drinking water, damage to buildings.

5 important questions

Q1. What are heterocysts?

Heterocysts are large, thick-walled, pale cells found in filaments of Nostoc and Anabaena. They have polar nodules at the junction with neighbour cells and are the site of nitrogen fixation because they keep oxygen away from nitrogenase.

Q2. Why are cyanobacteria called prokaryotes?

Because they have no membrane-bound nucleus, no plastids and no mitochondria; DNA lies free in the centroplasm and ribosomes are 70S, like bacteria.

Q3. Describe the structure and reproduction of Nostoc.

• Colony of beaded, unbranched trichomes in a common gelatinous matrix.
• Cells round or barrel-shaped; heterocysts at intervals.
• Hormogonia formed by breaking at heterocysts.
• Akinetes formed in unfavourable conditions; germinate later.
• Labelled diagram: trichome, sheath, vegetative cell, heterocyst, akinete.

Q4. Give an illustrated account of Oscillatoria.

• Free-living, blue-green, unbranched trichomes; no heterocysts.
• Short disc-like cells; terminal cell convex, may have a calyptra.
• Shows oscillating (to-and-fro) movement.
• Reproduction by hormogonia formed between separation discs.

Q5. Discuss the economic importance of cyanobacteria.

• Biological nitrogen fixation in rice fields; Azolla–Anabaena biofertiliser.
• Food and supplement: Spirulina.
• Soil reclamation; pioneers on bare rock.
• Harmful blooms and toxins in ponds and reservoirs.

Exam tip

Draw Nostoc with a clear heterocyst and akinete, and Oscillatoria with separation discs – the comparison table above is a ready-made answer for "distinguish between".

Quick summary

Algae are simple, mostly aquatic, chlorophyll-bearing thalloid plants. Their body is not divided into root, stem and leaf. They range from single cells (Chlamydomonas) to large seaweeds. This topic covers general characters, Fritsch's classification, life cycles of type examples and economic importance.

Key points

• Study of algae is phycology (phycos = seaweed). Algae is called शैवाल / शेवाळ in Marathi.
• Body is a thallus; no vascular tissue.
• Found in fresh water, sea water, moist soil, tree bark; some live in symbiosis (lichens).
• Cell wall mostly of cellulose. Food stored as starch (green algae), floridean starch (red algae), laminarin and mannitol (brown algae).
• Pigments: chlorophyll a in all; others decide colour – chlorophyll b (green), fucoxanthin (brown), phycoerythrin (red).
• Sex organs are unicellular and not covered by a jacket of sterile cells.
• No embryo formation after fertilisation.
• Reproduction: vegetative (fragmentation), asexual (zoospores, aplanospores, akinetes), sexual (isogamy, anisogamy, oogamy).
• F. E. Fritsch (1935, 1945) divided algae into 11 classes in "The Structure and Reproduction of the Algae".
• Main classes: Chlorophyceae, Xanthophyceae, Bacillariophyceae, Phaeophyceae, Rhodophyceae, Myxophyceae (Cyanophyceae).

Important terms

• Thallus – plant body not divided into root, stem and leaf.
• Pyrenoid – protein body in the chloroplast around which starch is stored.
• Isogamy – fusion of similar gametes.
• Oogamy – fusion of a large non-motile egg with a small motile sperm.
• Heterocyst – thick-walled cell in blue-green algae that fixes nitrogen (e.g. Nostoc).
• Zygospore / Oospore – thick-walled zygote.

Key facts

• **Life cycle of Spirogyra: filamentous green alga with ribbon-shaped spiral chloroplasts. Sexual reproduction by conjugation** – scalariform (ladder-like, between two filaments) or lateral (between cells of the same filament). Zygospore undergoes meiosis; only one of four nuclei survives. Life cycle is haplontic.
• ***Oedogonium*:** oogamous; shows cap cells; may be macrandrous or nannandrous (dwarf males).

5 important questions

Q1. What is a pyrenoid?

A pyrenoid is a dense protein body found in the chloroplast of many algae. Starch is deposited around it. It is seen clearly in Spirogyra and Chlamydomonas.

Q2. Name the pigments of brown and red algae.

Brown algae have fucoxanthin with chlorophyll a and c. Red algae have r-phycoerythrin and phycocyanin with chlorophyll a (and d in some).

Q3. Describe the life cycle of Spirogyra.

• Haploid filament; each cell has spiral chloroplasts with pyrenoids.
• Vegetative reproduction by fragmentation.
• Scalariform conjugation: two filaments lie side by side, conjugation tubes form a ladder; contents of male cell move to female cell.
• Fusion forms diploid zygospore.
• Zygospore undergoes meiosis; 3 nuclei degenerate; one haploid germling grows.
• Diagram labels: cell wall, chloroplast, pyrenoid, nucleus, conjugation tube, zygospore.

Q4. Give the general characters and classification of algae according to Fritsch.

• Thalloid, autotrophic, mostly aquatic.
• Pigments and stored food differ by class.
• Sex organs unicellular, no jacket, no embryo.
• Fritsch: 11 classes based on pigments, stored food, flagella and reproduction (list the main six with examples).

Q5. Explain the economic importance of algae.

• Food: Ulva, Porphyra, Spirulina (protein-rich).
• Agar-agar from red algae (Gelidium, Gracilaria); alginic acid from brown algae.
• Nitrogen fixation in paddy fields by blue-green algae (Nostoc, Anabaena).
• Diatomaceous earth used in filters and polishes.
• Harmful: water blooms, poisoning of water.

Exam tip

Learn one table of classes with pigment, food and example. A labelled Spirogyra conjugation diagram is very common in exams.

Quick summary

This topic covers three advanced algae often asked as type studies: Chara (green alga, Charophyceae), Ectocarpus (brown alga, Phaeophyceae) and Polysiphonia (red alga, Rhodophyceae). For each, learn the thallus structure, reproduction and life cycle, with labelled diagrams.

Key points

• Chara (stonewort): freshwater, attached by rhizoids; main axis with nodes and internodes; whorls of branches at nodes; often coated with calcium carbonate.
• Chara has the most advanced sex organs among algae: female nucule (oogonium) above and male globule (antheridium) below, at the same node.
• Nucule has a crown of 5 corona cells and 5 spirally twisted tube cells; globule has 8 shield cells, manubria and antheridial filaments.
• Chara life cycle is haplontic; the zygote (oospore) undergoes meiosis on germination and forms a protonema.
• Ectocarpus: marine, branched filamentous brown alga with a prostrate and an erect system (heterotrichous).
• Ectocarpus bears unilocular sporangia (meiosis → haploid zoospores) and plurilocular sporangia (mitosis → diploid zoospores) on the diploid plant.
• Gametes are pear-shaped with two laterally inserted unequal flagella. Fertilisation is isogamous to physiologically anisogamous.
• Ectocarpus shows isomorphic alternation of generations (diplohaplontic).
• Polysiphonia: marine red alga; each axis has a central siphon surrounded by pericentral siphons; cells joined by pit connections.
• Polysiphonia has three free-living or attached phases: gametophyte (n), carposporophyte (2n) on the female plant, and tetrasporophyte (2n). Life cycle is triphasic (haplo-diplobiontic).

Important terms

• Nucule / globule – female and male sex organs of Chara.
• Heterotrichous – thallus with prostrate and erect parts.
• Trichogyne – receptive hair-like tip of the red algal carpogonium.
• Cystocarp – urn-shaped structure on the female Polysiphonia that holds carpospores.
• Tetraspore – one of four haploid spores formed by meiosis in a tetrasporangium.

Key facts

5 important questions

Q1. What are corona cells?

Corona cells are the five small cells that form a crown on top of the nucule (oogonium) of Chara. They are formed by the tips of the five spiral tube cells.

Q2. Distinguish between unilocular and plurilocular sporangia of Ectocarpus.

Unilocular sporangia are single-chambered; the nucleus divides by meiosis and gives haploid zoospores. Plurilocular sporangia are many-chambered; they form diploid zoospores by mitosis that repeat the sporophyte.

Q3. Describe the sex organs and fertilisation in Chara.

• Nucule: oogonium, 5 tube cells, 5 corona cells; single egg.
• Globule: 8 shield cells, manubrium, capitulum, antheridial filaments with biflagellate antherozoids.
• Antherozoids enter between corona cells; fertilisation forms oospore.
• Oospore → meiosis → protonema → new plant. Labelled diagram of a node with both organs.

Q4. Explain the life cycle of Ectocarpus.

• Diploid sporophyte with both kinds of sporangia.
• Haploid zoospores → haploid gametophytes (look the same).
• Gametes fuse → diploid zygote → sporophyte.
• Isomorphic alternation of generations; draw a cycle diagram.

Q5. Describe the triphasic life cycle of Polysiphonia.

• Haploid male and female gametophytes; spermatia and carpogonium with trichogyne.
• Fertilised carpogonium → carposporophyte inside cystocarp → diploid carpospores.
• Carpospores → diploid tetrasporophyte → tetrasporangia → meiosis → haploid tetraspores.
• Tetraspores → male and female gametophytes. Three phases: n, 2n, 2n.

Exam tip

Diagrams decide marks here: a Chara node with nucule above and globule below, Ectocarpus sporangia, and the Polysiphonia life-cycle chart. Remember "nucule up, globule down".

Quick summary

Fungi are eukaryotic, achlorophyllous, heterotrophic organisms with a body made of thread-like hyphae. They live as saprophytes, parasites or symbionts. This topic covers general characters, classification, type examples and the importance of fungi.

Key points

• Study of fungi is mycology. Fungi are called बुरशी in Marathi.
• P. A. Micheli is called the father of mycology.
• Body is a mycelium, a network of hyphae. Hyphae may be septate (with cross walls) or aseptate and coenocytic (many nuclei in common cytoplasm).
• Cell wall is made mainly of chitin (fungal cellulose in some lower forms).
• No chlorophyll; food stored as glycogen and oil, not starch.
• Nutrition: saprophytic (Rhizopus, Mucor), parasitic (Puccinia, Albugo), symbiotic (lichens, mycorrhiza).
• Parasitic fungi absorb food through special hyphal branches called haustoria.
• Asexual reproduction: sporangiospores, conidia, zoospores, oidia, chlamydospores; yeast reproduces by budding.
• Sexual reproduction has three stages: plasmogamy (fusion of cytoplasm), karyogamy (fusion of nuclei) and meiosis.
• In many fungi a dikaryotic stage (n + n) lies between plasmogamy and karyogamy.

Important terms

• Hypha – single thread of a fungal body.
• Mycelium – mass of hyphae.
• Conidia – asexual spores formed at the tip of conidiophores (e.g. Penicillium, Aspergillus).
• Ascus – sac-like structure in which ascospores (usually 8) are formed.
• Basidium – club-shaped structure bearing basidiospores (usually 4) externally.
• Mycorrhiza – association between a fungus and plant roots.
• Dikaryon – cell with two unfused nuclei of different strains.

Key facts

• Albugo candida causes white rust of crucifers (mustard).
• Puccinia graminis tritici causes black (stem) rust of wheat; it is heteroecious (wheat is the primary host, barberry the alternate host) and has five spore stages.
• Penicillium notatum – source of penicillin (Alexander Fleming, 1928).

5 important questions

Q1. What is a coenocytic mycelium?

A coenocytic mycelium has hyphae without cross walls, so many nuclei lie in one common mass of cytoplasm. Example: Rhizopus and Albugo.

Q2. Define haustoria.

Haustoria are small hyphal outgrowths of parasitic fungi that enter host cells and absorb food. Example: Albugo.

Q3. Describe the life cycle of Rhizopus (bread mould).

• Mycelium of aseptate hyphae: stolons, rhizoids and sporangiophores.
• Asexual: sporangia on sporangiophores; columella inside; sporangiospores spread by air.
• Sexual: conjugation between + and – strains (heterothallic); progametangia → gametangia fuse → zygospore.
• Zygospore germinates after meiosis to form a germ sporangium.
• Labels: stolon, rhizoids, sporangiophore, sporangium, columella, spores, zygospore.

Q4. Give the life cycle of Puccinia graminis tritici.

• On wheat: uredospores (red rust stage, repeat infection) then teleutospores (black rust stage).
• Teleutospore germinates to form basidium and four basidiospores.
• Basidiospores infect barberry leaf: pycnidia (spermogonia) on upper side and aecidia (cluster cups) on lower side.
• Aecidiospores carried back to wheat.
• Thus five spore types: uredospore, teleutospore, basidiospore, pycniospore, aecidiospore.

Q5. Discuss the economic importance of fungi.

• Food: mushrooms (Agaricus), yeast in bread and alcohol.
• Medicines: penicillin, griseofulvin; ergot alkaloids.
• Enzymes and organic acids (citric acid from Aspergillus niger).
• Decomposers; mycorrhiza helps plants absorb phosphorus.
• Harmful: plant diseases (rusts, smuts, wilts), food spoilage, aflatoxins, ringworm.

Exam tip

Remember the three stages of sexual reproduction (plasmogamy, karyogamy, meiosis). For Puccinia, write the spore stage on each host in a neat table.

Quick summary

This topic covers three fungi that are common type studies: Albugo (white rust, an oomycete), Penicillium (green/blue mould, an ascomycete) and Agaricus (mushroom, a basidiomycete). Learn their mycelium, asexual and sexual reproduction, life cycle and importance, with labelled diagrams.

Key points

• Albugo candida is an obligate parasite causing white rust of crucifers (mustard, radish, cabbage). White blister-like pustules appear on leaves and stems.
• Albugo mycelium is coenocytic (aseptate, many nuclei) and intercellular; it absorbs food through small knob-like haustoria.
• Asexual: sporangiophores below the host epidermis cut off chains of sporangia (basipetal); sporangia release biflagellate zoospores in water.
• Sexual: oogamous – antheridium and oogonium; fertilisation tube; thick-walled oospore.
• Penicillium: saprophyte on bread, fruits and leather; mycelium septate, branched.
• Asexual by conidia borne on a brush-like penicillus – conidiophore → metulae → phialides (sterigmata) → chains of conidia.
• Sexual stage (rare): ascogonium and antheridium; asci with 8 ascospores inside a closed cleistothecium.
• Penicillium notatum gave penicillin (Alexander Fleming, 1928). Others make cheese (P. roquefortii, P. camemberti).
• Agaricus (button mushroom, A. bisporus): saprophyte on humus and dung. Underground mycelium forms an above-ground basidiocarp (fruit body) with stipe, pileus, gills and annulus.
• Gills carry the hymenium with basidia; each basidium bears 4 (2 in A. bisporus) basidiospores on sterigmata. Mycelium passes through primary (n), secondary (dikaryotic, n + n) and tertiary stages.

Important terms

• Haustorium – absorbing branch of a parasitic hypha inside a host cell.
• Coenocytic – hypha without cross walls, with many nuclei.
• Conidium – non-motile asexual spore cut off at the tip of a hypha.
• Cleistothecium – closed ascocarp without an opening.
• Dikaryon – cell with two genetically different nuclei (n + n).
• Clamp connection – hook-like bridge that keeps dikaryotic cells paired in basidiomycetes.

Key facts

5 important questions

Q1. What is a penicillus?

A penicillus is the brush-like conidial apparatus of Penicillium. A conidiophore branches into metulae, which bear flask-shaped phialides; each phialide cuts off a chain of conidia.

Q2. Name the disease caused by Albugo and give one symptom.

Albugo candida causes white rust of crucifers. Shiny white pustules form on leaves and stems; infected flower parts become swollen and deformed.

Q3. Describe the asexual and sexual reproduction of Albugo.

• Club-shaped sporangiophores under the epidermis; basipetal chains of sporangia; epidermis bursts.
• Sporangia germinate in water to give biflagellate zoospores, which infect new plants.
• Sexual: oogonium with periplasm and ooplasm, antheridium; fertilisation tube; thick-walled oospore with warty exine.
• Oospore germinates to release zoospores. Diagrams: T.S. of infected leaf, oogonium.

Q4. Give an account of the structure of the basidiocarp of Agaricus.

• Stipe, pileus, annulus (remains of veil); gills on the underside.
• T.S. of gill: trama, sub-hymenium, hymenium with basidia and paraphyses.
• Basidium: karyogamy then meiosis → four basidiospores on sterigmata.
• Labelled diagrams of the fruit body and gill section.

Q5. Discuss the economic importance of Penicillium.

• Penicillin from P. notatum and P. chrysogenum.
• Cheese ripening (Roquefort, Camembert).
• Griseofulvin and organic acids.
• Harmful: spoilage of fruits (blue/green mould of citrus), bread and leather.

Exam tip

A three-column comparison like the table above is useful for "distinguish" questions. Always draw the penicillus and the gill T.S. neatly – they are very common diagram questions.

Quick summary

Fungi often live in close partnership with other organisms. The most important example is mycorrhiza – a mutually useful association between a fungus and the roots of a higher plant. This topic covers types of mycorrhiza, how each partner benefits, other fungal associations (lichens, endophytes, fungi with insects) and their use as biofertilisers.

Key points

• The term mycorrhiza ("fungus-root") was coined by A. B. Frank in 1885. More than 80% of land plants form mycorrhiza.
• It is symbiosis (mutualism): the plant gives sugars to the fungus; the fungus gives water and minerals, especially phosphorus, to the plant.
• Ectomycorrhiza: fungus forms a thick mantle around the root tip and a Hartig net between cortical cells; it does not enter the cells. Seen in pine, oak, eucalyptus. Fungi are mostly basidiomycetes.
• Ectomycorrhizal roots are short, swollen and branched, with no root hairs.
• Endomycorrhiza: hyphae enter the cortical cells. The main type is arbuscular mycorrhiza (AM), earlier called VAM, formed by fungi of Glomeromycota (e.g. Glomus).
• AM fungi form arbuscules (tree-like branches inside cells, site of exchange) and vesicles (storage sacs). Found in most crops – wheat, maize, legumes.
• Special endomycorrhiza: orchid mycorrhiza (fungus feeds the tiny orchid seedling) and ericoid mycorrhiza.
• Ectendomycorrhiza shows both a mantle and cell penetration.
• Benefits to plants: better uptake of P, Zn, Cu and water; drought tolerance; protection from root pathogens; better soil structure.
• Other associations: lichens (fungus + alga), endophytes living inside leaves and stems, fungus-growing ants and termites.

Important terms

• Mantle – sheath of fungal hyphae around an ectomycorrhizal root.
• Hartig net – network of hyphae between cortical cells.
• Arbuscule – finely branched fungal structure inside a root cell.
• Vesicle – swollen lipid-filled storage structure of AM fungi.
• Biofertiliser – living microbes used to improve plant nutrition.

Key facts

5 important questions

Q1. Define mycorrhiza.

Mycorrhiza is a mutually beneficial association between a fungus and the roots of a higher plant. The fungus absorbs minerals and water for the plant and receives carbohydrates in return.

Q2. What are arbuscules?

Arbuscules are tree-like, much-branched hyphae formed inside cortical cells by AM fungi. They are the main site of exchange of nutrients between fungus and plant.

Q3. Distinguish between ectomycorrhiza and endomycorrhiza.

Use the table: hyphae inside or outside cells, mantle, Hartig net, arbuscules and vesicles, fungal groups, host examples. Add a labelled diagram of each.

Q4. Explain the role of mycorrhiza in agriculture and forestry.

• Phosphorus uptake from poor soils; less fertiliser needed.
• Drought and salt tolerance.
• Protection against root pathogens.
• Essential for pine plantations and orchid seed germination.
• Used as AM biofertiliser inoculum in nurseries.

Q5. Write a note on fungal associations other than mycorrhiza.

• Lichens: fungus with alga or cyanobacterium.
• Endophytes: fungi living harmlessly inside plants, sometimes giving pest resistance.
• Fungus gardens of ants and termites.
• Parasitic associations (rusts, smuts) for contrast.

Exam tip

For a short note on mycorrhiza, always give the definition, Frank 1885, the two types with one example each, and the phosphorus benefit. Draw a root T.S. showing mantle and Hartig net.

Quick summary

Lichens are dual organisms formed by a close, long-term association of an alga and a fungus. The fungus gives shelter, water and minerals; the alga makes food by photosynthesis. They grow on rocks, tree bark and soil, even in very harsh places. This topic covers their types, structure, reproduction and importance.

Key points

• Lichens are called दगडफूल in Marathi (the spice "dagadphool" is a lichen).
• The association is called symbiosis (mutualism). The fungal partner is the mycobiont; the algal partner is the phycobiont (photobiont).
• Fungal partner is mostly an Ascomycete (ascolichens), rarely a Basidiomycete (basidiolichens).
• Algal partner is usually a green alga (Trebouxia) or a blue-green alga (Nostoc).
• The fungus forms most of the body and decides its shape.
• Lichens are slow-growing and very sensitive to air pollution, especially sulphur dioxide (SO₂). They do not grow in polluted cities.
• They are pioneer colonisers on bare rocks; they secrete acids that break rocks and start soil formation.
• Study of lichens is called lichenology.

Important terms

• Crustose – crust-like lichen, firmly stuck to the substratum (e.g. Graphis, Lecanora).
• Foliose – leaf-like, flat lobed lichen, loosely attached by rhizines (e.g. Parmelia, Peltigera).
• Fruticose – shrub-like, branched, erect or hanging lichen (e.g. Usnea, Cladonia).
• Soredia – small groups of algal cells wrapped in fungal hyphae; used for vegetative reproduction.
• Isidia – small outgrowths on the upper surface that break off and grow into new lichens.
• Rhizines – root-like hyphal strands for attachment.
• Bioindicator – organism whose presence or absence shows the quality of the environment.

Key facts

• **Internal structure (heteromerous foliose lichen, e.g. Parmelia):**
• Upper cortex – compact fungal hyphae.
• Algal zone (gonidial layer) – algal cells among loose hyphae.
• Medulla – loosely arranged hyphae with air spaces.
• Lower cortex – compact hyphae giving rhizines.
• Homoiomerous thallus: algal cells evenly spread through the thallus. Heteromerous: algae in a definite layer.
• Reproduction: vegetative (fragmentation, soredia, isidia), asexual (fungal spores) and sexual (only the fungal partner forms apothecia or perithecia).

5 important questions

Q1. What are lichens?

Lichens are composite organisms made of an alga and a fungus living together in mutual benefit. The alga makes food; the fungus gives protection and absorbs water and minerals. Example: Parmelia, Usnea.

Q2. Why are lichens called pollution indicators?

Lichens absorb water and gases directly from the air and cannot get rid of toxic substances. They die quickly in air polluted with sulphur dioxide. Their absence near cities shows polluted air.

Q3. Classify lichens on the basis of thallus form with examples.

• Crustose: flat crust, firmly attached, no lower cortex – Graphis, Lecanora.
• Foliose: leaf-like lobes, attached by rhizines – Parmelia, Peltigera.
• Fruticose: shrubby, branched, attached by a small disc – Usnea, Cladonia.
• Draw one sketch of each form.

Q4. Describe the internal structure of a foliose lichen.

• Upper cortex of thick-walled, closely packed hyphae.
• Algal layer just below with algal cells and hyphae.
• Medulla of loose hyphae; stores water, allows gas exchange.
• Lower cortex with rhizines.
• Labels: upper cortex, algal zone, medulla, lower cortex, rhizines.

Q5. Write the economic importance of lichens.

• Pioneers of plant succession on rocks; help soil formation.
• Food: reindeer moss (Cladonia rangiferina) for animals; some used as spice (dagadphool).
• Dyes: litmus is obtained from lichens such as Roccella.
• Medicines: usnic acid has antibiotic action.
• Bioindicators of air pollution.
• Harmful: some damage stone monuments and glass.

Exam tip

Learn the three forms with one example each and the term "mycobiont/phycobiont". Litmus from lichens is a favourite one-mark fact.