Botany वनस्पतिशास्त्र

Quick summary

Palaeobotany is the study of plants of the past, known from their fossils. Fossils tell us how plant groups appeared and changed through geological time. This topic covers what fossils are, how they form, the main types of fossils, the geological time scale, important fossil plants and the work of Birbal Sahni.

Key points

• Fossil – any remains or trace of an ancient organism preserved in rocks (usually sedimentary rocks).
• Fossilisation needs quick burial in mud or sand, lack of oxygen, and slow replacement or compression by minerals.
• Petrifaction – plant tissues replaced by minerals (silica, calcite); cell details are preserved. Best for anatomy.
• Compression – plant part flattened by pressure; thin carbon film remains.
• Impression – only the outline print on rock, no organic matter.
• Cast and mould – a hollow mould filled later by minerals forms a cast (e.g. pith casts of Calamites).
• Coal balls – lumps of petrified plants found in coal seams.
• Types of fossils:
• Fossil plant parts are often found separately, so each part gets its own form genus name, e.g. Lepidodendron (stem), Stigmaria (root), Lepidostrobus (cone).
• Radiometric dating (uranium–lead, potassium–argon) gives the age of rocks; carbon-14 dates only young material (up to about 50,000 years).
• Rhynia (Devonian, Rhynie chert, Scotland) – among the earliest vascular land plants: dichotomous leafless axes with terminal sporangia.
• Other key fossils: Lepidodendron (giant club moss), Calamites (giant horsetail), Lyginopteris (seed fern), Williamsonia (Bennettitales, Jurassic India).
• Birbal Sahni (1891–1949), father of Indian palaeobotany, described the Pentoxyleae (Pentoxylon) from the Rajmahal Hills and founded the Birbal Sahni Institute of Palaeosciences, Lucknow (1946).

Important terms

• Form genus – name given to an isolated fossil organ.
• Index fossil – fossil of a short time range used to date rocks.
• Chert – fine-grained silica rock that preserves fossils well.
• Coal – rock formed from compressed plant matter of ancient swamp forests (mainly Carboniferous).

Key facts

5 important questions

Q1. What is a petrifaction?

A petrifaction is a fossil in which the original tissues are slowly replaced by minerals like silica or calcium carbonate, so the internal cell structure is preserved and can be studied in thin sections.

Q2. Who is called the father of Indian palaeobotany?

Prof. Birbal Sahni. He studied Indian fossil plants, described Pentoxylon from the Rajmahal Hills, and founded the institute at Lucknow now named after him.

Q3. Describe the process of fossilisation and the types of fossils.

• Quick burial, lack of oxygen, mineral replacement, pressure.
• Types: petrifaction, compression, impression, cast and mould, coal ball – with one line and an example each.
• Note on form genera.

Q4. Explain the geological time scale with reference to plant evolution.

• Eras: Palaeozoic, Mesozoic, Cenozoic.
• Write the table: first land plants, pteridophyte age, gymnosperm age, angiosperm age.
• Mention coal formation in the Carboniferous.

Q5. Give an account of Rhynia.

• Devonian; Rhynie chert, Scotland.
• Rhizome with rhizoids; erect, leafless, dichotomously branched aerial axes.
• Protostele; stomata on epidermis.
• Terminal, elongated sporangia with homosporous spores.
• Importance: shows the simple structure of early vascular plants.

Exam tip

Learn three fossil types with one example each and five rows of the time scale. A short note on Birbal Sahni is a favourite question in Maharashtra universities.

Quick summary

Bryophytes are the simplest land plants. They need water for fertilisation, so they grow in moist, shady places. They are called the "amphibians of the plant kingdom". The main plant body is the gametophyte; the sporophyte depends on it. This topic covers characters, classification and the life cycles of Riccia, Marchantia, Anthoceros and Funaria.

Key points

• Bryophytes have no true roots, stem or leaves; they are fixed by rhizoids.
• No vascular tissue (xylem and phloem absent).
• The dominant, independent plant is the gametophyte (haploid, n).
• The sporophyte (diploid, 2n) is attached to and depends on the gametophyte for food (partly or fully).
• Sex organs are multicellular and jacketed: male antheridium, female archegonium (flask-shaped, with neck and venter).
• Sperms (antherozoids) are biflagellate and swim in water to reach the egg.
• After fertilisation an embryo is formed (they are embryophytes).
• Life cycle shows clear alternation of generations (heteromorphic).
• Classification: Hepaticopsida (liverworts – Riccia, Marchantia), Anthocerotopsida (hornworts – Anthoceros), Bryopsida (mosses – Funaria, Sphagnum, Polytrichum).

Important terms

• Thallus – flat, dorsiventral body of liverworts.
• Rhizoids – hair-like structures for attachment; smooth-walled and tuberculate in liverworts, multicellular in mosses.
• Protonema – green, branched, filamentous juvenile stage of mosses that grows from a spore.
• Capsule – spore-producing part of the sporophyte.
• Elaters – hygroscopic cells in the capsule that help scatter spores (Marchantia).
• Pseudoelaters – elater-like cells in Anthoceros.
• Gemma cup – cup-like structure in Marchantia bearing gemmae for vegetative reproduction.
• Peristome – teeth at the mouth of moss capsule that help spore dispersal.

Key facts

• Sphagnum (peat moss) forms peat used as fuel and in gardening; it holds a lot of water.

5 important questions

Q1. Why are bryophytes called amphibians of the plant kingdom?

They live on land but need water for fertilisation, as their sperms must swim to the archegonium. So they depend on both land and water, like amphibians.

Q2. What is protonema?

Protonema is a green, branched filament that grows from a germinating moss spore. Buds on it develop into leafy gametophores. Example: Funaria.

Q3. Describe the sporophyte of Funaria with a labelled diagram.

• Parts: foot (in gametophore), long seta, capsule.
• Capsule: apophysis (with stomata), theca (spore sac, columella, air spaces) and operculum.
• Annulus below operculum; peristome teeth (outer and inner rows) control spore release.
• Calyptra (from archegonium wall) covers young capsule.
• Labels: foot, seta, apophysis, columella, spore sac, annulus, peristome, operculum, calyptra.

Q4. Give the general characters of bryophytes.

• Thalloid or leafy; rhizoids; no vascular tissue.
• Gametophyte dominant and independent.
• Jacketed sex organs; biflagellate sperms; water needed.
• Embryo formed; sporophyte dependent.
• Heteromorphic alternation of generations.

Q5. Explain the life cycle of Marchantia.

• Dichotomously branched thallus with gemma cups (vegetative reproduction).
• Dioecious: antheridiophore (lobed disc) on male, archegoniophore (star-like rays) on female plant.
• Sperms swim to archegonia; zygote forms embryo.
• Sporophyte: foot, seta, capsule with spores and elaters.
• Spores (after meiosis) germinate into new thalli.

Exam tip

Always state "gametophyte dominant, sporophyte dependent" – it is the key difference from pteridophytes. Practise the Funaria capsule L.S. diagram.

Quick summary

Riccia (a liverwort) and Anthoceros (a hornwort) are two important type studies of bryophytes. Riccia has the simplest sporophyte among bryophytes, while Anthoceros has the most advanced one. This topic covers their thallus, sex organs, sporophyte and life cycle.

Key points

• Riccia (class Hepaticopsida, order Marchantiales): small, dichotomously branched, dorsiventral thallus on moist soil; a median dorsal groove; rhizoids and scales below.
• Thallus V.S.: upper photosynthetic zone of vertical chlorophyllous filaments with air canals, and lower storage zone of colourless cells.
• Rhizoids are of two types: smooth-walled and tuberculate. Multicellular scales are present on the ventral side.
• Sex organs (antheridia and archegonia) are sunk in the dorsal groove; flask-shaped archegonium with neck and venter.
• ***Riccia* sporophyte is the simplest: only a capsule** – no foot, no seta. It stays embedded in the thallus.
• All inner cells of the capsule form spores (no elaters). Spores are released only when the thallus decays.
• Anthoceros (class Anthocerotopsida): dark green lobed thallus; each cell has one large chloroplast with a pyrenoid (like algae).
• Ventral mucilage cavities contain the cyanobacterium Nostoc (fixes nitrogen). Only smooth rhizoids; no scales.
• Sex organs are endogenous (develop inside the thallus).
• ***Anthoceros* sporophyte: bulbous foot, a meristematic (intercalary) zone and a long horn-like capsule. It grows for a long time. The capsule has a central columella, spores, pseudo-elaters and a green wall with stomata** – it can photosynthesise, so it is partly independent.

Important terms

• Tuberculate rhizoid – rhizoid with peg-like ingrowths on the inner wall.
• Columella – central sterile column in the capsule.
• Pseudo-elaters – multicellular, branched sterile cells among spores in Anthoceros.
• Intercalary meristem – zone at the base of the Anthoceros capsule that keeps adding tissue.
• Spore tetrad – group of four spores formed by meiosis.

Key facts

5 important questions

Q1. Why is the sporophyte of Riccia called the simplest?

Because it is only a capsule, without foot and seta. All inner cells are fertile (no columella, no elaters) and it remains enclosed in the thallus.

Q2. What are pseudo-elaters?

They are sterile, multicellular, often branched cells found among the spores in the Anthoceros capsule. They help in spore dispersal but lack the spiral thickening of true elaters.

Q3. Describe the internal structure of the Riccia thallus.

• Dorsal photosynthetic zone with chlorophyllous filaments and air canals.
• Ventral storage zone with starch-filled cells.
• Lower epidermis bearing smooth and tuberculate rhizoids and scales.
• Labelled V.S. diagram.

Q4. Describe the sporophyte of Anthoceros.

• Foot embedded in thallus; intercalary meristem; long capsule.
• Capsule L.S.: epidermis with stomata, green assimilatory tissue, sporogenous layer, central columella of 16 cell rows, spores and pseudo-elaters.
• Dehiscence by two valves from the tip.
• Semi-independent nature; draw L.S.

Q5. Compare Riccia and Anthoceros.

Use the comparison table above, and add habitat and the importance of Anthoceros as a link in the origin of the land plant sporophyte.

Exam tip

The Anthoceros capsule L.S. and the Riccia thallus V.S. are the two most-asked bryophyte diagrams after Funaria. Learn the comparison table for "distinguish" questions.

Quick summary

Pteridophytes are the first true vascular plants. They have xylem and phloem but no seeds and no flowers. They are often called "vascular cryptogams" or "seedless vascular plants". The main plant body is the sporophyte. This topic covers characters, classification, stelar types and life cycles of Selaginella, Equisetum and ferns.

Key points

• Pteridophytes (नेचे वनस्पती, ferns and their allies) grow mostly in moist, shady places.
• The plant body is a sporophyte (2n), differentiated into true root, stem and leaves.
• Vascular tissue is present, but xylem has tracheids (no vessels, except a few like Selaginella), and phloem has no companion cells.
• Leaves may be small (microphylls, e.g. Lycopodium, Selaginella, Equisetum) or large (megaphylls, e.g. ferns).
• Spores form in sporangia, often borne on special leaves called sporophylls. Sporophylls may form a compact strobilus (cone).
• Most are homosporous (one kind of spore, e.g. Lycopodium, Equisetum, Pteris). Some are heterosporous (microspores and megaspores, e.g. Selaginella, Marsilea, Salvinia).
• Spores grow into a small, free-living gametophyte called the prothallus.
• Sex organs are antheridia and archegonia; water is needed for fertilisation.
• Heterospory in Selaginella is seen as the first step towards the seed habit.

Important terms

• Stele – central vascular cylinder of stem and root.
• Protostele – solid core of xylem surrounded by phloem (simplest type).
• Siphonostele – stele with a central pith.
• Dictyostele – siphonostele broken into separate strands (meristeles) by leaf gaps (ferns).
• Sorus (sori) – group of sporangia on the underside of fern leaves.
• Indusium – protective flap covering a sorus.
• Ligule – small tongue-like outgrowth at the base of the leaf of Selaginella.
• Rhizophore – leafless, root-producing branch in Selaginella.

Key facts

• Selaginella stem shows trabeculae (radial elongated endodermal cells) holding the stele in an air space.
• Equisetum stem has vallecular canals, carinal canals and a central canal; spores have elaters.
• Young fern leaves are coiled (circinate vernation).

5 important questions

Q1. Why are pteridophytes called vascular cryptogams?

They have vascular tissues (xylem and phloem) but reproduce by spores and not by seeds or flowers. "Cryptogam" means plants with hidden reproduction.

Q2. What is heterospory? Give an example.

Heterospory is the formation of two kinds of spores: small microspores (forming male gametophytes) and large megaspores (forming female gametophytes). Examples: Selaginella, Marsilea.

Q3. Describe the life cycle of Selaginella.

• Sporophyte: creeping stem with four rows of ligulate leaves and rhizophores.
• Strobilus with microsporophylls (microsporangia) and megasporophylls (megasporangium with usually four megaspores).
• Microspore → reduced male gametophyte → antherozoids.
• Megaspore → female gametophyte with archegonia, partly inside the spore wall.
• Fertilisation in water → embryo with suspensor → new sporophyte.
• Diagram labels: strobilus, microsporangium, megasporangium, ligule, rhizophore.

Q4. Explain the types of stele in pteridophytes.

• Protostele: haplostele (Selaginella some species), actinostele, plectostele (Lycopodium).
• Siphonostele: ectophloic (phloem outside) and amphiphloic (phloem both sides).
• Solenostele and dictyostele (ferns).
• Polystele (several steles, Selaginella some species).
• Mention that the stelar theory was given by Van Tieghem and Douliot (1886).

Q5. Write the general characters of pteridophytes.

• Sporophyte dominant; true roots, stem, leaves.
• Xylem with tracheids, phloem without companion cells.
• Sporangia on sporophylls; homosporous or heterosporous.
• Gametophyte (prothallus) small, independent.
• Water needed for fertilisation; embryo formed; no seeds.

Exam tip

Compare bryophytes and pteridophytes in a table: which generation is dominant, vascular tissue, and spore type. Draw the T.S. of Selaginella stem with trabeculae.

Quick summary

Equisetum (horsetail) and Marsilea (water clover) are two pteridophyte type studies. Equisetum is a homosporous plant with jointed, ribbed stems and spores with elaters. Marsilea is an aquatic heterosporous fern whose spores form inside hard bean-like sporocarps. This topic covers their external form, anatomy, reproduction and life cycle.

Key points

• Equisetum (class Sphenopsida) – the only living genus of its group; called "horsetail" or "scouring rush" (silica in the stem).
• Sporophyte has an underground rhizome and aerial stems with clear nodes and internodes. Internodes are ribbed (ridges and furrows).
• Leaves are tiny, scale-like and fused into a sheath at each node; photosynthesis is done mainly by the green stem.
• Stem T.S.: ridges with sclerenchyma, vallecular canals under furrows, carinal canals in vascular bundles (opposite ridges), and a central pith cavity. Stele is an eustele-like siphonostele.
• Sporangia are borne on umbrella-shaped sporangiophores grouped in a terminal strobilus (cone).
• Homosporous: all spores look alike; each spore has 4 hygroscopic elaters (bands from the outer wall) that coil and uncoil with humidity and help dispersal.
• Gametophyte is a small green prothallus; antherozoids are multiflagellate.
• Marsilea (order Salviniales/Marsileales, water fern): creeping rhizome in mud; long-petioled leaves with 4 leaflets (like a clover); shows sleep movements.
• Rhizome T.S.: amphiphloic siphonostele (solenostele), aerenchyma with air chambers in the cortex.
• Sporangia develop inside a hard, bean-shaped sporocarp on a short stalk near the petiole base.
• Heterosporous: microsporangia with many microspores and megasporangia with one megaspore, both in the same sorus. The sporocarp opens in water by a swelling gelatinous ring (sorophore) that carries the sori out.
• Gametophytes are very reduced and develop inside the spore wall (endosporic). Heterospory is seen as a step towards the seed habit.

Important terms

• Sporangiophore – stalked, peltate structure bearing sporangia (Equisetum).
• Elaters – hygroscopic bands on Equisetum spores.
• Sporocarp – hard capsule containing sori in Marsilea.
• Sorophore – gelatinous ring that swells and pulls the sori out of the sporocarp.
• Heterospory – production of two kinds of spores (micro and mega).
• Endosporic development – gametophyte develops inside the spore wall.

Key facts

5 important questions

Q1. What are elaters in Equisetum?

Elaters are four band-like appendages formed from the outer layer of the spore wall. They are hygroscopic: they coil in moist air and uncoil in dry air, helping spores to move and disperse in groups.

Q2. What is a sporocarp?

A sporocarp is a hard, bean-shaped, stalked reproductive body of Marsilea. It contains sori with both microsporangia and megasporangia and can survive drought for many years.

Q3. Describe the anatomy of the aerial stem of Equisetum.

• Ribbed outline; epidermis with silica and stomata in furrows.
• Hypodermal sclerenchyma under ridges; chlorenchyma under furrows.
• Vallecular canals in the cortex; endodermis; vascular bundles with carinal canals.
• Central pith cavity. Labelled T.S. diagram.

Q4. Give an account of reproduction in Marsilea.

• Sporocarp structure; sori on a gelatinous sorophore.
• Germination of sporocarp in water.
• Microspores → male gametophyte with antherozoids; megaspore → female gametophyte with one archegonium.
• Fertilisation in water → embryo → new sporophyte. Draw the sporocarp L.S.

Q5. Write a note on heterospory and seed habit.

• Heterospory in Selaginella and Marsilea.
• Retention of megaspore, endosporic female gametophyte, reduction to one megaspore — steps leading to the seed.
• Compare with gymnosperm ovule.

Exam tip

For Equisetum, remember "carinal canal opposite ridge, vallecular canal opposite furrow". For Marsilea, the sporocarp section and germination in water are favourites.

Quick summary

Gymnosperms are seed plants whose seeds are naked, that is, not enclosed in a fruit. They have no ovary and no flowers. Most are woody trees or shrubs, many of them evergreen conifers. This topic covers their characters, classification, type examples (Cycas, Pinus, Gnetum) and importance.

Key points

• Gymnosperm means "naked seed" (gymnos = naked, sperma = seed). In Marathi, अनावृत्तबीजी वनस्पती.
• Plant body is a sporophyte with root, stem and leaves.
• Ovules are borne openly on megasporophylls (scales); pollen on microsporophylls.
• Sporophylls are usually grouped in cones (strobili): male cones and female cones.
• Xylem has tracheids (vessels absent, except in Gnetales); phloem has no companion cells.
• Pollination is by wind (anemophily). Pollen lands directly on the ovule at the micropyle (pollination drop).
• Female gametophyte (endosperm) is formed before fertilisation and is haploid (n).
• Polyembryony (more than one embryo in a seed) is common.
• No double fertilisation; no fruit formation.
• Cycas has motile, multiflagellate sperms – among the largest sperms in plants.

Important terms

• Coralloid roots – coral-like, upward growing roots of Cycas containing blue-green algae (Anabaena, Nostoc).
• Megasporophyll – leaf-like structure bearing ovules.
• Nucellus – tissue inside the ovule where the megaspore forms.
• Integument – protective covering of the ovule.
• Archegonial chamber – space above archegonia where fertilisation happens (Cycas).
• Winged pollen – pollen of Pinus with two air sacs for wind dispersal.
• Dwarf shoot – short shoot of Pinus bearing needles (needle-like leaves).

Key facts

• Cycas is dioecious; female plant bears loose megasporophylls (no compact female cone).
• Pinus is monoecious; the seed takes about two years from pollination to maturity.
• Ephedra gives ephedrine (used for asthma); Pinus gives turpentine and resin; Taxus gives taxol (anti-cancer).

5 important questions

Q1. Why are gymnosperms called naked-seeded plants?

Their ovules lie exposed on megasporophylls and are not enclosed in an ovary. After fertilisation the seeds remain uncovered, as no fruit is formed.

Q2. What are coralloid roots?

Coralloid roots are short, branched, upward-growing roots of Cycas that look like coral. They contain nitrogen-fixing blue-green algae such as Anabaena in their cortex.

Q3. Describe the structure of the ovule of Cycas.

• Large, orthotropous ovule with a single thick integument.
• Integument has three layers: outer fleshy, middle stony, inner fleshy.
• Nucellus with a beak and pollen chamber at the top.
• Female gametophyte (endosperm) with archegonia at the micropylar end.
• Labels: micropyle, integument, nucellus, pollen chamber, archegonium, female gametophyte.

Q4. Give the general characters of gymnosperms.

• Woody perennial plants, mostly evergreen.
• Naked ovules on sporophylls; cones present.
• Tracheids in xylem; no companion cells.
• Wind pollination; haploid endosperm formed before fertilisation.
• No fruit; polyembryony common.

Q5. Write the economic importance of gymnosperms.

• Timber: Pinus, Cedrus, Abies (soft wood).
• Resin and turpentine from Pinus; Canada balsam from Abies.
• Food: sago from Cycas pith; edible seeds of Pinus gerardiana (chilgoza).
• Medicines: ephedrine, taxol.
• Ornamental plants: Cycas, Thuja, Araucaria.

Exam tip

Remember three unique points: haploid endosperm, naked seeds, and no fruit. Draw the L.S. of the Cycas ovule neatly.

Quick summary

Morphology is the study of the external form of plants. This topic covers the normal form and functions of the root, stem and leaf of angiosperms and their modifications for storage, support, protection and other special jobs. It is a base for taxonomy and for identifying plants in the practical exam.

Key points

• Root – develops from the radicle, grows down, has no nodes, buds or leaves, and has a root cap.
• Tap root system (dicots: mustard, gram) and fibrous root system (monocots: wheat, rice). Roots growing from any part other than the radicle are adventitious.
• Storage: conical (carrot), fusiform (radish), napiform (beet, turnip); tuberous adventitious roots (sweet potato).
• Support: prop roots (banyan), stilt roots (maize, sugarcane).
• Respiration: pneumatophores (Rhizophora, mangroves).
• Others: epiphytic roots with velamen (orchids), haustoria (Cuscuta), nodules (legumes).
• Root modifications:
• Stem – develops from the plumule; has nodes, internodes and buds; bears leaves, flowers and fruits.
• Underground stem modifications (have nodes and buds): tuber (potato), rhizome (ginger, turmeric), corm (Colocasia, Amorphophallus), bulb (onion).
• Sub-aerial: runner (grass, Oxalis), stolon (strawberry), offset (Pistia, water hyacinth), sucker (mint, chrysanthemum).
• Aerial: stem tendril (grapevine, passion flower), thorn (Bougainvillea, citrus), phylloclade (Opuntia), cladode (Asparagus), bulbils.
• Leaf – lateral, flat outgrowth of the stem at a node with an axillary bud. Parts: leaf base, petiole, lamina; stipules may be present.
• Venation: reticulate (dicots) and parallel (monocots). Leaves are simple or compound (pinnate – neem; palmate – silk cotton).
• Phyllotaxy: alternate (hibiscus), opposite (guava, Calotropis), whorled (Alstonia).
• Leaf modifications: leaf tendril (pea), spines (Opuntia, Aloe margins), phyllode (Australian Acacia), pitcher (Nepenthes), fleshy scale leaves (onion).

Important terms

• Adventitious root – root arising from stem, leaf or any part other than the radicle.
• Velamen – spongy water-absorbing tissue on orchid aerial roots.
• Phylloclade – flattened green stem of many internodes that does the leaf's work.
• Phyllode – flattened green petiole working as a leaf.
• Phyllotaxy – arrangement of leaves on the stem.

Key facts

5 important questions

Q1. Why is the potato a stem and not a root?

Because the potato has "eyes" which are nodes with axillary buds, and scale leaves. Roots never have nodes or buds.

Q2. What are pneumatophores?

Negatively geotropic, aerial roots of mangrove plants growing in marshy saline soil. They have pores (lenticels) through which air reaches the submerged roots.

Q3. Describe the modifications of roots with examples.

Group into storage, support, respiration and special functions; give at least eight examples with labelled sketches of carrot, banyan prop roots and pneumatophores.

Q4. Describe underground modifications of stem.

• Tuber, rhizome, corm, bulb – structure, how each shows stem characters, examples.
• Role in storage and vegetative propagation. Add sketches.

Q5. Explain the modifications of leaves.

• Tendrils, spines, phyllodes, pitchers, bladders (Utricularia), scale leaves.
• One line on how each helps the plant; sketches of pea tendril and Nepenthes pitcher.

Exam tip

In "identify and give reasons" practicals, always name the organ, the modification and one proof (nodes, buds, position). The table above is a quick revision sheet.

Quick summary

The cell is the basic unit of life. A plant cell is a eukaryotic cell with a rigid cell wall, large vacuole and plastids. This topic covers the cell theory, the ultrastructure of the plant cell as seen under the electron microscope, the structure and functions of each organelle, and the fluid mosaic model of the plasma membrane.

Key points

• Cell theory: Schleiden (1838, plants) and Schwann (1839, animals); Virchow (1855) added omnis cellula e cellula – every cell comes from a pre-existing cell.
• Cell wall: primary wall (cellulose, hemicellulose, pectin), secondary wall (cellulose with lignin) and middle lamella (calcium pectate) between cells. Plasmodesmata connect neighbouring cells.
• Plasma membrane: fluid mosaic model (Singer and Nicolson, 1972) – a phospholipid bilayer with proteins floating in it; selectively permeable.
• Nucleus: double nuclear envelope with pores, nucleoplasm, chromatin and nucleolus (rRNA synthesis, ribosome assembly).
• Mitochondria: double membrane; inner membrane folded into cristae with F₀–F₁ particles; matrix has its own circular DNA and 70S ribosomes. Site of aerobic respiration (Krebs cycle, ETS) – "powerhouse of the cell".
• Chloroplast: double envelope, stroma and thylakoids stacked into grana; light reactions in thylakoids, Calvin cycle in stroma; own DNA and 70S ribosomes.
• Mitochondria and chloroplasts are semi-autonomous; the endosymbiotic theory says they came from ancient bacteria.
• Endoplasmic reticulum: rough ER (with ribosomes, protein synthesis) and smooth ER (lipid synthesis).
• Golgi apparatus (dictyosomes in plants): packages and modifies proteins; forms the cell plate during cytokinesis and makes wall polysaccharides.
• Ribosomes: 80S in cytoplasm (60S + 40S); 70S in plastids and mitochondria; site of protein synthesis.
• Vacuole: large central sac surrounded by tonoplast; holds cell sap, keeps turgor.
• Microbodies: peroxisomes (photorespiration) and glyoxysomes (fat to sugar in oily seeds).

Important terms

• Plasmodesmata – cytoplasmic channels through cell walls joining adjacent cells.
• Cristae – folds of the inner mitochondrial membrane.
• Granum – stack of thylakoids in a chloroplast.
• Tonoplast – membrane around the vacuole.
• Semi-autonomous organelle – organelle with its own DNA and ribosomes that can divide on its own.

Key facts

5 important questions

Q1. Why are mitochondria and chloroplasts called semi-autonomous?

Because they have their own circular DNA, 70S ribosomes and can make some of their own proteins and divide by fission, but they still depend on nuclear genes for most proteins.

Q2. What is the middle lamella?

It is the thin cementing layer, mainly of calcium and magnesium pectate, that holds the walls of two neighbouring plant cells together.

Q3. Describe the fluid mosaic model of the plasma membrane.

• Proposed by Singer and Nicolson (1972).
• Phospholipid bilayer with hydrophilic heads outside, hydrophobic tails inside.
• Integral and peripheral proteins; glycoproteins and glycolipids on the surface.
• "Fluid": lipids and proteins move sideways. Labelled diagram; functions of the membrane.

Q4. Give the ultrastructure and functions of the chloroplast.

• Outer and inner membranes, stroma, thylakoids, grana and stroma lamellae.
• Pigments and photosystems in thylakoids; enzymes of Calvin cycle in stroma.
• DNA, ribosomes, starch grains, plastoglobuli. Labelled diagram.

Q5. Draw and describe the ultrastructure of a plant cell.

Label wall, plasma membrane, nucleus, nucleolus, ER, Golgi, mitochondria, chloroplast, ribosomes, vacuole and tonoplast, peroxisome; one-line function of each.

Exam tip

Practise the labelled ultrastructure diagrams of the plant cell, mitochondrion and chloroplast. Remember: 80S in cytoplasm, 70S in organelles.

Quick summary

Cells multiply by cell division. Mitosis gives two daughter cells with the same chromosome number as the parent and is used for growth and repair. Meiosis halves the chromosome number and produces variation; it happens during spore or gamete formation. This topic covers the cell cycle, the stages of mitosis and meiosis, and their importance.

Key points

• Cell cycle = interphase (G₁, S, G₂) + M phase (karyokinesis + cytokinesis). DNA doubles in the S phase. Non-dividing cells rest in G₀.
• Mitosis (equational division) occurs in meristems – root tip and shoot tip.
• Prophase: chromatin condenses into chromosomes, each with two sister chromatids; nucleolus and nuclear envelope disappear; spindle forms.
• Metaphase: chromosomes line up at the equatorial (metaphase) plate; spindle fibres attach at kinetochores. Best stage to count and study chromosomes.
• Anaphase: centromeres split; sister chromatids move to opposite poles.
• Telophase: chromosomes reach poles and uncoil; nuclear envelope and nucleolus reappear.
• Cytokinesis in plants is by cell plate formation (from Golgi vesicles), growing from the centre outwards; in animals by furrowing.
• Meiosis (reductional division) happens in spore mother cells (anthers and ovules) – one DNA doubling, two divisions, four haploid cells.
• Prophase I has five sub-stages: leptotene (thin threads), zygotene (pairing of homologues = synapsis, synaptonemal complex), pachytene (bivalents/tetrads; crossing over), diplotene (homologues separate except at chiasmata), diakinesis (terminalisation of chiasmata).
• Anaphase I separates homologous chromosomes (not chromatids) – this halves the number.
• Meiosis II is like mitosis: sister chromatids separate.
• Importance: mitosis keeps chromosome number constant; meiosis keeps the number constant across generations and creates variation by crossing over and independent assortment.

Important terms

• Chromatid – one of the two identical halves of a duplicated chromosome.
• Bivalent / tetrad – a pair of homologous chromosomes (four chromatids) in prophase I.
• Chiasma – X-shaped point where non-sister chromatids crossed over.
• Synapsis – pairing of homologous chromosomes in zygotene.
• Cell plate – partition formed between daughter nuclei in plant cytokinesis.

Key facts

5 important questions

Q1. What is a chiasma?

A chiasma is the X-shaped point of contact between non-sister chromatids of homologous chromosomes, seen in diplotene. It marks the place where crossing over has occurred.

Q2. Why is meiosis called reductional division?

Because the chromosome number is halved: a diploid (2n) cell forms four haploid (n) cells, since homologous chromosomes separate in anaphase I.

Q3. Describe the stages of mitosis with diagrams.

• Prophase, metaphase, anaphase, telophase – main events of each.
• Cytokinesis by cell plate.
• Diagrams from an onion root tip squash.
• Significance of mitosis.

Q4. Describe prophase I of meiosis.

• Leptotene, zygotene, pachytene, diplotene, diakinesis – events and diagrams.
• Synaptonemal complex, recombination nodules, chiasma formation and terminalisation.

Q5. Give the significance of meiosis and distinguish it from mitosis.

• Constant chromosome number across generations; variation; basis of evolution and plant breeding.
• Use the comparison table above.

Exam tip

Remember the order of prophase I with "Little Zebras Play During Days" (leptotene, zygotene, pachytene, diplotene, diakinesis). Onion root tip is the standard slide for mitosis; onion/Tradescantia flower bud for meiosis.

Quick summary

A tissue is a group of cells with a common origin and similar function. Plant tissues are of two main types: meristematic (dividing) and permanent (non-dividing). Permanent tissues are simple or complex. This topic also covers tissue systems and the anatomy of root, stem and leaf.

Key points

• The word "tissue" was coined by N. Grew. Tissue is ऊती in Marathi.
• Meristematic tissue: small, living cells with dense cytoplasm, large nucleus, thin cellulose walls, no intercellular spaces; they keep dividing.
• By position, meristems are apical (root and shoot tips; increase length), intercalary (base of internodes, e.g. grasses) and lateral (vascular cambium and cork cambium; increase girth).
• By origin: primary meristems (from embryo) and secondary meristems (from permanent tissue, e.g. cork cambium).
• Simple permanent tissues have one type of cell: parenchyma, collenchyma and sclerenchyma.
• Complex permanent tissues have more than one type of cell: xylem and phloem.
• Xylem conducts water and minerals; elements: tracheids, vessels, xylem parenchyma, xylem fibres.
• Phloem conducts food; elements: sieve tubes, companion cells, phloem parenchyma, phloem fibres.
• Only xylem parenchyma is living in xylem; only phloem fibres are dead in phloem.
• Three tissue systems (Sachs): epidermal, ground and vascular tissue systems.

Important terms

• Parenchyma – living, thin-walled cells; storage, photosynthesis (chlorenchyma), buoyancy (aerenchyma).
• Collenchyma – living cells thickened at corners with cellulose and pectin; gives flexibility (e.g. hypodermis of dicot stem).
• Sclerenchyma – dead cells with lignified walls; fibres and sclereids (stone cells in pear).
• Tracheid – long, dead, lignified cell with tapering ends.
• Vessel – tube formed of cells joined end to end with dissolved end walls.
• Sieve plate – perforated end wall of a sieve tube.
• Casparian strip – band of suberin on the radial walls of endodermal cells.
• Bulliform cells – large cells in the upper epidermis of grass leaves; help leaf rolling.

Key facts

• Root: radial vascular bundles; exarch xylem. Dicot root usually 2–4 (up to 6) xylem bundles; monocot root many (more than 6) xylem bundles with a large pith.
• Stem: endarch xylem (protoxylem towards centre).
• Dicot leaf: dorsiventral; palisade and spongy mesophyll. Monocot leaf: isobilateral; only spongy mesophyll.

5 important questions

Q1. Define meristem and give its types by position.

A meristem is a group of actively dividing cells. By position it is apical (tips of root and shoot), intercalary (base of internodes) and lateral (cambium, increasing girth).

Q2. Differentiate between collenchyma and sclerenchyma.

Collenchyma is living and thickened at corners with cellulose and pectin; it gives flexible support. Sclerenchyma is dead, with uniform lignified walls; it gives rigid strength.

Q3. Describe xylem with its elements.

• Complex tissue conducting water and minerals upward; also gives support.
• Tracheids: dead, elongated, lignified, with pits.
• Vessels: dead, tube-like; main conducting element in angiosperms.
• Xylem parenchyma: living; stores food; radial conduction.
• Xylem fibres: dead; mechanical support.
• Protoxylem forms first, metaxylem later.

Q4. Describe the internal structure of a dicot stem with a labelled diagram.

• Epidermis with cuticle and multicellular hairs.
• Cortex: collenchymatous hypodermis, parenchyma, endodermis (starch sheath).
• Pericycle of sclerenchyma patches.
• Vascular bundles in a ring: conjoint, collateral, open, endarch.
• Large parenchymatous pith and medullary rays.
• Labels: cuticle, epidermis, hypodermis, cortex, endodermis, pericycle, phloem, cambium, xylem, pith.

Q5. Compare the anatomy of dicot and monocot root.

• Xylem bundles: dicot 2–6; monocot many.
• Pith: absent or small in dicot; large in monocot.
• Secondary growth: present in dicot; absent in monocot.
• Both have epiblema with root hairs, cortex, endodermis with Casparian strips, pericycle, radial bundles, exarch xylem.

Exam tip

Diagrams carry many marks here. Practise T.S. of dicot stem, monocot stem, dicot root and dicot leaf with all labels.