वनस्पतिशास्त्र Botany

थोडक्यात सारांश

Plant taxonomy is the science of identifying, naming and classifying plants. It gives every plant a correct scientific name and a place in a system of classification. This topic covers the aims of taxonomy, types of classification systems, the Bentham and Hooker system, the rules of botanical nomenclature (ICN) and the use of herbaria and botanical gardens.

महत्त्वाचे मुद्दे

• Taxonomy (वर्गीकरणशास्त्र) has three parts: identification, nomenclature (naming) and classification.
• The word "taxonomy" was coined by A. P. de Candolle (1813).
• Systems of classification:
• Artificial – based on one or a few easily seen characters (e.g. Linnaeus' sexual system, based on number of stamens; 24 classes).
• Natural – based on many characters showing overall similarity (e.g. Bentham and Hooker, Genera Plantarum, 1862–1883).
• Phylogenetic – based on evolutionary relationships (e.g. Engler and Prantl; Hutchinson).
• Bentham and Hooker's system is widely used in Indian herbaria and for flowering plants in Indian syllabi.
• It divides seed plants into three classes: Dicotyledons, Gymnospermae and Monocotyledons.
• Dicots are divided into Polypetalae, Gamopetalae and Monochlamydeae.
• Polypetalae has series Thalamiflorae, Disciflorae and Calyciflorae; Gamopetalae has Inferae, Heteromerae and Bicarpellatae.
• Limitation: gymnosperms are placed between dicots and monocots; it is not phylogenetic.
• Modern trend: the APG (Angiosperm Phylogeny Group) system uses DNA sequence data.

महत्त्वाच्या संज्ञा

• Binomial nomenclature – two-word scientific name (genus + specific epithet), started by Linnaeus in Species Plantarum (1753).
• ICN – International Code of Nomenclature for algae, fungi and plants (earlier ICBN).
• Type specimen – the specimen on which a name is based. Holotype is the single specimen chosen by the author.
• Priority – the earliest validly published name is the correct name.
• Author citation – name of the scientist who first described the species, written after the name (e.g. Mangifera indica L., where L. = Linnaeus).
• Herbarium – collection of pressed, dried, mounted and labelled plant specimens.
• Flora – book listing and describing the plants of an area.
• Taxonomic key – tool with pairs of contrasting statements (couplets) used for identification.

महत्त्वाची माहिती

• Main rules of ICN: names in Latin; one correct name for each taxon; principle of priority (starting point for most plants: Species Plantarum, 1 May 1753); type method; names are italicised or underlined.
• Standard herbarium sheet size: about 29 × 42 cm.
• Important herbaria and gardens: Royal Botanic Gardens, Kew (England); Central National Herbarium at the Acharya Jagadish Chandra Bose Indian Botanic Garden, Howrah; Botanical Survey of India (BSI) has its headquarters in Kolkata (founded 1890).
• Steps of herbarium preparation: collection, pressing, drying, poisoning (to prevent insects and fungi), mounting, labelling, storing.

५ महत्त्वाचे प्रश्न

Q1. What is a herbarium?

A herbarium is a store-house of pressed, dried and labelled plant specimens mounted on standard sheets and arranged by a system of classification. It helps in identification and research.

Q2. State the principle of priority.

When a plant has more than one name, the earliest validly published name is accepted as the correct name. For most plants, the starting date is the publication of Linnaeus' Species Plantarum (1753).

Q3. Give an outline of Bentham and Hooker's system of classification.

• Published in Genera Plantarum (3 volumes, 1862–1883).
• Seed plants → Dicotyledons, Gymnospermae, Monocotyledons.
• Dicots → Polypetalae (Thalamiflorae, Disciflorae, Calyciflorae), Gamopetalae (Inferae, Heteromerae, Bicarpellatae), Monochlamydeae.
• Monocots divided into seven series.
• Total about 202 natural orders (families).
• Merits: easy, practical. Demerits: not phylogenetic; gymnosperms placed between dicots and monocots.

Q4. Explain the main rules of botanical nomenclature.

• Each species has a binomial: genus (capital) + specific epithet (small).
• Names in Latin or Latinised form; printed in italics.
• One correct name; principle of priority.
• Type method for each name.
• Author citation after the name.
• Later homonyms are rejected.

Q5. Describe the method of preparing herbarium specimens.

• Collect healthy specimens with flowers/fruits; note field data.
• Press between blotting papers; change papers until dry.
• Poison with mercuric chloride or other chemicals.
• Mount on herbarium sheet with glue or tape.
• Attach label: name, family, place, date, collector.
• Store in cabinets by family order.

परीक्षेसाठी टीप

Learn the Bentham and Hooker outline as a branching chart. Quote dates: Species Plantarum 1753, Genera Plantarum 1862–1883.

थोडक्यात सारांश

Classical taxonomy uses mainly external morphology. Modern taxonomy adds evidence from anatomy, embryology, chromosomes, chemistry, DNA and computers, so that classification shows true relationships (phylogeny). This topic covers numerical taxonomy, cytotaxonomy, chemotaxonomy, molecular taxonomy (DNA barcoding), cladistics and the APG system.

महत्त्वाचे मुद्दे

• Alpha taxonomy is based on morphology alone; omega taxonomy uses all available data. Modern trends move us from alpha towards omega.
• Anatomy and embryology in taxonomy: stomata types, wood structure, embryo sac type, endosperm type help place doubtful taxa.
• Cytotaxonomy: uses chromosome number, size, shape (karyotype) and behaviour in meiosis. Example: polyploid series in wheat (2n = 14, 28, 42).
• Chemotaxonomy: uses plant chemicals such as alkaloids, flavonoids, betalains, essential oils and proteins. Example: betalain pigments occur in Caryophyllales (beet, Amaranthus, cacti) instead of anthocyanins.
• Numerical taxonomy (taximetrics): Sneath and Sokal (1963). Many characters (often 50 or more) are scored and given equal weight; similarity between Operational Taxonomic Units (OTUs) is calculated by computer and shown as a tree-like phenogram (dendrogram).
• Cladistics (Willi Hennig): groups taxa by shared derived characters (synapomorphies); result is a cladogram. Only monophyletic groups are accepted.
• Molecular taxonomy: compares DNA sequences (chloroplast genes rbcL, matK; nuclear ITS). It gives large, objective data sets.
• DNA barcoding: a short standard gene region identifies species; for land plants, ***rbcL* + *matK*** is the core barcode.
• APG system (Angiosperm Phylogeny Group, 1998; APG IV 2016) is based mainly on DNA. It recognises orders and families, groups such as monocots and eudicots, and basal angiosperms (e.g. Amborella, water lilies).
• Digital tools: online floras, herbarium databases and identification keys help modern taxonomists.

महत्त्वाच्या संज्ञा

• OTU – Operational Taxonomic Unit, the basic unit compared in numerical taxonomy.
• Phenogram – tree showing overall similarity between OTUs.
• Cladogram – branching diagram showing shared derived characters.
• Monophyletic group – a group with a common ancestor and all its descendants.
• Karyotype – the complete set of chromosomes of a species described by number, size and shape.
• DNA barcode – a short standard DNA sequence used to identify a species.

महत्त्वाची माहिती

५ महत्त्वाचे प्रश्न

Q1. What is chemotaxonomy?

Chemotaxonomy is the use of chemical constituents of plants – alkaloids, flavonoids, pigments, proteins – to solve problems of classification. For example, betalain pigments mark most families of Caryophyllales.

Q2. What is DNA barcoding?

It is the identification of a species using a short, standard DNA region. In land plants the chloroplast genes rbcL and matK are used together as the core barcode.

Q3. Explain the principles and steps of numerical taxonomy.

• Sneath and Sokal (1963); equal weight to all characters.
• Steps: choose OTUs → record many characters → code them → calculate similarity coefficients → cluster analysis → phenogram.
• Merits: objective, uses computers; demerits: needs many characters, ignores evolution.

Q4. Discuss the role of cytology and chemistry in taxonomy.

• Chromosome number, karyotype, polyploidy, meiotic pairing with examples.
• Chemical characters: primary metabolites (proteins, serology) and secondary metabolites.
• Examples and limitations.

Q5. Write a note on molecular systematics and the APG system.

• DNA sequences as characters; cladistic analysis.
• APG history (1998, 2003, 2009, 2016).
• Main groups: basal angiosperms, magnoliids, monocots, eudicots.
• Changes from Bentham and Hooker (e.g. families merged or split).

परीक्षेसाठी टीप

For "modern trends" questions, write a short paragraph on each branch with one example. Never forget the year 1963 (Sneath and Sokal) and the rbcL + matK barcode.

थोडक्यात सारांश

A flower is a modified shoot meant for sexual reproduction. An inflorescence is the arrangement of flowers on the floral axis. This topic covers the parts of a typical flower, floral terms, aestivation, placentation, types of inflorescence, and how to write a floral formula and draw a floral diagram.

महत्त्वाचे मुद्दे

• A flower (फूल) has four whorls on the thalamus: calyx (sepals), corolla (petals), androecium (stamens) and gynoecium (carpels).
• Calyx and corolla are accessory whorls; androecium and gynoecium are essential whorls.
• When calyx and corolla look alike, they are called perianth (tepals), e.g. lily.
• Symmetry: actinomorphic (radial, e.g. mustard), zygomorphic (bilateral, e.g. pea), asymmetric (e.g. Canna).
• Position of ovary: hypogynous (superior ovary, e.g. mustard), perigynous (half-inferior, e.g. rose), epigynous (inferior ovary, e.g. sunflower, guava).
• Aestivation is the arrangement of sepals or petals in a bud: valvate (Calotropis), twisted (cotton, china rose), imbricate (Cassia), vexillary or papilionaceous (pea).
• Placentation is the arrangement of ovules in the ovary: marginal (pea), axile (china rose, tomato), parietal (mustard), free central (Dianthus), basal (sunflower, marigold).
• Racemose inflorescence: main axis keeps growing; flowers in acropetal order (older at the base). Types: raceme, spike, catkin, spadix, corymb, umbel, head (capitulum).
• Cymose inflorescence: main axis ends in a flower; flowers in basipetal order. Types: monochasial (helicoid, scorpioid), dichasial, polychasial.
• Special inflorescences: cyathium (Euphorbia), hypanthodium (Ficus), verticillaster (Ocimum, tulsi).

महत्त्वाच्या संज्ञा

• Bract – reduced leaf at the base of a flower stalk.
• Bisexual / unisexual – flower with both or only one type of essential whorl.
• Epipetalous – stamens attached to petals (e.g. brinjal).
• Monadelphous – stamens fused into one bundle (china rose); diadelphous – two bundles (pea, 9 + 1).
• Syngenesious – anthers fused, filaments free (sunflower).
• Didynamous – four stamens, two long and two short (tulsi); tetradynamous – six stamens, four long and two short (mustard).
• Syncarpous / apocarpous – carpels fused / free.

महत्त्वाची माहिती

Floral formula symbols: Br – bracteate; ⊕ – actinomorphic; % – zygomorphic; ⚥ – bisexual; ♂ male; ♀ female; K – calyx; C – corolla; P – perianth; A – androecium; G – gynoecium; G with a line below it – superior ovary; G with a line above it – inferior ovary; brackets ( ) – fusion; a number above or ∞ – many.

• Floral formula of mustard (Brassicaceae): ⊕ ⚥ K2+2 C4 A2+4 G(2), ovary superior.
• Floral diagram: drawn as seen from above; the mother axis is shown as a dot at the top; whorls drawn as concentric circles from outside (calyx) to inside (gynoecium) with a T.S. of the ovary in the centre.

५ महत्त्वाचे प्रश्न

Q1. Differentiate between racemose and cymose inflorescence.

In racemose, the main axis grows on and flowers open in acropetal order, older at the base. In cymose, the main axis ends in a flower and flowers open in basipetal order.

Q2. What is placentation? Name its types.

Placentation is the arrangement of ovules inside the ovary. Types: marginal, axile, parietal, free central, basal, and superficial (water lily).

Q3. Describe the types of aestivation with examples.

• Valvate: margins just touch – Calotropis.
• Twisted: one margin overlaps the next regularly – china rose, cotton.
• Imbricate: irregular overlap – Cassia, gulmohur.
• Vexillary: large standard covers two wings, which cover keel – pea, bean.
• Draw a small sketch of each.

Q4. Explain the types of racemose inflorescence.

• Raceme: stalked flowers on long axis – mustard.
• Spike: sessile flowers – Achyranthes.
• Spadix: fleshy axis with spathe – banana, Colocasia.
• Catkin: drooping spike of unisexual flowers – mulberry.
• Corymb, umbel (coriander, onion) and capitulum/head (sunflower).

Q5. What is a floral formula? Write the floral formula of a pea flower and explain it.

• Short way of expressing floral characters with symbols.
• Pea (Fabaceae): % ⚥ K(5) C1+2+(2) A(9)+1 G1, ovary superior.
• Zygomorphic, bisexual; 5 fused sepals; vexillary corolla (standard, 2 wings, 2 fused keel petals).
• Diadelphous stamens; monocarpellary, superior ovary with marginal placentation.

परीक्षेसाठी टीप

Practise drawing one floral diagram (mustard or pea) and writing its formula. Examiners give marks for correct symbols and bracket use.

थोडक्यात सारांश

After fertilisation, the ovary develops into a fruit and the ovules into seeds. Fruits protect seeds and help in their dispersal. This topic covers the structure of a fruit, the classification of fruits (simple, aggregate and composite) with examples, the structure of dicot and monocot seeds, and the agents of seed and fruit dispersal.

महत्त्वाचे मुद्दे

• A true fruit develops only from the ovary (mango, tomato). A false fruit (pseudocarp) has other floral parts too – thalamus in apple and strawberry, whole inflorescence in fig.
• Parthenocarpy – fruit formed without fertilisation, usually seedless (banana, seedless grapes).
• Pericarp (fruit wall) has three layers: epicarp, mesocarp, endocarp.
• Drupe – stony endocarp: mango, coconut (fibrous mesocarp).
• Berry – fleshy throughout: tomato, grape, guava, banana.
• Pepo – cucumber, watermelon. Hesperidium – orange (juicy hairs from endocarp). Pome – apple (fleshy thalamus).
• Simple fleshy fruits:
• Dehiscent: legume (pea, bean), capsule (cotton, lady's finger), siliqua (mustard).
• Indehiscent: caryopsis (wheat, rice, maize; pericarp fused with seed coat), cypsela (sunflower), nut (cashew).
• Schizocarpic: lomentum (Mimosa), cremocarp (coriander).
• Simple dry fruits:
• Aggregate fruit – from many free carpels of one flower: custard apple, strawberry, Michelia.
• Composite (multiple) fruit – from a whole inflorescence: sorosis (pineapple, jackfruit), syconus (fig).
• Dicot seed (gram, bean): seed coat (testa and tegmen), hilum, micropyle, embryo with two cotyledons, plumule, radicle; usually non-endospermic.
• Monocot seed (maize grain): endosperm large with aleurone layer, single cotyledon called scutellum, coleoptile over plumule and coleorhiza over radicle.
• Dispersal agents: wind (light seeds, wings – Moringa; hairs – Calotropis, cotton; pappus – Tridax), water (coconut – fibrous buoyant mesocarp; lotus), animals (hooks – Xanthium, Achyranthes; fleshy edible fruits), explosive mechanism (balsam, castor).

महत्त्वाच्या संज्ञा

• Pericarp – wall of the fruit developed from the ovary wall.
• Pseudocarp – false fruit formed with non-ovarian parts.
• Caryopsis – one-seeded dry fruit with pericarp fused to the seed coat.
• Scutellum – shield-shaped cotyledon of grasses.
• Pappus – modified calyx of hairs in Asteraceae that helps wind dispersal.

महत्त्वाची माहिती

५ महत्त्वाचे प्रश्न

Q1. What is a false fruit? Give two examples.

A false fruit is a fruit in which parts other than the ovary, such as the thalamus or the inflorescence axis, form the fleshy part. Examples: apple, strawberry, fig.

Q2. Distinguish between a legume and a siliqua.

A legume comes from a monocarpellary ovary and splits along both sutures (pea). A siliqua comes from a bicarpellary ovary with a false septum (replum) and opens from below upwards (mustard).

Q3. Classify fruits with suitable examples.

Simple (fleshy and dry: dehiscent, indehiscent, schizocarpic), aggregate and composite fruits; at least two examples each and labelled sketches of mango, legume and pineapple.

Q4. Compare the structure of a dicot seed and a monocot seed.

Gram/bean seed vs maize grain: seed coat, cotyledons, endosperm, scutellum, coleoptile, coleorhiza – labelled L.S. diagrams.

Q5. Describe the methods of seed and fruit dispersal.

Wind, water, animals, explosive mechanism – adaptations with two examples each; importance of dispersal (less competition, new habitats).

परीक्षेसाठी टीप

Questions like "edible part of mango, coconut, apple, wheat" are common one-mark items. Learn the table and one dispersal example for each agent.

थोडक्यात सारांश

University syllabi ask students to describe important dicot families: their vegetative and floral characters, floral formula, floral diagram and economic importance. This topic covers five commonly prescribed families – Malvaceae, Fabaceae, Asteraceae, Solanaceae and Lamiaceae – following Bentham and Hooker's system, with their position in the APG system.

महत्त्वाचे मुद्दे

• Malvaceae (cotton family; Thalamiflorae): mucilage, stellate hairs; epicalyx present; calyx valvate; corolla twisted; stamens many, monadelphous (staminal tube), anthers monothecous (one-celled), kidney-shaped; superior ovary with axile placentation; capsule. Examples: Hibiscus, cotton (Gossypium), lady's finger.
• Fabaceae / Papilionaceae (pea family; Calyciflorae): leaves pinnately compound with stipules; root nodules; papilionaceous corolla – 1 standard, 2 wings, 2 keel petals; vexillary (descendingly imbricate) aestivation; stamens 10, diadelphous (9) + 1; monocarpellary ovary, marginal placentation; fruit legume. Examples: pea, gram, groundnut, soybean.
• Asteraceae / Compositae (sunflower family; Inferae): inflorescence a capitulum (head) with ray and disc florets surrounded by an involucre; calyx modified into pappus; stamens 5, syngenesious (anthers fused, filaments free), epipetalous; bicarpellary, inferior ovary, one ovule, basal placentation; fruit cypsela. Examples: sunflower, marigold, Tridax.
• Solanaceae (potato family; Bicarpellatae): calyx persistent; corolla rotate or funnel-shaped; stamens 5, epipetalous; bicarpellary, superior ovary, obliquely placed carpels, swollen axile placentae; berry or capsule. Examples: potato, tomato, brinjal, chilli, Datura.
• Lamiaceae / Labiatae (mint family; Bicarpellatae): square stem, opposite-decussate aromatic leaves; verticillaster inflorescence; bilabiate corolla (2/3); stamens 4, didynamous; ovary four-lobed with gynobasic style; fruit of 4 nutlets. Examples: tulsi (Ocimum), mint, Leucas.

महत्त्वाच्या संज्ञा

• Epicalyx – whorl of bracteoles outside the calyx.
• Monadelphous – all filaments fused in one bundle.
• Syngenesious – anthers fused but filaments free.
• Didynamous – four stamens, two long and two short.
• Gynobasic style – style arising from the base of the lobed ovary.
• Floral formula – short code of a flower's parts, e.g. Br, ⊕ or %, ⚥, K, C, A, G.

महत्त्वाची माहिती

(Brackets mean the parts are fused; in A5 of Solanaceae the stamens are free from each other but fused to the petals.)

५ महत्त्वाचे प्रश्न

Q1. What is a papilionaceous corolla?

A butterfly-like corolla of five petals: one large posterior standard (vexillum), two lateral wings (alae) and two anterior keel petals fused along one edge (carina). It is typical of Fabaceae.

Q2. Give two distinguishing characters of Lamiaceae.

Square stem with opposite aromatic leaves, and a four-lobed ovary with a gynobasic style (also bilabiate corolla and didynamous stamens).

Q3. Describe the family Malvaceae with economic importance.

Vegetative characters, inflorescence, flower (epicalyx, twisted petals, monadelphous monothecous stamens, axile placentation), floral formula and diagram; uses: cotton fibre, lady's finger, ornamental Hibiscus.

Q4. Describe Asteraceae and explain why it is called the most advanced dicot family.

Capitulum, florets, pappus, syngenesious stamens, inferior ovary, cypsela; advanced because of head inflorescence, reduced calyx for dispersal, efficient pollination, huge number of species. Economic importance: sunflower oil, safflower, ornamentals, weeds.

Q5. Compare Solanaceae and Lamiaceae.

Stem, leaves, inflorescence, corolla, stamens, ovary, style and fruit in a table; one floral diagram each.

परीक्षेसाठी टीप

In practicals, always open a flower and check: free or fused petals, number and fusion of stamens, and ovary position – these three features usually give the family. Write the floral formula correctly.

थोडक्यात सारांश

Monocot families are recognised by parallel venation, trimerous flowers and a single cotyledon. This topic covers three families commonly prescribed in B.Sc. syllabi – Liliaceae, Musaceae and Poaceae (Gramineae) – with their vegetative and floral characters, floral formulae, special features (such as the grass spikelet) and economic importance.

महत्त्वाचे मुद्दे

• General monocot features: fibrous adventitious roots; scattered closed vascular bundles; leaves with sheathing base and parallel venation; flowers usually trimerous; perianth (tepals) instead of separate calyx and corolla.
• Liliaceae (lily family; Bentham and Hooker's Coronarieae): herbs with bulbs, rhizomes or corms; flowers actinomorphic, bisexual; perianth 6 in two whorls of 3 (petaloid); stamens 6, often epiphyllous (on tepals); ovary superior, tricarpellary, syncarpous, trilocular, axile placentation; fruit capsule or berry.
• Liliaceae examples: lily, Gloriosa (glory lily), Asparagus, Aloe, onion and garlic (now often placed in Amaryllidaceae in APG). Uses: food (onion, garlic, Asparagus), medicine (Aloe, Gloriosa gives colchicine), ornamentals.
• Musaceae (banana family; Epigynae/Scitamineae): giant herbs with an underground rhizome and a pseudostem formed by leaf sheaths; huge leaves with pinnate-parallel venation; flowers in spadix-like inflorescence covered by large coloured spathes; flowers zygomorphic, unisexual or bisexual; perianth 6; stamens 5 fertile + 1 staminode; ovary inferior, tricarpellary, axile; fruit a berry (parthenocarpic in cultivated banana).
• Poaceae / Gramineae (grass family; Glumaceae): stem a culm with hollow internodes and solid nodes; leaves with sheath, ligule and long blade; inflorescence of spikelets arranged in spikes or panicles.
• Grass floret: enclosed by lemma and palea; perianth reduced to 2–3 lodicules; stamens usually 3 (6 in rice) with versatile anthers; ovary monocarpellary (with 2–3 feathery stigmas), superior, one ovule, basal; fruit caryopsis.
• Each spikelet has two sterile glumes at the base and one or more florets.
• Poaceae is the most important family for humans: rice, wheat, maize, jowar, bajra, sugarcane, bamboo, fodder grasses.

महत्त्वाच्या संज्ञा

• Tepal – a perianth member when sepals and petals look alike.
• Pseudostem – false stem made of rolled leaf sheaths (banana).
• Spathe – large bract covering an inflorescence.
• Ligule – membranous outgrowth at the junction of leaf sheath and blade in grasses.
• Lemma and palea – outer and inner bracts enclosing a grass floret.
• Lodicules – tiny scales (reduced perianth) that swell to open the floret.

महत्त्वाची माहिती

५ महत्त्वाचे प्रश्न

Q1. What is a spikelet?

A spikelet is the unit of the grass inflorescence. It has two sterile glumes at the base and one or more florets on a short axis (rachilla); each floret is enclosed by a lemma and a palea.

Q2. Why is the banana stem called a pseudostem?

Because the aerial "stem" is formed by tightly rolled leaf sheaths. The true stem is an underground rhizome; it grows up through the sheaths only at flowering.

Q3. Describe the family Poaceae with its economic importance.

Culm, leaf with ligule, spikelet structure, floret (lemma, palea, lodicules, 3 stamens, feathery stigmas), caryopsis; floral formula and diagram; cereals, millets, sugarcane, bamboo, fodder.

Q4. Give the distinguishing features of Liliaceae.

Bulbous habit, trimerous actinomorphic flowers, 6 petaloid tepals, 6 epiphyllous stamens, superior trilocular ovary with axile placentation; examples and uses; note its splitting under APG.

Q5. Describe Musaceae with a floral diagram.

Rhizome and pseudostem, leaves, spathe-covered inflorescence, zygomorphic flowers, 5 stamens + staminode, inferior ovary, berry; uses – fruit, fibre (Musa textilis, Manila hemp), leaves as plates.

परीक्षेसाठी टीप

For grasses, examiners look for the labelled spikelet diagram – glumes, lemma, palea, lodicules, stamens and feathery stigma. Write "caryopsis" for the fruit, not "grain".

थोडक्यात सारांश

All primary organs of a plant are formed by groups of always-dividing cells at the tips of the shoot and root, called apical meristems. Different theories explain how these meristems are organised. This topic covers the apical cell theory, histogen theory, tunica–corpus theory, the organisation of the root apex and the quiescent centre.

महत्त्वाचे मुद्दे

• Meristem – a tissue of small, thin-walled, densely cytoplasmic cells with large nuclei and no intercellular spaces, able to divide.
• By position: apical (tips), intercalary (bases of internodes, grasses), lateral (cambium, cork cambium).
• Apical cell theory (Hofmeister; supported by Nägeli, 19th century): a single large apical cell at the tip forms the whole plant body. True for many algae, bryophytes and pteridophytes (e.g. Equisetum), not for seed plants.
• Dermatogen → epidermis,
• Periblem → cortex,
• Plerome → stele (vascular tissue and pith).
• Histogen theory (Hanstein, 1868): the apex has three layers (histogens):

The theory fits the root of many plants but not the shoot, because the layers do not always give these fixed tissues.

• Tunica–corpus theory (A. Schmidt, 1924) for the shoot apex: an outer tunica of one or more layers that divide only anticlinally (adding surface), and an inner corpus whose cells divide in all planes (adding volume). It is based on planes of division, not on fate of tissues.
• Cytohistological zonation in gymnosperm and angiosperm shoot apices: central mother cell zone, peripheral zone (forms leaves) and rib meristem (forms pith).
• Root apex is covered by a root cap produced by the calyptrogen (in monocots) or by a common initial layer (in many dicots).
• Körper–Kappe theory (Schüepp, 1917) for roots: T-divisions in the root apex.
• Quiescent centre (F. A. L. Clowes, 1956): a group of cells at the root tip that divide very slowly; it is a reserve that can replace damaged active initials.
• Leaves start as leaf primordia on the flanks of the shoot apex; the order of their origin decides phyllotaxy.

महत्त्वाच्या संज्ञा

• Anticlinal division – wall formed at right angles to the surface; increases surface area.
• Periclinal division – wall parallel to the surface; increases the number of layers.
• Histogen – a layer of the apex that forms a definite tissue.
• Calyptrogen – separate initial layer forming the root cap in monocots.
• Quiescent centre – slowly dividing central region of the root apex.

महत्त्वाची माहिती

५ महत्त्वाचे प्रश्न

Q1. What is the quiescent centre?

It is a group of cells at the centre of the root apex that divide very rarely. Discovered by Clowes (1956), it acts as a reserve of initials when active cells are damaged.

Q2. Name the three histogens and what they form.

Dermatogen forms the epidermis, periblem forms the cortex and plerome forms the central stele.

Q3. Explain the tunica–corpus theory with a diagram.

• Schmidt (1924); tunica layers divide anticlinally; corpus divides in all planes.
• Number of tunica layers varies (1–5).
• Merits over the histogen theory. Labelled L.S. of shoot apex.

Q4. Describe the organisation of the root apex.

• Root cap, calyptrogen (monocots), histogens.
• Körper–Kappe concept, quiescent centre.
• Diagram of root tip L.S.

Q5. Compare the theories of shoot apex organisation.

Apical cell, histogen and tunica–corpus theories in a table: basis, layers, merits, limits; add cytohistological zonation.

परीक्षेसाठी टीप

Learn the five names and years in the table. In a long answer, always end with why tunica–corpus is preferred for the shoot (it is based on division planes, not fixed tissue fate).

थोडक्यात सारांश

Secondary growth is the increase in thickness (girth) of stems and roots due to the activity of lateral meristems: the vascular cambium and the cork cambium. It occurs in dicots and gymnosperms, but usually not in monocots. This topic covers the formation of the cambium ring, secondary xylem and phloem, annual rings, heartwood and sapwood, periderm and lenticels.

महत्त्वाचे मुद्दे

• Primary growth increases length (apical meristems). Secondary growth (द्वितीयक वाढ) increases girth.
• In a dicot stem, the cambium inside the vascular bundles is intrafascicular cambium.
• Parenchyma cells of medullary rays between bundles become meristematic to form interfascicular cambium.
• Both join to form a complete vascular cambium ring.
• Cambium cuts off cells on both sides: more towards the inside as secondary xylem (wood) and fewer towards the outside as secondary phloem.
• Primary xylem gets pushed towards the centre; primary phloem gets crushed outside.
• Cambium also forms secondary medullary rays for radial conduction.
• Cork cambium (phellogen) arises in the cortex. It forms cork (phellem) outside and secondary cortex (phelloderm) inside.
• Phellem + phellogen + phelloderm = periderm.
• Bark = all dead tissues outside the vascular cambium (periderm plus secondary phloem in a wide sense).
• In the dicot root, cambium arises from conjunctive parenchyma and pericycle opposite the protoxylem; it is first wavy and later becomes circular.

महत्त्वाच्या संज्ञा

• Spring wood (early wood) – light, wide vessels; formed when cambium is very active.
• Autumn wood (late wood) – dark, narrow vessels; formed when activity is low.
• Annual ring (growth ring) – one band of spring wood plus autumn wood formed in one year.
• Dendrochronology – estimating the age of a tree by counting annual rings.
• Heartwood (duramen) – dark, central, dead wood filled with tannins, resins and tyloses; gives strength and is durable.
• Sapwood (alburnum) – light, outer wood that conducts water.
• Tyloses – balloon-like ingrowths of parenchyma into vessels, blocking them.
• Lenticels – lens-shaped openings in bark for gas exchange.

महत्त्वाची माहिती

• Clear annual rings form in temperate climates; in tropical regions with no sharp seasons, rings are often not distinct.
• Anomalous secondary growth (unusual pattern) is seen in some plants, e.g. Dracaena (a monocot that shows secondary growth), Boerhaavia, Bignonia.

५ महत्त्वाचे प्रश्न

Q1. What are annual rings?

An annual ring is a pair of spring wood and autumn wood formed in one year by the vascular cambium. Counting these rings gives the approximate age of the tree.

Q2. Differentiate between heartwood and sapwood.

Heartwood is the dark, central, non-functional wood with tannins and tyloses; it is hard and durable. Sapwood is the light, outer, living-cell-containing wood that conducts water and minerals.

Q3. Describe secondary growth in a dicot stem.

• Intrafascicular and interfascicular cambium join to form a ring.
• Cambium forms secondary xylem inside and secondary phloem outside.
• Secondary medullary rays formed.
• Annual rings formed due to seasonal activity.
• Cork cambium forms periderm; lenticels develop.
• Diagram stages: young stem, cambium ring, T.S. of old stem showing rings, pith, rays, phloem, periderm.

Q4. Explain the formation and structure of periderm.

• Phellogen arises from outer cortex (or epidermis/pericycle in some).
• Outer cells form phellem (cork): dead, suberised, compact.
• Inner cells form phelloderm: living, parenchymatous.
• Function: protection, prevents water loss.
• Lenticels: loose complementary cells allow gas exchange.

Q5. Explain secondary growth in a dicot root.

• Cambium forms from conjunctive parenchyma below phloem.
• Pericycle opposite protoxylem also becomes meristematic.
• Wavy ring becomes circular.
• Secondary xylem and phloem formed; broad medullary rays opposite protoxylem.
• Cork cambium from pericycle forms periderm; cortex sheds.

परीक्षेसाठी टीप

Draw stage-wise diagrams of a dicot stem (cambium ring formation to old stem). Remember: cambium gives more xylem than phloem.

थोडक्यात सारांश

Embryology of angiosperms deals with the formation of male and female gametophytes, pollination, fertilisation and the development of the endosperm and embryo. Angiosperms show a special process called double fertilisation. This topic covers microsporogenesis, megasporogenesis, embryo sac types, double fertilisation, endosperm, embryo development and polyembryony.

महत्त्वाचे मुद्दे

• Stamen = anther + filament. A typical anther is dithecous with four microsporangia (pollen sacs).
• Anther wall (outside to inside): epidermis, endothecium (helps dehiscence), middle layers, tapetum (nourishes developing pollen).
• Microsporogenesis: each microspore mother cell (2n) divides by meiosis to form a tetrad of four haploid microspores (pollen grains).
• Pollen wall: outer exine of sporopollenin (very resistant) with germ pores, and inner intine of cellulose and pectin.
• Male gametophyte: pollen divides into a large vegetative (tube) cell and a small generative cell; the generative cell forms two male gametes (in the pollen grain or in the pollen tube).
• Ovule parts: funicle, hilum, integuments, micropyle, chalaza, nucellus and embryo sac.
• Megasporogenesis: megaspore mother cell (2n) undergoes meiosis to give four megaspores; usually three degenerate and the chalazal one is functional.
• Polygonum type (monosporic) embryo sac is the most common: 8 nuclei in 7 cells – egg apparatus (egg + two synergids) at the micropylar end, three antipodals at the chalazal end, and a central cell with two polar nuclei.
• Double fertilisation (discovered by S. G. Nawaschin, 1898): one male gamete fuses with the egg (syngamy) → zygote (2n); the other fuses with the two polar nuclei (triple fusion) → primary endosperm nucleus (3n).
• Endosperm types: nuclear (coconut water), cellular, helobial.
• Dicot embryo development (Crucifer / Onagrad type, e.g. Capsella): zygote → proembryo with suspensor → globular → heart-shaped → mature embryo with two cotyledons.

महत्त्वाच्या संज्ञा

• Pollination – transfer of pollen to the stigma. Self (autogamy, geitonogamy) and cross (xenogamy).
• Filiform apparatus – finger-like wall thickenings of synergids that guide the pollen tube.
• Porogamy / chalazogamy / mesogamy – pollen tube entering through micropyle / chalaza / integuments.
• Perisperm – remaining nucellus in a seed (black pepper, beet).
• Polyembryony – more than one embryo in a seed (citrus, mango).
• Apomixis – seed formation without fertilisation.
• Parthenocarpy – fruit formation without fertilisation (seedless banana, grapes).

महत्त्वाची माहिती

• Capsella bursa-pastoris (shepherd's purse) is the standard type for dicot embryo; grass embryo has a scutellum (single cotyledon) and coleoptile/coleorhiza.

५ महत्त्वाचे प्रश्न

Q1. What is triple fusion?

Triple fusion is the fusion of the second male gamete with the two polar nuclei (or the secondary nucleus) in the central cell. It forms the triploid primary endosperm nucleus, which develops into the endosperm.

Q2. What is the role of the tapetum?

The tapetum is the innermost layer of the anther wall. It nourishes developing pollen grains and contributes materials to the pollen wall, including sporopollenin and pollenkitt.

Q3. Describe the structure of a mature embryo sac (Polygonum type).

• Monosporic, 8-nucleate, 7-celled.
• Micropylar end: egg apparatus (egg cell + two synergids with filiform apparatus).
• Chalazal end: three antipodal cells.
• Centre: large central cell with two polar nuclei.
• Labels: micropyle, synergids, filiform apparatus, egg, polar nuclei, central cell, antipodals, chalaza.

Q4. Explain double fertilisation and its significance.

• Pollen tube enters the embryo sac through a synergid and releases two male gametes.
• Syngamy: male gamete + egg → zygote (2n).
• Triple fusion: male gamete + two polar nuclei → PEN (3n).
• Significance: forms nutritive endosperm only when fertilisation occurs (saves energy); unique to angiosperms; gives vigour.

Q5. Describe the development of a dicot embryo.

• Zygote divides transversely: basal cell (forms suspensor and hypophysis) and terminal cell (forms embryo proper).
• Quadrant and octant stages → globular embryo.
• Dermatogen forms epidermis.
• Heart-shaped stage as cotyledons start.
• Mature embryo: two cotyledons, plumule, radicle, hypocotyl.

परीक्षेसाठी टीप

Remember ploidy of each structure (table above). Draw a labelled anther T.S., ovule L.S. and embryo sac.

थोडक्यात सारांश

Plants absorb water from the soil through roots, carry it up through the xylem and lose most of it as water vapour from leaves. This topic explains diffusion, osmosis, water potential, plasmolysis, imbibition, absorption of water, ascent of sap and transpiration.

महत्त्वाचे मुद्दे

• Diffusion – net movement of molecules from higher to lower concentration.
• Osmosis (परासरण) – movement of water through a semi-permeable membrane from a region of higher water potential (dilute solution) to lower water potential (concentrated solution).
• Endosmosis is entry of water into a cell; exosmosis is exit of water.
• Water potential (Ψw) is the chemical potential of water. Pure water at atmospheric pressure has Ψw = 0; adding solutes makes it negative. Water always moves from higher (less negative) to lower (more negative) Ψw.
• Water potential has two main components: solute potential (Ψs) (always negative) and pressure potential (Ψp) (usually positive in turgid cells).
• Plasmolysis – shrinking of protoplasm away from the cell wall when a cell is placed in a hypertonic solution. Reversing it in water is deplasmolysis.
• Imbibition – absorption of water by solid hydrophilic substances (dry seeds, wood) causing swelling.
• Absorption of water is mainly through root hairs. Active absorption uses energy (root pressure); passive absorption is due to transpiration pull (the main way).
• Water moves across the root by the apoplast pathway (through cell walls and spaces) and the symplast pathway (through cytoplasm and plasmodesmata). At the endodermis the Casparian strip forces water into the symplast.
• Ascent of sap is best explained by the cohesion–tension (transpiration pull) theory of Dixon and Joly (1894).
• Transpiration – loss of water as vapour from aerial parts; mostly through stomata (stomatal), some through cuticle (cuticular) and lenticels (lenticular).

महत्त्वाच्या संज्ञा

• Turgor pressure – pressure of cell contents against the cell wall.
• Root pressure – positive pressure in xylem due to active absorption; seen as guttation (water drops at leaf tips through hydathodes) and bleeding.
• Cohesion – attraction between water molecules.
• Adhesion – attraction between water and xylem walls.
• Guard cells – kidney-shaped cells (dumb-bell shaped in grasses) around a stoma.
• Antitranspirant – substance that reduces transpiration (e.g. phenyl mercuric acetate, abscisic acid).

सूत्रे

• Water potential: Ψw = Ψs + Ψp (in some texts also + Ψm, matric potential).
• Units: pascals (Pa), usually megapascals (MPa); 1 MPa = 10 bar.
• Example: a cell with Ψs = −0.8 MPa and Ψp = +0.3 MPa has Ψw = −0.8 + 0.3 = −0.5 MPa.
• If this cell is placed next to a cell with Ψw = −0.7 MPa, water moves from the first cell (−0.5) to the second (−0.7).

५ महत्त्वाचे प्रश्न

Q1. Define plasmolysis.

Plasmolysis is the shrinkage of the protoplast away from the cell wall due to exosmosis when a living plant cell is kept in a hypertonic solution.

Q2. A cell has solute potential −1.2 MPa and pressure potential 0.4 MPa. Find its water potential.

Ψw = Ψs + Ψp = −1.2 + 0.4 = −0.8 MPa. Water will enter this cell from any neighbour whose water potential is higher (less negative) than −0.8 MPa.

Q3. Explain the cohesion–tension theory of ascent of sap.

• Proposed by Dixon and Joly.
• Continuous water column from root to leaf in xylem.
• Cohesion keeps the column unbroken; adhesion holds it to xylem walls.
• Transpiration from leaf cells creates tension (negative pressure).
• This pull is transmitted down the column, lifting water.
• Evidence: high tensile strength of water; negative pressure in xylem; reduced flow when transpiration stops.

Q4. Describe the mechanism of stomatal opening and closing.

• Guard cells have thick inner walls and thin outer walls.
• Opening: K⁺ ions enter guard cells (proton pump), malate forms; Ψ falls, water enters, guard cells become turgid and bow outward.
• Closing: K⁺ leaves, water leaves, guard cells become flaccid.
• Abscisic acid causes closure during water stress.
• Older starch–sugar hypothesis (Steward) also mentioned in syllabi.

Q5. Give the factors affecting transpiration and its significance.

• External: light, temperature, humidity, wind, soil water.
• Internal: number and position of stomata, leaf area, cuticle thickness.
• Significance: pull for ascent of sap, cooling, mineral distribution.
• Called a "necessary evil" (Curtis) because it also wastes much water.

परीक्षेसाठी टीप

Practise one numerical on Ψw = Ψs + Ψp and remember that water flows towards the more negative value.

थोडक्यात सारांश

Plant cells are built from a few kinds of large organic molecules – carbohydrates, proteins, lipids and nucleic acids – along with water and minerals. This topic covers the structure, classification and functions of carbohydrates, amino acids and proteins, and lipids, which form the base for studying enzymes, photosynthesis and respiration.

महत्त्वाचे मुद्दे

• Carbohydrates are polyhydroxy aldehydes or ketones with the general formula (CH₂O)n.
• Monosaccharides: simple sugars – trioses (glyceraldehyde), pentoses (ribose, deoxyribose), hexoses (glucose – aldose; fructose – ketose).
• Disaccharides: two monosaccharides joined by a glycosidic bond – sucrose (glucose + fructose; the transport sugar of plants, non-reducing), maltose (glucose + glucose), lactose.
• Polysaccharides: starch (storage; amylose – unbranched α-1,4; amylopectin – branched with α-1,6), cellulose (structural; β-1,4 glucose; most abundant organic compound on Earth), inulin (fructose polymer in dahlia tubers), hemicellulose, pectin.
• Amino acids have an amino group (–NH₂), a carboxyl group (–COOH) and an R-group on one carbon. 20 standard amino acids make proteins. They are joined by peptide bonds.
• Protein structure: primary (sequence), secondary (α-helix, β-pleated sheet held by hydrogen bonds), tertiary (3-D folding: disulphide bonds, ionic and hydrophobic forces), quaternary (several polypeptide chains, e.g. RuBisCO with 8 large + 8 small subunits).
• Protein functions in plants: enzymes, storage proteins in seeds (gluten in wheat), structural proteins, transport and pigment-binding proteins.
• Simple lipids: fats and oils = triglycerides (glycerol + 3 fatty acids, ester bonds); waxes (cuticle).
• Compound lipids: phospholipids (membranes), glycolipids (chloroplast membranes).
• Derived lipids: sterols, carotenoids.
• Lipids: insoluble in water, soluble in organic solvents.
• Saturated fatty acids have no double bonds (palmitic, stearic); unsaturated have double bonds (oleic, linoleic) – plant oils are mostly unsaturated and liquid.
• Nucleic acids (DNA, RNA) are polymers of nucleotides (sugar + phosphate + base).

महत्त्वाच्या संज्ञा

• Glycosidic bond – link between two sugar units.
• Reducing sugar – sugar with a free aldehyde or ketone group that reduces Benedict's/Fehling's solution.
• Peptide bond – –CO–NH– link between two amino acids.
• Denaturation – loss of a protein's 3-D shape by heat, pH or chemicals.
• Triglyceride – ester of glycerol with three fatty acids.

महत्त्वाची माहिती

• Tests: iodine – blue-black for starch; Benedict's – brick red for reducing sugar; Biuret – violet for protein; Sudan III – red for oil.

५ महत्त्वाचे प्रश्न

Q1. Distinguish between starch and cellulose.

Starch is a storage polysaccharide of α-glucose with α-1,4 (and α-1,6) bonds; it gives blue-black colour with iodine. Cellulose is a structural polysaccharide of β-glucose with β-1,4 bonds forming straight fibres; it gives no colour with iodine.

Q2. What is a peptide bond?

A peptide bond is the –CO–NH– covalent bond formed between the carboxyl group of one amino acid and the amino group of the next, with loss of a water molecule.

Q3. Classify carbohydrates with examples and functions.

Monosaccharides, disaccharides (reducing and non-reducing), polysaccharides (storage and structural); structure of glucose; role of sucrose in transport.

Q4. Describe the levels of protein structure.

Primary, secondary (α-helix, β-sheet), tertiary, quaternary – bonds involved at each level, examples, and the meaning of denaturation.

Q5. Write an account of plant lipids.

Simple, compound and derived lipids; triglyceride formation; saturated and unsaturated fatty acids; roles in storage, membranes, cuticle; commercial oils.

परीक्षेसाठी टीप

Learn the bond type for each polymer and the four colour tests – they are frequent short-answer and practical questions.

थोडक्यात सारांश

Enzymes are biological catalysts, mostly proteins, that speed up chemical reactions in cells without being used up. Every step of photosynthesis, respiration and growth is run by enzymes. This topic covers the nature, properties, classification, mechanism of action, factors affecting activity and inhibition of enzymes.

महत्त्वाचे मुद्दे

• The term enzyme was given by W. Kühne (1878). J. B. Sumner (1926) first crystallised an enzyme (urease, from jack bean) and showed it is a protein.
• Most enzymes are proteins; some RNA molecules (ribozymes) also act as catalysts.
• Holoenzyme = apoenzyme (protein part) + cofactor. Cofactors may be metal ions (Mg²⁺, Zn²⁺, Fe²⁺), coenzymes (NAD⁺, NADP⁺, FAD, coenzyme A – often from vitamins) or tightly bound prosthetic groups (haem).
• Enzymes lower the activation energy of a reaction; they do not change the equilibrium.
• Active site – the small pocket where the substrate binds.
• Lock and key model (Emil Fischer, 1894): substrate fits the rigid active site exactly.
• Induced fit model (Daniel Koshland, 1958): the active site changes shape slightly to fit the substrate.
• Properties: high specificity, high efficiency (turnover number), work in small amounts, sensitive to temperature and pH, reversible action in many cases.
• Factors: temperature (optimum ~25–40 °C for most plant enzymes; denatured at high temperature), pH (each enzyme has an optimum), substrate concentration (rate rises then becomes constant – Vmax), enzyme concentration, inhibitors.
• Michaelis–Menten constant (Km): substrate concentration at which the rate is half of Vmax. Low Km = high affinity.
• Inhibition: competitive (inhibitor resembles substrate, binds active site; e.g. malonate inhibits succinate dehydrogenase; Km increases, Vmax unchanged), non-competitive (binds elsewhere; Vmax decreases), allosteric/feedback inhibition (end product inhibits the first enzyme of a pathway).
• IUB classification – six classes (below).

महत्त्वाच्या संज्ञा

• Apoenzyme – protein part of an enzyme, inactive alone.
• Coenzyme – organic, loosely bound non-protein helper (NAD⁺).
• Activation energy – minimum energy needed to start a reaction.
• Isoenzymes – different molecular forms of an enzyme with the same action (e.g. lactate dehydrogenase).
• Allosteric site – regulatory site other than the active site.

सूत्रे

• v = rate of reaction, Vmax = maximum rate, [S] = substrate concentration, Km = Michaelis constant (same unit as [S], e.g. mM).
• Michaelis–Menten equation: v = Vmax [S] / (Km + [S])
• When [S] = Km, v = Vmax/2.

५ महत्त्वाचे प्रश्न

Q1. What is a holoenzyme?

A holoenzyme is the complete active enzyme made of a protein part (apoenzyme) and a non-protein cofactor such as a metal ion or coenzyme.

Q2. What is Km?

Km (Michaelis constant) is the substrate concentration at which the reaction rate is half of its maximum. A low Km shows high affinity of the enzyme for its substrate.

Q3. Explain the mechanism of enzyme action.

Activation energy concept with a graph; enzyme–substrate complex (E + S ⇌ ES → E + P); lock and key vs induced fit models with diagrams.

Q4. Discuss the factors affecting enzyme activity.

Temperature, pH, substrate and enzyme concentration (with graphs), activators and inhibitors; Michaelis–Menten curve.

Q5. Describe the IUB classification of enzymes.

Six classes with reaction type and examples, the four-digit EC number (e.g. EC 3.2.1.1 for α-amylase).

परीक्षेसाठी टीप

Draw the substrate-concentration curve with Vmax and Km marked, and remember the six classes with the order "Ox-Trans-Hydro-Ly-Iso-Lig".

थोडक्यात सारांश

Plants need mineral elements from the soil for normal growth. These are divided into macronutrients and micronutrients based on the amount needed. This topic covers criteria of essentiality, hydroponics, roles and deficiency symptoms of elements, mechanism of mineral absorption and the nitrogen cycle including biological nitrogen fixation.

महत्त्वाचे मुद्दे

• Julius von Sachs (1860) grew plants in nutrient solutions without soil – hydroponics (soilless culture).
• Criteria of essentiality (Arnon and Stout, 1939): the element must be needed for completing the life cycle; it cannot be replaced by another element; it must be directly involved in plant metabolism.
• About 17 elements are essential for most higher plants.
• Macronutrients (needed in large amounts, more than 10 mmol per kg dry matter): C, H, O, N, P, K, S, Ca, Mg.
• Micronutrients (trace elements): Fe, Mn, Cu, Mo, Zn, B, Cl, Ni.
• C, H and O come from air and water; others from soil.
• Absorption of minerals occurs by passive (diffusion, ion exchange) and active (carrier proteins, using ATP) methods.
• Nitrogen cycle steps: nitrogen fixation, ammonification, nitrification, nitrate assimilation, denitrification.
• Biological nitrogen fixation (N₂ → NH₃) is done by the enzyme nitrogenase, which works only in the absence of oxygen.
• In legume root nodules, Rhizobium fixes nitrogen; leghaemoglobin (pink pigment) protects nitrogenase from oxygen.

महत्त्वाच्या संज्ञा

• Chlorosis – yellowing of leaves due to loss of chlorophyll (deficiency of N, K, Mg, S, Fe, Mn, Zn, Mo).
• Necrosis – death of tissue (deficiency of Ca, Mg, Cu, K).
• Mobile elements – N, P, K, Mg; deficiency appears first in older leaves.
• Immobile elements – Ca, S, Fe, B; deficiency appears first in young leaves.
• Nitrification – NH₃ → NO₂⁻ (Nitrosomonas) → NO₃⁻ (Nitrobacter).
• Denitrification – NO₃⁻ → N₂ (Pseudomonas, Thiobacillus).
• Toxicity – excess of a mineral that reduces dry weight by about 10%.

महत्त्वाची माहिती

• Overall nitrogenase reaction: N₂ + 8e⁻ + 8H⁺ + 16 ATP → 2NH₃ + H₂ + 16 ADP + 16 Pi.

५ महत्त्वाचे प्रश्न

Q1. What is hydroponics?

Hydroponics is the method of growing plants in a balanced nutrient solution without soil. It was started by Sachs (1860) and helps find essential elements and grow crops in small spaces.

Q2. What is leghaemoglobin? Give its role.

Leghaemoglobin is a pink, oxygen-binding pigment in legume root nodules. It keeps oxygen level low around nitrogenase, protecting the enzyme while still supplying oxygen for bacterial respiration.

Q3. Explain the criteria of essentiality of mineral elements.

• Given by Arnon and Stout.
• Absence prevents completion of life cycle.
• Specific; cannot be replaced by another element.
• Directly involved in metabolism.
• List macro and micronutrients with examples.

Q4. Describe the formation of root nodules in legumes.

• Root secretes chemicals; Rhizobium multiplies near root hairs.
• Root hair curls around bacteria.
• Infection thread carries bacteria into the cortex.
• Cortical and pericycle cells divide to form the nodule.
• Bacteria become bacteroids; leghaemoglobin and nitrogenase formed.
• N₂ fixed to NH₃, used to make amino acids.

Q5. Explain the nitrogen cycle.

• Fixation: lightning, industrial (Haber process), biological.
• Ammonification by decomposers.
• Nitrification by Nitrosomonas and Nitrobacter.
• Assimilation of nitrate by plants; animals eat plants.
• Denitrification returns N₂ to air.
• Draw a cycle diagram with arrows.

परीक्षेसाठी टीप

Learn the deficiency-symptom table well; questions like "whiptail is caused by deficiency of …" are common.

थोडक्यात सारांश

Photosynthesis is the process by which green plants use light energy to make glucose from carbon dioxide and water, releasing oxygen. It occurs in chloroplasts and has two stages: the light reactions and the dark (carbon-fixing) reactions. This topic covers pigments, photosystems, the Z-scheme, photophosphorylation, the Calvin cycle, C₄ pathway, CAM, photorespiration and limiting factors.

महत्त्वाचे मुद्दे

• Overall equation: 6CO₂ + 12H₂O → C₆H₁₂O₆ + 6O₂ + 6H₂O (in light, with chlorophyll). Photosynthesis is प्रकाशसंश्लेषण in Marathi.
• Van Niel showed that the oxygen released comes from water, not CO₂ (later confirmed with ¹⁸O by Ruben and Kamen).
• Site: chloroplast. Light reactions in thylakoid membranes (grana); dark reactions in the stroma.
• Pigments: chlorophyll a (main pigment, reaction centre), chlorophyll b, carotenoids (carotenes and xanthophylls) as accessory pigments.
• Photosystem I (PS I) has reaction centre P700; Photosystem II (PS II) has P680.
• Emerson effect (enhancement effect): the rate of photosynthesis is higher when red light (680 nm) and far-red light (above 680 nm) are given together. This proved two photosystems.
• Photolysis of water at PS II: 2H₂O → 4H⁺ + O₂ + 4e⁻ (needs Mn²⁺ and Cl⁻).
• Non-cyclic photophosphorylation (Z-scheme) uses both PS II and PS I; produces ATP, NADPH and O₂.
• Cyclic photophosphorylation uses only PS I; produces only ATP.
• ATP is made by chemiosmosis (Peter Mitchell) through ATP synthase as protons flow from the thylakoid lumen to the stroma.
• Calvin cycle (C₃ cycle), worked out by Melvin Calvin with ¹⁴C in Chlorella: carboxylation, reduction, regeneration. First stable product is 3-phosphoglyceric acid (3-PGA). Enzyme: RuBisCO.
• C₄ pathway (Hatch–Slack pathway): first product is oxaloacetic acid (OAA); CO₂ acceptor is PEP; enzyme PEP carboxylase. Found in maize, sugarcane, sorghum. Leaves show Kranz anatomy.
• CAM (Crassulacean Acid Metabolism): stomata open at night; CO₂ stored as malic acid; used in the day (e.g. Bryophyllum, pineapple, Opuntia).

महत्त्वाच्या संज्ञा

• Action spectrum – rate of photosynthesis at different wavelengths (peaks in blue and red).
• Absorption spectrum – light absorbed by a pigment at different wavelengths.
• Quantasome – unit of photosynthesis on thylakoid membranes (older term).
• Photorespiration – light-dependent uptake of O₂ and release of CO₂ when RuBisCO acts as an oxygenase; involves chloroplast, peroxisome and mitochondria; common in C₃ plants and wasteful.
• Kranz anatomy – bundle sheath cells with large chloroplasts surrounded by mesophyll cells, like a wreath.
• Blackman's law of limiting factors (1905) – when a process depends on several factors, its rate is limited by the factor in shortest supply.

सूत्रे

• Overall: 6CO₂ + 12H₂O → C₆H₁₂O₆ + 6H₂O + 6O₂
• Carboxylation: RuBP (5C) + CO₂ → 2 × 3-PGA (3C), by RuBisCO.
• For one glucose (6 turns of Calvin cycle): 18 ATP and 12 NADPH are used.
• C₄ plants need 30 ATP per glucose (extra ATP for regenerating PEP).

५ महत्त्वाचे प्रश्न

Q1. What is the Emerson enhancement effect?

When far-red light (above 680 nm) and shorter red light are given together, the rate of photosynthesis is more than the sum of the rates with each alone. It shows that two photosystems work together.

Q2. Differentiate between cyclic and non-cyclic photophosphorylation.

Cyclic uses only PS I; electrons return to P700; only ATP is formed, no O₂ or NADPH. Non-cyclic uses PS II and PS I; electrons go to NADP⁺; ATP, NADPH and O₂ are formed.

Q3. Describe the Calvin cycle.

• Carboxylation: CO₂ + RuBP → 2 molecules of 3-PGA (RuBisCO).
• Reduction: 3-PGA → 1,3-bisphosphoglycerate → glyceraldehyde-3-phosphate using ATP and NADPH.
• Regeneration: some G3P regenerates RuBP using ATP.
• Some G3P forms glucose/sucrose/starch.
• Six turns fix 6 CO₂ for one glucose; 18 ATP and 12 NADPH used.

Q4. Explain the C₄ pathway and its advantages.

• In mesophyll cells: PEP + CO₂ → OAA (PEP carboxylase) → malate.
• Malate moves to bundle sheath cells; decarboxylated to release CO₂ and pyruvate.
• CO₂ enters Calvin cycle in bundle sheath.
• Pyruvate returns to mesophyll; PEP regenerated using ATP.
• Advantages: little photorespiration, high efficiency at high temperature and light, better water use.

Q5. Explain the Z-scheme of light reaction.

• PS II absorbs light; P680 excited; electrons to pheophytin → plastoquinone → cytochrome b₆f → plastocyanin.
• Electrons from water replace those lost (photolysis, O₂ released).
• PS I absorbs light; P700 excited; electrons → ferredoxin → NADP⁺ reductase → NADPH.
• Proton gradient drives ATP synthesis.
• Energy diagram looks like the letter Z.

परीक्षेसाठी टीप

Learn the first stable products (3-PGA in C₃, OAA in C₄) and the ATP/NADPH count for one glucose. Draw the Z-scheme with carriers in the right order.

थोडक्यात सारांश

Sugars made in leaves must reach roots, fruits, seeds and growing tips. This long-distance movement of organic food through the phloem is called translocation. This topic covers the evidence that phloem carries food, the source–sink concept, phloem loading and unloading, and the theories of the mechanism, especially Münch's pressure flow (mass flow) hypothesis.

महत्त्वाचे मुद्दे

• Food moves in the sieve tubes of phloem, helped by companion cells. Sieve tube elements have no nucleus at maturity and are joined end to end through sieve plates.
• Main sugar translocated is sucrose (non-reducing, stable, highly soluble). Some plants also carry raffinose, stachyose or sugar alcohols. Amino acids, hormones and some minerals also move in phloem.
• Girdling (ringing) experiment (Malpighi): removing a ring of bark (with phloem) causes swelling above the ring as food collects there; roots below starve.
• Radioactive tracers: leaves given ¹⁴CO₂ – the labelled sugar appears in sieve tubes.
• Aphid stylet technique: aphids feed on sieve tubes; the cut stylet exudes phloem sap rich in sucrose.
• Evidence for phloem transport:
• Source – organ that makes or releases sugar (mature leaf, germinating storage organ). Sink – organ that uses or stores it (roots, fruits, young leaves, tubers). Direction is from source to sink, so it can be upward or downward (bidirectional).
• Phloem loading – sucrose enters sieve tube–companion cell complex in the leaf; often active, by a sucrose–H⁺ symport powered by a proton pump (ATP). It may be apoplastic or symplastic (via plasmodesmata).
• Phloem unloading – sucrose leaves sieve tubes at the sink; it may be converted to starch or hexoses.
• Sugar loaded at source → water potential falls → water enters from xylem by osmosis → high turgor pressure.
• Sugar unloaded at sink → water leaves → low pressure.
• Sap flows in bulk from high to low pressure along the sieve tube.
• Pressure flow hypothesis (E. Münch, 1930):
• Other theories: diffusion (too slow), protoplasmic streaming (de Vries), electro-osmotic theory – less accepted.
• Speed of translocation is about 0.5–1 m per hour.

महत्त्वाच्या संज्ञा

• Translocation – movement of organic solutes through phloem.
• Source / sink – supplier and user of sugars.
• Phloem loading – transfer of sugars into the sieve tubes.
• Symport – carrier moving two substances in the same direction.
• P-protein and callose – substances that seal sieve plates after injury.

महत्त्वाची माहिती

५ महत्त्वाचे प्रश्न

Q1. Why is sucrose the main form of sugar translocated?

Sucrose is non-reducing and chemically stable, so it does not react on the way; it is highly soluble and carries a lot of energy per molecule.

Q2. What is the girdling experiment?

Removing a complete ring of bark (including phloem) from a stem. Food collects and the bark swells above the ring, while the root side starves – showing food moves down through phloem.

Q3. Explain the pressure flow hypothesis with a diagram.

Münch (1930); source loading, osmotic water entry, high turgor; sink unloading; bulk flow; model of two osmometers joined by a tube; merits and objections (bidirectional flow, energy need).

Q4. Describe phloem loading and unloading.

Apoplastic and symplastic routes; sucrose–proton symport; role of companion cells (transfer cells); unloading at sinks and fate of sucrose.

Q5. Give experimental evidence that phloem translocates food.

Girdling, radioactive ¹⁴C tracer, aphid stylet, analysis of sap, blocking of sieve plates by callose.

परीक्षेसाठी टीप

Draw the Münch two-bulb model or a leaf–stem–root diagram with arrows showing sugar and water movement – it earns most of the marks in a long answer.

थोडक्यात सारांश

Respiration is the breakdown of food (mainly glucose) in living cells to release energy in the form of ATP. Aerobic respiration uses oxygen; anaerobic respiration does not. This topic covers glycolysis, link reaction, Krebs cycle, electron transport chain, fermentation, respiratory quotient and the energy balance sheet.

महत्त्वाचे मुद्दे

• Respiration (श्वसन) is a catabolic, energy-releasing process occurring in all living cells.
• Overall aerobic equation: C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + energy.
• Glycolysis (EMP pathway – Embden, Meyerhof, Parnas): in the cytoplasm; glucose → 2 pyruvate; net gain of 2 ATP and 2 NADH. Common to aerobic and anaerobic respiration.
• Link reaction (oxidative decarboxylation): pyruvate → acetyl CoA + CO₂ + NADH in the mitochondrial matrix (enzyme complex pyruvate dehydrogenase).
• Krebs cycle (TCA / citric acid cycle), by Hans Krebs (1937), in the mitochondrial matrix. Acetyl CoA (2C) + OAA (4C) → citric acid (6C). Per turn: 2 CO₂, 3 NADH, 1 FADH₂, 1 ATP/GTP.
• Electron transport chain (ETS) on the inner mitochondrial membrane; oxygen is the final electron acceptor, forming water.
• Oxidative phosphorylation forms ATP by chemiosmosis through ATP synthase (F₀–F₁ particles).
• Anaerobic respiration / fermentation: pyruvate → ethanol + CO₂ (alcoholic fermentation, yeast) or → lactic acid (lactic acid bacteria, muscles). Net gain only 2 ATP per glucose.
• Pentose phosphate pathway (HMP shunt) is an alternative route producing NADPH and 5-carbon sugars.
• Respiration is called an amphibolic pathway because it is both catabolic and anabolic (its intermediates are used to make fats, amino acids).

महत्त्वाच्या संज्ञा

• Respiratory quotient (RQ) – ratio of CO₂ given out to O₂ taken in.
• Substrate-level phosphorylation – direct ATP formation from a substrate (e.g. in glycolysis, Krebs cycle).
• Oxidative phosphorylation – ATP formation using energy of electron transport.
• Pasteur effect – decrease in sugar breakdown when oxygen is supplied to cells doing anaerobic respiration.
• Cytochrome oxidase – last enzyme of ETS (complex IV) that passes electrons to O₂.

सूत्रे

• RQ = volume of CO₂ evolved ÷ volume of O₂ consumed.
• Carbohydrate: C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O, RQ = 6/6 = 1.
• Fat (tripalmitin): 2C₅₁H₉₈O₆ + 145O₂ → 102CO₂ + 98H₂O, RQ = 102/145 ≈ 0.7.
• Organic acid (oxalic acid): 2(COOH)₂ + O₂ → 4CO₂ + 2H₂O, RQ = 4/1 = 4 (more than 1).
• Anaerobic: RQ is infinite (CO₂ released, no O₂ used).
• ATP balance (aerobic, one glucose): modern value about 30–32 ATP (taking 1 NADH ≈ 2.5 ATP and 1 FADH₂ ≈ 1.5 ATP); older textbooks give 36–38 ATP (taking NADH = 3, FADH₂ = 2).

५ महत्त्वाचे प्रश्न

Q1. What is RQ? Give its value for carbohydrates and fats.

RQ is the ratio of the volume of CO₂ released to the volume of O₂ used in respiration. It is 1 for carbohydrates and about 0.7 for fats.

Q2. Why is respiration called an amphibolic pathway?

Respiration breaks down food (catabolism), but its intermediates like acetyl CoA and α-ketoglutarate are used to make fatty acids and amino acids (anabolism). Hence it is both catabolic and anabolic.

Q3. Describe glycolysis.

• Occurs in cytoplasm; no O₂ needed.
• Glucose phosphorylated twice using 2 ATP → fructose-1,6-bisphosphate.
• Split into two 3C molecules (G3P and DHAP).
• Oxidation forms 2 NADH; substrate-level phosphorylation gives 4 ATP.
• End product: 2 pyruvate; net gain 2 ATP + 2 NADH.

Q4. Explain the Krebs cycle.

• Acetyl CoA + OAA → citric acid (citrate synthase).
• Citric acid → isocitric acid → α-ketoglutaric acid (CO₂, NADH).
• α-KG → succinyl CoA (CO₂, NADH) → succinic acid (GTP/ATP).
• Succinic → fumaric (FADH₂) → malic → OAA (NADH).
• Two turns per glucose.

Q5. Calculate the RQ of tripalmitin and explain its meaning.

• 2C₅₁H₉₈O₆ + 145O₂ → 102CO₂ + 98H₂O.
• RQ = 102 ÷ 145 = 0.70 (approx.).
• RQ less than 1 means fats need more oxygen because they have less oxygen in their molecule than carbohydrates.

परीक्षेसाठी टीप

Write the place of each stage (cytoplasm, matrix, inner membrane). If asked for total ATP, mention both the older (38) and modern (about 30–32) values with the reason.

थोडक्यात सारांश

Plants store energy as oils in seeds such as groundnut, sunflower and castor. When these seeds germinate, the oil is broken down and changed into sugar for the growing seedling. This topic covers the breakdown of fats (lipolysis and β-oxidation), the glyoxylate cycle that turns fat into sugar, and a short outline of fatty acid synthesis.

महत्त्वाचे मुद्दे

• Lipolysis: the enzyme lipase hydrolyses triglycerides into glycerol + 3 fatty acids. In oil seeds this happens in oleosomes (oil bodies).
• Glycerol is phosphorylated to glycerol-3-phosphate and oxidised to dihydroxyacetone phosphate (DHAP), which joins glycolysis or gluconeogenesis.
• Activation of fatty acid: fatty acid + CoA + ATP → fatty acyl-CoA (by acyl-CoA synthetase).
• β-oxidation (Knoop, 1904): fatty acyl-CoA is shortened by 2 carbons per cycle, releasing acetyl-CoA. Each cycle has four steps: oxidation (FAD → FADH₂), hydration, oxidation (NAD⁺ → NADH) and thiolysis.
• In plants, β-oxidation takes place mainly in glyoxysomes (in germinating oily seeds) and peroxisomes, not mainly in mitochondria as in animals. In glyoxysomes the first oxidation passes electrons to O₂, forming H₂O₂, which catalase breaks down.
• A fatty acid with n carbons (even) needs (n/2) – 1 cycles and gives n/2 acetyl-CoA. Palmitic acid (C16): 7 cycles, 8 acetyl-CoA.
• Glyoxylate cycle (Kornberg and Krebs, 1957): a modified Krebs cycle in glyoxysomes that skips the two decarboxylation steps, so carbon is saved.
• Two special enzymes: isocitrate lyase (isocitrate → succinate + glyoxylate) and malate synthase (glyoxylate + acetyl-CoA → malate).
• Net result: 2 acetyl-CoA → 1 succinate. Succinate goes to mitochondria → malate → oxaloacetate → PEP (by PEP carboxykinase) → sucrose by gluconeogenesis in the cytosol.
• Animals lack the glyoxylate cycle, so they cannot make sugar from fat; oily seedlings can.
• Fatty acid synthesis occurs in plastids: acetyl-CoA → malonyl-CoA (acetyl-CoA carboxylase); fatty acid synthase adds 2 C at a time using NADPH, forming palmitate (C16) and stearate (C18).

महत्त्वाच्या संज्ञा

• Lipase – enzyme hydrolysing fats into glycerol and fatty acids.
• β-oxidation – stepwise removal of two-carbon units from fatty acids at the β-carbon.
• Glyoxysome – microbody containing glyoxylate-cycle enzymes in fat-storing seedlings.
• Gluconeogenesis – formation of glucose/sucrose from non-carbohydrate sources.
• Oleosome – oil body storing triglycerides in seeds.

सूत्रे

• Number of β-oxidation cycles for an even-carbon fatty acid = (n/2) – 1; acetyl-CoA formed = n/2.
• Worked example: stearic acid (C18) → cycles = 18/2 – 1 = 8; acetyl-CoA = 18/2 = 9.
• Glyoxylate cycle (net): 2 Acetyl-CoA + NAD⁺ → Succinate + 2 CoA + NADH + H⁺

५ महत्त्वाचे प्रश्न

Q1. Name the two key enzymes of the glyoxylate cycle.

Isocitrate lyase and malate synthase. They are present in glyoxysomes and are absent in animals.

Q2. How many acetyl-CoA molecules are formed from palmitic acid?

Palmitic acid has 16 carbons, so it gives 16/2 = 8 acetyl-CoA in 7 cycles of β-oxidation.

Q3. Describe β-oxidation of fatty acids.

Activation to acyl-CoA; entry into glyoxysome/peroxisome; four reactions of each cycle; product acetyl-CoA; energy yield; difference between plant and animal sites.

Q4. Explain the glyoxylate cycle and its significance.

Location, steps with the two special enzymes, net reaction, conversion of succinate to sucrose; significance in germinating oily seeds; draw the cycle.

Q5. Write a note on the conversion of fats into carbohydrates in germinating seeds.

Lipolysis in oil bodies → β-oxidation in glyoxysomes → glyoxylate cycle → mitochondria (succinate → oxaloacetate) → cytosol (PEP → sucrose); role of three organelles.

परीक्षेसाठी टीप

Learn the "three-organelle route" (oil body → glyoxysome → mitochondrion → cytosol) and practise the β-oxidation count for C16 and C18 – easy marks.

थोडक्यात सारांश

Plant growth regulators (plant hormones) are organic substances produced in small amounts that control growth and development. Auxins, gibberellins and cytokinins mostly promote growth; abscisic acid and ethylene mostly inhibit it or cause ageing. This topic covers their discovery, physiological effects and uses in agriculture, plus photoperiodism and vernalisation.

महत्त्वाचे मुद्दे

• Plant hormones are also called phytohormones (वनस्पती संप्रेरके).
• Auxins: first discovered. Charles and Francis Darwin (1880) observed bending of canary grass coleoptile towards light. F. W. Went (1928) isolated auxin from Avena coleoptile tips using agar blocks (Avena curvature test). Natural auxin: indole-3-acetic acid (IAA). Synthetic: 2,4-D, NAA, IBA.
• Gibberellins (GA): discovered by E. Kurosawa (1926) from the fungus Gibberella fujikuroi, which causes bakanae (foolish seedling) disease of rice. More than 100 gibberellins are known; GA₃ is the most common.
• Cytokinins: kinetin discovered by Skoog and Miller (1955) from autoclaved herring sperm DNA. Natural cytokinin zeatin from maize. Found in coconut milk.
• Abscisic acid (ABA): a growth inhibitor; called the stress hormone. Causes stomatal closure, seed and bud dormancy.
• Ethylene: a gaseous hormone; promotes fruit ripening, senescence and abscission. Ethephon releases ethylene.

महत्त्वाच्या संज्ञा

• Apical dominance – the apical bud suppresses lateral buds; controlled by auxin.
• Parthenocarpy – seedless fruit formation without fertilisation (auxins, gibberellins).
• Bolting – sudden elongation of internodes before flowering in rosette plants (gibberellin), e.g. cabbage.
• Richmond–Lang effect – delay of leaf senescence by cytokinins.
• Photoperiodism – response of plants to the relative length of day and night (Garner and Allard, 1920). Plants are short-day (e.g. Xanthium, chrysanthemum), long-day (e.g. wheat, radish) or day-neutral (e.g. tomato, maize).
• Vernalisation – promotion of flowering by a period of low temperature.
• Florigen – hypothetical flowering hormone (Chailakhyan).

महत्त्वाची माहिती

• In tissue culture: high auxin/cytokinin ratio → roots; low ratio → shoots (Skoog and Miller).

५ महत्त्वाचे प्रश्न

Q1. What is apical dominance?

Apical dominance is the suppression of the growth of lateral buds by the apical bud. It is due to auxin from the shoot tip. Removing the tip (as in tea plucking or hedge cutting) allows lateral branches to grow.

Q2. Why is ABA called the stress hormone?

During stress like drought, ABA level rises and causes stomata to close, reducing water loss. It also induces dormancy, helping plants survive bad conditions.

Q3. Describe the discovery and physiological effects of gibberellins.

• Kurosawa (1926) – bakanae disease of rice due to Gibberella fujikuroi.
• Seedlings grow abnormally tall and weak.
• Effects: internode elongation, bolting, breaking seed dormancy, parthenocarpy, α-amylase formation in cereal grains, reversal of dwarfism.
• Uses: sugarcane yield, grape size, malting industry.

Q4. Explain the role of auxins in plants.

• Cell elongation in shoots; phototropism and geotropism.
• Apical dominance.
• Root initiation in stem cuttings.
• Prevents abscission of leaves and fruits.
• Parthenocarpy (tomato).
• Synthetic auxins as weedicides (2,4-D).
• Describe Went's Avena coleoptile experiment briefly.

Q5. What is photoperiodism? Classify plants on its basis.

• Response of flowering to day length (Garner and Allard).
• Short-day plants flower when the day is shorter than a critical length (actually need a long dark period).
• Long-day plants flower when the day is longer than a critical length.
• Day-neutral plants flower regardless.
• Site of perception: leaves; pigment phytochrome is involved.

परीक्षेसाठी टीप

Make a one-line table of each hormone: discoverer, first source, two effects, one use. It answers most short questions.

थोडक्यात सारांश

Plants cannot walk, but they do move – whole cells swim, organs bend towards light, and leaves fold at night or on touch. This topic covers the types of plant movements: movements of locomotion, tropic movements (growth towards or away from a stimulus), nastic movements (not directed by the stimulus) and autonomic movements, with their mechanisms and examples.

महत्त्वाचे मुद्दे

• Movements of locomotion – whole organism or cell moves: ciliary/flagellar (Chlamydomonas, antherozoids), amoeboid (slime moulds), cytoplasmic streaming (cyclosis in Hydrilla leaf cells).
• Movements of curvature – a fixed organ bends. Two kinds: growth movements (permanent, due to unequal growth) and turgor (variation) movements (reversible, due to change in turgor).
• Autonomic (spontaneous) movements: caused by internal factors – nutation (zig-zag growth of the stem tip), circumnutation (spiral growth of tendrils, twiners), and the jerky leaflet movement of the telegraph plant (Desmodium gyrans).
• Paratonic (induced) movements: caused by external stimuli.
• Phototropism: shoot positive, root negative to light. Explained by Cholodny–Went theory – auxin moves to the shaded side, cells there elongate more, so the shoot bends towards light. Went's Avena coleoptile curvature test.
• Geotropism (gravitropism): root positive, shoot negative. Statoliths (starch grains, amyloplasts) in root-cap cells settle and signal gravity; auxin collects on the lower side, which inhibits root cell growth and promotes shoot cell growth.
• Hydrotropism (roots towards water), thigmotropism (tendrils coil around supports), chemotropism (pollen tube towards ovule).
• Tropic movements – direction decided by the stimulus:
• Photonasty: flowers opening in light (sunflower) or at night (Cestrum, night queen).
• Thermonasty: tulip and crocus flowers open with warmth.
• Nyctinasty (sleep movements): leaflets of tamarind, Cassia, Oxalis fold at night.
• Seismonasty/thigmonasty: Mimosa pudica leaflets fold within seconds of touch; insectivorous Drosera tentacles and Dionaea (Venus flytrap) lobes close on prey.
• Nastic movements – direction not decided by the stimulus:
• In Mimosa pudica, touch sends an electrical signal to the pulvinus; K⁺ and water leave the lower motor cells, they lose turgor and the leaf droops. Recovery takes 10–15 minutes.
• Hygroscopic movements (physical, in dead tissue): opening of capsules, Funaria peristome teeth, elaters of Equisetum.

महत्त्वाच्या संज्ञा

• Tropism – directional growth movement in response to a one-sided stimulus.
• Nastic movement – non-directional movement in response to a diffuse stimulus.
• Pulvinus – swollen leaf base with motor cells that cause turgor movements.
• Statolith – starch grain that senses gravity.
• Nutation – zig-zag growth of the stem tip.

महत्त्वाची माहिती

५ महत्त्वाचे प्रश्न

Q1. Differentiate between tropic and nastic movements.

Tropic movements are directional growth movements; the organ bends towards or away from the stimulus (phototropism). Nastic movements are non-directional, often turgor movements, and the direction is fixed by the organ's structure (Mimosa leaf folding).

Q2. What are statoliths?

Statoliths are dense starch grains (amyloplasts) in root-cap and shoot endodermis cells. They settle under gravity and help the plant sense the direction of gravity.

Q3. Describe the mechanism of seismonastic movement in Mimosa pudica.

Stimulus at leaflet; electrical and chemical signal; pulvinus structure; loss of K⁺ and water from lower motor cells; drooping; recovery; diagram of pulvinus.

Q4. Explain phototropism with the Cholodny–Went theory.

Darwin and Boysen-Jensen experiments; Went's agar block test; lateral auxin transport to the shaded side; differential growth; diagrams.

Q5. Classify plant movements with examples.

Locomotion vs curvature; autonomic vs paratonic; growth vs turgor; tropic vs nastic; hygroscopic – a flow chart with examples.

परीक्षेसाठी टीप

A flow chart of plant movements, plus the Mimosa pulvinus diagram, covers most questions in this topic. Remember: tropic = direction from stimulus, nastic = direction from structure.

थोडक्यात सारांश

Plants often grow in unfavourable conditions – too little water, too much salt, extreme heat or cold, flooding or pollution. Such conditions are called stress. This topic covers types of stress, how they harm plants, and the avoidance and tolerance mechanisms plants use, including the roles of abscisic acid, osmolytes, heat-shock proteins and antioxidants.

महत्त्वाचे मुद्दे

• Stress – any external factor that reduces growth, development or yield below the plant's potential. Biotic stress comes from pathogens, pests and weeds; abiotic stress from water, temperature, salt, light, flooding, heavy metals and pollutants.
• Stress resistance has two strategies: avoidance (prevents the stress reaching the tissues) and tolerance (tissues withstand it).
• Effects: stomatal closure, less photosynthesis, wilting, reduced cell expansion, early leaf fall.
• ABA (abscisic acid) rises in leaves and closes stomata – the "stress hormone".
• Adaptations: deep roots, thick cuticle, sunken stomata, leaf rolling, CAM pathway, and accumulation of osmolytes such as proline, glycine betaine and sugars (osmotic adjustment).
• Drought (water stress):
• High Na⁺ and Cl⁻ cause osmotic stress (physiological drought) and ion toxicity.
• Halophytes survive by excluding salt at roots, secreting it through salt glands (Avicennia), storing it in vacuoles, or succulence (Salicornia, Suaeda).
• Salt stress:
• Heat stress: proteins denature, membranes become leaky. Plants make heat-shock proteins (HSPs) that act as molecular chaperones; transpirational cooling helps.
• Cold and freezing stress: chilling damages membranes of tropical plants (banana, mango); freezing forms ice crystals. Tolerance by cold acclimation (hardening), unsaturated membrane lipids, antifreeze proteins and sugars.
• Flooding (anaerobic) stress: roots get little oxygen; plants form aerenchyma, adventitious roots and use fermentation. Ethylene promotes aerenchyma.
• Oxidative stress is common to most stresses: reactive oxygen species (ROS) such as superoxide and H₂O₂ build up. Antioxidant enzymes superoxide dismutase (SOD), catalase and peroxidase, and antioxidants like ascorbate and glutathione remove them.
• Breeding and biotechnology produce stress-tolerant varieties (e.g. submergence-tolerant rice with the Sub1 gene).

महत्त्वाच्या संज्ञा

• Osmolyte (compatible solute) – small molecule like proline that lowers water potential without harming the cell.
• Halophyte / glycophyte – salt-tolerant plant / salt-sensitive plant.
• Acclimation – gradual increase in tolerance after exposure to mild stress.
• Heat-shock proteins – chaperones made under high temperature to protect proteins.
• ROS – reactive oxygen species that damage lipids, proteins and DNA.

महत्त्वाची माहिती

५ महत्त्वाचे प्रश्न

Q1. Why is ABA called the stress hormone?

Because its level rises quickly under drought, salinity and cold, and it triggers protective responses such as stomatal closure and synthesis of protective proteins.

Q2. What is the role of proline in stress?

Proline accumulates in the cytoplasm under drought and salt stress. It lowers the cell's water potential (osmotic adjustment), protects proteins and membranes, and helps remove ROS.

Q3. Describe the effects of water stress and adaptations to it.

Effects on growth, stomata, photosynthesis, enzymes; avoidance (roots, cuticle, leaf rolling) and tolerance (osmolytes, ABA, CAM, dehydrins).

Q4. Explain the mechanisms of salt tolerance in plants.

Osmotic and ionic phases; exclusion, compartmentation in vacuoles, salt glands, succulence; examples of halophytes in mangroves.

Q5. Write a note on oxidative stress and antioxidant defence.

Formation of ROS; damage to lipids, proteins and DNA; enzymes SOD, catalase, peroxidase; non-enzymatic antioxidants.

परीक्षेसाठी टीप

Use the table to answer "short notes" quickly, and always link each stress to one hormone or molecule: drought – ABA/proline, heat – HSPs, flooding – ethylene/aerenchyma.