Botany वनस्पतिशास्त्र

Quick summary

Genetics is the study of heredity and variation. Gregor Johann Mendel discovered the basic laws of inheritance by working on the garden pea. This topic covers Mendel's experiments, monohybrid and dihybrid crosses, his laws, test cross and back cross, and deviations from Mendelian ratios such as incomplete dominance, codominance, epistasis and multiple alleles.

Key points

• Gregor Johann Mendel (1822–1884), the "father of genetics", worked on the garden pea Pisum sativum (1856–1863) and published his results in 1865/1866.
• His work was rediscovered in 1900 by Hugo de Vries, Carl Correns and Erich von Tschermak.
• The term genetics was coined by William Bateson (1905); the word gene by W. Johannsen (1909).
• Mendel studied seven pairs of contrasting characters, e.g. tall/dwarf stem, round/wrinkled seed, yellow/green seed, violet/white flower.
• Reasons for success: pea is self-pollinating, has clear contrasting characters, short life cycle; he used pure lines, studied one character at a time and used statistics.
• Monohybrid cross (tall × dwarf): F₁ all tall; F₂ phenotypic ratio 3 : 1, genotypic ratio 1 : 2 : 1.
• Dihybrid cross (round yellow × wrinkled green): F₂ phenotypic ratio 9 : 3 : 3 : 1.
• Law of dominance: in a heterozygote, one factor (dominant) expresses itself and the other (recessive) does not.
• Law of segregation (purity of gametes): the two factors of a pair separate during gamete formation; each gamete gets only one.
• Law of independent assortment: factors of different characters are distributed to gametes independently of each other.

Important terms

• Allele – alternative forms of a gene (e.g. T and t).
• Homozygous / heterozygous – having identical (TT, tt) / different (Tt) alleles.
• Genotype / phenotype – genetic make-up / visible character.
• Test cross – cross of F₁ with the homozygous recessive parent; monohybrid test cross ratio 1 : 1, dihybrid 1 : 1 : 1 : 1.
• Back cross – cross of F₁ with either parent.
• Incomplete dominance – F₁ shows an intermediate character; e.g. Mirabilis jalapa (4 o'clock plant) red × white → pink; F₂ ratio 1 : 2 : 1 (both phenotypic and genotypic).
• Codominance – both alleles fully expressed in the heterozygote; e.g. AB blood group, roan coat in cattle.
• Epistasis – one gene masks the effect of another non-allelic gene.
• Multiple alleles – more than two alleles of one gene in a population; e.g. Iᴬ, Iᴮ, i of ABO blood groups.

Formulas

• Number of gamete types = 2ⁿ (n = number of heterozygous gene pairs).
• Number of F₂ genotypes = 3ⁿ; F₂ phenotypes (complete dominance) = 2ⁿ; F₂ combinations in Punnett square = 4ⁿ.
• Example: for a dihybrid (n = 2): gametes 4, genotypes 9, phenotypes 4, combinations 16.

5 important questions

Q1. State the law of segregation.

The two alleles of a gene, which stay together in an individual, separate during gamete formation. Each gamete receives only one allele, so gametes are always pure.

Q2. What is a test cross? Give its significance.

A test cross is the cross between an individual of dominant phenotype and its homozygous recessive. A 1 : 1 result shows the individual is heterozygous; all dominant offspring show it is homozygous.

Q3. Explain a dihybrid cross with a Punnett square.

• Parents: RRYY (round yellow) × rryy (wrinkled green).
• F₁: RrYy – all round yellow.
• F₁ gametes: RY, Ry, rY, ry.
• F₂ (16 boxes): 9 round yellow : 3 round green : 3 wrinkled yellow : 1 wrinkled green.
• Proves law of independent assortment.

Q4. Explain incomplete dominance with an example.

• Neither allele is fully dominant.
• Mirabilis jalapa: RR (red) × rr (white) → Rr (pink).
• F₂: 1 red : 2 pink : 1 white.
• Phenotypic and genotypic ratios are the same.
• Shows that factors do not blend; they separate again in F₂.

Q5. Explain complementary gene interaction (9 : 7).

• Two dominant genes needed together to produce a character.
• Bateson and Punnett: two white-flowered sweet pea varieties (CCpp × ccPP) gave purple F₁ (CcPp).
• F₂: 9 purple (C_P_) : 7 white (C_pp, ccP_, ccpp).
• Reason: one gene makes a precursor, the other converts it into pigment.

Exam tip

Always draw Punnett squares neatly and write both phenotypic and genotypic ratios. Memorise the gene-interaction ratio table.

Quick summary

Not all inheritance follows simple Mendelian ratios. Some traits such as height, seed colour intensity and yield are controlled by many genes with small additive effects (polygenic or quantitative inheritance). Other traits are inherited through genes outside the nucleus, in chloroplasts and mitochondria (extranuclear or cytoplasmic inheritance). This topic explains both with classic examples.

Key points

• Qualitative traits show clear classes (tall/dwarf). Quantitative traits show continuous variation (height, weight, yield) and are measured, not counted.
• Polygenic inheritance: several genes (polygenes) each add a small, equal and cumulative (additive) effect; environment also affects the trait.
• Nilsson-Ehle (1909) – kernel colour in wheat: two gene pairs (R₁R₁R₂R₂ dark red × r₁r₁r₂r₂ white). F₁ is medium red; F₂ gives five colour classes in the ratio 1 : 4 : 6 : 4 : 1 (by number of dominant alleles 4, 3, 2, 1, 0).
• With three gene pairs (e.g. Nilsson-Ehle's other wheat crosses), F₂ gives 7 classes in the ratio 1 : 6 : 15 : 20 : 15 : 6 : 1.
• Rule: with n gene pairs, F₂ has 2n + 1 phenotypic classes, and the fraction like either parent is (1/4)ⁿ.
• Graph of a polygenic trait is a bell-shaped normal curve.
• Other examples: ear length in maize (East), human skin colour, plant height.
• Extranuclear inheritance: controlled by plasmagenes in chloroplast DNA (cpDNA) or mitochondrial DNA (mtDNA).
• Features: reciprocal crosses give different results; inheritance is mostly maternal (uniparental) because the egg gives almost all the cytoplasm; Mendelian ratios are not seen; traits are not linked to chromosomes.
• **Plastid inheritance in Mirabilis jalapa (four o'clock plant) – Correns (1909)**: branches can be green, white or variegated. Seeds from a flower on a white branch give only white seedlings, whatever the pollen; from a green branch only green; from a variegated branch green, white and variegated.
• Cytoplasmic male sterility (CMS): a mitochondrial gene makes pollen sterile; inherited through the female. Used in hybrid seed production of maize, jowar, bajra, rice, sunflower; fertility is restored by nuclear restorer (Rf) genes.
• Other examples: Chlamydomonas streptomycin resistance (Sager), poky mutant of Neurospora, "kappa" particles in Paramecium.

Important terms

• Polygenes – several genes with small additive effects on one trait.
• Continuous variation – variation with many intermediate grades.
• Plasmagene – gene located in the cytoplasm (organelle DNA).
• Maternal inheritance – inheritance through the female parent only.
• CMS – male sterility controlled by mitochondrial genes.

Formulas

• Phenotypic classes in F₂ = 2n + 1 (n = number of gene pairs).
• Proportion of F₂ like one parent = (1/4)ⁿ.
• Worked example: 2 gene pairs → classes = 2(2) + 1 = 5; proportion like the dark red parent = (1/4)² = 1/16.

5 important questions

Q1. What is quantitative inheritance?

Inheritance of traits that show continuous variation and are controlled by many genes, each adding a small cumulative effect, along with the environment. Example: kernel colour in wheat.

Q2. Why do reciprocal crosses differ in cytoplasmic inheritance?

Because the cytoplasm, with its plastid and mitochondrial genes, comes mostly from the egg. The female parent therefore decides the trait.

Q3. Explain kernel colour inheritance in wheat.

Nilsson-Ehle's cross; gene symbols; F₁; F₂ checkerboard or binomial expansion (a + b)⁴; ratio 1 : 4 : 6 : 4 : 1; normal curve; features of polygenic inheritance.

Q4. Describe plastid inheritance in Mirabilis jalapa.

Correns' experiment; three branch types; results in a table for each female branch; conclusion – maternal plastid inheritance; diagram.

Q5. Write a note on cytoplasmic male sterility and its use.

Origin in mitochondrial genome; A-line (male sterile), B-line (maintainer), R-line (restorer); hybrid seed production; example in maize (Texas cytoplasm).

Exam tip

Remember "2n + 1 classes" and the wheat ratio 1 : 4 : 6 : 4 : 1. For cytoplasmic inheritance, always mention that reciprocal crosses differ.

Quick summary

Chromosomes are thread-like structures in the nucleus that carry genes. Cytogenetics studies chromosomes and their link with heredity. This topic covers chromosome structure and types, special chromosomes, the chromosome theory of inheritance, linkage and crossing over, sex determination, and changes in chromosome structure and number.

Key points

• The term chromosome was given by W. Waldeyer (1888). Chromosome is गुणसूत्र in Marathi.
• A metaphase chromosome has two sister chromatids joined at the centromere (primary constriction). Some also have a secondary constriction (nucleolar organiser) and a satellite.
• Tips of chromosomes are telomeres; they protect the ends.
• Chromatin: euchromatin (lightly stained, active genes) and heterochromatin (darkly stained, mostly inactive).
• The DNA–histone unit is the nucleosome (about 200 base pairs of DNA around an octamer of histones).
• Types by centromere position: metacentric (middle; V-shape at anaphase), submetacentric (J/L-shape), acrocentric (near one end), telocentric (at the end).
• Special chromosomes: polytene chromosomes (salivary glands of Drosophila larvae; many DNA strands; show bands and puffs/Balbiani rings) and lampbrush chromosomes (oocytes of amphibians; lateral loops).
• Chromosome theory of inheritance: Sutton and Boveri (1902–1903) – genes lie on chromosomes, and chromosome behaviour in meiosis explains Mendel's laws.
• Linkage (studied in Drosophila by T. H. Morgan) – genes on the same chromosome tend to be inherited together.
• Crossing over – exchange of segments between non-sister chromatids of homologous chromosomes during pachytene of meiosis I; it forms recombinants. The visible cross points are chiasmata.

Important terms

• Karyotype – chromosome set of a species arranged by size and shape; its diagram is an idiogram.
• Deletion, duplication, inversion, translocation – structural changes in chromosomes.
• Euploidy – change in whole sets (monoploid, triploid, tetraploid).
• Aneuploidy – gain or loss of one or a few chromosomes (2n + 1 trisomy, 2n − 1 monosomy).
• Autopolyploid – multiple sets from the same species; allopolyploid – sets from different species (e.g. wheat, Raphanobrassica).
• Down syndrome – trisomy of chromosome 21 (47 chromosomes).
• Turner syndrome – 45, XO; Klinefelter syndrome – 47, XXY.

Formulas

• Recombination frequency (%) = (number of recombinant offspring ÷ total offspring) × 100.
• 1% recombination = 1 map unit (centimorgan, cM).
• Example: in a test cross of 1000 offspring, 80 are recombinants. RF = 80/1000 × 100 = 8%. The genes are 8 map units apart.
• The maximum recombination frequency between two genes is 50%.

5 important questions

Q1. What are polytene chromosomes?

Polytene chromosomes are giant chromosomes found in salivary gland cells of Drosophila larvae. They form by repeated DNA replication without cell division. They show dark bands and swellings called puffs (Balbiani rings) where genes are active.

Q2. In a test cross, 170 out of 1000 offspring are recombinants. Find the map distance.

RF = (170 ÷ 1000) × 100 = 17%. Map distance = 17 map units (17 cM).

Q3. Explain linkage and its types.

• Tendency of genes on the same chromosome to be inherited together.
• Complete linkage: no recombinants (male Drosophila).
• Incomplete linkage: some recombinants due to crossing over.
• Morgan's Drosophila experiments (body colour and wing size).
• Strength of linkage decreases as distance between genes increases.

Q4. Describe the mechanism of crossing over.

• Synapsis of homologues in zygotene; bivalent formation (synaptonemal complex).
• Pachytene: each bivalent is a tetrad; breakage and exchange between non-sister chromatids (enzyme recombinase).
• Diplotene: chiasmata visible.
• Terminalisation of chiasmata; separation at anaphase I.
• Significance: new combinations, variation, gene mapping.

Q5. Describe structural changes in chromosomes.

• Deletion: loss of a segment (cri-du-chat syndrome – part of chromosome 5).
• Duplication: segment repeated (Bar eye in Drosophila).
• Inversion: segment reversed (paracentric, pericentric).
• Translocation: segment moves to a non-homologous chromosome (reciprocal).
• Draw simple diagrams with letters ABCDEF.

Exam tip

Use lettered diagrams (ABC·DEF) for structural changes. Practise one map-distance numerical.

Quick summary

Molecular biology explains how genes work at the level of DNA, RNA and protein. The central dogma states that DNA makes RNA and RNA makes protein. This topic covers DNA structure, DNA replication, transcription, the genetic code, translation and gene regulation by the lac operon.

Key points

• Central dogma (Francis Crick, 1958): DNA → (transcription) → RNA → (translation) → protein. Reverse transcription (RNA → DNA) occurs in retroviruses.
• DNA double helix: Watson and Crick (1953), using X-ray data of Rosalind Franklin and Maurice Wilkins. Two antiparallel strands; sugar-phosphate backbone; bases inside.
• Base pairing: A = T (two hydrogen bonds), G ≡ C (three hydrogen bonds).
• One turn of the B-DNA helix has about 10 base pairs and is 3.4 nm long; distance between base pairs is 0.34 nm; diameter 2 nm.
• Chargaff's rule: A = T and G = C; total purines = total pyrimidines.
• Replication is semi-conservative – proved by Meselson and Stahl (1958) using ¹⁵N in E. coli.
• DNA polymerase adds nucleotides only in the 5′ → 3′ direction. The leading strand is made continuously; the lagging strand discontinuously as Okazaki fragments, joined by DNA ligase.
• Transcription: RNA polymerase copies the template (antisense) strand. In eukaryotes, the primary transcript (hnRNA) is processed: capping (5′), poly-A tail (3′) and splicing (introns removed, exons joined).
• Genetic code: triplet, non-overlapping, commaless, degenerate, nearly universal; 64 codons – 61 sense codons and 3 stop codons (UAA, UAG, UGA). AUG codes methionine and is the start codon.
• Translation on ribosomes: initiation, elongation, termination. tRNA brings amino acids; its anticodon pairs with the mRNA codon.

Important terms

• Replication fork – Y-shaped region where DNA strands separate.
• Helicase – unwinds DNA; primase – makes RNA primer; topoisomerase (gyrase) – relieves supercoiling.
• Promoter – DNA sequence where RNA polymerase binds.
• Intron / exon – non-coding / coding parts of a eukaryotic gene.
• Operon – group of genes under one promoter and operator (in prokaryotes).
• Wobble hypothesis (Crick) – the third base of a codon can pair loosely, so one tRNA reads more than one codon.

Formulas

• In double-stranded DNA: A + G = T + C, so (A + G)/(T + C) = 1.
• Example: if a DNA has 20% adenine, then T = 20%, A + T = 40%, G + C = 60%, so G = 30% and C = 30%.
• Length of DNA = number of base pairs × 0.34 nm. Example: 1000 bp → 340 nm.

5 important questions

Q1. A DNA sample has 30% guanine. Find the percentage of other bases.

G = C = 30%, so G + C = 60%. A + T = 40%, so A = 20% and T = 20%.

Q2. What are Okazaki fragments?

Okazaki fragments are short DNA pieces formed on the lagging strand during replication, because DNA polymerase works only 5′ → 3′. They are later joined by DNA ligase.

Q3. Describe the Meselson–Stahl experiment.

• E. coli grown many generations in ¹⁵NH₄Cl (heavy DNA).
• Shifted to ¹⁴N medium.
• After one generation: all DNA hybrid (intermediate density) in CsCl density gradient.
• After two generations: half hybrid, half light.
• Proves semi-conservative replication.

Q4. Explain the lac operon.

• Proposed by Jacob and Monod (1961) in E. coli; inducible operon.
• Parts: regulator gene (i, makes repressor), promoter, operator, structural genes z (β-galactosidase), y (permease), a (transacetylase).
• No lactose: repressor binds operator; genes off.
• Lactose present: allolactose (inducer) binds repressor; repressor leaves operator; RNA polymerase transcribes genes.
• Example of negative control; also positive control by CAP-cAMP.

Q5. Describe the process of translation.

• Activation: amino acid + tRNA (aminoacyl-tRNA synthetase, ATP).
• Initiation: small ribosomal subunit binds mRNA; initiator tRNA (Met) at AUG; large subunit joins.
• Elongation: next aminoacyl-tRNA at A site; peptide bond (peptidyl transferase); translocation.
• Termination: stop codon; release factor; polypeptide freed.

Exam tip

Learn key experiments with names and years (Watson–Crick 1953, Meselson–Stahl 1958, Jacob–Monod 1961). Draw the lac operon in both "off" and "on" states.

Quick summary

A mutation is a sudden, heritable change in the genetic material. Mutations are the raw material of evolution and of mutation breeding, but they can also cause harm. This topic covers types of gene (point) mutations, physical and chemical mutagens, how they act, and how cells repair damaged DNA.

Key points

• The term mutation was given by Hugo de Vries (1901) from his work on Oenothera lamarckiana. H. J. Muller (1927) first induced mutations with X-rays (in Drosophila); Stadler (1928) did so in barley and maize.
• Mutations may be spontaneous (natural, from replication errors) or induced (by mutagens). They may be somatic (not passed to offspring in animals; can be propagated vegetatively in plants – bud sports) or germinal.
• Base substitution: transition (purine → purine or pyrimidine → pyrimidine, e.g. A→G) or transversion (purine ↔ pyrimidine, e.g. A→T).
• Frameshift: insertion or deletion of bases shifts the reading frame.
• Gene (point) mutations change one or a few bases:
• Effects on protein: silent (same amino acid), missense (different amino acid), nonsense (stop codon; short protein). Frameshifts usually ruin the protein.
• Physical mutagens: ionising radiation (X-rays, gamma rays – break DNA strands) and non-ionising UV light – forms thymine dimers between adjacent thymines.
• Base analogues – 5-bromouracil (mimics thymine), 2-aminopurine.
• Alkylating agents – EMS (ethyl methanesulphonate), mustard gas.
• Deaminating agents – nitrous acid (cytosine → uracil, adenine → hypoxanthine).
• Intercalating agents – acridine dyes, ethidium bromide → frameshifts.
• Chemical mutagens:
• Photoreactivation: enzyme photolyase, activated by visible light, splits thymine dimers directly.
• Excision repair: damaged part is cut out by endonuclease, the gap is filled by DNA polymerase and sealed by ligase (nucleotide excision repair, base excision repair).
• Mismatch repair: corrects wrongly paired bases left after replication.
• SOS / recombination repair: emergency repair of serious damage; error-prone.
• DNA repair systems:
• Use in plants: mutation breeding – e.g. many crop varieties released in India developed with gamma rays.

Important terms

• Mutagen – agent that increases the rate of mutation.
• Transition / transversion – substitution of a base by the same type / the other type.
• Frameshift mutation – addition or loss of bases not in multiples of three.
• Thymine dimer – covalent link between two adjacent thymines caused by UV.
• Photoreactivation – light-dependent repair of thymine dimers.

Key facts

5 important questions

Q1. Distinguish between transition and transversion.

Transition is replacement of a purine by another purine or a pyrimidine by another pyrimidine (A ↔ G, C ↔ T). Transversion is replacement of a purine by a pyrimidine or vice versa (A ↔ T, G ↔ C).

Q2. How does UV light cause mutation?

UV light joins two adjacent thymine bases on the same strand to form a thymine dimer. This distorts DNA and blocks replication, causing errors if not repaired.

Q3. Classify mutations and describe point mutations with examples.

Spontaneous and induced, somatic and germinal, gene and chromosomal; substitution and frameshift; silent, missense and nonsense effects with codon examples.

Q4. Describe the action of chemical mutagens.

Base analogues, alkylating, deaminating and intercalating agents with one example and mechanism each.

Q5. Explain the mechanisms of DNA repair.

Photoreactivation, excision repair (steps), mismatch repair and SOS repair; significance for keeping the genome stable.

Exam tip

Make a mutagen table and learn one repair process in detail with a diagram – excision repair is the most often asked.

Quick summary

Plant breeding is the art and science of improving the genetic make-up of crop plants to get better varieties – higher yield, better quality, and resistance to diseases, pests and stress. This topic covers aims, methods (introduction, selection, hybridisation, mutation and polyploidy breeding), heterosis, and India's achievements such as the Green Revolution.

Key points

• Aims: higher yield, better quality (protein, oil, taste), disease and insect resistance, tolerance to drought, salinity and heat, early maturity, suitability for machines.
• Plant introduction – bringing plants from another region or country. Primary introduction: used directly; secondary: used after selection or crossing. In India, the National Bureau of Plant Genetic Resources (NBPGR), New Delhi, handles introduction and germplasm.
• Germplasm – the total collection of genes (varieties, wild relatives) of a crop.
• Selection – choosing superior plants from a mixed population. Types: mass selection (many plants with good features; seeds mixed), pure line selection (progeny of a single self-pollinated plant; W. Johannsen), clonal selection (in vegetatively propagated crops like potato, sugarcane).
• Hybridisation – crossing two genetically different plants to combine useful characters. Steps: choice of parents, emasculation (removing anthers from bisexual flowers before they shed pollen), bagging, artificial pollination, labelling, collection of seeds, and selection of desirable progeny over generations.
• Types of crosses: intravarietal, intervarietal, interspecific, intergeneric (e.g. Triticale = wheat × rye).
• Heterosis (hybrid vigour) – F₁ hybrid is superior to both parents (term by G. H. Shull). Used in hybrid maize, bajra, jowar, cotton.
• Mutation breeding – inducing mutations with radiation (X-rays, gamma rays) or chemicals (e.g. EMS, colchicine for polyploidy) and selecting useful mutants.
• Polyploidy breeding – doubling chromosomes with colchicine; gives larger organs or seedless fruit (triploid watermelon, banana).

Important terms

• Emasculation – removal of stamens from a flower to prevent self-pollination.
• Bagging – covering emasculated flowers with butter-paper bags to prevent unwanted pollen.
• Pure line – progeny of a single homozygous self-pollinated plant.
• Inbreeding depression – loss of vigour on repeated inbreeding of cross-pollinated plants.
• Back-cross method – repeated crossing with a parent to transfer one gene (e.g. disease resistance) into a good variety.
• Biofortification – breeding crops with higher vitamins and minerals.
• Male sterility – inability to produce viable pollen; used to make hybrid seed without emasculation.

Key facts

• Green Revolution (1960s): high-yielding semi-dwarf wheat (from Norman Borlaug, CIMMYT, Mexico – e.g. Sonalika, Kalyan Sona) and rice varieties (IR-8 from IRRI, Philippines; Jaya and Ratna in India). Dr. M. S. Swaminathan is called the father of the Green Revolution in India.
• Sugarcane: Saccharum barberi (north India) was crossed with Saccharum officinarum (south India) to combine thick stems and high sugar with better adaptation.
• Disease-resistant varieties (examples taught in India): Himgiri (wheat; resistant to leaf and stripe rust, hill bunt), Pusa Komal (cowpea; bacterial blight), Pusa Sadabahar (chilli; chilli mosaic virus, tobacco mosaic virus and leaf curl), Pusa Shubhra (cauliflower; black rot and curl blight black rot).
• Insect-resistant examples: Pusa Gaurav (Brassica; aphids), Pusa Sawani and Pusa A-4 (okra; shoot and fruit borer).

5 important questions

Q1. What is heterosis?

Heterosis or hybrid vigour is the superiority of an F₁ hybrid over its parents in yield, size or vigour. It is used to produce hybrid seeds of crops like maize and bajra.

Q2. What is emasculation? Why is it necessary?

Emasculation is the removal of anthers from a bisexual flower before they burst. It prevents self-pollination so that only the pollen of the chosen male parent fertilises the flower.

Q3. Describe the steps of hybridisation.

• Choose parents with desired characters.
• Emasculate female parent flowers (bud stage).
• Bag the flowers.
• Dust pollen from male parent on stigma; re-bag; label.
• Collect F₁ seed; grow; select desirable plants in F₂ and later generations.
• Test in trials; release as a new variety.

Q4. Compare mass selection, pure line selection and clonal selection.

• Mass selection: many good plants; seeds bulked; quick but mixed.
• Pure line: single self-pollinated plant's progeny; uniform and stable.
• Clonal: in vegetatively propagated crops; selection among clones; keeps hybrid vigour.
• Give one crop example for each.

Q5. Write a note on the Green Revolution in India.

• Period: mid-1960s onwards.
• Semi-dwarf HYV of wheat and rice; Borlaug and Swaminathan.
• Inputs: irrigation, fertilisers, pesticides, mechanisation.
• Results: India became self-sufficient in food grains.
• Problems: soil and water damage, regional imbalance, loss of traditional varieties.

Exam tip

Write the hybridisation steps in order with the words emasculation and bagging. Name one disease-resistant variety and its crop.

Quick summary

Plant tissue culture is the growing of plant cells, tissues or organs on an artificial nutrient medium under sterile conditions. It is possible because plant cells are totipotent. Biotechnology uses living cells and genetic engineering to make useful products. This topic covers the technique of tissue culture, its types and uses, and recombinant DNA technology including transgenic plants like Bt cotton.

Key points

• G. Haberlandt (1902) is called the father of plant tissue culture. He first proposed culturing isolated plant cells.
• Totipotency – the ability of a single plant cell to grow into a complete plant.
• Explant – any part of a plant (leaf, stem, root tip, anther) used to start a culture.
• MS medium (Murashige and Skoog, 1962) is the most common medium: inorganic salts, sucrose (carbon source), vitamins, amino acids, growth regulators (auxin and cytokinin) and agar (for solid medium).
• Aseptic conditions are essential: work in a laminar air flow cabinet; medium sterilised in an autoclave (121 °C, 15 lb/in² pressure, about 15–20 minutes); explants surface-sterilised (e.g. with sodium hypochlorite or mercuric chloride).
• Callus – unorganised mass of dividing cells formed on the explant.
• Organogenesis – formation of shoots or roots from callus; high cytokinin → shoots; high auxin → roots (Skoog and Miller).
• Somatic embryogenesis – formation of embryo-like structures from somatic cells; used to make artificial (synthetic) seeds.
• Micropropagation – rapid multiplication of thousands of identical plants (somaclones) in a short time, e.g. banana, sugarcane, orchids.
• Meristem culture – culturing shoot tips to get virus-free plants (e.g. potato, banana).
• Anther culture gives haploid plants (Guha and Maheshwari, 1964, Datura).
• Protoplast fusion (somatic hybridisation) produces somatic hybrids, e.g. pomato (potato + tomato).

Important terms

• Recombinant DNA (rDNA) – DNA made by joining DNA from two different sources.
• Restriction enzymes – "molecular scissors" that cut DNA at specific sequences (e.g. EcoRI recognises GAATTC).
• DNA ligase – "molecular glue" that joins DNA pieces.
• Vector – carrier that takes foreign DNA into a host (plasmids like pBR322; Ti plasmid of Agrobacterium tumefaciens for plants).
• Transgenic plant – plant carrying a foreign gene.
• PCR – polymerase chain reaction (Kary Mullis) for making many copies of DNA; uses Taq polymerase.

Key facts

• Steps of rDNA technology: isolate DNA → cut with restriction enzyme → join gene to vector with ligase → introduce into host (transformation) → select transformed cells (antibiotic markers) → grow and get product.
• Bt cotton: carries cry genes from the bacterium Bacillus thuringiensis; the Cry protein kills bollworms. Approved in India in 2002.
• Golden rice: rice engineered to make β-carotene (provitamin A).
• Flavr Savr tomato: first commercial GM food (1994), with delayed softening.

5 important questions

Q1. What is totipotency?

Totipotency is the inherent ability of a living plant cell to divide, differentiate and grow into a whole plant. It is the basis of plant tissue culture.

Q2. Why is meristem culture used to obtain virus-free plants?

The apical meristem divides very fast and has no vascular connection, so viruses usually do not reach it. Plants grown from cultured meristems are therefore free of viruses.

Q3. Describe the general technique of plant tissue culture.

• Preparation of MS medium; sterilisation in autoclave.
• Selection and surface sterilisation of explant.
• Inoculation in laminar air flow.
• Incubation at about 25 °C with light/dark cycle.
• Callus formation; sub-culturing; regeneration of shoots and roots.
• Hardening of plantlets and transfer to soil.

Q4. Give the applications of plant tissue culture.

• Micropropagation of elite plants.
• Virus-free plants by meristem culture.
• Haploids by anther culture (fast homozygous lines).
• Somatic hybrids by protoplast fusion.
• Synthetic seeds; germplasm conservation (cryopreservation).
• Secondary metabolites (e.g. shikonin).

Q5. Explain the production of Bt cotton.

• cry gene from Bacillus thuringiensis isolated.
• Inserted into a vector (Ti plasmid of Agrobacterium).
• Cotton cells transformed; transformed cells selected and regenerated by tissue culture.
• Bt toxin is inactive protoxin; becomes active in the alkaline gut of insect larvae and damages gut cells.
• Benefits: less insecticide use; concerns: resistance in pests, biosafety.

Exam tip

Mention Haberlandt (father of tissue culture), MS medium and the auxin–cytokinin ratio in every long answer. A flow chart of rDNA steps earns full marks.

Quick summary

Modern biology produces huge amounts of DNA and protein sequence data. Bioinformatics uses computers, databases and software to store, search and analyse these data. Genomics is the study of whole genomes – their sequencing, mapping and function. This topic covers biological databases, sequence alignment and BLAST, genome sequencing methods, plant genome projects and applications in crop improvement.

Key points

• The term bioinformatics was used by Paulien Hogeweg and Ben Hesper (1970). It joins biology, computer science and statistics.
• Primary (nucleotide) databases: GenBank (NCBI, USA), ENA (EMBL, Europe) and DDBJ (Japan). These three share data daily (INSDC).
• Protein databases: UniProt (sequences and functions) and PDB (Protein Data Bank – 3-D structures).
• Secondary databases (patterns, motifs, families): Pfam, PROSITE. Plant-specific: TAIR (Arabidopsis), Gramene (cereals).
• Sequence alignment compares two or more sequences to find similarity: pairwise or multiple (Clustal); global (whole length; Needleman–Wunsch) or local (similar regions; Smith–Waterman).
• BLAST (Basic Local Alignment Search Tool, Altschul et al., 1990) quickly finds similar sequences in a database. Types: blastn (DNA vs DNA), blastp (protein vs protein), blastx (translated DNA vs protein).
• Phylogenetic trees built from aligned sequences show evolutionary relationships (e.g. MEGA software).
• Genomics branches: structural (sequencing and mapping), functional (what genes do – transcriptomics, proteomics) and comparative (comparing genomes of species).
• Sanger (dideoxy chain-termination) sequencing (Frederick Sanger, 1977) uses ddNTPs that stop chain growth. Next-generation sequencing (NGS) reads millions of fragments in parallel, making genomes cheap and fast.
• Plant genomes sequenced: Arabidopsis thaliana – first plant genome (2000, about 135 Mb, 5 chromosome pairs); rice (Oryza sativa, 2002/2005; India contributed to the International Rice Genome Sequencing Project); later tomato, maize, wheat and others.
• Applications: finding genes for disease and drought resistance, marker-assisted selection (MAS) in breeding, DNA barcoding, drug discovery, studying evolution.

Important terms

• Database – organised collection of data that can be searched by computer.
• Accession number – unique ID of a sequence entry in a database.
• Sequence alignment – arranging sequences to show matching regions.
• Genome – complete set of DNA of an organism.
• Proteomics – study of all proteins of a cell or organism.
• Molecular marker – DNA sequence used to tag a gene or trait (RFLP, RAPD, SSR, SNP).

Key facts

5 important questions

Q1. What is BLAST?

BLAST (Basic Local Alignment Search Tool) is a computer program that compares a query DNA or protein sequence with sequences in a database and lists the most similar ones with scores.

Q2. Name the first plant whose genome was sequenced.

Arabidopsis thaliana (thale cress), in the year 2000. Its genome is small (about 135 Mb) with 5 chromosome pairs.

Q3. Describe biological databases with examples.

Primary and secondary databases; nucleotide (GenBank, ENA, DDBJ), protein (UniProt, PDB), specialised plant databases; how data are retrieved by accession number.

Q4. Explain sequence alignment and its types.

Purpose; pairwise vs multiple; global vs local; scoring with matches, mismatches and gaps; tools (BLAST, Clustal); use in phylogeny.

Q5. Write a note on plant genome projects and applications of genomics.

Sanger and NGS methods; Arabidopsis and rice projects; structural, functional and comparative genomics; marker-assisted breeding, gene discovery.

Exam tip

Learn the full forms (BLAST, NCBI, PDB, EMBL, DDBJ) – they are common one-mark questions. Mention Arabidopsis 2000 and rice in any genomics answer.

Quick summary

Biostatistics is the use of statistics to collect, present and analyse biological data, such as leaf length, plant height, seed yield or results of genetic crosses. This topic covers sampling, frequency distribution, measures of central tendency (mean, median, mode), measures of dispersion (range, standard deviation, coefficient of variation) and the chi-square test, with worked examples.

Key points

• Population – the whole group under study; sample – a part chosen to represent it. Random sampling gives every unit an equal chance.
• Variables: continuous (height, weight) and discrete (number of petals, seeds per pod).
• Data are presented as tables, frequency distributions, histograms, frequency polygons, bar diagrams and pie charts.
• Mean (arithmetic average) = sum of observations ÷ number of observations.
• Median – middle value when data are arranged in order; for an even number, average of the two middle values.
• Mode – the value that occurs most often.
• Range = highest value − lowest value (simple but crude).
• Standard deviation (σ) – square root of the mean of squared deviations from the mean; the best measure of spread (Karl Pearson, 1893).
• Coefficient of variation (CV) compares variability of data in different units or with different means.
• In a normal distribution, mean = median = mode; about 68% of values lie within mean ± 1σ and 95% within mean ± 2σ.
• Chi-square (χ²) test (Karl Pearson, 1900) checks whether observed results fit expected ratios (e.g. Mendelian 3 : 1). If calculated χ² is less than the table value at 5% level, the difference is due to chance and the hypothesis is accepted.
• Degrees of freedom (df) = number of classes − 1.

Important terms

• Frequency – number of times a value occurs.
• Deviation – difference between an observation and the mean.
• Null hypothesis – assumption that there is no real difference between observed and expected values.
• Level of significance – probability (usually 5%, P = 0.05) used to accept or reject the hypothesis.

Formulas

• Mean: x̄ = Σx / n
• Standard deviation: σ = √[Σ(x − x̄)² / n] (for a small sample many books use n − 1 in place of n)
• Coefficient of variation: CV = (σ / x̄) × 100
• Chi-square: χ² = Σ (O − E)² / E, where O = observed, E = expected frequency
• Table χ² at 5% level: df 1 = 3.84, df 2 = 5.99, df 3 = 7.82

5 important questions

Q1. Define standard deviation.

Standard deviation is the square root of the arithmetic mean of the squared deviations of observations from their mean. It shows how widely values are spread around the mean.

Q2. What is the null hypothesis in the chi-square test?

It assumes that there is no significant difference between observed and expected frequencies and that any difference is due to chance.

Q3. Find the mean, median, mode, SD and CV of leaf lengths (cm): 10, 12, 12, 14, 17.

1. Mean = 65 / 5 = 13 cm.
2. Median (3rd value of 5 in order) = 12 cm; Mode = 12 cm.
3. σ = √(28 / 5) = √5.6 = 2.37 cm.
4. CV = (2.37 / 13) × 100 = 18.2%.

Q4. In a monohybrid cross, 400 F₂ plants gave 290 tall and 110 dwarf. Test the fit to 3 : 1.

1. Expected: tall = 400 × 3/4 = 300; dwarf = 400 × 1/4 = 100.
2. χ² = (290 − 300)²/300 + (110 − 100)²/100 = 100/300 + 100/100 = 0.33 + 1.00 = 1.33.
3. df = 2 − 1 = 1; table value at 5% = 3.84.
4. 1.33 < 3.84, so the difference is due to chance – the data fit the 3 : 1 ratio.

Q5. Explain measures of central tendency and dispersion with their merits.

Mean, median, mode – definitions, formulas, merits and demerits; range, mean deviation, standard deviation, CV; normal curve diagram.

Exam tip

In numericals, always draw the table of x, deviation and squared deviation, show each step and write the unit. In χ², state the conclusion clearly – "accepted" or "rejected" at 5% level.

Quick summary

Organic evolution is the slow, continuous change of living organisms over many generations, by which new species arise from earlier ones. This topic covers the evidences of evolution (with plant examples), the theories of Lamarck, Darwin and de Vries, the modern synthetic theory, and the ideas of speciation and isolation.

Key points

• Palaeontological – fossils show a sequence from simple to complex (algae → bryophytes → pteridophytes → gymnosperms → angiosperms) and connecting links such as seed ferns (Pteridospermae).
• Morphological and anatomical – homologous organs (same origin, different function: thorn of Bougainvillea and tendril of Passiflora, both modified stems) and analogous organs (different origin, same function: tendril of pea – leaflet – and tendril of grapevine – stem).
• Connecting links – Gnetum (between gymnosperms and angiosperms), Psilotum among pteridophytes.
• Embryological, biochemical (same genetic code, similar cytochrome c) and biogeographical evidences.
• Evidences of evolution:
• Lamarckism (Jean-Baptiste Lamarck, Philosophie Zoologique, 1809): use and disuse of organs and inheritance of acquired characters. Rejected after Weismann's experiments (germplasm theory).
• Darwinism (Charles Darwin, On the Origin of Species, 1859; Wallace proposed the same idea): overproduction, struggle for existence, variation, survival of the fittest (Herbert Spencer's phrase) and natural selection, leading to new species.
• Limits of Darwinism: could not explain the origin and inheritance of variation; did not distinguish heritable from non-heritable variation.
• Mutation theory (Hugo de Vries, 1901) from Oenothera lamarckiana: new species arise by sudden large heritable changes (mutations) in one step.
• Modern synthetic theory (Neo-Darwinism) (Dobzhansky, Huxley, Mayr, Stebbins): gene mutation, chromosomal changes, recombination, natural selection and reproductive isolation together cause evolution. Genetic drift and gene flow also act.
• Hardy–Weinberg principle (1908): allele frequencies stay constant in a large, randomly mating population without mutation, migration, selection or drift: p² + 2pq + q² = 1.
• Speciation: allopatric (geographically separated) and sympatric (in the same area). In plants, polyploidy gives instant sympatric speciation (e.g. bread wheat, Primula kewensis).
• Isolating mechanisms: pre-zygotic (seasonal, habitat, mechanical, gametic) and post-zygotic (hybrid inviability, hybrid sterility).

Important terms

• Homologous organs – organs of same origin and structure but different functions.
• Analogous organs – organs of different origin but similar function.
• Natural selection – survival and reproduction of individuals best suited to the environment.
• Speciation – formation of new species.
• Genetic drift – random change in allele frequency in small populations.

Key facts

5 important questions

Q1. Give one plant example each of homologous and analogous organs.

Homologous: thorn of Bougainvillea and tendril of Cucurbita (both modified stem/branch). Analogous: tendril of pea (modified leaflet) and tendril of grapevine (modified stem).

Q2. What is the Hardy–Weinberg principle?

It states that in a large, random-mating population with no mutation, migration, selection or drift, allele and genotype frequencies remain constant from generation to generation (p² + 2pq + q² = 1).

Q3. Explain Darwin's theory of natural selection and its limitations.

Five main points with plant examples; criticism – source of variation unknown, overemphasis on small variations; how modern genetics filled the gap.

Q4. Discuss evidences of evolution with special reference to plants.

Fossils and geological record; connecting links; homologous and analogous organs; comparative biochemistry and DNA sequences.

Q5. Describe the modern synthetic theory of evolution.

Factors: gene mutation, chromosomal mutation, recombination, natural selection, isolation, genetic drift; speciation by polyploidy in plants.

Exam tip

Use the table to compare theories. Plant examples (Oenothera, wheat polyploidy, Gnetum as connecting link) score more marks in a botany paper than animal examples.

Quick summary

Ecology is the study of the relationship between organisms and their environment. The growth and distribution of plants depend on many environmental factors. This topic covers the scope of plant ecology, the classification of ecological factors – climatic, edaphic, topographic and biotic – and their effects on plants, along with the laws of limiting factors and tolerance.

Key points

• The term ecology (oikos = house, logos = study) was coined by Ernst Haeckel (1869). Autecology studies a single species; synecology studies communities.
• Habitat – the place where an organism lives; ecological niche – its role and position in the community.
• Light – needed for photosynthesis; plants are heliophytes (sun plants) or sciophytes (shade plants); day length controls flowering (photoperiodism).
• Temperature – controls enzyme activity, germination, growth; plants are megatherms, mesotherms, microtherms, hekistotherms.
• Water – rainfall, humidity, dew; decides hydrophytes, mesophytes and xerophytes.
• Wind – causes dwarfing, deformed trees, transpiration loss; helps pollination and dispersal.
• Climatic factors:
• Soil formation from rocks by weathering; soil profile with horizons O, A, B, C and R.
• Soil texture – sand, silt, clay; loam is best for most crops.
• Soil water: gravitational, capillary water (available to plants), hygroscopic.
• Soil pH, soil air, organic matter (humus) and soil organisms (earthworms, microbes).
• Edaphic factors (soil):
• Topographic (physiographic) factors: altitude, slope, aspect (direction of slope) and height of mountain chains. With rising altitude, temperature falls, and vegetation changes much as it does with latitude.
• Biotic factors: effects of plants, animals and humans – grazing, trampling, deforestation, pollination, competition, parasitism, symbiosis (mycorrhiza, root nodules), epiphytism.
• Liebig's law of the minimum (1840): growth is controlled by the nutrient present in the least amount.
• Blackman's law of limiting factors (1905): when a process depends on several factors, its rate is limited by the factor present in the least favourable amount.
• Shelford's law of tolerance (1913): every organism has a minimum, optimum and maximum for each factor; stenotypic species have narrow and eurytypic wide tolerance.

Important terms

• Edaphic factor – a soil-related factor affecting plants.
• Humus – dark, decomposed organic matter in soil.
• Soil profile – vertical section showing soil layers (horizons).
• Heliophyte / sciophyte – plant adapted to bright light / shade.
• Limiting factor – the factor that controls the rate of a process when in short supply.

Key facts

5 important questions

Q1. Define ecological niche.

An ecological niche is the functional role of a species in its community – what it eats, where it lives, when it is active and how it interacts with other species and the environment.

Q2. State Shelford's law of tolerance.

Each organism can survive only within a range of each environmental factor, between a minimum and a maximum, with the best growth at the optimum. Its distribution is controlled by the factor for which its tolerance is narrowest.

Q3. Describe climatic factors and their effects on vegetation.

Light (intensity, quality, duration), temperature, water, wind – effects and plant adaptations with examples.

Q4. Explain edaphic factors.

Soil formation, profile, texture, soil water types, soil air, pH, organic matter, soil organisms; importance for plant growth; diagram of soil profile.

Q5. Write notes on topographic and biotic factors.

Altitude, slope and aspect; biotic effects of animals, humans, microbes; positive and negative interactions.

Exam tip

Always draw the soil profile diagram for edaphic factors. Remember three laws with years: Liebig 1840, Blackman 1905, Shelford 1913.

Quick summary

An ecosystem is a functional unit of nature where living organisms interact with each other and with their physical environment. The term was coined by A. G. Tansley (1935). This topic covers components of an ecosystem, food chains and food webs, ecological pyramids, energy flow, productivity, biogeochemical cycles and ecological succession.

Key points

• Ecosystem (परिसंस्था) = biotic (living) + abiotic (non-living) components working together.
• Abiotic components: light, temperature, water, soil, air, minerals.
• Biotic components: producers (green plants), consumers (herbivores – primary; carnivores – secondary and tertiary) and decomposers (bacteria and fungi).
• Types: natural (forest, grassland, pond, desert, ocean) and artificial (crop field, garden, aquarium).
• Food chain – a series of organisms through which food energy passes: grass → grasshopper → frog → snake → eagle.
• Grazing food chain starts with green plants; detritus food chain starts with dead organic matter.
• Food web – interconnected food chains; it makes an ecosystem stable.
• Energy flow is unidirectional (sun → producers → consumers) and follows the laws of thermodynamics.
• Lindeman's 10% law (1942): only about 10% of energy at one trophic level passes to the next.
• Ecological pyramids (Charles Elton): pyramid of number, biomass and energy. The pyramid of energy is always upright. The pyramid of biomass in a pond (sea) is inverted; the pyramid of number in a tree ecosystem is inverted (spindle).
• Biogeochemical cycles recycle nutrients: carbon, nitrogen, phosphorus (sedimentary), water.
• Ecological succession: gradual, orderly change in a community until a stable climax community forms. Primary succession starts on bare areas (rocks – xerosere; water – hydrosere); pioneer species on rock are lichens.

Important terms

• Trophic level – feeding position in a food chain.
• Gross primary productivity (GPP) – total rate of organic matter produced by photosynthesis.
• Net primary productivity (NPP) – GPP minus respiration loss of producers.
• Standing crop – amount of living matter present at a given time.
• Ecotone – transition zone between two ecosystems.
• Ecological niche – the functional role and position of a species in its habitat.
• Seral stages (seres) – series of transitional communities in succession.

Formulas

• NPP = GPP − R (R = respiration of producers).
• 10% law example: if producers fix 10,000 J, primary consumers get about 1,000 J, secondary consumers about 100 J and tertiary consumers about 10 J.
• Ecological efficiency (%) = (energy at higher trophic level ÷ energy at lower trophic level) × 100.

5 important questions

Q1. Why is the pyramid of energy always upright?

Energy decreases at every higher trophic level because much is lost as heat during respiration and other activities. So the higher level always has less energy, and the pyramid can never be inverted.

Q2. If GPP of a grassland is 20,000 kcal/m²/year and respiration of producers is 8,000 kcal/m²/year, find NPP.

NPP = GPP − R = 20,000 − 8,000 = 12,000 kcal/m²/year. This is the energy available to herbivores.

Q3. Describe the structure and function of a pond ecosystem.

• Abiotic: water, dissolved gases, minerals, light, temperature.
• Producers: phytoplankton (algae), floating and rooted plants (Hydrilla, Vallisneria, water lily).
• Consumers: zooplankton, insects, fish, frogs, birds.
• Decomposers on the bottom.
• Zones: littoral, limnetic, profundal.
• Food chain example and energy flow.

Q4. Explain energy flow in an ecosystem.

• Sun is the source; producers trap about 1–2% of incident light (approx.).
• Flow is unidirectional; heat loss at each level.
• 10% law; long food chains are rare.
• Single-channel and Y-shaped energy flow models (Odum).
• Draw energy flow diagram with boxes and arrows showing loss as heat.

Q5. Describe hydrosere (succession in water).

• Phytoplankton stage → submerged plant stage (Hydrilla) → floating stage (Nymphaea, Pistia) → reed swamp (Typha, Phragmites) → sedge meadow → woodland → climax forest.
• Each stage changes the habitat (silt and organic matter build up, water becomes shallow).
• Ends in a stable climax community suited to the climate.

Exam tip

Draw the three ecological pyramids, including inverted examples. Remember Tansley (1935) and Lindeman (1942).

Quick summary

Plants do not grow alone; they live together in groups called plant communities. Ecologists describe communities by their composition, structure and life forms, and measure them in the field with quadrats and transects. This topic covers characters of a community, Raunkiaer's life forms, and quantitative analysis – frequency, density, abundance and the Importance Value Index – with a worked example.

Key points

• Plant community – an assemblage of plant populations living together in a common area and interacting with each other.
• Qualitative characters: floristic composition, physiognomy (general appearance), stratification (layering – trees, shrubs, herbs, ground layer), phenology (seasonal timing of leafing, flowering), sociability and life forms.
• Quantitative characters: frequency, density, abundance, cover/basal area.
• Synthetic characters: presence and constancy, dominance, fidelity, Importance Value Index (IVI).
• Dominant species controls the community and gives it its name (e.g. teak forest). Ecotone – transition zone between two communities, often rich in species (edge effect).
• Phanerophytes – buds high above ground (trees, shrubs); dominant in tropics.
• Chamaephytes – buds near ground surface (below 25 cm).
• Hemicryptophytes – buds at soil surface (grasses).
• Cryptophytes – buds below soil or water (bulbs, rhizomes).
• Therophytes – survive as seeds (annuals); common in deserts.
• Raunkiaer's life forms (1934) – based on the position of perennating buds:
• The percentage of each life form in a flora is its biological spectrum; it reflects the climate.
• Quadrat method – square sample plots (1 m × 1 m for herbs, 5 m × 5 m for shrubs, 10 m × 10 m or more for trees) placed at random. Minimum quadrat size is found from a species–area curve.
• Line transect / belt transect – used where vegetation changes along a gradient.
• Raunkiaer's frequency classes: A (1–20%), B (21–40%), C (41–60%), D (61–80%), E (81–100%); normal law A > B > C ≥ D < E.

Important terms

• Physiognomy – overall look of vegetation.
• Stratification – vertical layering of a community.
• Quadrat – sample plot of known size.
• Ecotone – transition zone between two communities.
• Biological spectrum – percentage distribution of life forms in a flora.

Formulas

• Frequency (%) = (Number of quadrats in which the species occurs ÷ Total quadrats studied) × 100
• Density = Total individuals of the species ÷ Total quadrats studied
• Abundance = Total individuals of the species ÷ Number of quadrats in which it occurs
• IVI = Relative frequency + Relative density + Relative dominance (maximum 300)

5 important questions

Q1. What is an ecotone?

An ecotone is the transition zone between two different communities, such as forest and grassland. It often has more species than either community, which is called the edge effect.

Q2. Name Raunkiaer's five life forms.

Phanerophytes, chamaephytes, hemicryptophytes, cryptophytes and therophytes.

Q3. In 10 quadrats, species X was found in 6 quadrats with 30 individuals in all. Find frequency, density and abundance.

1. Frequency = (6 ÷ 10) × 100 = 60% (Raunkiaer class C).
2. Density = 30 ÷ 10 = 3 individuals per quadrat.
3. Abundance = 30 ÷ 6 = 5 individuals per quadrat of occurrence.

Q4. Describe the characters of a plant community.

Qualitative (composition, physiognomy, stratification, phenology, life forms), quantitative (frequency, density, abundance, cover) and synthetic (dominance, IVI) characters with examples.

Q5. Explain the quadrat method of vegetation study.

Choosing quadrat size (species–area curve), laying quadrats randomly, recording data, calculations of frequency, density, abundance; transect method for gradients.

Exam tip

Practise the three formulas – frequency, density and abundance – they appear as practical numericals every year. Keep units clear: density is per quadrat (or per m²).

Quick summary

Plants living in very wet, very dry or very salty places show special structural and physiological features called ecological adaptations. Based on water relations, plants are grouped as hydrophytes, mesophytes and xerophytes; plants of saline soils are halophytes. This topic covers their morphological, anatomical and physiological adaptations with examples.

Key points

• Hydrophytes – plants growing in water or very wet soil. Types: free-floating (Pistia, Eichhornia, Lemna, Wolffia), rooted with floating leaves (Nymphaea, Nelumbo), submerged (Hydrilla, Vallisneria), amphibious (Sagittaria, Ranunculus) and emergent (Typha).
• Roots poorly developed or absent; root pockets in place of root caps (Eichhornia, Pistia).
• Stems and petioles spongy; aerenchyma gives buoyancy and stores air (petiole of Eichhornia swollen).
• Submerged leaves thin, ribbon-like or finely dissected; heterophylly in amphibious plants.
• Thin or no cuticle; epidermis takes in gases and minerals; stomata absent in submerged leaves and on the upper surface only in floating leaves.
• Vascular tissue (especially xylem) and mechanical tissue reduced.
• Hydrophyte adaptations:
• Xerophytes – plants of dry habitats (deserts, rocky soils). Types: ephemerals (drought escapers – short life cycle in rainy season), succulents (drought avoiders – store water: Opuntia, Aloe, Euphorbia), non-succulents (drought endurers – Calotropis, Nerium, Casuarina, Acacia).
• Very long tap roots; extensive root system.
• Leaves reduced, modified into spines (Opuntia), scales (Casuarina); phylloclades do photosynthesis.
• Thick cuticle, multiple epidermis (Nerium), sunken stomata in pits with hairs (Nerium).
• Leaf rolling (grasses like Ammophila with hinge/bulliform cells), hairy coverings.
• Well-developed sclerenchyma and xylem; water-storage tissue in succulents.
• CAM photosynthesis: stomata open at night (cacti, pineapple).
• Xerophyte adaptations:
• Halophytes – plants of saline soils, e.g. mangroves of coasts (Rhizophora, Avicennia, Sonneratia).
• Halophyte adaptations: pneumatophores (negatively geotropic breathing roots with lenticels), stilt roots for support, succulent leaves, salt glands that excrete salt, high osmotic pressure of cell sap, and vivipary (seed germinates on the parent tree, e.g. Rhizophora).
• Mesophytes grow in moderate conditions (most crops) and show intermediate features.

Important terms

• Aerenchyma – parenchyma with large air spaces.
• Heterophylly – different leaf forms on the same plant.
• Sunken stomata – stomata in pits below the epidermis, reducing water loss.
• Pneumatophore – breathing root of mangroves.
• Vivipary – germination of seeds while still attached to the parent.

Key facts

5 important questions

Q1. What is vivipary?

Vivipary is the germination of seeds while the fruit is still attached to the parent plant. It is seen in mangroves like Rhizophora; the seedling drops into the mud and fixes itself quickly.

Q2. What are sunken stomata? Give an example.

Stomata placed in pits (stomatal crypts) below the leaf surface, often covered with hairs, which reduce water loss. Example: Nerium leaf.

Q3. Describe the morphological and anatomical adaptations of hydrophytes.

Types with examples; root, stem and leaf adaptations; aerenchyma, reduced xylem, stomata; T.S. of Hydrilla stem.

Q4. Explain the adaptations of xerophytes.

Ephemerals, succulents, non-succulents; morphological, anatomical (Nerium leaf T.S.) and physiological (CAM, osmotic adjustment) adaptations.

Q5. Write a note on mangrove vegetation.

Habitat, examples, pneumatophores, stilt roots, vivipary, salt glands; importance in coastal protection (Sundarbans, Konkan coast).

Exam tip

In practicals, Nerium leaf T.S. (xerophyte) and Hydrilla stem T.S. (hydrophyte) are the standard slides. Write three clear anatomical features for each identification.

Quick summary

Phytogeography (plant geography) studies the distribution of plants on the Earth and the reasons for it. India, with its varied climate and landforms, has very rich vegetation. This topic covers the principles of plant distribution, endemism, the phytogeographical regions of India, the main forest types and the vegetation of Maharashtra.

Key points

• Phytogeography has two branches: descriptive (floristic) – where plants grow, and interpretive (ecological) – why they grow there.
• Factors controlling distribution: climate (temperature, rainfall), soil, topography, geological history (continental drift, glaciation) and dispersal barriers.
• Endemism – a species restricted to a particular area. India has many endemics, especially in the Western Ghats, Eastern Himalaya and Andaman–Nicobar Islands.
• Continuous distribution – species found over wide areas (cosmopolitan, e.g. Cynodon). Discontinuous distribution – species in widely separated areas.
• Phytogeographical regions of India – D. Chatterjee (1939; revised 1962) recognised 9 regions; Champion and Seth (1968) classified Indian forests into 16 major types.
• Common 9 regions (Chatterjee): Western Himalaya, Eastern Himalaya, Indus Plain, Gangetic Plain, Central India, Deccan, Western Ghats (Malabar), Assam, Andaman and Nicobar.
• Major forest types (Champion and Seth): tropical wet evergreen, tropical semi-evergreen, tropical moist deciduous (sal, teak), tropical dry deciduous (teak, tendu), tropical thorn, littoral and swamp (mangroves), subtropical, temperate, subalpine and alpine.
• Western Ghats – one of the world's biodiversity hotspots; wet evergreen forests with many endemic orchids and Impatiens species.
• Konkan coast – mangroves (Rhizophora, Avicennia) and semi-evergreen forests.
• Western Ghats (Sahyadri) – evergreen and semi-evergreen forests, Kaas plateau with seasonal flowers (UNESCO World Heritage with the Western Ghats).
• Deccan plateau – dry deciduous and thorn forests.
• Vidarbha (Nagpur, Bhandara, Gondia, Chandrapur) – tropical dry deciduous forests dominated by teak (Tectona grandis), with tendu, mahua, bamboo; protected areas like Tadoba-Andhari and Nagzira sanctuaries.
• Maharashtra vegetation:
• Other phytogeographic ideas: age and area hypothesis (Willis) – older species occupy larger areas; continental drift (Wegener) explains discontinuous distributions.

Important terms

• Endemic species – species found naturally only in one region.
• Biodiversity hotspot – region very rich in endemic species and under threat.
• Discontinuous distribution – occurrence of a taxon in widely separated areas.
• Flora – all plant species of a region.
• Vegetation – the plant cover of an area.

Key facts

5 important questions

Q1. What is endemism?

Endemism is the restriction of a species to a particular geographical area where it occurs naturally. Example: many orchids and balsams of the Western Ghats are endemic.

Q2. Name the dominant tree of the forests of Vidarbha.

Teak (Tectona grandis) dominates the tropical dry deciduous forests of Vidarbha, along with tendu, mahua and bamboo.

Q3. Describe the phytogeographical regions of India.

Name each region with climate and dominant vegetation (use the table), and draw a rough outline map.

Q4. Give an account of forest types of India.

Champion and Seth's classification; main groups with climate, distribution and examples.

Q5. Write a note on the vegetation of Maharashtra.

Konkan, Western Ghats, Deccan plateau and Vidarbha – forest types, examples, protected areas.

Exam tip

Learn the region names with one dominant plant each. A note on the vegetation of your own area (Vidarbha teak forests) adds local value in RTMNU exams.

Quick summary

A plant disease is any harmful change in the normal structure or function of a plant caused by a pathogen or by bad environmental conditions. Plant pathology studies the causes, symptoms, spread and control of plant diseases. This topic covers classification of diseases, common symptoms, the disease triangle, important Indian crop diseases and methods of control.

Key points

• Plant pathology (phytopathology) is the study of plant diseases. Disease is रोग in Marathi.
• Anton de Bary is called the father of plant pathology. In India, E. J. Butler is called the father of Indian plant pathology.
• Pathogens: fungi (most diseases), bacteria, viruses, viroids, phytoplasma (mycoplasma-like organisms), nematodes, and parasitic plants (Cuscuta, Striga).
• Non-parasitic diseases are caused by nutrient deficiency, pollution, frost, drought, etc.
• By spread: endemic (always present in a region), epidemic (sudden, widespread), sporadic (occasional), pandemic (over continents).
• Disease triangle: disease needs a susceptible host, a virulent pathogen and a favourable environment.
• Koch's postulates are used to prove that a particular organism causes a disease.
• Spread (dissemination): wind, water, insects (vectors), seeds, soil, tools and humans.
• Historic example: the Bengal famine of 1943 is linked to brown spot of rice (Helminthosporium oryzae, now Cochliobolus miyabeanus); the Irish famine (1845–1846) was due to late blight of potato (Phytophthora infestans).

Important terms

• Symptom – visible change caused by disease (e.g. spot, wilt, rot).
• Leaf spot – dead areas on leaves.
• Blight – sudden browning and death of leaves and shoots.
• Rust – reddish-brown powdery pustules (rust fungi).
• Smut – black powdery spore masses (smut fungi).
• Wilt – drooping due to blocked xylem or root damage.
• Mildew – white powdery or downy growth on leaves.
• Mosaic – patchy light and dark green colour (viruses).
• Canker – sunken dead lesion on stem, fruit or leaf.
• Damping off – death of young seedlings near soil level.

Key facts

• Control methods: cultural (crop rotation, removing infected plants, clean seed), chemical (fungicides like Bordeaux mixture – copper sulphate + lime; seed treatment), biological (Trichoderma, Pseudomonas fluorescens), resistant varieties, quarantine laws, and integrated disease management (IDM).

5 important questions

Q1. What is the disease triangle?

The disease triangle shows that a plant disease develops only when three factors meet: a susceptible host, a virulent pathogen and a favourable environment. If any one is absent, disease does not occur.

Q2. What is Bordeaux mixture?

Bordeaux mixture is a fungicide made by mixing copper sulphate and lime (calcium hydroxide) in water. It was discovered by Millardet (1882) in France while fighting downy mildew of grapes.

Q3. Describe late blight of potato.

• Pathogen: Phytophthora infestans.
• Symptoms: water-soaked spots on leaves that turn brown-black; white growth on lower side in humid weather; tubers rot.
• Favoured by cool, humid, cloudy weather.
• Spread: sporangia by wind and rain; infected seed tubers.
• Control: healthy seed, resistant varieties, fungicide sprays (e.g. mancozeb, Bordeaux), destroying infected plants.

Q4. Explain the methods of controlling plant diseases.

• Exclusion: quarantine, certified seed.
• Eradication: removing alternate hosts and infected plants; crop rotation.
• Protection: chemical fungicides and seed treatment.
• Biological control: antagonistic microbes.
• Host resistance: resistant varieties.
• IDM: combining these.

Q5. Describe red rot of sugarcane.

• Pathogen: Colletotrichum falcatum.
• Symptoms: drying of leaves; split stalk shows red patches with white cross bands; sour (alcoholic) smell.
• Spread: infected setts, soil, water.
• Control: healthy setts, hot-water/ fungicide treatment, resistant varieties, crop rotation.

Exam tip

Learn the pathogen name for each Indian crop disease; questions often ask "name the causal organism of…".

Quick summary

Economic botany studies plants that are useful to humans – for food, fibre, oil, medicine, timber, beverages, spices and more. India is rich in such plants. This topic covers cereals, pulses, oilseeds, fibres, sugar crops, beverages, spices, medicinal plants and timber, giving the botanical name, family and useful part of each.

Key points

• Economic botany links plant science with agriculture, industry and trade.
• Cereals belong to the grass family Poaceae (Gramineae); their grain is a caryopsis; they supply most of our carbohydrates.
• Pulses belong to Fabaceae (Leguminosae); their seeds are rich in protein; their root nodules fix nitrogen.
• Oilseeds give edible and industrial oils.
• Fibres are surface fibres (cotton), bast/stem fibres (jute, flax) or leaf fibres (sisal).
• Medicinal plants give drugs from roots, bark, leaves, seeds or latex.
• Spices and condiments add flavour and colour.

Important terms

• Caryopsis – one-seeded dry fruit where the seed coat is fused with the fruit wall (cereals).
• Bast fibre – fibre from phloem (secondary phloem) of stems.
• Retting – soaking stems in water so that microbes loosen the fibres (jute).
• Ginning – separating cotton fibres (lint) from seeds.
• Alkaloid – nitrogen-containing plant compound with strong action on the body (e.g. quinine, reserpine).

Key facts

• Maharashtra (especially Vidarbha) is a major cotton-growing region; Vidarbha also grows soybean, tur and oranges (Nagpur oranges).
• Bhandara and Gondia districts are known for paddy (rice) cultivation.

5 important questions

Q1. Give the botanical name, family and useful part of turmeric.

Turmeric is Curcuma longa of family Zingiberaceae. Its underground stem (rhizome) is used as a spice, a colouring agent and in medicine (curcumin).

Q2. What is retting?

Retting is the process of soaking harvested jute stems in slow-moving water for some days. Microbes decompose the soft tissues, so the bast fibres can be separated easily.

Q3. Write a note on cotton.

• Botanical name Gossypium spp. (G. hirsutum, G. arboreum, G. herbaceum); family Malvaceae.
• Fibres are epidermal hairs of the seed coat (lint); short fuzz is linters.
• Grown on black cotton soil (regur) – Maharashtra, Gujarat, Telangana.
• Processing: picking, ginning, baling, spinning.
• Uses: textiles; seed oil and oil cake (cattle feed).

Q4. Describe the economic importance of the family Fabaceae.

• Pulses: tur, gram, moong, urad, masoor – protein.
• Oilseeds: groundnut, soybean.
• Fodder: berseem, lucerne.
• Timber: shisham (Dalbergia sissoo).
• Soil fertility via Rhizobium nodules.
• Medicinal: liquorice (Glycyrrhiza glabra).

Q5. Name five medicinal plants with their uses.

• Rauvolfia serpentina – reserpine, high blood pressure.
• Cinchona – quinine, malaria.
• Azadirachta indica – antiseptic, insecticide.
• Withania somnifera – tonic.
• Aloe vera – skin care, burns.
• Ocimum – cough and cold.

Exam tip

Learn "botanical name – family – useful part" for at least two plants in each group. Write botanical names in italics or underline them.

Quick summary

Ethnobotany studies the relationship between people – especially tribal and rural communities – and plants: how they use plants for food, medicine, fibre, rituals and daily life. Medicinal plants contain active compounds used to treat diseases. This topic covers the scope and methods of ethnobotany, important tribes and ethnobotanical plants of Maharashtra, traditional systems of medicine, and important medicinal plants with their active principles.

Key points

• The term ethnobotany was coined by J. W. Harshberger (1895). In India, S. K. Jain is called the father of Indian ethnobotany.
• Branches: ethnomedicine, ethnoagriculture, ethnopharmacology, ethnoecology, ethnotaxonomy.
• Methods: field surveys with tribal healers (vaidus), interviews and questionnaires, herbarium specimens, study of old texts and folklore, market surveys, and laboratory testing of claims.
• Tribes of Maharashtra with rich plant knowledge: Gond and Madia (Gadchiroli, Chandrapur, Vidarbha), Korku (Melghat), Bhil, Warli and Katkari, Kolam.
• Ethnobotanical uses common in Vidarbha: mahua (Madhuca longifolia) flowers as food and liquor, seeds for oil; tendu (Diospyros melanoxylon) leaves for bidi; bamboo for houses and baskets; charoli (Buchanania lanzan) seeds; gum from Sterculia urens (karaya).
• Traditional systems of medicine: Ayurveda, Siddha, Unani, Homoeopathy, folk medicine (AYUSH). Ayurveda texts: Charaka Samhita, Sushruta Samhita.
• Active principles (secondary metabolites): alkaloids, glycosides, tannins, essential oils, resins, flavonoids, saponins.
• Pharmacognosy – study of crude drugs of natural origin (identification, quality, active compounds).
• Conservation concerns: overharvesting of roots and bark endangers species (e.g. Rauvolfia, Gloriosa, sarpagandha); cultivation and sustainable collection are needed.
• Intellectual property: traditional knowledge is recorded in India's Traditional Knowledge Digital Library (TKDL) to prevent biopiracy (neem and turmeric patent cases).

Important terms

• Ethnobotany – study of plant use by people of a particular culture or region.
• Crude drug – dried, unprocessed plant part used as medicine.
• Alkaloid – nitrogen-containing basic compound with strong physiological action.
• Glycoside – compound of a sugar with a non-sugar part (aglycone).
• Biopiracy – commercial use of biological resources or traditional knowledge without permission or benefit sharing.

Key facts

5 important questions

Q1. Who is the father of Indian ethnobotany?

Dr. S. K. Jain, who carried out extensive ethnobotanical surveys among tribal communities of India and established ethnobotany as a discipline in the country.

Q2. Name the active principle and use of Rauvolfia serpentina.

Its roots contain the alkaloid reserpine, which is used to lower high blood pressure and as a sedative.

Q3. Explain the scope and methods of ethnobotany.

Definition; branches; field methods (survey, interview, herbarium), literature and laboratory methods; importance in drug discovery and conservation.

Q4. Describe ethnobotanical uses of plants by tribes of Maharashtra.

Gond, Madia, Korku, Warli, Bhil; uses of mahua, tendu, bamboo, charoli, karaya gum; medicinal uses for wounds, fever, snake bite.

Q5. Write an account of any five medicinal plants.

For each: botanical name, family, part used, active principle and medicinal use (use the table).

Exam tip

Learn five medicinal plants in the format "name – family – part – principle – use". Local Vidarbha examples (mahua, tendu, Gond tribe) are valued in RTMNU answers.

Quick summary

Biodiversity is the variety of all living organisms on Earth at the level of genes, species and ecosystems. It gives us food, medicine, clean air and water, and keeps ecosystems stable. Today biodiversity is being lost very fast. This topic covers levels of biodiversity, its value, hotspots, threats, IUCN categories and methods of in-situ and ex-situ conservation, with Indian examples.

Key points

• The term biodiversity was made popular by E. O. Wilson (the word was first used by Walter G. Rosen, 1985). Biodiversity is जैवविविधता in Marathi.
• Levels: genetic diversity (variation within a species, e.g. many varieties of rice and mango in India), species diversity (number of species in an area), ecosystem diversity (forests, deserts, wetlands, coral reefs).
• India is one of the world's megadiverse countries, with about 2.4% of the world's land area but a much larger share of its species.
• Biodiversity hotspots (concept by Norman Myers, 1988): regions very rich in endemic species and under severe threat. Four hotspots include parts of India: Western Ghats and Sri Lanka, Himalaya, Indo-Burma, and Sundaland (Nicobar Islands).
• Threats (the "evil quartet"): habitat loss and fragmentation, over-exploitation, invasion of alien species (e.g. Parthenium, Lantana, water hyacinth Eichhornia), and co-extinctions. Also pollution and climate change.
• IUCN Red List categories: Extinct, Extinct in the Wild, Critically Endangered, Endangered, Vulnerable, Near Threatened, Least Concern (and Data Deficient, Not Evaluated).
• In-situ conservation (on-site): national parks, wildlife sanctuaries, biosphere reserves, sacred groves.
• Ex-situ conservation (off-site): botanical gardens, zoos, seed banks, gene banks, cryopreservation, tissue culture.
• Convention on Biological Diversity was signed at the Earth Summit, Rio de Janeiro, 1992.
• India passed the Biological Diversity Act, 2002, and set up the National Biodiversity Authority (Chennai).

Important terms

• Endemic species – found only in a particular region.
• Biosphere reserve – large protected area with a core zone (no disturbance), buffer zone (limited activity) and transition zone (human settlements). India's first was Nilgiri (1986).
• Sacred groves – forest patches protected by local communities for religious reasons (called devrai in Maharashtra).
• Seed bank – store of seeds kept at low temperature and humidity.
• Cryopreservation – storage of cells, tissues or seeds in liquid nitrogen at −196 °C.
• Bioprospecting – searching for useful products (drugs, genes) from living organisms.

Key facts

• Protected areas in Maharashtra and Vidarbha: Tadoba–Andhari Tiger Reserve (Chandrapur), Pench Tiger Reserve (Nagpur), Melghat Tiger Reserve (Amravati), Navegaon–Nagzira Tiger Reserve (Gondia–Bhandara), Sanjay Gandhi National Park (Mumbai).
• India's important in-situ programmes: Project Tiger (1973), Project Elephant (1992).
• Ex-situ examples: National Bureau of Plant Genetic Resources (NBPGR) gene bank, New Delhi; botanical gardens such as the Indian Botanic Garden, Howrah.
• Values of biodiversity: direct (food, fuel, fibre, medicine, timber), indirect (pollination, soil formation, climate regulation, water cycle), aesthetic, ethical and cultural.

5 important questions

Q1. What is a biodiversity hotspot?

A hotspot is a region that has a very high number of endemic species and has already lost much of its natural habitat. The concept was given by Norman Myers. The Western Ghats is an example in India.

Q2. What are sacred groves?

Sacred groves are patches of forest protected by local people because of religious beliefs. Cutting trees there is not allowed, so they preserve many rare plants. In Maharashtra they are called devrai.

Q3. Explain the levels of biodiversity.

• Genetic diversity: differences in genes within a species; e.g. varieties of rice and mango; helps adaptation.
• Species diversity: number and abundance of species; e.g. Western Ghats amphibians.
• Ecosystem diversity: variety of habitats and communities; e.g. deserts, forests, mangroves, wetlands in India.
• All three levels are linked.

Q4. Describe the causes of loss of biodiversity.

• Habitat loss and fragmentation (deforestation, mining, cities).
• Over-exploitation (over-hunting, over-collection of medicinal plants).
• Alien invasive species (Lantana, Parthenium, Eichhornia).
• Co-extinctions (plant–pollinator pairs).
• Pollution and climate change.

Q5. Compare in-situ and ex-situ conservation.

• In-situ: in natural habitat; whole ecosystem protected; examples – national parks, sanctuaries, biosphere reserves, sacred groves.
• Ex-situ: outside natural habitat; for highly threatened species; examples – botanical gardens, zoos, seed banks, cryopreservation, tissue culture.
• Both are needed together.
• Mention Vidarbha tiger reserves as local examples.

Exam tip

Use Indian and Maharashtra examples (Tadoba, Melghat, devrai) – they make answers stand out. Learn the zones of a biosphere reserve with a simple circle diagram.

Quick summary

Good seed and healthy planting material are the base of good crops. Seed technology deals with producing, processing, testing, storing and certifying quality seed. A plant nursery raises seedlings and grafts for farms, gardens and forests. This topic covers seed quality, classes of seed, seed testing, dormancy and its breaking, seed storage, and nursery types, structures and propagation methods.

Key points

• Seed – fertilised, ripened ovule with an embryo, food reserve and seed coat. In agriculture, "seed" means any material used for planting (seeds, tubers, cuttings).
• Qualities of good seed: genetic purity, physical purity, high germination percentage, vigour, correct moisture content, freedom from diseases, pests and weed seeds.
• Classes of seed (Indian seed system): Nucleus seed (by the plant breeder) → Breeder seed (golden-yellow tag) → Foundation seed (white tag) → Certified seed (blue tag) → farmers.
• The Seeds Act, 1966 regulates quality of notified seeds in India; seed certification agencies inspect fields and seed lots. (Check current rules – a new Seeds Bill has been under discussion.)
• Seed testing (ISTA rules): sampling; purity test; germination test (between paper, on paper, sand); moisture test; viability test with tetrazolium (TZ) – living tissue turns red; vigour tests.
• Seed dormancy – failure of viable seed to germinate in favourable conditions. Causes: hard seed coat, immature embryo, inhibitors (ABA), need of light or chilling.
• Breaking dormancy: scarification (mechanical scratching or acid treatment), stratification (moist chilling), soaking in water, hormones (gibberellic acid, GA₃), potassium nitrate.
• Seed storage: keep dry and cool; "Harrington's rules" – every 1% fall in seed moisture or 5 °C fall in temperature roughly doubles seed life (within limits). Orthodox seeds tolerate drying; recalcitrant seeds (mango, jackfruit, cocoa) do not.
• Seed processing: drying, cleaning, grading, seed treatment (fungicides, biofertilisers), packing and labelling.
• Nursery – place where plants are raised and cared for until planting. Types: temporary and permanent; by plants – fruit, vegetable, flower, forest and ornamental nurseries.
• Nursery structures and tools: mother plant block, propagation beds, polyhouse/greenhouse, shade net house, mist chamber, polybags, pro-trays, potting mixture (soil + sand + farmyard manure or cocopeat).
• Propagation methods: by seed (sexual) and vegetative – cuttings (rose, hibiscus), layering (air layering/gootee in guava, litchi), grafting (approach, wedge/cleft grafting in mango), budding (T-budding in rose, citrus), and micropropagation (tissue culture).
• Nursery management: seedbed preparation, sowing, watering, shading, hardening, plant protection, record keeping and licensing of commercial nurseries.

Important terms

• Germination percentage – (seeds germinated ÷ seeds tested) × 100.
• Scarification – weakening the seed coat to allow water entry.
• Stratification – keeping seeds moist at low temperature to break dormancy.
• Stock and scion – rooted lower part and upper shoot part joined in grafting.
• Hardening – gradually exposing nursery plants to outside conditions before field planting.

Key facts

• Worked example: 100 seeds tested, 92 germinated → germination percentage = (92 ÷ 100) × 100 = 92%.

5 important questions

Q1. What is the tetrazolium test?

A quick viability test. Seeds are soaked in 2,3,5-triphenyl tetrazolium chloride solution; living tissues reduce it to a red compound (formazan), while dead tissues stay colourless.

Q2. Distinguish between orthodox and recalcitrant seeds.

Orthodox seeds can be dried to low moisture and stored for long at low temperature (wheat, rice). Recalcitrant seeds die if dried and cannot be stored long (mango, jackfruit).

Q3. Describe the classes of seed and seed certification.

Nucleus, breeder, foundation and certified seed; who produces each; tags; field inspection and seed testing standards; Seeds Act 1966.

Q4. Explain seed dormancy and methods to break it.

Types and causes; scarification, stratification, GA₃, KNO₃, light treatment; importance for nursery work.

Q5. Write an account of nursery management and vegetative propagation.

Types of nursery, site and structures, potting mixture; cuttings, layering, grafting, budding with sketches; hardening and plant protection.

Exam tip

Learn the seed class–tag colour table and draw one grafting and one budding diagram – they are frequently asked in skill-based (SEC/VSC) papers too.