This chapter explains how plants reproduce. It covers asexual and vegetative reproduction, the structure of the flower's male and female parts, formation of pollen (microsporogenesis) and embryo sac (megasporogenesis), pollination and outbreeding devices, pollen–pistil interaction, double fertilization, development of endosperm, embryo, seed and fruit, and special cases like apomixis, parthenocarpy and polyembryony.
The stamen has an anther (usually bilobed, dithecous, with four microsporangia) and a filament. The anther wall layers are epidermis, endothecium, middle layers and tapetum (nourishes developing pollen).
Microsporogenesis: each microspore mother cell (2n) divides by meiosis into a tetrad of four haploid microspores, which become pollen grains. Pollen wall: outer exine (sporopollenin, with germ pores) and inner intine.
Mature pollen has a large vegetative (tube) cell and a small generative cell, which divides to form two male gametes.
The common ovule is anatropous (inverted). Parts: funicle, hilum, integuments, micropyle, nucellus, chalaza, embryo sac.
Megasporogenesis: megaspore mother cell divides by meiosis into four megaspores; usually one functions. In the Polygonum type, it forms a 7-celled, 8-nucleate embryo sac (egg apparatus of 3, central cell with 2 polar nuclei, 3 antipodals).
Pollination types: autogamy (same flower), geitonogamy (another flower of same plant), xenogamy (another plant). Agents: wind (anemophily), water (hydrophily), insects (entomophily), birds, bats.
Outbreeding devices prevent self-pollination: dichogamy (anthers and stigma mature at different times), herkogamy (physical barrier), self-incompatibility, unisexual flowers.
Double fertilization (unique to angiosperms): one male gamete + egg → zygote (2n); the other male gamete + two polar nuclei (secondary nucleus) → primary endosperm nucleus (3n).
Apomixis: seed formation without fertilization. Parthenocarpy: fruit without fertilization (seedless banana, grapes). Polyembryony: more than one embryo in a seed (citrus, mango).
महत्त्वाच्या संज्ञा
Cleistogamy – flowers that never open, so they are always self-pollinated (e.g. Commelina benghalensis; Viola and Commelina have both open and closed flowers).
Pollen–pistil interaction – the stigma recognises compatible pollen and rejects incompatible pollen.
Triple fusion – fusion of a male gamete with the two polar nuclei, forming the 3n endosperm nucleus.
Synergids – two cells beside the egg; the filiform apparatus guides the pollen tube.
Perisperm – remains of nucellus in some seeds (black pepper).
Monocot embryo has one cotyledon (scutellum), coleoptile and coleorhiza; dicot embryo has two cotyledons.
५ महत्त्वाचे प्रश्न
Q1. What is double fertilization? Why is it called so?
In the embryo sac one male gamete fuses with the egg (syngamy) forming the 2n zygote, and the second male gamete fuses with two polar nuclei (triple fusion) forming the 3n primary endosperm nucleus. Since two fusions occur, it is called double fertilization.
Q2. Describe the structure of a mature embryo sac.
It is 7-celled and 8-nucleate. At the micropylar end: egg apparatus (one egg + two synergids). At the chalazal end: three antipodal cells. In the centre: a large central cell with two polar nuclei.
Q3. Explain any two outbreeding devices.
Dichogamy: anthers and stigma mature at different times (protandry or protogyny), so self-pollination is avoided. Self-incompatibility: pollen of the same flower cannot germinate or grow on its own stigma because of genetic control.
Q4. Distinguish between autogamy and xenogamy.
Autogamy is transfer of pollen to the stigma of the same flower; offspring are genetically similar. Xenogamy is transfer of pollen to the stigma of a flower on another plant; it brings genetic variation.
Q5. What is parthenocarpy? Give its importance.
Development of fruit without fertilization; such fruits are seedless (banana, grapes, pineapple). It is commercially important because seedless fruits are preferred and can be induced by plant hormones.
परीक्षेसाठी टीप
Practise labelled diagrams of the anatropous ovule, mature embryo sac and pollen grain — diagrams carry fixed marks in the board paper.
This chapter covers asexual reproduction in lower animals and sexual reproduction in humans. It explains the male and female reproductive systems, the menstrual cycle, gametogenesis, fertilization, embryonic development, pregnancy, placenta, birth and lactation, and ends with reproductive health, birth control, STDs and infertility.
Oogenesis: oogonia → primary oocyte (arrested in prophase I before birth) → secondary oocyte + first polar body; ovulation releases the secondary oocyte. One primary oocyte gives 1 ovum.
Fertilization happens in the ampullary-isthmic junction of the fallopian tube; the acrosome enzymes help the sperm enter.
Cleavage forms morula, then blastocyst, which gets embedded in the endometrium (implantation, normally in the fundus of the uterus).
Three germ layers form during gastrulation: ectoderm, mesoderm, endoderm.
The placenta gives nutrients and oxygen, removes wastes, and secretes hCG, hPL, oestrogen and progesterone. Pregnancy lasts about 9 months.
Parturition is triggered by the foetal ejection reflex; oxytocin causes strong uterine contractions. Prolactin starts milk production; colostrum gives antibodies (IgA) to the baby.
STDs: gonorrhoea, syphilis, genital herpes, AIDS, hepatitis B. Infertility can be helped by ART: IVF with embryo transfer, ZIFT, GIFT, ICSI, artificial insemination.
महत्त्वाच्या संज्ञा
Gametogenesis – formation of gametes (sperm or ovum) by meiosis.
Corpus luteum – yellow body formed from the ruptured follicle; secretes progesterone.
Implantation – attachment of the blastocyst to the uterine wall.
Menarche / menopause – first menstruation / permanent stopping of menstruation (around 45–50 years).
Amniocentesis – test of amniotic fluid to detect genetic disorders (misuse for sex determination is banned).
महत्त्वाची माहिती
Hormone
Source
Main role
FSH
Anterior pituitary
Follicle growth / spermatogenesis
LH
Anterior pituitary
Ovulation / testosterone secretion
Oestrogen
Growing follicle
Repair of endometrium
Progesterone
Corpus luteum, placenta
Maintains pregnancy
hCG
Placenta
Keeps corpus luteum active
Oxytocin
Posterior pituitary
Uterine contraction, milk ejection
५ महत्त्वाचे प्रश्न
Q1. Distinguish between spermatogenesis and oogenesis.
Spermatogenesis occurs in testes, starts at puberty, continues for life and one primary spermatocyte forms four sperms. Oogenesis occurs in ovaries, starts before birth, stops at menopause, and one primary oocyte forms one ovum and polar bodies.
Q2. Describe the phases of the menstrual cycle.
Menstrual phase (days 1–5): endometrium breaks down and flows out. Follicular phase (days 6–13): follicle grows, oestrogen rebuilds endometrium. Ovulation (day 14): LH surge releases the ovum. Luteal phase (days 15–28): corpus luteum secretes progesterone; if no fertilization it degenerates and the cycle repeats.
Q3. Give the functions of the placenta.
Supplies oxygen and nutrients to the foetus, removes CO₂ and wastes, acts as a barrier against some germs, and works as an endocrine gland secreting hCG, hPL, oestrogen and progesterone.
Q4. What is IVF?
In vitro fertilization: ovum and sperm are fused outside the body in the laboratory; the early embryo is then transferred into the woman's body (into the fallopian tube in ZIFT, or the uterus) to develop. It is also called the "test tube baby" programme.
Q5. Name the cells that secrete testosterone and nourish sperms.
Leydig (interstitial) cells secrete testosterone. Sertoli cells in the seminiferous tubules nourish developing sperms.
परीक्षेसाठी टीप
Draw and label the L.S. of human testis, the ovary section and a sperm — and learn the hormone table, which answers many short questions.
Genetics studies how characters pass from parents to offspring (inheritance) and why offspring differ (variation). This chapter covers Mendel's laws, test cross, deviations from Mendel (incomplete dominance, codominance, multiple alleles, pleiotropy, polygenic inheritance), the chromosomal theory, linkage and crossing over, sex-linked inheritance, sex determination and genetic disorders.
महत्त्वाचे मुद्दे
Mendel worked on garden pea (Pisum sativum) and studied 7 pairs of contrasting characters.
Law of dominance: in a hybrid, only the dominant factor shows. Law of segregation (purity of gametes): the two alleles separate during gamete formation. Law of independent assortment: alleles of different genes assort independently.
Homozygous / heterozygous – same alleles (TT, tt) / different alleles (Tt).
Back cross – F₁ crossed with either parent.
Linkage group – all genes present on one chromosome.
Carrier – a heterozygous person who carries a recessive allele without showing the disease.
महत्त्वाची माहिती
Blood group
Genotypes
A
IᴬIᴬ, Iᴬi
B
IᴮIᴮ, Iᴮi
AB
IᴬIᴮ
O
ii
Recombination frequency (%) = (number of recombinants / total offspring) × 100; 1% = 1 map unit (centimorgan).
५ महत्त्वाचे प्रश्न
Q1. State Mendel's law of segregation and explain with a monohybrid cross.
The two alleles of a gene separate during gamete formation so each gamete gets only one. Tall (TT) × dwarf (tt) gives Tt (tall). F₁ gametes are T and t; F₂ gives TT : Tt : tt = 1 : 2 : 1, phenotype 3 tall : 1 dwarf.
Q2. Explain incomplete dominance in Mirabilis jalapa.
Red (RR) × white (rr) gives pink (Rr) F₁, because neither allele is fully dominant. F₂: 1 red (RR) : 2 pink (Rr) : 1 white (rr) — phenotypic and genotypic ratios are the same.
Q3. What is a test cross? Why is it important?
Crossing an organism of dominant phenotype with a homozygous recessive. If all offspring are dominant, the organism is homozygous; if 1:1, it is heterozygous. It reveals an unknown genotype.
Q4. Why is haemophilia more common in males than females?
The gene is recessive and on the X chromosome. Males have only one X (XY), so a single recessive allele shows the disease. Females need two recessive alleles; with one they are only carriers.
Q5. Give the chromosome number and features of Down's syndrome.
Trisomy of chromosome 21 (47 chromosomes). Features: short stature, small round head, furrowed tongue, partly open mouth, broad palm with a single crease, slow mental development.
परीक्षेसाठी टीप
Show crosses with a checkerboard (Punnett square), gametes in circles, and write both phenotypic and genotypic ratios — marks are given for each step.
This chapter explains how DNA works as the genetic material. It covers the experiments that proved DNA is the genetic material, packaging of DNA in chromosomes, semi-conservative replication, protein synthesis (transcription, genetic code, translation), gene regulation by the lac operon, genomics, the Human Genome Project and DNA fingerprinting.
महत्त्वाचे मुद्दे
Griffith (1928) worked with Streptococcus pneumoniae: heat-killed S strain + live R strain killed mice — the R strain was "transformed" by some substance.
Avery, MacLeod and McCarty showed that the transforming substance is DNA (DNase destroyed it; protease and RNase did not).
Hershey and Chase used bacteriophages labelled with ³²P (DNA) and ³⁵S (protein): only ³²P entered the bacteria, proving DNA is the genetic material.
DNA is a double helix of two antiparallel polynucleotide strands; A pairs with T (2 H-bonds), G pairs with C (3 H-bonds).
Packaging: DNA wraps around a histone octamer to form a nucleosome (about 200 bp; about 146 bp wound around the octamer, rest is linker DNA). Nucleosomes look like "beads on a string" and coil further into chromatin fibres.
Replication is semi-conservative — proved by Meselson and Stahl (1958) using ¹⁵N and ¹⁴N with E. coli.
Replication enzymes: helicase (unwinds), primase (RNA primer), DNA polymerase (adds nucleotides in 5'→3' direction), ligase (joins Okazaki fragments). Leading strand is continuous; lagging strand is discontinuous.
Central dogma: DNA → (transcription) → mRNA → (translation) → protein.
The genetic code is a triplet code; 64 codons; AUG is the start codon (methionine); UAA, UAG, UGA are stop codons. The code is universal, non-overlapping and degenerate.
Translation occurs on ribosomes; tRNA brings amino acids and has an anticodon.
Lac operon (Jacob and Monod, 1961) in E. coli: regulator gene, promoter, operator and structural genes (lacZ, lacY, lacA). Lactose acts as an inducer by removing the repressor.
Human Genome Project: started 1990, completed 2003; human genome has about 3 billion base pairs.
DNA fingerprinting (Alec Jeffreys, 1984) uses VNTRs; steps include DNA extraction, restriction digestion, gel electrophoresis, Southern blotting, probe hybridisation and autoradiography. Used in forensics and paternity tests.
महत्त्वाच्या संज्ञा
Transformation – change in a bacterium's character by taking up foreign DNA.
Okazaki fragments – short DNA pieces made on the lagging strand.
Codon / anticodon – triplet on mRNA / complementary triplet on tRNA.
Operon – a group of genes controlled together with a promoter and operator.
VNTR – variable number tandem repeats; short repeated DNA sequences that differ between people.
Exons / introns – coding / non-coding parts of a eukaryotic gene; introns are removed by splicing.
महत्त्वाची माहिती
Enzyme
Role
Helicase
Unwinds the double helix
Topoisomerase
Releases tension from supercoiling
Primase
Makes RNA primer
DNA polymerase
Adds nucleotides 5'→3'
DNA ligase
Joins Okazaki fragments
RNA polymerase
Makes RNA during transcription
५ महत्त्वाचे प्रश्न
Q1. Describe the Hershey–Chase experiment.
Phages were grown in ³⁵S (labels protein coat) or ³²P (labels DNA) medium, then allowed to infect E. coli. After blending and centrifuging, ³²P was found inside the bacteria, while ³⁵S stayed outside. So DNA, not protein, enters the host and is the genetic material.
Q2. Explain the Meselson–Stahl experiment.
E. coli was grown in ¹⁵N (heavy) medium, then shifted to ¹⁴N. After one generation, DNA had intermediate density (¹⁵N/¹⁴N hybrid); after two generations, half was hybrid and half light. This proved replication is semi-conservative.
Q3. Give the features of the genetic code.
Triplet; 61 sense codons code for 20 amino acids; AUG is start codon; three stop codons (UAA, UAG, UGA); universal; non-overlapping; commaless; degenerate (one amino acid may have several codons).
Q4. Explain the lac operon when lactose is present.
The regulator gene makes a repressor. Lactose (inducer) binds the repressor and inactivates it, so it cannot bind the operator. RNA polymerase then transcribes lacZ, lacY and lacA, producing β-galactosidase, permease and transacetylase, which break down lactose.
Q5. Give two applications of DNA fingerprinting.
Identifying criminals in forensic cases; settling paternity/maternity disputes; identifying bodies after disasters; studying evolution and populations (any two).
परीक्षेसाठी टीप
Diagrams of the replication fork, nucleosome and lac operon are often asked; label the 5' and 3' ends correctly.
This chapter explains how life may have begun on Earth (chemical evolution) and how living forms changed over time (organic evolution). It covers Oparin–Haldane theory, the Urey–Miller experiment, Darwinism, mutation theory, modern synthetic theory, Hardy–Weinberg principle, adaptive radiation, evidences of evolution, speciation, the geological time scale and human evolution.
महत्त्वाचे मुद्दे
Oparin (1924) and Haldane (1929): life arose from non-living matter through slow chemical reactions in the primitive oceans (the "hot dilute soup"). The early atmosphere was reducing (CH₄, NH₃, H₂, water vapour, no free O₂).
Urey and Miller passed electric sparks through CH₄, NH₃, H₂ and water vapour and obtained amino acids, supporting chemical evolution.
Organic molecules aggregated into coacervates and microspheres (Sidney Fox, proteinoids), possible forerunners of the first cells.
Darwinism (natural selection): overproduction, struggle for existence, variation, survival of the fittest, and origin of new species. Darwin studied finches of the Galapagos Islands.
Mutation theory by Hugo de Vries, based on evening primrose (Oenothera lamarckiana): new species arise by sudden large changes (mutations).
Modern synthetic theory combines gene mutation, recombination, genetic drift, gene flow (migration), natural selection and reproductive isolation.
Hardy–Weinberg principle: allele and genotype frequencies stay constant from generation to generation if there is no mutation, migration, genetic drift or selection, and mating is random.
Adaptive radiation: one ancestral form spreads into many habitats and gives many species (Darwin's finches, Australian marsupials).
Evidences of evolution: palaeontology (fossils), comparative anatomy (homologous and analogous organs, vestigial organs), embryology, molecular biology/biochemistry and biogeography.
Speciation happens when populations become reproductively isolated (allopatric — geographical barrier; sympatric — same area).
The geological time scale divides Earth's history into eras, periods and epochs.
Human evolution: Dryopithecus → Ramapithecus → Australopithecus → Homo habilis → Homo erectus → Homo neanderthalensis → Homo sapiens.
महत्त्वाच्या संज्ञा
Homologous organs – same origin, different function (forelimbs of man, whale, bat) — show divergent evolution.
Analogous organs – different origin, same function (wings of insect and bird) — show convergent evolution.
Genetic drift – random change in allele frequency, important in small populations (founder effect).
Gene pool – all the genes of a population.
महत्त्वाची माहिती
Hardy–Weinberg equation: p + q = 1 and p² + 2pq + q² = 1 p = frequency of dominant allele, q = frequency of recessive allele; p² = AA, 2pq = Aa, q² = aa.
Example: if q² (aa) = 0.16, then q = 0.4, p = 0.6, and carriers 2pq = 0.48.
५ महत्त्वाचे प्रश्न
Q1. Describe the Urey–Miller experiment and its significance.
A mixture of CH₄, NH₃, H₂ and water vapour was circulated in a closed glass apparatus and electric sparks were passed (like lightning) while water was boiled and condensed. After about a week, amino acids and other simple organic compounds formed. It supported the Oparin–Haldane idea of chemical evolution.
Q2. State the main points of Darwin's theory of natural selection.
Organisms overproduce; this causes struggle for existence; individuals vary; those with useful variations survive and reproduce (survival of the fittest); favourable variations accumulate over generations, leading to new species.
Q3. State the Hardy–Weinberg principle and the factors that disturb it.
Allele and genotype frequencies in a population remain constant across generations in the absence of disturbing factors. Factors: mutation, gene migration (gene flow), genetic drift, genetic recombination and natural selection.
Q4. Distinguish between homologous and analogous organs.
Homologous organs have the same basic structure and origin but different functions (divergent evolution). Analogous organs have different structure and origin but the same function (convergent evolution).
Q5. What is adaptive radiation? Give an example.
Evolution of many different species from one ancestral species, each adapted to a different habitat. Example: Darwin's finches of the Galapagos, which developed different beak shapes for different foods.
परीक्षेसाठी टीप
Hardy–Weinberg problems are easy marks: always start from q² (recessive phenotype), take the square root, then find p and 2pq.
This chapter explains how plants take in water and minerals, move them up the stem, transport food, and lose water. It covers properties of water, root hairs, water potential, plasmolysis, absorption (active and passive), ascent of sap (cohesion–tension theory), transport of minerals and food (Munch's mass flow), transpiration and the working of stomata.
महत्त्वाचे मुद्दे
Water has high specific heat, high latent heat, strong cohesion and adhesion, and is a universal solvent — properties that make it suitable for life.
Root hairs in the root hair zone are the main water-absorbing structures; they give a large surface area.
Soil water forms: gravitational water, hygroscopic water, combined water and capillary water — capillary water is the main water available to plants.
Absorption involves imbibition, diffusion and osmosis.
Water potential (ψ) is the free energy of water; pure water has ψ = 0 and solutions have negative ψ. Water moves from higher (less negative) to lower (more negative) ψ.
Plasmolysis: in a hypertonic solution, a cell loses water and the protoplast shrinks away from the wall. Deplasmolysis happens when it is put back in water.
Water crosses the root by the apoplast (cell walls and spaces) and symplast (cytoplasm through plasmodesmata) paths; the Casparian strip in the endodermis forces water into the symplast.
Active absorption uses root energy (root pressure); passive absorption is due to transpiration pull and is the main method.
Ascent of sap: the cohesion–tension (transpiration pull) theory of Dixon and Jolly (1894) is the most accepted explanation.
Food (sucrose) moves through the phloem by Munch's pressure flow (mass flow) theory, from source (leaf) to sink (root, fruit, storage organ).
Transpiration is loss of water as vapour from aerial parts: stomatal (most), cuticular and lenticular. It cools the plant and creates transpiration pull, but wastes water.
Stomata open when guard cells become turgid. By the K⁺ ion pump theory (Levitt, 1974), K⁺ ions (with Cl⁻) enter guard cells, water follows by osmosis and the stoma opens.
महत्त्वाच्या संज्ञा
Imbibition – absorption of water by solid hydrophilic substances (dry seeds swell).
Root pressure – pressure in the xylem of roots that pushes water up (seen as guttation and bleeding).
Guttation – loss of water as droplets from leaf margins through hydathodes.
Cohesion / adhesion – attraction between water molecules / between water and xylem walls.
Turgor pressure – pressure of cell contents against the cell wall.
सूत्रे
Water potential: ψw = ψs + ψp (units: bar or MPa)
Pure water at atmospheric pressure: ψw = 0
Water flows from higher ψ to lower ψ.
५ महत्त्वाचे प्रश्न
Q1. Explain the cohesion–tension theory of ascent of sap.
Xylem vessels form continuous water columns from root to leaf. Water molecules stick together (cohesion) and to vessel walls (adhesion). Transpiration from leaves creates a pull (tension) on this column, so water is lifted continuously from roots to leaves. Proposed by Dixon and Jolly.
Q2. What is plasmolysis? Give its significance.
Shrinking of the protoplast away from the cell wall when a cell is placed in a hypertonic solution, due to exosmosis. Significance: shows that the cell membrane is semipermeable; salting of pickles and killing of weeds by salt work on this principle.
Q3. Distinguish between the apoplast and symplast pathways.
Apoplast: water moves through cell walls and intercellular spaces, without crossing membranes; it is fast and blocked by the Casparian strip. Symplast: water moves through cytoplasm from cell to cell via plasmodesmata; it is slower.
Q4. Explain the mechanism of stomatal opening by K⁺ ion uptake.
In light, H⁺ ions are pumped out of guard cells and K⁺ ions move in (with Cl⁻ or malate). Solute concentration rises, water enters by osmosis, guard cells swell and bend because of their unevenly thick walls, and the stoma opens. At night K⁺ leaves and the stoma closes.
Q5. Explain Munch's mass flow hypothesis.
In leaves (source) sugar is loaded into sieve tubes, so water enters from xylem and pressure rises. At the sink, sugar is removed and water leaves, lowering pressure. Food solution flows from high pressure (source) to low pressure (sink).
परीक्षेसाठी टीप
Draw the stomatal apparatus (open and closed) and a labelled diagram of water's path across the root — they appear often.
This chapter explains how plants grow and develop and what nutrients they need. It covers phases and types of growth, the growth curve, differentiation, plant growth hormones, photoperiodism, vernalization, essential mineral elements and their deficiency symptoms, and the nitrogen cycle including biological nitrogen fixation.
महत्त्वाचे मुद्दे
Growth is a permanent, irreversible increase in size, mass or volume. In plants it is open (indeterminate) and occurs at meristems.
Phases of growth: cell division (formative), cell enlargement (elongation) and cell maturation (differentiation).
Arithmetic growth: only one daughter cell keeps dividing — linear curve (e.g. root elongation). Geometric growth: both daughter cells divide — exponential curve.
The sigmoid (S-shaped) growth curve has a lag phase, log (exponential) phase and stationary phase.
Differentiation, dedifferentiation (permanent cells regain division, e.g. cork cambium) and redifferentiation.
Plasticity: a plant forms different structures in response to environment (heterophylly in cotton, coriander, buttercup).
Photoperiodism (Garner and Allard, 1920): flowering response to day length. Short day plants: Dahlia, Aster, tobacco, chrysanthemum, soybean, Xanthium. Long day plants: pea, radish, sugar beet, cabbage, spinach, wheat. Day neutral: cucumber and others.
The light signal is received by phytochrome in leaves: Pr absorbs red (660 nm) → Pfr; Pfr absorbs far red (730 nm) → Pr. The flowering stimulus is called florigen.
Vernalization: low temperature treatment that speeds up flowering (term by T.D. Lysenko). Its reversal by high temperature is devernalization.
Essential elements: macronutrients (C, H, O, N, P, K, S, Ca, Mg) and micronutrients (Fe, Mn, Cu, Zn, B, Mo, Cl, Ni).
Deficiency symptoms include chlorosis (yellowing, e.g. lack of N, Mg, Fe), necrosis (death of tissue) and stunted growth.
Rhizobium fixes nitrogen in root nodules of legumes using the enzyme nitrogenase, protected by leghaemoglobin.
महत्त्वाच्या संज्ञा
Critical photoperiod – day length above or below which a plant flowers.
Apical dominance – suppression of lateral buds by the apical bud (due to auxin).
Bolting – sudden elongation of stem before flowering (by gibberellins).
Chlorosis – loss of chlorophyll, leaves turn yellow.
Biological nitrogen fixation – conversion of N₂ into ammonia by living organisms.
महत्त्वाची माहिती
Hormone
Main effect
Auxin (IAA)
Cell elongation, apical dominance, root formation
Gibberellin (GA₃)
Stem elongation, bolting, breaks seed dormancy
Cytokinin
Cell division, delays senescence
Ethylene
Fruit ripening, leaf fall
Abscisic acid
Stomatal closure, dormancy, stress
Growth rate: absolute growth rate = growth per unit time; relative growth rate = growth per unit time ÷ initial size.
५ महत्त्वाचे प्रश्न
Q1. Explain the sigmoid growth curve.
When growth is plotted against time, an S-shaped curve results. Lag phase: slow growth at start. Log (exponential) phase: rapid growth. Stationary phase: growth slows and stops as resources become limited.
Q2. Distinguish between short day and long day plants.
Short day plants flower when day length is shorter than the critical photoperiod; they need a long, uninterrupted night (Dahlia, tobacco). Long day plants flower when day length is longer than the critical photoperiod; they need short nights (wheat, radish).
Q3. What is vernalization? Give its advantages.
Speeding up of flowering by exposing plants (or soaked seeds) to low temperature. Advantages: shortens the vegetative period, crops can be grown earlier, and plants can be grown where they normally would not flower.
Q4. Give the role of phytochrome in flowering.
Phytochrome is a light-receiving pigment protein in leaves. Red light (660 nm) converts Pr to Pfr; far red (730 nm) converts Pfr back to Pr. The Pr/Pfr balance tells the plant the length of the night and controls flowering.
Q5. Explain the role of Rhizobium in nitrogen fixation.
Rhizobium infects legume roots and forms root nodules. Inside, the enzyme nitrogenase converts N₂ into ammonia. Leghaemoglobin (pink pigment) keeps oxygen low so that nitrogenase works. Ammonia is then used to make amino acids.
परीक्षेसाठी टीप
Learn one example plant for each hormone use and each photoperiod type — examiners often ask "give two examples".
This chapter describes how humans breathe and how blood moves around the body. The first part covers the respiratory system, mechanism of breathing, gas exchange and transport, lung volumes, regulation and disorders. The second part covers blood, the heart, cardiac cycle, blood vessels, blood pressure, ECG and the lymphatic system.
महत्त्वाचे मुद्दे
Respiratory organs in animals: body surface, gills, trachea, lungs. Human pathway: nostrils → pharynx → larynx → trachea → bronchi → bronchioles → alveoli.
Lungs are covered by double-layered pleura with pleural fluid. Alveoli give a huge surface for gas exchange.
Inspiration: diaphragm and external intercostal muscles contract, chest volume increases, pressure falls, air enters. Expiration: muscles relax, volume decreases, air goes out.
Gas exchange happens by diffusion: alveolar pO₂ is 104 mmHg and blood pO₂ is 40 mmHg; blood pCO₂ is 45 mmHg and alveolar pCO₂ is 40 mmHg.
O₂ is carried mainly as oxyhaemoglobin; CO₂ is carried mostly as bicarbonate, some as carbaminohaemoglobin and some dissolved.
Breathing is controlled by the respiratory centres in the medulla oblongata and pons.
The diaphragm contracts and flattens, and the external intercostal muscles contract, raising the ribs and sternum. The chest cavity and lungs expand, so pressure inside the lungs falls below atmospheric pressure and air rushes in.
Q2. How is CO₂ transported in blood?
About 7% dissolved in plasma, about 23% as carbaminohaemoglobin, and about 70% as bicarbonate ions (formed in RBCs with the help of carbonic anhydrase; HCO₃⁻ moves to plasma and Cl⁻ moves in — chloride shift).
Q3. Describe the conducting system of the heart.
SA node in the right atrium starts the impulse (pacemaker); it spreads over the atria to the AV node, then through the bundle of His and its branches to Purkinje fibres in the ventricle walls, making the ventricles contract.
Q4. Calculate cardiac output if stroke volume is 70 mL and heart rate is 72/min.
CO = SV × HR = 70 × 72 = 5040 mL/min (about 5 litres per minute).
Q5. What does an ECG show? Name its waves.
An ECG records the electrical activity of the heart. P wave: atrial depolarisation; QRS complex: ventricular depolarisation; T wave: ventricular repolarisation. It helps diagnose heart diseases.
परीक्षेसाठी टीप
Draw the internal structure of the heart and a normal ECG with labels; learn lung volume values exactly as given in the textbook table.
Control and co-ordination keep all body parts working together. This chapter covers the simple nervous systems of Hydra and Planaria, neurons, synapse and transmission of nerve impulses, the human nervous system (brain, spinal cord, reflex action), sense receptors, nervous disorders, and the endocrine system with its major glands and hormones.
महत्त्वाचे मुद्दे
Hydra has a diffuse nerve net (no brain). Planaria has a simple brain (cerebral ganglia) with two longitudinal nerve cords — a ladder-like system.
A neuron has a cell body (cyton) with Nissl's granules, dendrites and an axon; many axons are covered by a myelin sheath with nodes of Ranvier.
Resting membrane potential of a neuron is about −70 mV; the Na⁺–K⁺ pump sends out 3 Na⁺ and takes in 2 K⁺.
On stimulation, Na⁺ gates open, Na⁺ rushes in (depolarisation, action potential); then K⁺ moves out (repolarisation).
In myelinated fibres the impulse jumps from node to node (saltatory conduction), which is faster.
At a chemical synapse, neurotransmitters such as acetylcholine are released into the synaptic cleft and carry the signal to the next neuron.
The human nervous system has the CNS (brain and spinal cord) and the PNS (cranial and spinal nerves; somatic and autonomic). Humans have 12 pairs of cranial nerves and 31 pairs of spinal nerves.
Reflex action is a quick automatic response through a reflex arc: receptor → sensory neuron → spinal cord → motor neuron → effector.
Sense receptors: photoreceptors (eye: rods for dim light, cones for colour), phonoreceptors and balance (ear), chemoreceptors (nose, tongue), thermoreceptors, mechanoreceptors.
Disorders: Alzheimer's disease (memory loss), Parkinson's disease (lack of dopamine, tremors), epilepsy and others.
Endocrine glands are ductless and secrete hormones directly into blood. The pituitary is called the "master gland" and is controlled by the hypothalamus.
Hormone deficiencies/excess cause disorders: diabetes mellitus (insulin), goitre and cretinism (thyroxine), gigantism/dwarfism (growth hormone), Addison's disease (adrenal cortex).
महत्त्वाच्या संज्ञा
Action potential – sudden reversal of membrane charge when a nerve is stimulated.
Synapse – junction between two neurons.
Neurotransmitter – chemical that carries the signal across a synapse (acetylcholine, adrenaline, dopamine).
Reflex arc – the pathway followed in a reflex action.
Hormone – chemical messenger secreted by an endocrine gland in small amounts.
Feedback control – the level of a hormone controls its own secretion.
महत्त्वाची माहिती
Gland
Hormone
Main function
Pituitary
GH, TSH, ACTH, FSH, LH, prolactin, ADH, oxytocin
Growth, controls other glands
Thyroid
Thyroxine (T₄), T₃, calcitonin
Metabolism; calcitonin lowers blood Ca
Parathyroid
Parathormone
Raises blood calcium
Adrenal cortex
Cortisol, aldosterone
Stress, salt–water balance
Adrenal medulla
Adrenaline, noradrenaline
"Fight or flight"
Pancreas (islets)
Insulin, glucagon
Lowers / raises blood glucose
Testis / ovary
Testosterone / oestrogen, progesterone
Sex characters, reproduction
५ महत्त्वाचे प्रश्न
Q1. Explain the conduction of a nerve impulse along an axon.
At rest, the inside is negative (−70 mV) due to the Na⁺–K⁺ pump. On stimulation, Na⁺ channels open and Na⁺ enters, making the inside positive (depolarisation). Then K⁺ channels open and K⁺ goes out (repolarisation). This change spreads along the axon as the impulse.
Q2. Describe transmission of an impulse across a chemical synapse.
The impulse reaches the axon terminal; Ca²⁺ enters and synaptic vesicles release acetylcholine into the cleft. It binds to receptors on the next neuron and opens ion channels, starting a new impulse. Acetylcholinesterase then breaks down acetylcholine.
Q3. What is a reflex action? Draw the reflex arc (describe).
A quick, automatic, involuntary response to a stimulus (e.g. knee jerk, pulling hand from a hot object). Path: receptor → sensory neuron → spinal cord (interneuron) → motor neuron → effector muscle.
Q4. Why is the pituitary called the master gland? Why is this not fully true?
It secretes hormones (TSH, ACTH, FSH, LH, GH) that control other endocrine glands. But it is itself controlled by releasing and inhibiting hormones from the hypothalamus.
Q5. Write the functions of insulin and glucagon.
Insulin (β-cells) lowers blood glucose by helping cells take up glucose and storing it as glycogen. Glucagon (α-cells) raises blood glucose by breaking glycogen into glucose in the liver.
परीक्षेसाठी टीप
Diagrams of a neuron, synapse and reflex arc are often asked. Learn the endocrine table — matching questions come from it.
Health is a state of complete physical, mental and social well-being. This chapter explains immunity (innate and acquired), the structure of antibodies, common human diseases caused by protozoa, worms, bacteria and viruses (including AIDS), adolescence, and the harmful effects of addiction and drug abuse.
महत्त्वाचे मुद्दे
Innate (inborn) immunity is non-specific: physical barriers (skin, mucus), physiological barriers (stomach acid, saliva), cellular barriers (phagocytes, NK cells) and cytokine barriers (interferons).
Acquired immunity is specific and has memory. B-lymphocytes give humoral (antibody-mediated) immunity; T-lymphocytes give cell-mediated immunity (important in graft rejection).
Active immunity: body makes its own antibodies (infection or vaccine) — slow but long-lasting. Passive immunity: ready-made antibodies are given (colostrum, anti-venom) — quick but short.
An antibody (immunoglobulin) is Y-shaped, made of 2 heavy and 2 light chains joined by disulfide bonds; it has antigen-binding sites at the tips. Types: IgG, IgA, IgM, IgD, IgE.
Malaria: caused by Plasmodium (P. vivax, P. ovale, P. malariae, P. falciparum), spread by female Anopheles mosquito; cyclic fever with chills. P. falciparum causes the most serious (cerebral) malaria.
Amoebiasis: Entamoeba histolytica, spread by contaminated food and water (houseflies carry cysts).
Ascariasis: roundworm Ascaris lumbricoides, from contaminated food, water or soil.
Filariasis (elephantiasis): Wuchereria bancrofti (and Brugia), spread by Culex mosquito; causes swelling of limbs.
Typhoid: Salmonella typhi, through contaminated food and water; Widal test confirms it.
AIDS: caused by HIV, a retrovirus (RNA virus) that destroys helper T-cells; spread by unsafe sex, infected blood/needles and mother to child. ELISA is the first test.
Adolescence is the period between childhood and adulthood with physical, mental and emotional changes; it is a vulnerable time.
Addiction to alcohol, tobacco and drugs harms the liver, lungs, brain and family/social life. Opioids, cannabinoids, cocaine and others are commonly abused. Prevention: awareness, family support, counselling, and seeking medical help.
महत्त्वाच्या संज्ञा
Antigen – a foreign substance that triggers antibody formation.
Vaccination – giving weakened/killed germs or their parts to produce active immunity.
Interferons – proteins released by virus-infected cells that protect nearby cells.
Pathogen – disease-causing organism.
Withdrawal symptoms – unpleasant effects when a habitual drug is suddenly stopped.
महत्त्वाची माहिती
Disease
Pathogen
Spread by
Malaria
Plasmodium (protozoan)
Female Anopheles mosquito
Amoebiasis
Entamoeba histolytica
Contaminated food/water
Ascariasis
Ascaris lumbricoides
Contaminated food/water/soil
Filariasis
Wuchereria bancrofti
Culex mosquito
Typhoid
Salmonella typhi
Contaminated food/water
AIDS
HIV (retrovirus)
Body fluids, blood, mother to child
५ महत्त्वाचे प्रश्न
Q1. Draw and describe the structure of an antibody.
An antibody is a Y-shaped protein of four polypeptide chains: two long heavy chains and two short light chains held together by disulfide bonds. Each arm has a variable region at its tip which binds a specific antigen; the rest is the constant region.
Q2. Distinguish between active and passive immunity.
Active: body produces its own antibodies after infection or vaccination; takes time to develop but lasts long. Passive: ready-made antibodies are given from outside (colostrum, anti-tetanus serum); acts quickly but lasts a short time.
Q3. Give the cause, mode of spread and symptoms of malaria.
Cause: Plasmodium. Spread: bite of an infected female Anopheles mosquito. Symptoms: cyclic high fever with chills and shivering, headache, sweating, anaemia.
Q4. How does HIV damage the immune system?
HIV enters helper T-lymphocytes, makes DNA from its RNA using reverse transcriptase, and multiplies inside them. The number of helper T-cells falls, so the person cannot fight infections and gets many opportunistic infections.
Q5. Why is adolescence a vulnerable period? Suggest ways to prevent drug abuse.
Rapid physical and emotional changes, curiosity and peer pressure make teenagers try harmful habits. Prevention: avoid peer pressure, education and counselling, help from parents and teachers, look for warning signs early, and get professional help.
परीक्षेसाठी टीप
Learn the disease table (pathogen + vector) thoroughly — it is the quickest source of MCQs and 2-mark answers in this chapter.
This chapter explains how science helps produce more and better food. It covers plant breeding and the Green Revolution, tissue culture, single cell protein, biofortification, animal husbandry (dairy, poultry, fisheries, bee keeping, sericulture), and the many uses of microbes in food, industry, sewage treatment, biogas, biocontrol and biofertilizers.
महत्त्वाचे मुद्दे
Green Revolution greatly increased food grain production in India. Dr. Norman E. Borlaug (Nobel Peace Prize, 1970) developed semi-dwarf, high-yielding wheat; Dr. M. S. Swaminathan led the Green Revolution in India.
Plant breeding steps: collection of variability (germplasm), evaluation and selection of parents, hybridisation, selection and testing of superior recombinants, and release of new varieties.
Breeding aims include higher yield, disease and pest resistance, and better quality (e.g. wheat Atlas 66 with high protein).
Tissue culture uses the totipotency of plant cells to grow whole plants on a nutrient medium; micropropagation gives many identical plants quickly; meristem culture gives virus-free plants; protoplast fusion makes somatic hybrids.
Single cell protein (SCP) is protein-rich microbial biomass used as food or feed: Spirulina, Chlorella (algae); Methylophilus methylotrophus (bacteria); yeast and fungi.
Biofortification: breeding crops with more vitamins, minerals, protein or healthier fats to fight hidden hunger.
Animal husbandry includes dairy, poultry, fisheries, apiculture (bee keeping — honey, wax) and sericulture (silk). Good management needs good breeds, feed, clean housing and disease control.
Microbes in food: Lactobacillus turns milk into curd; yeast (Saccharomyces) raises bread dough and ferments idli/dosa batter; microbes ripen cheese.
Industrial products: antibiotics (penicillin from Penicillium), alcohol by yeast fermentation, organic acids (citric acid by Aspergillus niger, lactic acid by Lactobacillus), enzymes (streptokinase, a clot buster; pectinase for clearing juices), statins from Monascus (lower cholesterol).
Sewage treatment: primary (physical removal of solids) and secondary/biological (aerobic microbes in aeration tanks form flocs and reduce BOD; activated sludge then digested anaerobically, giving biogas).
Biogas (mostly methane) is produced by methanogenic bacteria like Methanobacterium from cattle dung (gobar gas).
Biofertilizers: Rhizobium (legume nodules), Azotobacter and Azospirillum (free-living), cyanobacteria like Anabaena and Nostoc, Azolla (water fern with Anabaena) in rice fields, and mycorrhizal fungi (help phosphorus uptake).
महत्त्वाच्या संज्ञा
Germplasm collection – all the varieties/wild relatives of a crop collected for breeding.
Totipotency – ability of a single plant cell to grow into a complete plant.
Somaclones – genetically identical plants produced by tissue culture.
BOD (biological oxygen demand) – amount of oxygen used by microbes to break down organic matter in water; high BOD means more pollution.
Biofertilizer – living organisms that enrich soil nutrients.
महत्त्वाची माहिती
Microbe
Product / use
Lactobacillus
Curd, lactic acid
Saccharomyces cerevisiae
Bread, alcohol
Aspergillus niger
Citric acid
Penicillium
Penicillin
Streptococcus
Streptokinase
Monascus
Statins
Methanobacterium
Biogas
Bacillus thuringiensis
Bio-insecticide
५ महत्त्वाचे प्रश्न
Q1. What are the steps in plant breeding?
Collection of variability; evaluation and selection of parents; cross hybridisation between selected parents; selection and testing of superior recombinants; testing, release and commercialisation of new varieties.
Q2. What is micropropagation? Give its advantages.
Producing a large number of plants from a small piece of tissue (explant) through tissue culture. Advantages: many genetically identical plants in a short time, independent of season, and disease-free plants from meristem culture.
Q3. What is SCP? Why is it useful?
Single cell protein is protein-rich biomass of microbes (Spirulina, Methylophilus methylotrophus) used as food or feed. Microbes grow very fast on cheap materials, so they can help solve protein shortage and reduce pollution.
Q4. Explain the secondary treatment of sewage.
Primary effluent is passed into aeration tanks where air is pumped in. Aerobic microbes form flocs and digest organic matter, lowering the BOD. The flocs settle as activated sludge; part is returned to the tank and the rest is digested anaerobically, producing biogas.
Q5. How does Bacillus thuringiensis act as a biocontrol agent?
Spores of Bt are sprayed on plants. When insect larvae eat them, a toxin is released in their gut which kills them. It controls caterpillars without harming other organisms.
परीक्षेसाठी टीप
Make a quick table of "microbe → product" — it answers many 1-mark and matching questions.
Biotechnology uses living organisms or their parts to make useful products. This chapter explains the tools and steps of recombinant DNA (rDNA) technology, PCR, ways of putting genes into cells, applications in agriculture, medicine and industry (Bt cotton, golden rice, human insulin), and the issues of bioethics, biopatents and biopiracy.
महत्त्वाचे मुद्दे
Modern biotechnology began with rDNA technology, established by Stanley Cohen and Herbert Boyer in 1973.
Tools of rDNA technology: restriction enzymes (molecular scissors), DNA ligase (molecular glue), vectors (plasmids like pBR322, pUC, Ti plasmid; bacteriophages), and host cells (E. coli, Agrobacterium tumefaciens).
Restriction endonucleases cut DNA at specific palindromic sites. EcoRI cuts between G and A in GAATTC, producing sticky ends.
A good vector has an origin of replication (ori), selectable markers (antibiotic resistance genes) and cloning sites.
Steps: isolate DNA → cut with restriction enzyme → join gene to vector with ligase (rDNA) → introduce rDNA into host → select transformed cells → grow (clone) and obtain the product.
DNA fragments are separated by gel electrophoresis (smaller fragments move farther).
PCR (polymerase chain reaction) makes millions of copies of a DNA segment in vitro: denaturation, annealing of primers and extension by heat-stable Taq polymerase, repeated in a thermal cycler.
Gene transfer methods: transformation, microinjection, electroporation, lipofection, biolistic (gene gun) method, and Agrobacterium Ti plasmid in plants.
Agriculture: Bt cotton (Bt toxin gene kills bollworms), golden rice (rich in β-carotene, vitamin A), pest- and stress-resistant GM crops.
Medicine: human insulin from E. coli, vaccines, gene therapy, molecular diagnosis (PCR, ELISA).
In India, GM research and release are reviewed by the Genetic Engineering Appraisal Committee (GEAC).
Bioethics deals with moral issues of biotechnology. Biopatent is a patent on a biological product/process. Biopiracy is using bioresources or traditional knowledge without permission or fair payment (e.g. patents on basmati rice, turmeric, neem).
महत्त्वाच्या संज्ञा
Recombinant DNA – DNA made by joining DNA from two different sources.
Vector – a DNA molecule that carries foreign DNA into a host cell.
Palindrome – DNA sequence that reads the same on both strands in the 5'→3' direction (GAATTC).
Transgenic organism (GMO) – organism carrying a foreign gene.
PCR steps: denaturation (high temperature, strands separate) → annealing (primers bind) → extension (Taq polymerase adds nucleotides). Each cycle doubles the DNA; n cycles give 2ⁿ copies.
EcoRI site: 5'–G↓AATTC–3' / 3'–CTTAA↑G–5'
५ महत्त्वाचे प्रश्न
Q1. Describe the steps of rDNA technology.
Isolate the desired gene and vector DNA; cut both with the same restriction enzyme; join the gene into the vector using DNA ligase; transfer the rDNA into a host (e.g. E. coli); select transformed cells using markers; multiply the host cells and extract the product.
Q2. What are restriction enzymes? How do they produce sticky ends?
Enzymes that cut DNA at specific recognition (palindromic) sequences. EcoRI cuts between G and A on both strands of GAATTC, leaving short single-stranded overhangs (sticky ends) that easily join with complementary ends.
Q3. Explain the steps of PCR.
Denaturation: DNA is heated so the two strands separate. Annealing: on cooling, primers attach to complementary sites. Extension: Taq polymerase adds nucleotides to the primers. Repeating these cycles in a thermal cycler gives millions of copies.
Q4. How is Bt cotton made pest resistant?
The cry gene from Bacillus thuringiensis is inserted into cotton. The plant makes an inactive Bt protein; in the alkaline gut of bollworm larvae it becomes an active toxin, damages the gut and kills the pest. So less pesticide is needed.
Q5. What is biopiracy? Give an example.
Using biological resources or traditional knowledge of a country by others (often companies) without permission or fair compensation. Examples: attempts to patent turmeric, neem and basmati rice.
परीक्षेसाठी टीप
Draw the EcoRI cutting and a labelled pBR322-type vector; write PCR steps in correct order with what happens at each step.
This chapter is about how organisms relate to their surroundings. It covers the major abiotic factors (temperature, water, light, soil), how organisms respond and adapt to them, the attributes and growth of populations (exponential and logistic), and the interactions between populations such as predation, competition, parasitism, commensalism, mutualism and amensalism.
महत्त्वाचे मुद्दे
Ecology studies the interactions of organisms with each other and with their environment. Levels: organism → population → community → biome.
Major abiotic factors: temperature (most important; eurythermal vs stenothermal organisms), water (euryhaline vs stenohaline), light (needed for photosynthesis, controls flowering and behaviour) and soil (texture, pH, minerals).
Responses to stress: regulate (keep body conditions constant, e.g. mammals, birds), conform (body condition changes with surroundings), migrate (move away temporarily to a better area and return later) or suspend activity (hibernation in winter, e.g. polar bear; aestivation in summer by some snails and fish; dormancy of seeds and spores).
Adaptations help survival: desert plants have a thick cuticle, stomata in deep pits, the CAM pathway (stomata open at night) and leaves reduced to spines (Opuntia); Allen's rule — mammals of cold climates have shorter ears and limbs to reduce heat loss.
Population attributes: density, birth rate (natality), death rate (mortality), sex ratio and age distribution (age pyramids: expanding, stable, declining).
Population size changes by natality (+), immigration (+), mortality (−) and emigration (−).
Exponential growth: with unlimited resources, the population grows in geometric proportion — J-shaped curve.
Logistic growth (Verhulst–Pearl): with limited resources, growth slows near the carrying capacity (K) — S-shaped (sigmoid) curve. It is more realistic.
Gause's competitive exclusion principle: two closely related species competing for the same limited resource cannot live together forever; the weaker one is eliminated.
Predation keeps prey populations in check and maintains species diversity; prey defend themselves by camouflage, poison, etc.
महत्त्वाच्या संज्ञा
Habitat – place where an organism lives; niche – its role and functions in the habitat.
Carrying capacity (K) – maximum population a habitat can support.
Intrinsic rate of natural increase (r) – the natural growth rate of a population under ideal conditions.
Mutualism – both partners benefit (lichens: fungus + alga/cyanobacteria; flowering plants and their pollinators such as humming birds).
Commensalism – one benefits, other unaffected (orchid on a mango branch, cattle egret with grazing cattle, clown fish among sea anemone tentacles).
Amensalism – one species is harmed, the other is unaffected.
Brood parasitism – the koel lays its eggs in a crow's nest and the crow feeds the hatchlings.
सूत्रे
Exponential growth: dN/dt = rN ; Nt = N₀ e^(rt)
Logistic growth: dN/dt = rN × ((K − N)/K) N = population size, r = intrinsic rate of increase, K = carrying capacity, t = time.
Interaction
Species A
Species B
Mutualism
+
+
Competition
−
−
Predation / Parasitism
+
−
Commensalism
+
0
Amensalism
−
0
५ महत्त्वाचे प्रश्न
Q1. Distinguish between exponential and logistic growth.
Q2. How do organisms respond to abiotic stress? Explain with examples.
They may regulate (birds and mammals keep a constant body temperature), conform (most animals and plants — body temperature changes with surroundings), migrate (move temporarily to a better habitat and return later) or suspend activity (polar bear hibernates in winter, some snails and fish aestivate in summer, seeds stay dormant).
Q3. State Gause's competitive exclusion principle.
Two closely related species competing for the same limited resource cannot coexist indefinitely; the competitively inferior one will be eliminated eventually.
Q4. Give two adaptations of desert plants.
Thick cuticle and sunken stomata reduce water loss; leaves reduced to spines and photosynthesis by flattened green stems (Opuntia); CAM pathway, where stomata open at night.
Q5. Explain commensalism with an example.
An interaction where one species benefits and the other is neither harmed nor benefited. Example: cattle egret feeds on insects disturbed by grazing cattle; orchid growing on a mango branch.
परीक्षेसाठी टीप
Draw both growth curves with axes labelled (population vs time) and mark K on the logistic curve — this alone can fetch 2 marks.
An ecosystem is a functional unit of nature where living organisms interact with each other and their physical environment. This chapter covers the structure and function of an ecosystem, productivity, decomposition, energy flow through food chains and food webs, ecological pyramids, nutrient cycles, ecological succession and ecosystem services.
महत्त्वाचे मुद्दे
An ecosystem has biotic components (producers, consumers, decomposers) and abiotic components (light, water, soil, minerals, temperature).
Ecosystems can be natural (forest, pond, grassland, ocean) or man-made (crop field, aquarium).
Productivity: Gross primary productivity (GPP) is the total rate of organic matter production by photosynthesis; Net primary productivity (NPP) = GPP − respiration losses (R). NPP is available to consumers.
Decomposition steps: fragmentation (by detritivores like earthworm), leaching, catabolism (by bacteria and fungi), humification and mineralisation. It is faster in warm, moist conditions rich in nitrogen.
Energy flow is unidirectional: sun → producers → herbivores → carnivores. It is not cyclic.
10% law (Lindeman): only about 10% of energy at one trophic level passes to the next; the rest is lost mostly as heat. So food chains usually have only 3–4 levels.
Food chains: grazing food chain (starts from green plants) and detritus food chain (starts from dead organic matter). Interlinked food chains form a food web.
Ecological pyramids: pyramid of numbers, biomass and energy. The pyramid of energy is always upright. The pyramid of biomass in a sea (ocean) is inverted because phytoplankton biomass is small compared to fish. A tree ecosystem gives an inverted pyramid of numbers.
Nutrient cycles (biogeochemical cycles): gaseous (carbon, nitrogen) and sedimentary (phosphorus, sulfur). Phosphorus has no significant gaseous phase.
Ecological succession is the gradual, predictable change in species composition of an area until a stable climax community forms. Primary succession starts on bare areas (rock, new pond); secondary succession on areas where a community was destroyed (burnt forest, abandoned farm).
Hydrarch succession begins in water; xerarch succession begins on dry areas (pioneer species on rocks are lichens).
Ecosystem services: purifying air and water, pollination, soil formation, nutrient cycling, climate regulation, wildlife habitat.
महत्त्वाच्या संज्ञा
Trophic level – the position of an organism in a food chain.
Standing crop – mass of living material at a trophic level at a given time.
Detritus – dead plant and animal remains.
Pioneer species – the first organisms to colonise a bare area.
Climax community – final, stable community in succession.
Sere – the series of communities in a succession.
सूत्रे
NPP = GPP − R (R = energy used in respiration)
10% law example: if producers trap 10,000 J → herbivores 1000 J → primary carnivores 100 J → secondary carnivores 10 J.
५ महत्त्वाचे प्रश्न
Q1. Distinguish between GPP and NPP.
GPP is the total rate of production of organic matter by producers during photosynthesis. NPP is what remains after the producers' respiration losses (NPP = GPP − R); it is the energy available to consumers.
Q2. Why is the pyramid of energy always upright?
Energy decreases at each higher trophic level, because only about 10% is transferred and the rest is lost as heat. So each level always has less energy than the level below it.
Q3. Why is the pyramid of biomass inverted in an ocean?
The producers (phytoplankton) are tiny and short-lived, so their standing biomass at any moment is small, while the fish feeding on them have a much larger biomass. Hence the pyramid is inverted.
Q4. Explain the steps of decomposition.
Fragmentation: detritivores break detritus into small pieces. Leaching: soluble nutrients go down into the soil. Catabolism: bacteria and fungi break it into simple substances. Humification: dark humus forms. Mineralisation: humus is broken down to release inorganic nutrients.
Q5. Differentiate between primary and secondary succession.
Primary succession starts in an area with no soil or life (bare rock, new pond) and is very slow. Secondary succession starts where a community was destroyed but soil remains (burnt forest, abandoned field) and is faster.
परीक्षेसाठी टीप
Draw neat pyramids (upright energy, inverted ocean biomass, inverted tree numbers) and practise 10% law numericals — both appear often.
Biodiversity, Conservation and Environmental Issues
थोडक्यात सारांश
Biodiversity is the variety of life on Earth at all levels. This chapter covers levels and patterns of biodiversity, its current status and loss, methods of conservation, the Biological Diversity Act 2002, and major environmental issues — pollution, greenhouse effect and global warming, ozone depletion and deforestation — ending with Mission Harit Maharashtra.
महत्त्वाचे मुद्दे
The term biodiversity was popularised by Edward Wilson. Levels: genetic diversity (within a species, e.g. many rice varieties), species diversity and ecological diversity (variety of ecosystems).
Patterns: diversity decreases from the equator towards the poles (latitudinal gradient), and tropical areas are richest.
Rivet popper hypothesis (Paul Ehrlich): each species is like a rivet in an aeroplane; losing more species, especially key ones, threatens the whole ecosystem.
Causes of biodiversity loss — the "Evil Quartet": habitat loss and fragmentation (the main cause), over-exploitation, alien species invasion and co-extinctions.
IUCN Red List categories include Extinct (EX), Extinct in the Wild (EW), Critically Endangered (CR), Endangered (EN), Vulnerable (VU), Near Threatened (NT), Least Concern (LC).
Reasons to conserve: narrowly utilitarian (food, medicine, timber), broadly utilitarian (oxygen, pollination, climate) and ethical.
In situ conservation (in natural habitat): biosphere reserves, national parks, wildlife sanctuaries, sacred groves, biodiversity hotspots. About 34 hotspots are identified worldwide; India has four — Western Ghats, Indo-Burma, Sundaland and Eastern Himalaya.
Biological Diversity Act 2002 protects India's biodiversity and ensures fair sharing of its benefits.
Greenhouse effect: CO₂, CH₄, N₂O, CFCs and water vapour trap heat; their increase causes global warming, melting of ice, rising sea levels and climate change.
Ozone depletion: CFCs release chlorine which breaks ozone in the stratosphere, letting harmful UV rays reach Earth. Ozone thickness is measured in Dobson units. The Montreal Protocol (1987) controls ozone-depleting substances.
Deforestation causes soil erosion, floods, loss of habitat and more CO₂. Solutions include afforestation and social forestry.
Mission Harit Maharashtra: Government of Maharashtra's 2016 drive to plant 50 crore trees in four years, in line with the National Forest Policy aim of 33% forest cover.
महत्त्वाच्या संज्ञा
Endemic species – found only in one particular region.
Biodiversity hotspot – region with very high species richness and endemism that is under threat.
Sacred groves – forest patches protected by local tribes for religious reasons.
Co-extinction – when a species becomes extinct, species dependent on it (like its parasites) also die out.
Cryopreservation – storing cells, seeds or gametes at very low temperature (−196 °C, liquid nitrogen).
महत्त्वाची माहिती
Conservation
Examples
In situ
National parks, sanctuaries, biosphere reserves, sacred groves
Ex situ
Zoos, botanical gardens, seed banks, gene banks
Ozone layer lies in the stratosphere; UV damages DNA and proteins.
Montreal Protocol: 1987, Montreal (Canada).
५ महत्त्वाचे प्रश्न
Q1. Explain the three levels of biodiversity.
Genetic diversity: variation in genes within a species (many varieties of mango or rice). Species diversity: variety of species in an area. Ecological diversity: variety of ecosystems such as forests, grasslands, deserts and wetlands.
Q2. What is the "Evil Quartet"?
The four main causes of biodiversity loss: habitat loss and fragmentation, over-exploitation, invasion of alien species, and co-extinctions.
Q3. Distinguish between in situ and ex situ conservation.
In situ: species are protected in their natural habitat (national parks, sanctuaries); whole ecosystem is conserved. Ex situ: species are protected outside their natural habitat (zoos, seed banks); used for highly threatened species.
Q4. What is the greenhouse effect? Give its effects.
Warming of the Earth because gases like CO₂, CH₄, N₂O and CFCs trap infrared heat radiated from Earth's surface. Excess gases cause global warming, melting of polar ice, rising sea level, changes in rainfall and harm to crops.
Q5. How do CFCs deplete the ozone layer?
In the stratosphere, UV rays break CFCs and release chlorine atoms. Each Cl atom breaks many ozone molecules into oxygen (acting like a catalyst). This thins the ozone layer, so more harmful UV reaches the Earth.
परीक्षेसाठी टीप
Remember India's four hotspots, the Evil Quartet and the Montreal Protocol year — they are favourite one-mark questions.