Reproduction in Organisms
Key Points to Remember
- →Reproduction is essential for continuation of species. Types: Asexual (one parent) and Sexual (two parents).
- →Asexual reproduction: binary fission (Amoeba), budding (Hydra, yeast), fragmentation (Spirogyra), vegetative propagation, sporulation.
- →Life span varies: mayfly (1 day) to banyan tree (200+ years) — not related to body size.
- →Sexual reproduction involves gamete formation and fusion (syngamy). External fertilisation (frogs) vs internal (reptiles, mammals).
- →Oviparous: lay eggs (birds, reptiles) | Viviparous: give birth (most mammals).
- →Parthenogenesis: development from unfertilised egg — e.g., Drones (male honeybees) from unfertilised eggs.
Exam Tips
Most asked: differences between oviparous and viviparous, examples of asexual reproduction types.
Remember: vegetative propagation is a type of asexual reproduction — gives rise to clones.
Life span vs reproduction — shorter life spans often mean more offspring (r-strategy).
Sexual Reproduction in Flowering Plants
Key Points to Remember
- →Flower is the site of sexual reproduction. Parts: calyx, corolla, androecium (stamens), gynoecium (pistil/carpel).
- →Microsporogenesis: formation of pollen grains (microspores) in anther. Megasporogenesis: formation of ovule in ovary.
- →Pollen grain: 2-celled (generative cell + vegetative cell) or 3-celled at maturity.
- →Pollination: transfer of pollen to stigma. Types — Autogamy, Geitonogamy, Xenogamy (cross-pollination).
- →Agents: Anemophily (wind), Entomophily (insect), Hydrophily (water), Ornithophily (birds).
- →Double fertilisation: one sperm fuses with egg (syngamy → zygote 2n), other with polar nuclei (triple fusion → primary endosperm nucleus 3n).
- →Fruit from ovary; seed from ovule. Endosperm nourishes the embryo.
- →Apomixis: seed formation without fertilisation (mango, citrus). Polyembryony: more than one embryo per seed.
Exam Tips
Most asked diagram: L.S. of a flower (labelling), T.S. of anther, mature embryo sac (7 cells, 8 nuclei).
Double fertilisation is unique to angiosperms — always in the paper.
Pollen viability: 30 minutes (cereals) to months (some legumes).
Embryo sac: 7 cells — 3 antipodal, 2 synergids, 1 egg, 1 central cell (2 polar nuclei).
Human Reproduction
Key Points to Remember
- →Male reproductive system: testes (outside body — temperature-sensitive), seminiferous tubules (spermatogenesis), vas deferens, seminal vesicle, prostate gland, penis.
- →Female reproductive system: ovaries, fallopian tubes, uterus, cervix, vagina.
- →Spermatogenesis: Spermatogonia → Primary spermatocyte (meiosis I) → Secondary spermatocyte (meiosis II) → Spermatid → Sperm.
- →Oogenesis: Oogonia → Primary oocyte (arrested in prophase I from birth) → meiosis I at puberty → Secondary oocyte (meiosis II arrested in metaphase II) → completed only if fertilised.
- →Menstrual cycle: 28 days. Menstruation (1–5), Proliferative (6–13), Ovulation (14), Secretory/luteal (15–28).
- →Fertilisation: in ampulla of fallopian tube. Zygote divides → morula → blastocyst → implantation in endometrium.
- →Placenta: formed by chorion and uterine tissue. Functions: nutrition, gas exchange, waste removal, hormone secretion (hCG, progesterone, estrogen).
- →Parturition: triggered by oxytocin. Labour contractions → birth.
Exam Tips
Diagrams most asked: spermatogenesis pathway, oogenesis pathway, structure of sperm.
hCG (human chorionic gonadotropin) is the basis of pregnancy test strips.
The secondary oocyte completes meiosis II only after fertilisation — this is a favourite MCQ trap.
Sertoli cells: nourish developing sperm | Leydig cells: secrete testosterone.
Reproductive Health
Key Points to Remember
- →Reproductive health: total well-being in all aspects of reproduction.
- →Population explosion: rapid increase — India crossed 1 billion mark (2000). Causes: high birth rate, declining death rate.
- →Contraceptive methods: Natural (rhythm, coitus interruptus), Barriers (condoms, diaphragm, cervical cap, vault), IUDs, Oral pills (estrogen+progestin), Injectables, Implants, Surgical (vasectomy, tubectomy).
- →MTP (Medical Termination of Pregnancy): legal under the MTP Act. Safe up to 12 weeks.
- →STIs: Gonorrhoea (Neisseria gonorrhoeae), Syphilis (Treponema pallidum), HIV/AIDS, Hepatitis B, Genital herpes (HSV), Genital warts (HPV).
- →Infertility: inability to conceive after unprotected sex for 1 year. Causes: hormonal, structural, psychological.
- →ART (Assisted Reproductive Technologies): IVF-ET (test tube baby), ZIFT, GIFT, ICSI, AI.
Exam Tips
Most asked: differences between vasectomy and tubectomy, types of contraceptives with examples.
IUDs work by: increasing phagocytosis, releasing copper ions (toxic to sperm), hormonal suppression.
ART abbreviations: IVF = In Vitro Fertilisation; ZIFT = Zygote Intra Fallopian Transfer; GIFT = Gamete Intra Fallopian Transfer.
Principles of Inheritance and Variation
Key Points to Remember
- →Mendel's laws: Law of Segregation (one pair), Law of Independent Assortment (two pairs).
- →Monohybrid cross: Tt × Tt → 3:1 (phenotypic ratio), 1:2:1 (genotypic ratio).
- →Dihybrid cross: TtRr × TtRr → 9:3:3:1 phenotypic ratio.
- →Dominance: complete (Mendel's peas), incomplete (snapdragon — pink from red × white), co-dominance (ABO blood groups — IA and IB are co-dominant).
- →Multiple alleles: ABO blood group — three alleles IA, IB, i. Blood groups: A (IAIA/IAi), B (IBIB/IBi), AB (IAIB), O (ii).
- →Pleiotropy: one gene affects multiple traits — sickle cell anaemia.
- →Chromosomal theory of inheritance: Sutton and Boveri. Morgan's work on linked genes in Drosophila.
- →Sex determination: XX-XY (humans, Drosophila), XO (grasshopper), ZW-ZZ (birds, some insects).
- →Sex-linked traits: Haemophilia (X-linked recessive), Colour blindness (X-linked recessive).
- →Mutations: Chromosomal aberrations (Down syndrome — trisomy 21, Klinefelter XXY, Turner XO) and Point mutations (sickle cell anaemia — substitution mutation).
- →Pedigree analysis: circle = female, square = male, filled = affected, horizontal line = mating.
Exam Tips
Mendel chose pea because: short life span, bisexual, large offspring, 7 pairs of contrasting traits, easy cultivation.
Down syndrome = trisomy 21 (47 chromosomes). Most common chromosomal disorder.
Haemophilia: Queen Victoria was carrier, disease expressed only in sons.
Solve numerical problems on blood group inheritance — very common.
Molecular Basis of Inheritance
Key Points to Remember
- →DNA double helix (Watson and Crick, 1953): antiparallel strands, A=T (2 H-bonds), G≡C (3 H-bonds).
- →Central Dogma: DNA → RNA → Protein (Crick). Reverse transcription: RNA → DNA (in retroviruses).
- →Replication: semiconservative (proved by Meselson and Stahl using ¹⁵N/¹⁴N). Enzymes: helicase, DNA polymerase, ligase.
- →Transcription: DNA → mRNA. In eukaryotes: hnRNA → mRNA (capping, tailing, splicing). Template strand = antisense strand.
- →Translation (eukaryotes): mRNA → protein at ribosomes. Aminoacyl-tRNA synthetase charges tRNA.
- →Genetic code: triplet codon, 64 codons, 61 sense (code for amino acids), 3 stop codons (UAA, UAG, UGA). AUG = start codon (Methionine).
- →Degenerate code: multiple codons for same amino acid. Unambiguous: one codon → one amino acid only.
- →Gene regulation: lac operon (E. coli) — inducible operon. Repressor + allolactose (inducer) → repressor inactivated → structural genes expressed.
- →Human Genome Project: 3164.7 Mb genome size, 20,000–25,000 genes, <2% coding. Key techniques: BAC, YAC, EST.
- →DNA fingerprinting (Alec Jeffreys): VNTR (Variable Number Tandem Repeats). Used in forensics, paternity testing.
Exam Tips
Meselson and Stahl experiment: MUST know in detail — proves semiconservative replication.
Lac operon: most frequently asked regulation topic. Know operator, promoter, repressor, inducer.
Genetic code properties: universal, triplet, degenerate, non-overlapping, non-punctuated.
DNA fingerprinting: Southern blotting → probe hybridisation → autoradiography.
Evolution
Key Points to Remember
- →Origin of Life: Big Bang → chemical evolution (Oparin-Haldane hypothesis) → Miller-Urey experiment (amino acids from CH₄, NH₃, H₂O, H₂).
- →Theories: Lamarckism (inheritance of acquired characters — discredited), Darwinism (natural selection), Neo-Darwinism (Modern Synthetic Theory).
- →Natural selection: variation + heredity + struggle for existence + survival of fittest.
- →Types of natural selection: stabilising, directional, disruptive.
- →Hardy-Weinberg principle: gene pool remains constant if — no mutation, no migration, large population, random mating, no selection. Equation: p² + 2pq + q² = 1.
- →Speciation: geographic isolation → reproductive isolation → new species. Allopatric (geographic) vs Sympatric (same area).
- →Adaptive radiation: divergent evolution from common ancestor (Darwin's finches, Australian marsupials).
- →Human evolution: Homo habilis → Homo erectus → Homo sapiens (archaic) → Homo sapiens sapiens (modern). Out-of-Africa theory.
- →Industrial melanism: Biston betularia — evidence for natural selection.
Exam Tips
Miller-Urey experiment: frequently asked. Know inputs (CH₄, NH₃, H₂O, H₂ + electric discharge) and output (amino acids).
Hardy-Weinberg: calculate allele frequencies from given data — common numerical.
Darwin's finches: adaptive radiation, different beak shapes for different food sources in Galapagos.
Convergent evolution: unrelated organisms → similar structures (analogous organs e.g. bat wing and bird wing).
Human Health and Disease
Key Points to Remember
- →Disease types: Infectious (caused by pathogens) and Non-infectious (genetic, lifestyle, cancer).
- →Malaria: Plasmodium (P. falciparum most severe) — vector Anopheles mosquito. Life cycle: gametocytes → sporozoites (liver) → merozoites (RBCs → rupture → fever cycle).
- →Typhoid (Salmonella typhi): Widal test for diagnosis. Amoebiasis (Entamoeba histolytica): bloody stools.
- →Pneumonia (Streptococcus pneumoniae): fluid in alveoli. Common cold (rhinovirus).
- →Immunity types: Innate (non-specific: skin, mucus, fever, phagocytosis) and Acquired (specific: humoral B-cell antibodies, cell-mediated T-cell).
- →Lymphoid organs: primary (thymus — T-cell maturation, bone marrow — B-cell) and secondary (spleen, lymph nodes, MALT, tonsils).
- →HIV/AIDS: retrovirus infects T-helper (CD4+) cells. Transmission: unprotected sex, contaminated needles, mother-to-child. ELISA for detection.
- →Cancer: benign (localised) vs malignant (spreads — metastasis). Carcinogens: tobacco, radiation, chemicals.
- →Drugs and alcohol: marijuana (Cannabis), cocaine (Erythroxylum coca), heroin (diacetylmorphine). Effects on CNS.
- →Vaccines: provide active immunity. Antibiotics: kill bacteria. Cannot treat viral infections.
Exam Tips
Plasmodium life cycle: gametocytes in human → sexual reproduction in mosquito → sporozoites → human liver → RBCs.
Primary vs secondary immune response: secondary is faster, stronger (memory cells).
HIV cannot be transmitted by casual contact — mosquito bites, handshakes, sharing meals.
Colostrum (mother's first milk) contains IgA antibodies — passive immunity for newborn.
Strategies for Enhancement in Food Production
Key Points to Remember
- →Plant breeding: hybridisation, mutation breeding, polyploidy, genetic engineering. Steps: germplasm collection → evaluation → cross-hybridisation → selection → release.
- →Biofortification: breeding for higher nutrition — Golden Rice (β-carotene), Atlas 66 wheat (high protein), IARI varieties.
- →Mutation breeding: creating mutant varieties — Sharbati Sonora wheat (gamma radiation).
- →SCP (Single Cell Protein): Spirulina, Chlorella — high protein, grown on waste materials.
- →Animal husbandry: selective breeding for high-yielding cattle. Exotic breeds: Jersey, Holstein-Friesian (milk). Indigenous: Sahiwal, Gir (heat-resistant).
- →Bee-keeping (apiculture): Apis cerana indica (Indian bee), A. mellifera (Italian bee). Products: honey, wax, royal jelly.
- →Fisheries: inland (freshwater), mariculture (marine). India 2nd largest fish producer. Blue Revolution = fishery development.
- →MOET (Multiple Ovulation Embryo Transfer): superovulation in cows, embryo transfer to surrogate mothers.
Exam Tips
Saccharomyces cerevisiae (baker's yeast) and Spirulina are SCP examples.
Hybrid vigour (heterosis): F₁ hybrids outperform both parents. Used in maize, sunflower, millet.
MOET: used to produce high-quality offspring from superior cows.
Biofortification examples: Golden Rice (Vit A), Maize hybrid (amino acids), IARI wheat (protein, fat, vitamins).
Microbes in Human Welfare
Key Points to Remember
- →Microbes in household: Lactobacillus (curd), Saccharomyces (bread, beer), Aspergillus niger (citric acid).
- →Industrial products: penicillin (Penicillium), cyclosporin A (Trichoderma polysporum — immunosuppressant), statins (Monascus purpureus — lower cholesterol).
- →Biogas: methanogens (bacteria in cattle dung + slurry → CH₄ + CO₂). Biogas plants.
- →Sewage treatment: Primary (physical screening), Secondary (biological — BOD reduction using aerobic bacteria), Tertiary (chemical).
- →BOD (Biological Oxygen Demand): higher BOD = more polluted water.
- →Biofertilisers: Rhizobium (legume root nodules, nitrogen fixation), Azospirillum (free-living, associative), Cyanobacteria (Anabaena, Nostoc — paddy fields), Mycorrhiza (symbiotic fungi).
- →Biopesticides: Bacillus thuringiensis (Bt): produces cry proteins (crystalline insecticidal protein) toxic to insect larvae.
- →Biocontrol: Trichoderma (fungal pathogen control), Baculovirus (moth caterpillar control, safe for non-target organisms).
Exam Tips
Microbes in sewage: aerobic microbes reduce BOD in secondary treatment. Flocs form and settle.
Biogas plant: anaerobic conditions. Effluent is used as biofertiliser.
Bt toxin is activated by alkaline pH of insect gut — doesn't harm mammals (acidic gut).
Mycorrhiza: helps in mineral (phosphorus) and water absorption. Symbiotic relationship with plant roots.
Biotechnology — Principles and Processes
Key Points to Remember
- →Core tools of biotechnology: restriction endonucleases (molecular scissors), DNA ligase (joining), vectors (carriers), host organism (expression).
- →Restriction enzymes: recognize palindromic sequences, cut at specific sites. Create sticky ends or blunt ends. e.g. EcoRI (GAATTC), BamHI (GGATCC).
- →Vectors: plasmids (pBR322 — has ampR and tetR genes), bacteriophages, cosmids, BAC, YAC.
- →Cloning: insert gene into vector → transform into host (E. coli) → select recombinant colonies using antibiotic resistance (insertional inactivation).
- →Gel electrophoresis: separates DNA fragments by size. Smaller fragments move farther.
- →PCR (Polymerase Chain Reaction): amplify specific DNA sequences. Steps: Denaturation (94°C) → Annealing (50–65°C) → Extension (72°C). Taq polymerase (thermostable).
- →Bioreactor: large-scale culture of recombinant organisms. Sparged type — provides aerobic conditions.
- →Downstream processing: after fermentation — extraction, purification (chromatography), formulation.
Exam Tips
EcoRI palindrome: 5'-GAATTC-3' / 3'-CTTAAG-5'. Draw sticky ends — very common question.
pBR322: has two antibiotic resistance genes. Insertional inactivation in tetR gene → white colonies = recombinant.
PCR: each cycle doubles the target DNA. After n cycles: 2ⁿ copies. 30 cycles = ~10⁹ copies.
Gel electrophoresis: agarose gel, ethidium bromide stain, UV visualisation, migration from −ve to +ve.
Biotechnology and Its Applications
Key Points to Remember
- →Genetically modified (GM) crops: Bt cotton (cry1Ac gene from Bacillus thuringiensis — resistant to bollworm), Bt brinjal, Golden Rice (psy and crtI genes).
- →Biopiracy: exploitation of biological resources and traditional knowledge without proper compensation. e.g. neem, turmeric patents.
- →RNA interference (RNAi): dsRNA silences specific mRNA — used to create nematode-resistant tobacco.
- →GMO applications: Herbicide-tolerant crops (Roundup Ready), virus-resistant papaya (PRSV resistance), drought/salinity tolerance.
- →Medicines from GMO: insulin (Eli Lilly — humulin using E. coli), human growth hormone, interferon, Hepatitis B vaccine.
- →Gene therapy: inserting correct gene into cells of patients with genetic disorders. ADA deficiency (adenosine deaminase) — first gene therapy case.
- →Molecular diagnostics: PCR (detect HIV, viral genes), ELISA (antigen-antibody detection).
- →Transgenic animals: for production of biological products, vaccine testing, understanding genetic diseases. Rosie the cow — human protein α-lactalbumin in milk.
Exam Tips
Bt cotton: cry1Ac protein → forms pores in midgut of bollworm → kills larva. Bt is safe for humans.
Insulin production: pre-pro-insulin → cleavage of signal peptide → pro-insulin → C-peptide removed → active insulin (A and B chains).
ADA deficiency gene therapy: introduced functional ADA gene into lymphocytes from patient.
ELISA: used to detect HIV — detects antibodies against HIV, not the virus directly.
Organisms and Populations
Key Points to Remember
- →Ecology: study of interactions among organisms and between organisms and their environment.
- →Abiotic factors: temperature, water, light, soil — affect distribution and abundance of organisms.
- →Adaptations: temperature (conformers vs regulators), thermoregulation, hibernation, aestivation, migration.
- →Population attributes: birth rate, death rate, sex ratio, age distribution (pre-reproductive, reproductive, post-reproductive).
- →Population growth: Exponential (dN/dt = rN — unlimited resources) and Logistic (S-curve, K = carrying capacity, dN/dt = rN[(K−N)/K]).
- →r-strategists: many offspring, low parental care (insects, weeds) | K-strategists: few offspring, high care (elephants, humans).
- →Interspecific interactions: Mutualism (+/+), Commensalism (+/0), Competition (−/−), Predation (+/−), Parasitism (+/−), Amensalism (−/0).
- →Predator-prey cycles: Lotka-Volterra model. Prey increases → predator increases → prey decreases → predator decreases.
- →Competition: Lotka-Volterra competition equations. Competitive exclusion principle (Gause's law): two species competing for identical niche cannot coexist.
Exam Tips
Logistic growth curve (sigmoid/S-curve): most important graph. Label K, N, growth phases.
Symbiosis types: mutualism (lichen = alga + fungus), commensalism (barnacles on whale), parasitism (Cuscuta on crop plant).
Population growth equation r: intrinsic rate of natural increase. r = birth rate − death rate.
Age pyramids: expansive (triangular — developing countries), stationary (bell-shaped), declining (narrow base — developed countries).
Ecosystem
Key Points to Remember
- →Ecosystem: biotic + abiotic components. Types: natural (forest, lake, ocean) and artificial (aquarium, crop field).
- →Productivity: Primary (GPP by plants), NPP = GPP − Respiration. Secondary productivity: by consumers.
- →Decomposition: fragmentation → leaching → catabolism → humification → mineralisation. Controlled by temperature and moisture.
- →Energy flow: unidirectional. 10% law (Lindeman): only 10% of energy transferred from one trophic level to next.
- →Food chains and food webs. Ecological pyramids: pyramid of numbers (inverted in tree), biomass (inverted in sea), energy (always upright).
- →Ecological services: pollination, pest control, climate regulation, water purification — huge economic value.
- →Nutrient cycling: Carbon cycle (photosynthesis vs respiration/decomposition/combustion), Phosphorus cycle (no atmospheric reservoir).
- →Standing crop: amount of living organic matter in an ecosystem at a given time.
Exam Tips
Energy pyramid is always upright — energy decreases at each trophic level.
Pyramid of biomass in sea is inverted — phytoplankton (small biomass) supports zooplankton (larger biomass).
Carbon cycle: photosynthesis removes CO₂; respiration, decomposition, combustion release CO₂.
10% law: if grass has 1000 J, herbivore gets 100 J, carnivore gets 10 J.
Biodiversity and its Conservation
Key Points to Remember
- →Biodiversity types: genetic (within species), species (number of species), ecosystem (variety of habitats).
- →India: 12 mega biodiversity countries. Two biodiversity hotspots: Eastern Himalayas and Western Ghats.
- →Species diversity: measured by species richness and evenness. Tropics have greatest diversity.
- →Latitudinal gradient: biodiversity increases from poles to tropics. Species-area relationship: log S = log C + Z log A (Z = 0.1–0.2 on same continent, 0.6–1.2 on islands).
- →Loss of biodiversity: habitat loss and fragmentation (main cause), overexploitation, alien species invasion, co-extinctions.
- →IUCN categories: Extinct, Critically Endangered, Endangered, Vulnerable, Near Threatened, Least Concern.
- →Conservation: In-situ (national parks, wildlife sanctuaries, biosphere reserves, sacred groves) and Ex-situ (zoological parks, botanical gardens, seed banks, cryopreservation, gene banks).
- →India's biodiversity: 8.1% of world's species in 2.4% area. Tiger reserves: Project Tiger (1973).
Exam Tips
Hotspots: defined by high endemism and high threat. India has 4 hotspots (Eastern Himalayas, Western Ghats, Indo-Burma, Sundaland).
Sixth mass extinction: ongoing — caused by humans (habitat destruction). Previous 5 were natural.
Ex-situ vs In-situ: in-situ = in natural habitat; ex-situ = outside natural habitat.
CITES: Convention on International Trade in Endangered Species — regulates wildlife trade.
Environmental Issues
Key Points to Remember
- →Air pollution: CO₂ (greenhouse effect), CO (haemoglobin binding), NOx and SO₂ (acid rain), particulate matter (PM₂.₅ most dangerous).
- →Greenhouse effect: CO₂, CH₄, N₂O, CFC, water vapour. Global warming → climate change → sea level rise.
- →Ozone depletion: CFCs (chlorofluorocarbons) break down O₃. Ozone hole over Antarctica. Ultraviolet B causes skin cancer, cataracts.
- →Water pollution: BOD, eutrophication (excess nutrients → algal bloom → oxygen depletion), biomagnification (DDT accumulates up food chain).
- →Biomagnification: pesticides like DDT accumulate — highest concentration in top predator. Terns (seabirds) had highest DDT concentration.
- →Solid waste: e-waste most hazardous. Landfills vs incineration. Reduce, Reuse, Recycle (3Rs).
- →Noise pollution: >80 dB harmful. Effects: hearing loss, stress, hypertension.
- →Radioactive waste: half-life, nuclear plants. Chernobyl (1986) — worst nuclear disaster.
- →Chipko movement: Himalayan villagers hugged trees to prevent felling (1970s). Case study for conservation.
- →Montreal Protocol (1987): phase out of CFCs. Kyoto Protocol: reduce greenhouse gas emissions.
Exam Tips
Eutrophication: excess phosphates/nitrates (from fertilisers) → algal bloom → oxygen depletion → aquatic death. Correct sequence is crucial.
Biomagnification: DDT doesn't degrade → accumulates in fat → concentrates up the food chain. Osprey eggs failed to hatch.
Acid rain: pH < 5.6. SO₂ + H₂O → H₂SO₃/H₂SO₄ | NOx + H₂O → HNO₃.
Montreal Protocol: international agreement specifically for ozone protection — different from Kyoto (greenhouse gases).