🧬 Biology

📌 0. Exam Pattern & 2025 Analysis (2 min read)

• 10 Science questions: Physics 4 + Chemistry 3 + Biology 3. The official 2025 paper (16–21 Jan 2026, 12 shifts) had 36 Biology questions — 35 of them are given here.
• Topic-wise: Plant reproduction/physiology/agriculture — 6 | Human reproduction & contraception — 5 | Plant anatomy & tissues — 4 | DNA/genetics/evolution — 4 | Cell — 3 | Human systems — 3 | Biomolecules/enzymes — 3 | Biotechnology — 3 | Ecology — 2 | Hormone feedback — 1 | STD — 1.
• ⚠️ Many questions came from NCERT Class 11-12 (syngamy, microsporogenesis, phosphodiester bond, 0.34 nm, hypodermis collenchyma, flagship species). Keep the basic Class 6-10 facts (vitamins, diseases, blood groups) solid too — older MP police/Vyapam exams have asked them a lot.

📌 1. Cell (7 min read)

1.1 Discovery & Cell Theory

• Cell = the structural and functional unit of life.
• Robert Hooke (1665) — saw dead cells in a thin slice of cork and named them "cells". Leeuwenhoek — first to see living cells (bacteria, protozoa).
• Robert Brown (1831) — discovered the nucleus.
• Cell theory: Schleiden (1838, plants) and Schwann (1839, animals); Virchow (1855) added — "Omnis cellula-e cellula" (every cell arises from a pre-existing cell).
• Smallest cell: Mycoplasma (PPLO). Largest: ostrich egg. Longest in the human body: neuron (nerve cell).

1.2 Prokaryotic vs Eukaryotic

1.3 Cell Organelles

1.4 Cell Division

• Mitosis: in somatic (body) cells; 1 → 2 identical diploid (2n) cells; growth and repair.
• Meiosis: in reproductive cells; 1 → 4 haploid (n) cells (gametes); chromosome number halved; variation (crossing over).

📌 2. Tissues & Plant Anatomy (8 min read)

2.1 Plant Tissues

• Meristematic: divide continuously — apical — at root/shoot tips, increases length; lateral — cambium, increases thickness; intercalary — near the nodes of grasses.
• Permanent — Simple:
  • Parenchyma — thin walls, living, stores food; green = chlorenchyma; with air spaces = aerenchyma (helps aquatic plants float).
  • Collenchyma — living, walls thickened at the corners (cellulose/pectin); gives flexibility; leaf stalk (petiole), hypodermis of the dicot stem.
  • Sclerenchyma — dead, walls thickened with lignin; gives strength — coconut husk, jute; hypodermis of the monocot stem.
• Complex:
  • Xylem — carries water and minerals upward from the root (one direction); tracheids, vessels, xylem parenchyma, xylem fibres. The annual rings that tell a tree's age = layers of xylem (dendrochronology).
  • Phloem — carries food (from leaves to all parts, in both directions); sieve tubes, companion cells.

2.2 Dicot Stem & Root

• Dicot stem (outside to inside): epidermis (cuticle on top) → cortex [hypodermis (collenchyma) → general cortex (parenchyma) → endodermis] → pericycle → vascular bundles (in a ring, with cambium = "open") → pith.
• In the monocot stem the bundles are scattered, there is no cambium, and the hypodermis is sclerenchyma.
• Root regions (from the tip upward): root cap — protection → cell division (meristematic) → elongation → maturation — this is where the root hairs that absorb water are found.
• Stomata — tiny pores in the leaf epidermis (mainly the lower surface); two guard cells open/close them → transpiration and gas exchange. The cuticle (waxy layer) reduces water loss.

2.3 Animal Tissues

📌 3. Classification of Organisms (6 min read)

• Carolus Linnaeus — binomial nomenclature; "father of taxonomy". The first word is the genus (capital letter), the second the species — written in italics. Human = Homo sapiens.
• Hierarchy: Kingdom → Phylum/Division → Class → Order → Family → Genus → Species. Species = the basic unit.
• R.H. Whittaker (1969) — 5 kingdoms: Monera (bacteria), Protista (Amoeba, Euglena), Fungi (mushroom, yeast), Plantae, Animalia.
• Virus: acellular; multiplies only inside a living (host) cell — between living and non-living. Discovered by Ivanowsky (1892), tobacco mosaic virus.

📌 4. Plant Physiology, Reproduction & Agriculture (10 min read)

4.1 Photosynthesis & Respiration

• Photosynthesis: 6CO₂ + 12H₂O —(light, chlorophyll)→ C₆H₁₂O₆ + 6O₂ + 6H₂O. Takes place in the chloroplast. Chlorophyll contains magnesium (Mg). The O₂ released comes from water (not from CO₂). Light energy → chemical energy.
• Respiration: oxidation of glucose → energy (ATP). Aerobic: CO₂ + H₂O + more energy (mitochondria). Anaerobic: ethanol + CO₂ in yeast (fermentation — bread, alcohol); lactic acid in muscles (fatigue, cramps).
• Transpiration: loss of water as vapour through stomata → cools the plant and pulls water up from the roots (transpiration pull).

4.2 Plant Hormones

• Tropism: light — stem grows towards light (+), root away; gravity — root grows down (+); water — root grows towards water. The drooping of touch-me-not (Mimosa) on touch = nastic movement, not a tropism.

4.3 Reproduction in Flowering Plants

• Parts of a flower: sepals, petals, stamen (anther + filament; male), pistil/carpel (stigma + style + ovary; female).
• Microsporogenesis: formation of pollen grains in the anther. Megasporogenesis: formation of the megaspore in the ovule.
• Pollination: transfer of pollen grains to the stigma — self/cross; agents: wind, insects, water, birds.
• Syngamy: fusion of the male gamete with the egg → zygote (2n). Angiosperms show double fertilisation: syngamy + triple fusion (male gamete + 2 polar nuclei → endosperm, 3n).
• After fertilisation: ovary → fruit, ovule → seed.
• Study of pollen grains = Palynology. (Study of pollen in honey = melissopalynology; fruit growing = pomology.)
• Vegetative reproduction: potato (stem tuber — "eyes"), ginger (rhizome), onion (bulb), Bryophyllum (buds on leaf margins).
• Life cycle: in annual and biennial plants the vegetative, reproductive and senescent phases are clearly visible; in perennials they are hard to tell apart. Bamboo flowers once in its life (after 50–100 years); Neelakurinji (Strobilanthes kunthiana) once in 12 years.

4.4 Agriculture (Class 8)

• Sequence: preparing the soil (ploughing/tilling — turning and loosening the soil) → levelling → sowing → manure/fertiliser → irrigation → weeding → harvesting → threshing (separating the grain) → winnowing (separating the chaff) → storage.
• Kharif (rainy season, June–Sep): paddy, maize, soybean, groundnut, cotton. Rabi (winter, Oct–March): wheat, gram, pea, mustard, linseed.
• Rhizobium bacteria in the root nodules of legumes (pulse crops) carry out atmospheric nitrogen fixation → crop rotation keeps the soil fertile.

📌 5. Human Body Systems (12 min read)

5.1 Digestive System

• Liver = largest gland (~1.2–1.5 kg). An adult has 32 teeth; enamel = hardest substance in the body.

5.2 Respiratory System

• Nose → pharynx → larynx (voice box) → trachea (C-shaped cartilage rings) → bronchi → bronchioles → alveoli — gas exchange happens here (by diffusion).
• Pulmonary ventilation = breathing in and out — drawing in atmospheric air and pushing out CO₂-rich alveolar air. Diaphragm moves down → air comes in.
• Adult breathing rate ~12–16 per minute. O₂ is carried by haemoglobin (contains iron).
• Approximate partial pressure of O₂ (pO₂): alveoli ~104, oxygenated blood / pulmonary vein ~95, deoxygenated blood / tissues ~40 mm Hg.
• ⚠️ Carbon monoxide (CO) binds haemoglobin several hundred times more strongly than O₂ (carboxyhaemoglobin) → deaths from a stove/generator in a closed room — a common case in police investigations.

5.3 Circulatory System

• Heart: 4 chambers — 2 atria (upper) + 2 ventricles (lower). Double circulation. Right side = deoxygenated blood; left side = oxygenated blood.
• Arteries carry blood away from the heart; veins carry it towards the heart (they have valves). Exception: the pulmonary artery carries deoxygenated blood, the pulmonary vein carries oxygenated blood.
• SA node = pacemaker. Heart rate ~72/min. Normal BP 120/80 mm Hg (sphygmomanometer).

5.4 Excretory System

• Kidney — functional unit is the nephron. Urea is made in the liver; the kidney filters it out. Yellow colour of urine — urochrome. Kidney stones — usually calcium oxalate. Kidney failure → dialysis.

5.5 Nervous System

5.6 Skeletal & Muscular System

• An adult has 206 bones (about 300 at birth; some fuse later). Longest — femur (thigh); smallest — stapes (ear).
• Skeletal muscle fibres contain myofibrils; their functional unit = sarcomere (between two Z-lines) — contraction happens as actin and myosin filaments slide.

📌 6. Human Reproduction & Contraception (8 min read)

• Testes — sperm + testosterone. Ovary — ovum + estrogen, progesterone.
• Both sperm and ovum are haploid (n = 23); the zygote is diploid (2n = 46).
• Fertilisation — in the oviduct / fallopian tube (ampulla); implantation — in the uterus. Pregnancy lasts ~9 months (~280 days).
• Sex determination: female XX, male XY → the child's sex is decided by the father's sperm (X or Y).
• Hormones: receptors for pituitary FSH and LH are on ovarian cells (follicle/granulosa, theca). LH surge → ovulation (~day 14 of a 28-day cycle). After ovulation, the corpus luteum → progesterone (maintains the uterine lining). A fall in progesterone brings on menstruation.
• Prolactin — milk production. Continuously high prolactin after childbirth → ovulation and the menstrual cycle stay suppressed (lactational amenorrhoea). Oxytocin — uterine contractions during childbirth and milk ejection.

6.1 Contraceptive Methods (NCERT Class 12)

• To postpone menstruation, progesterone/progestin-containing drugs (such as norethisterone) are given.
• India's MTP (abortion) law was passed in 1971 (amended in 2021).

📌 7. Endocrine System & Hormones (7 min read)

• Hormone = a chemical messenger, released by ductless glands directly into the blood. The first hormone discovered was secretin (Bayliss & Starling, 1902).
• The hypothalamus controls the pituitary through releasing hormones (such as TRH, GnRH). Negative feedback: when thyroxine is high, it inhibits TRH and TSH.

📌 8. Nutrition, Vitamins & Minerals (7 min read)

• Carbohydrates (quick energy, ~4 kcal/g), proteins (body building, ~4 kcal/g), fats (most energy, ~9 kcal/g), vitamins, minerals, water, roughage/fibre — prevents constipation.
• Protein deficiency → kwashiorkor (swollen belly, oedema); deficiency of both protein and energy (calories) → marasmus (wasted body).
• The word "vitamine": Casimir Funk (1912). Water-soluble: B and C (not stored in the body, needed daily). Fat-soluble: A, D, E, K (trick: "KEDA").

📌 9. Diseases, Pathogens & Vaccines (10 min read)

9.1 Bacterial Diseases

DPT vaccine = Diphtheria + Pertussis + Tetanus. Today's pentavalent vaccine = DPT + Hepatitis B + Hib.

9.2 Viral Diseases

9.3 Protozoa, Fungi & Worms

9.4 Vaccines, Tests & Medicines

• Edward Jenner — "father of immunology"; Louis Pasteur — rabies and anthrax vaccines; pasteurisation.
• Penicillin — the first antibiotic, Alexander Fleming (1928), from the fungus Penicillium. Antibiotics do not work on viruses.
• Tests: Widal — typhoid; ELISA — HIV; Mantoux — TB; Schick — diphtheria.
• Universal Immunisation Programme (UIP) — 1985; Pulse Polio — 1995; Mission Indradhanush — 2014.

📌 10. Blood & Blood Groups (6 min read)

• Blood = a fluid connective tissue; ~5–6 litres in an adult; pH ~7.4 (slightly alkaline). Plasma ~55% + cells ~45%.
• RBC (red blood cells): carry O₂ through haemoglobin (iron); in mammals they have no nucleus; lifespan ~120 days; made in the bone marrow; spleen — "graveyard of RBCs".
• WBC (white blood cells): fight disease (lymphocytes — antibodies). Platelets: blood clotting (they fall in dengue).

10.1 ABO & Rh

• ABO — Karl Landsteiner (1900). Rh factor — Landsteiner & Wiener (1940), first found in the rhesus monkey.

• Including Rh: O⁻ = universal donor, AB⁺ = universal recipient.
• Erythroblastosis foetalis: Rh⁻ mother + Rh⁺ foetus → in the second pregnancy the foetus's RBCs are destroyed. Prevention: anti-Rh (anti-D) injection to the mother after the first delivery.
• ABO is controlled by 3 alleles of one gene (I) — multiple allelism; AB shows codominance.

📌 11. Genetics, DNA & Evolution (9 min read)

11.1 Mendel & Chromosomes

• Gregor Mendel — "father of genetics"; 7 pairs of traits in the pea (Pisum sativum). Monohybrid F₂ ratio: phenotype 3 : 1, genotype 1 : 2 : 1. Dihybrid: 9 : 3 : 3 : 1.
• Humans have 46 chromosomes (23 pairs) — 22 pairs of autosomes + 1 pair of sex chromosomes (XX/XY).
• Down syndrome — trisomy of chromosome 21; Turner — XO (female); Klinefelter — XXY (male).
• Haemophilia and colour blindness — X-linked recessive → more common in males. Sickle-cell anaemia — autosomal.

11.2 DNA & RNA

• Watson & Crick (1953) — the double helix model of DNA (based on X-ray data of Rosalind Franklin and Wilkins).
• Nucleotide = nitrogenous base + sugar + phosphate. Between the base and the sugar: N-glycosidic bond; between the phosphate of one nucleotide and the 3′-OH of the next sugar: phosphodiester bond (the backbone).
• DNA bases: A, T, G, C; in RNA, U (uracil) replaces T. Pairing: A = T (2 hydrogen bonds), G ≡ C (3 hydrogen bonds) (Chargaff). DNA has deoxyribose, RNA has ribose.
• Double helix: distance between two base pairs 0.34 nm; one turn = 3.4 nm with ~10 base pairs.
• The Human Genome Project was completed in 2003; ~3 × 10⁹ base pairs; ~20,000–25,000 genes.
• DNA fingerprinting — Alec Jeffreys; in India Dr. Lalji Singh ("father of DNA fingerprinting in India", CCMB Hyderabad). CDFD, Hyderabad — used in crime investigation and paternity disputes.

11.3 Evolution

• Lamarck — inheritance of acquired characters (giraffe's neck). Darwin — natural selection, "Origin of Species" (1859). Hugo de Vries — mutation theory.
• Types of natural selection: stabilizing — organisms with intermediate traits are favoured (e.g. birth weight); directional — one extreme; disruptive — both extremes.
• Homologous organs — same origin, different function (human arm, whale flipper, bat wing) → divergent evolution. Analogous organs — different origin, same function (wings of birds and insects) → convergent evolution.
• Archaeopteryx — the connecting link between reptiles and birds.

📌 12. Biomolecules & Enzymes (6 min read)

• Carbohydrates: glucose, fructose (fruit sugar, the sweetest natural sugar), sucrose (table sugar = glucose + fructose), lactose (milk = glucose + galactose), maltose (glucose + glucose). Storage: starch in plants, glycogen in animals (liver, muscles). Cellulose — cell wall; humans cannot digest it.
• Reducing sugars — glucose, fructose, maltose, lactose — reduce Fehling/Benedict (red precipitate). Sucrose is non-reducing → not detected by Fehling. Starch + iodine → blue-black.
• Proteins: amino acids joined by peptide bonds; 20 types. Structure: primary (sequence), secondary — α-helix / β-sheet (stabilised by hydrogen bonds), tertiary, quaternary (haemoglobin). Test: Biuret test.
• Lipids: fatty acids + glycerol.
• Enzymes: biocatalysts, mostly proteins (exception: RNA enzymes — ribozymes). They lower the activation energy — by stabilising the transition state. Specific (lock & key — Emil Fischer; induced fit — Koshland). Optimum temperature in humans ~37°C; high heat denatures them.

📌 13. Biotechnology & Microbes in Human Welfare (6 min read)

• Recombinant DNA (rDNA) technology: restriction enzyme — "molecular scissors" (cuts DNA), DNA ligase — "molecular glue" (joins), vector — plasmid; host — E. coli.
• The first human hormone made by rDNA — insulin (Humulin, Eli Lilly/Genentech, 1982). Earlier, insulin was extracted from the pancreas of cattle/pigs.
• GM crops: Flavr Savr tomato (1994, USA) — the first commercially grown GE food crop (stays fresh longer). Bt cotton — cry gene of Bacillus thuringiensis, protection from bollworm; the first GM crop approved for commercial cultivation in India, in 2002. Golden rice — vitamin A (β-carotene). Bt brinjal is under a moratorium in India since 2010.
• Dolly the sheep (1996) — the first mammal cloned from an adult somatic cell.

📌 14. Ecology & Biodiversity (8 min read)

14.1 Ecosystem

• The term "Ecology" — Ernst Haeckel; the term "Ecosystem" — A.G. Tansley (1935).
• Components: producers (green plants) → consumers (herbivores = primary, carnivores = secondary/tertiary) → decomposers — bacteria, fungi.
• 10% law (Lindeman): only ~10% of the energy at each trophic level passes to the next; energy flow is unidirectional.
• The pyramid of energy is always upright; in the sea the pyramid of biomass is inverted; for insects living on a single tree, the pyramid of numbers is inverted.
• Biomagnification: the concentration of toxins like DDT increases up the food chain (fish-eating birds — thin eggshells).
• Eutrophication: nutrients from fertilisers/sewage in a lake → algal bloom → O₂ shortage. Higher BOD = more organic pollution.
• Ozone depletion — CFCs; Montreal Protocol (1987). Greenhouse gases — CO₂, CH₄, N₂O, CFCs.

14.2 Biodiversity

• The term "Biodiversity" was popularised by Edward Wilson.
• Species-area relationship — Alexander von Humboldt: as area increases, the number of species increases up to a limit (log S = log C + Z log A).
• India — one of the 17 megadiverse countries; ~7–8% of the world's species on ~2.4% of its land area. India's 4 hotspots: Himalaya, Western Ghats–Sri Lanka, Indo-Burma, Sundaland (Nicobar). The "hotspot" concept — Norman Myers.
• Keystone species — an impact on the ecosystem far greater than its numbers. Flagship species — an attractive symbolic species chosen to raise awareness and funds for conservation (e.g. the tiger, giant panda).
• Conservation: in-situ — national parks, sanctuaries, biosphere reserves; ex-situ — zoos, botanical gardens, seed banks. IUCN Red List — threatened species.
• MP context: the 2022 All India Tiger Estimation counted 785 tigers in MP (the highest of all states — "Tiger State"). (As of Sep 2026 this is the latest published figure; the 2026 census report is expected in 2027.) Kuno National Park — cheetahs brought from Namibia on 17 Sep 2022. MP's state animal is the barasingha, state bird the dudhraj (Indian paradise flycatcher), state tree the banyan.