Part III: Biology
Free study material · concepts, shortcuts & solved questions
Biology in this exam bracket sits at the intersection of "human body facts everyone should know" and "school-level cell/genetics basics" — the questions are almost always factual-recall rather than conceptual-application, which makes tables the single best format for this whole part.
Taxonomy Basics
Taxonomy, in one line, is the science of classifying living organisms into a structured, nested hierarchy — a subject tested through both the hierarchy itself and the naming system built on top of it.
The classification hierarchy, broadest to narrowest (a classic peg-list, since the order never changes): Kingdom → Phylum → Class → Order → Family → Genus → Species. Modern biology recognises five kingdoms (per the widely taught Whittaker system): Monera (bacteria — prokaryotic, unicellular), Protista (single-celled eukaryotes like amoeba and paramecium), Fungi (yeasts, moulds, mushrooms — absorb nutrients rather than photosynthesising or ingesting), Plantae (plants — photosynthesise), and Animalia (animals — multicellular, ingest food). Why it's tested: exams often ask which kingdom a specific organism belongs to, or which level of the hierarchy is "broader" than another — the fixed seven-level order above answers both question types directly.
Binomial nomenclature, devised by Carl Linnaeus (see the Famous Biologists table below), names every species with exactly two Latin(ised) words: Genus (capitalised) followed by species (lowercase), both conventionally italicised. Examples worth knowing cold: Homo sapiens (humans), Panthera leo (lion), Panthera tigris (tiger — same genus as the lion, both "big cats," a fact exams like to test directly), Mangifera indica (mango), Oryza sativa (rice). Why the system matters: it gives every species one unambiguous scientific name recognised worldwide regardless of local-language common names, which can vary wildly or even overlap between unrelated species — the entire point of standardising on Latin.
Memory hook — "King Phillip Came Over For Good Soup": Kingdom, Phylum, Class, Order, Family, Genus, Species — a classic mnemonic sentence, one word per level, in the exact broad-to-narrow order.
Practice Recall: Recite the seven-level classification hierarchy from Kingdom to Species without looking, name the five kingdoms of the Whittaker system, and give the binomial name for humans and for the lion — then say which two big cats share the same genus.
Cell Biology Basics
The cell is the basic structural and functional unit of life — a principle first stated by Schleiden and Schwann (cell theory, 1838–39), later extended by Rudolf Virchow, who added that all cells arise from pre-existing cells.
| Organelle | Function |
|---|---|
| Nucleus | Controls cell activities; houses DNA/genetic material |
| Mitochondria | "Powerhouse of the cell" — site of aerobic respiration, produces ATP (energy currency) |
| Ribosomes | Site of protein synthesis |
| Endoplasmic Reticulum (ER) | Rough ER (studded with ribosomes) synthesises proteins; smooth ER synthesises lipids and detoxifies |
| Golgi apparatus | Packages and dispatches proteins/lipids, modifying them for transport out of the cell |
| Lysosomes | "Suicide bags" — contain digestive enzymes that break down waste and worn-out cell parts |
| Chloroplast (plants only) | Site of photosynthesis; contains chlorophyll |
| Cell wall (plants, fungi, bacteria — not animals) | Rigid outer layer providing structural support and protection |
| Vacuole | Storage of water, nutrients, waste; typically large and central in plant cells, small in animal cells |
Memory hook — "Never Mistake Ribosomes, Every Golgi Loves Coffee, Very much": Nucleus, Mitochondria, Ribosomes, ER, Golgi, Lysosomes, Chloroplast, Vacuole — eight organelles, one absurd sentence.
Prokaryotic vs eukaryotic cells, a standing comparison: prokaryotic cells (bacteria) lack a true, membrane-bound nucleus and membrane-bound organelles (DNA floats free in the cytoplasm); eukaryotic cells (plants, animals, fungi) have a true nucleus and membrane-bound organelles. Plant vs animal cells: plant cells uniquely have a cell wall, chloroplasts, and typically one large central vacuole; animal cells have neither a cell wall nor chloroplasts, and typically several small vacuoles. Why the mitochondria "powerhouse" nickname is tested so often: ATP (adenosine triphosphate), produced there, is the universal energy currency every cell reaction spends — knowing that the mitochondria is where this specific molecule is generated (rather than merely "energy" in the abstract) is what separates a correct answer from a vague guess on this frequently asked one-liner.
Human Body Systems
Digestive system — key organs and functions:
| Organ | Function |
|---|---|
| Mouth/salivary glands | Mechanical breakdown + salivary amylase begins starch digestion |
| Oesophagus | Muscular tube carrying food to the stomach via peristalsis |
| Stomach | Secretes hydrochloric acid and pepsin; churns food into a semi-liquid mass (chyme) |
| Liver | Produces bile (emulsifies fats); detoxifies blood; stores glycogen |
| Pancreas | Secretes digestive enzymes (for carbs, fats, proteins) and insulin/glucagon (blood sugar regulation) |
| Small intestine | Main site of digestion completion and nutrient absorption |
| Large intestine (colon) | Absorbs water; forms and stores solid waste |
Why the liver and pancreas both appear in two systems' worth of function: both are "accessory" digestive organs — food never physically passes through them — yet both are indispensable to digestion (bile from the liver, enzymes and hormones from the pancreas), which is exactly the kind of nuance ("is the liver part of the digestive system") that a well-set question probes.
Respiratory system — key organs and functions:
| Organ | Function |
|---|---|
| Nasal cavity | Filters, warms, and humidifies incoming air |
| Trachea (windpipe) | Carries air to the lungs; lined with cilia to trap dust/microbes |
| Bronchi/bronchioles | Branching airways within the lungs, carrying air to the alveoli |
| Alveoli | Tiny air sacs where actual gas exchange (O₂ in, CO₂ out) occurs with blood capillaries |
| Diaphragm | Dome-shaped muscle below the lungs; contracts/relaxes to drive breathing |
How gas exchange actually works, in one line: oxygen diffuses from the alveoli (high oxygen concentration) into the surrounding capillary blood (lower oxygen concentration), while carbon dioxide diffuses the opposite way — simple diffusion along a concentration gradient, requiring no active pumping at the alveolar level itself, which is why the enormous surface area of the roughly 300 million alveoli in a pair of human lungs matters so much for efficient exchange.
Circulatory system — key organs and functions:
| Organ/component | Function |
|---|---|
| Heart | Four-chambered muscular pump (two atria, two ventricles); pumps oxygenated blood to the body and deoxygenated blood to the lungs |
| Arteries | Carry blood away from the heart (usually oxygenated, except the pulmonary artery) |
| Veins | Carry blood toward the heart (usually deoxygenated, except the pulmonary vein) |
| Capillaries | Microscopic vessels where actual exchange of gases/nutrients with tissues occurs |
| Blood (plasma, RBC, WBC, platelets) | RBCs carry oxygen (via haemoglobin); WBCs fight infection; platelets enable clotting; plasma carries nutrients/waste |
Nervous system — key organs and functions:
| Organ/component | Function |
|---|---|
| Brain | Cerebrum (higher thought, voluntary action), cerebellum (balance and coordination), medulla oblongata (involuntary functions — heartbeat, breathing) |
| Spinal cord | Relays signals between brain and body; mediates simple reflex actions directly, without waiting for the brain |
| Neurons | Basic functional unit; transmit electrical/chemical signals |
| Peripheral nerves | Carry sensory information in, motor commands out |
Skeletal system — key facts: the adult human body has 206 bones (an infant is born with about 270–300, many of which fuse together during growth — a frequently tested contrast). The femur (thigh bone) is the longest and strongest bone in the body; the stapes, in the middle ear, is the smallest. Bones meet at joints, classified by movement type — ball-and-socket (hip, shoulder — widest range of motion), hinge (knee, elbow — one-directional movement), and pivot (neck — rotational movement). (See the dedicated Skeletal System section below for a fuller table.)
Memory hook — "DR CNS": Digestive, Respiratory, Circulatory, Nervous, Skeletal — the five systems this book covers, in table order, as one pronounceable string.
Practice Recall: Name the four chambers of the heart and state which two carry oxygenated blood — then name which bone is the longest in the human body and which is the smallest.
The Skeletal System in Detail
Beyond the headline "206 bones" fact, the skeletal system is commonly tested through its two structural divisions and a handful of specific bone facts:
- Axial skeleton (80 bones): the skull (22 bones, including the mandible/jaw — the only movable bone in the skull), the vertebral column (26 bones — 7 cervical/neck, 12 thoracic, 5 lumbar, plus the fused sacrum and coccyx), the ribs (24, in 12 pairs), and the sternum (breastbone).
- Appendicular skeleton (126 bones): the bones of the arms, legs, hands, feet, and the girdles (shoulder/pectoral girdle and hip/pelvic girdle) that attach the limbs to the axial skeleton.
- Notable individual bones: the femur (thigh) is both the longest and the strongest bone in the body; the stapes (one of three tiny middle-ear bones, alongside the malleus and incus — together nicknamed the "ossicles," and collectively responsible for transmitting sound vibrations to the inner ear) is the smallest bone; the mandible is the only freely movable bone of the skull, which is why it's singled out in "which skull bone can move" questions.
- Cartilage vs bone, one line: cartilage is a flexible connective tissue (found in the ear, nose tip, and joint surfaces) that is softer and more flexible than bone, lacking bone's blood supply and calcium-based rigidity — a human foetus's skeleton is initially made almost entirely of cartilage, which gradually ossifies (converts to bone) before and after birth, which is part of why an infant is born with more (and softer) bones than an adult ends up with.
- Joint types recap: ball-and-socket (hip, shoulder), hinge (knee, elbow), pivot (neck, allowing head rotation), and additionally gliding joints (between small bones of the wrist and ankle, allowing limited sliding movement) and immovable/fibrous joints (the sutures of the skull, which fuse solid in adulthood).
Memory hook — "80 axial (the core), 126 appendicular (the limbs), 206 total": picture the axial skeleton as literally the body's central axis (skull, spine, ribs — the trunk) and the appendicular skeleton as everything that appends onto it (arms, legs) — the two numbers (80 + 126) always add to the memorised total of 206.
Blood Groups and Transfusion
The ABO blood group system, combined with the Rh factor (present = positive, absent = negative), together define a person's blood type — a table tested both for its own sake and for the transfusion-compatibility logic beneath it.
| Blood group | Antigen on RBC | Antibody in plasma | Can donate to | Can receive from |
|---|---|---|---|---|
| A | A | Anti-B | A, AB | A, O |
| B | B | Anti-A | B, AB | B, O |
| AB | A and B | None | AB only | AB, A, B, O ("universal recipient") |
| O | None | Anti-A and Anti-B | O, A, B, AB ("universal donor") | O only |
Why the "universal donor/recipient" labels make sense, not just as a fact to memorise: a transfusion goes wrong when the recipient's antibodies attack antigens present on the donor's red blood cells — type O blood carries no A or B antigens at all, so no recipient's antibodies have anything on it to attack, making it (Rh factor aside) safe to give to anyone; type AB blood carries no antibodies of its own, so it can safely receive any ABO type, since there's nothing in the AB recipient's plasma to react against incoming A or B antigens. Rh factor, in one line: an additional antigen (named after the Rhesus monkey, in which it was first identified) that must also match between donor and recipient in most cases — Rh-negative blood can generally be given to Rh-positive recipients, but not the reverse, and Rh incompatibility between an Rh-negative mother and an Rh-positive foetus is a specific, separately tested obstetric fact.
Memory hook — "O gives to all, AB takes from all": the two "universal" labels are opposites of each other by design — O has nothing (no antigens) to trigger a reaction in anyone, so it can give to all; AB has no antibodies of its own to react with anything it receives, so it can take from all.
Practice Recall: State which blood group is the universal donor and which is the universal recipient, explain why in terms of antigens and antibodies (not just as a memorised label), and state the transfusion rule for the Rh factor.
The Endocrine System
The endocrine system is the body's chemical messaging network — a set of ductless glands that secrete hormones directly into the bloodstream, which then travel to and act on distant target organs, working alongside (and much more slowly than) the nervous system's electrical signalling.
| Gland | Location | Key hormone(s) | Main function |
|---|---|---|---|
| Pituitary | Base of the brain | Growth hormone (GH), and others regulating other glands | Called the "master gland" — regulates most other endocrine glands; GH controls body growth |
| Thyroid | Neck (front) | Thyroxine | Regulates metabolic rate; deficiency causes goitre (enlarged thyroid) and, in children, stunted growth/cretinism |
| Parathyroid | Behind the thyroid | Parathyroid hormone | Regulates blood calcium levels |
| Adrenal (suprarenal) | Above each kidney | Adrenaline (epinephrine), cortisol | Adrenaline drives the "fight-or-flight" stress response (raises heart rate, blood pressure); cortisol regulates metabolism and stress response over a longer term |
| Pancreas (endocrine portion) | Abdomen | Insulin, glucagon | Insulin lowers blood glucose (deficiency/resistance causes diabetes mellitus); glucagon raises blood glucose — the two work as opposite-direction regulators |
| Pineal | Brain (deep, midline) | Melatonin | Regulates sleep-wake cycles (circadian rhythm) |
| Testes (male) | Scrotum | Testosterone | Male secondary sexual characteristics; sperm production |
| Ovaries (female) | Pelvis | Oestrogen, progesterone | Female secondary sexual characteristics; regulate the menstrual cycle |
Why "master gland" is worth knowing precisely: the pituitary is called the master gland not because it does everything itself, but because it regulates several of the other glands in this table (thyroid, adrenal, and the gonads among them) via its own signalling hormones — a nuance exams sometimes test by asking which gland "controls the other endocrine glands" rather than which produces the most hormones.
Memory hook — "Insulin In, Glucagon Gets-it-up": Insulin brings blood sugar in (lowers it, letting cells absorb glucose); Glucagon gets it back up (raises blood sugar by releasing stored glucose) — opposite jobs from the same organ, the pancreas.
Practice Recall: Name four endocrine glands with one hormone and one function each, then explain why the pituitary is called the "master gland" and what distinguishes that role from simply "producing the most hormones."
The Reproductive System
- Male reproductive system, key organs: the testes (produce sperm and testosterone), the vas deferens (transports sperm), and the prostate gland (contributes fluid to semen). Sperm are produced continuously from puberty onward, in a process called spermatogenesis.
- Female reproductive system, key organs: the ovaries (produce eggs/ova and the hormones oestrogen and progesterone), the fallopian tubes (where fertilisation typically occurs, carrying the egg from ovary to uterus), the uterus (where a fertilised egg implants and a foetus develops), and the vagina (birth canal). A female is born with all the egg cells she will ever have already present in her ovaries (unlike sperm, which are produced continuously), a frequently tested male-vs-female reproductive-biology contrast.
- The menstrual cycle, in one line: a roughly 28-day hormonal cycle (regulated by oestrogen and progesterone) in which the uterine lining thickens in preparation for a possible pregnancy and is shed (menstruation) if fertilisation does not occur; ovulation (release of an egg from an ovary) typically occurs around the midpoint of the cycle.
- Fertilisation and development, one line: fertilisation is the fusion of a sperm and an egg to form a zygote, which develops first into an embryo and later, from about the ninth week in humans, is termed a foetus until birth — the placenta, formed during pregnancy, allows the exchange of nutrients, oxygen and waste between mother and foetus without their blood supplies directly mixing.
Important Diseases
| Disease | Causative agent type | Affected system |
|---|---|---|
| Tuberculosis (TB) | Bacterium (Mycobacterium tuberculosis) | Respiratory (primarily lungs) |
| Cholera | Bacterium (Vibrio cholerae) | Digestive/intestinal |
| Typhoid | Bacterium (Salmonella typhi) | Digestive/intestinal |
| Malaria | Protozoan parasite (Plasmodium, via Anopheles mosquito) | Blood/liver |
| Dengue | Virus (via Aedes aegypti mosquito) | Blood/systemic |
| Chikungunya | Virus (via Aedes mosquito) | Joints/systemic |
| Influenza (flu) | Virus | Respiratory |
| COVID-19 | Virus (SARS-CoV-2) | Respiratory |
| Hepatitis (A/B/C) | Virus | Liver |
| Polio | Virus | Nervous system (can cause paralysis) |
| Rabies | Virus | Nervous system |
| AIDS | Virus (HIV) | Immune system |
| Ringworm | Fungus | Skin |
| Athlete's foot | Fungus | Skin |
| Amoebiasis | Protozoan parasite | Digestive/intestinal |
Key distinguishing fact for this table: bacterial diseases are generally treatable with antibiotics, but antibiotics have no effect on viral diseases — a distinction tested constantly, and the reason viral diseases (flu, dengue, COVID-19) rely on antiviral drugs, vaccines, or supportive care rather than antibiotics.
Microbiology Basics
Why microbiology sits between chemistry-of-life and disease facts: questions in this bracket mostly test whether you can correctly sort a microbe into bacteria/virus/fungus and then correctly label it useful or harmful — not the deeper cell biology of microbes themselves.
- Bacteria, in one line: single-celled, prokaryotic organisms (no true nucleus), among the very oldest and most abundant life forms on Earth, capable of surviving almost everywhere, from soil to deep-sea vents to the human gut. Harmful examples: Mycobacterium tuberculosis (TB), Vibrio cholerae (cholera), Salmonella typhi (typhoid) — all in the Important Diseases table above. Useful examples: Lactobacillus (ferments milk into curd/yoghurt), nitrogen-fixing bacteria like Rhizobium (living in the root nodules of legume plants, converting atmospheric nitrogen into a form plants can use — a cornerstone fact of both biology and agriculture sections), and the vast community of gut bacteria that aid human digestion.
- Viruses, in one line: far smaller than bacteria, and not considered fully "living" by most biologists' definitions, because a virus cannot reproduce on its own — it must hijack a host cell's machinery to replicate. This is exactly why antibiotics (which target bacterial cell processes) are useless against them, and why antiviral strategies instead rely on vaccines (priming immunity in advance) or drugs that block specific steps of the virus's hijacking process. Examples: influenza, HIV, hepatitis viruses, SARS-CoV-2 — all in the Important Diseases table above.
- Fungi, in one line: eukaryotic organisms (yeasts, moulds, mushrooms) that absorb nutrients from their surroundings rather than photosynthesising (like plants) or ingesting food (like animals) — many decompose dead organic matter, an essential ecological role. Harmful examples: ringworm and athlete's foot (skin infections). Useful examples: yeast (Saccharomyces) ferments sugar into alcohol and carbon dioxide, the basis of both bread-making (the CO₂ makes dough rise) and brewing/alcohol production; Penicillium mould is the natural source of the antibiotic penicillin (see Alexander Fleming, below).
Memory hook — "Bacteria: alive & alone; Virus: needs a host; Fungus: feeds by absorbing": three microbes, three completely different survival strategies — remembering the strategy (not just the name) is what lets you correctly classify an unfamiliar microbe's description in an exam question you haven't seen phrased exactly this way before.
Vitamins and Deficiency Diseases
The single highest-yield table in the entire Biology part — a full "vitamin → deficiency" match-up appears in nearly every general-science paper.
| Vitamin | Chemical name | Deficiency disease | Major source |
|---|---|---|---|
| A | Retinol | Night blindness (xerophthalmia) | Carrots, milk, liver, leafy vegetables |
| B1 | Thiamine | Beriberi | Whole grains, legumes, nuts |
| B2 | Riboflavin | Ariboflavinosis (cracked lips/skin) | Milk, eggs, green vegetables |
| B3 | Niacin | Pellagra (diarrhoea, dermatitis, dementia) | Meat, fish, whole grains |
| B6 | Pyridoxine | Anaemia, skin disorders | Bananas, meat, potatoes |
| B12 | Cobalamin | Pernicious anaemia | Meat, eggs, dairy (notably absent in plant foods) |
| C | Ascorbic acid | Scurvy (bleeding gums, weak connective tissue) | Citrus fruits, amla, guava |
| D | Calciferol | Rickets (children)/Osteomalacia (adults) — weak bones | Sunlight exposure, fish oil, egg yolk |
| E | Tocopherol | Reproductive/neurological issues, weak muscles | Nuts, seeds, vegetable oils |
| K | Phylloquinone | Poor blood clotting (excessive bleeding) | Green leafy vegetables |
Fat-soluble vs water-soluble is a second layer this table always tests: A, D, E, K are fat-soluble (stored in the body's fat tissue, so deficiency develops slowly but excess/toxicity is also possible); B and C are water-soluble (not stored in significant amounts, so need regular dietary intake, but excess is simply excreted rather than building toward toxicity).
Memory hook — "ADEK stays, BC flows": fat-soluble vitamins A, D, E, K — "stay" in the body's fat stores; water-soluble B, C — "flow" straight through and need topping up daily.
Memory hook — deficiency chain: picture a body from head to toe failing in vitamin order: A — can't see at night (eyes); B1 — legs weaken and swell (beriberi means "I cannot, I cannot" in Sinhalese, describing the weakness); C — gums bleed; D — bones bend; K — a cut won't stop bleeding. One "body tour," five vitamins, five failures.
Practice Recall: Without looking, match each of the ten vitamins above to its deficiency disease — then separately list which four are fat-soluble.
Genetics Basics
Gregor Mendel, an Austrian monk working with pea plants in the 1860s, is called the "Father of Genetics" for formulating the foundational laws of inheritance, decades before chromosomes or DNA were even understood:
- Law of Dominance: when two contrasting alleles (forms of a gene) are present together, only one — the dominant allele — is expressed in the offspring's appearance (phenotype); the other, the recessive allele, is masked but not lost.
- Law of Segregation: the two alleles for a trait separate (segregate) during gamete formation, so each gamete (sperm/egg) carries only one allele for each trait, not both.
- Law of Independent Assortment: alleles for different traits are inherited independently of one another (this law holds for genes on different chromosomes, not genes closely linked on the same one — a nuance later genetics identified as an exception Mendel didn't observe with his particular pea traits).
DNA vs RNA, the core molecular-biology comparison:
| Feature | DNA | RNA |
|---|---|---|
| Full form | Deoxyribonucleic acid | Ribonucleic acid |
| Strands | Double-stranded (the famous double helix) | Usually single-stranded |
| Sugar | Deoxyribose | Ribose |
| Bases | Adenine, Thymine, Guanine, Cytosine (A-T-G-C) | Adenine, Uracil, Guanine, Cytosine (A-U-G-C — Uracil replaces Thymine) |
| Function | Long-term storage of genetic information | Carries genetic instructions from DNA to protein-making machinery (messenger RNA), among other roles |
Watson and Crick (1953), building on X-ray diffraction data produced by Rosalind Franklin and Maurice Wilkins, proposed the double-helix structure of DNA — one of the most significant discoveries in the history of biology, and a near-guaranteed "who discovered the structure of DNA" question.
Chromosomes, in one line: thread-like structures made of tightly coiled DNA wound around proteins, found in a cell's nucleus — humans have 23 pairs (46 total) chromosomes in every normal body cell, one member of each pair inherited from each parent; the 23rd pair is the sex chromosomes (XX in females, XY in males) — a fact worth knowing directly, since "which parent determines a baby's biological sex" questions hinge on it (the father's sperm carries either an X or a Y chromosome, so the father's contribution is what determines the outcome, not the mother's, which always contributes an X).
A few commonly tested genetic disorders, one line each: colour blindness (most often red-green) and haemophilia (impaired blood clotting) are both classic X-linked recessive disorders — carried on the X chromosome, which is exactly why both appear far more often in males (who have only one X chromosome, so a single recessive copy is enough to show the condition) than in females (who have two X chromosomes, so a second, normal copy usually masks the recessive one). Down syndrome, by contrast, is not inherited in the ordinary sense at all — it results from an extra copy of chromosome 21 (a condition called trisomy 21, giving 47 chromosomes instead of the usual 46), arising from an error during the formation of the egg or sperm rather than being passed down through a dominant/recessive pattern — a distinction worth keeping clear, since exams sometimes test whether you can tell an X-linked recessive disorder apart from a chromosomal-number disorder.
Practice Recall: State Mendel's three laws in one line each, then explain why colour blindness is far more common in men than in women, and name the chromosomal change responsible for Down syndrome.
Plant Biology Essentials
Photosynthesis (see the chemical equation in the Chemistry part above) occurs mainly in the leaf, specifically within chloroplasts containing chlorophyll, the green pigment that absorbs sunlight (chiefly red and blue wavelengths, reflecting green — which is why leaves appear green). It requires sunlight, carbon dioxide (absorbed via tiny pores called stomata), and water (absorbed via roots), producing glucose and releasing oxygen as a by-product.
Transpiration is the loss of water vapour from a plant, mainly through stomata on leaves — it seems wasteful but serves three real purposes: it cools the plant (like sweating), it creates a continuous upward "pull" of water and dissolved minerals from roots to leaves (the transpiration pull, part of what drives the ascent of sap in tall trees without any pump), and it helps regulate the plant's internal water balance. Transpiration rate increases with higher temperature, lower humidity, and more wind — and decreases in the dark, since stomata partly close at night to conserve water.
Ecology Basics
- Food chain, in one line: a straight-line sequence showing "who eats whom," starting from a producer (a plant/photosynthetic organism, which converts sunlight energy into food) through one or more consumers — a primary consumer (herbivore, eats producers), secondary consumer (carnivore/omnivore, eats primary consumers), and sometimes a tertiary consumer (eats secondary consumers) — ending, ultimately, with decomposers (bacteria/fungi) breaking down dead matter and returning nutrients to the soil. Example: grass → grasshopper → frog → snake → hawk.
- Food web, in one line: the realistic, interconnected network formed when multiple overlapping food chains are combined — most real organisms eat (and are eaten by) more than one species, so a "web" represents nature far more accurately than any single linear "chain."
- Ecological pyramid, in one line: a diagrammatic representation showing how a quantity (energy, biomass, or number of organisms) decreases at each successive step up a food chain — the pyramid of energy is always upright (energy is always lost at each step, mostly as heat, per the second law of thermodynamics met in the Physics part), typically only about 10% of energy transfers from one trophic level to the next (the rest is lost to metabolism, movement, heat) — this "10% rule" is the single most commonly tested ecology fact in this bracket, and directly explains why food chains rarely extend beyond four or five links: there simply isn't enough energy left by the fifth step to support a sixth.
- Biodiversity hotspots of India, one line each: a biodiversity hotspot is a region with an exceptionally high number of endemic species (found nowhere else) that is simultaneously under severe threat from habitat loss. India contains parts of four globally recognised hotspots: the Himalaya (spanning the entire Himalayan range), the Indo-Burma region (India's northeast), the Western Ghats and Sri Lanka (the hill range running along India's western coast, exceptionally rich in endemic amphibians and plants), and Sundaland (represented in India by the Nicobar Islands). Why this is tested: "name India's biodiversity hotspots" is a recurring environment-adjacent general-science question, and the number four itself is a frequently tested standalone fact.
Memory hook — "HIWS for India's four hotspots": Himalaya, Indo-Burma, Western Ghats & Sri Lanka, Sundaland (Nicobar) — four letters, four hotspots, always the same fixed peg order.
Practice Recall: Give an example food chain of at least four links, state the "10% rule" and what it implies about food-chain length, and name India's four biodiversity hotspots without checking.
Famous Biologists and Their Work
| Biologist | Known for |
|---|---|
| Gregor Mendel | Laws of inheritance (dominance, segregation, independent assortment), from pea-plant experiments |
| Charles Darwin | Theory of evolution by natural selection (On the Origin of Species, 1859) — "survival of the fittest" |
| Edward Jenner | Developed the world's first vaccine, against smallpox (1796), using cowpox material — the foundation of modern immunology |
| Alexander Fleming | Discovered penicillin (1928), the first true antibiotic, from a Penicillium mould contamination — ushering in the antibiotic era |
| James Watson & Francis Crick | Proposed the double-helix structure of DNA (1953), building on Rosalind Franklin's X-ray diffraction images |
| Louis Pasteur | Germ theory of disease; pasteurisation process; rabies vaccine |
| Robert Hooke | First observed and named the "cell," while examining cork under a microscope (1665) |
| Carl Linnaeus | Father of taxonomy; devised the binomial nomenclature system (genus + species) still used today |
| Ronald Ross | Discovered (1897, working in Secunderabad, India) that the Anopheles mosquito transmits malaria — won the Nobel Prize in Physiology or Medicine (1902); World Mosquito Day (20 August) commemorates this discovery, making Ross one of the most India-linked names in this entire table |
| Antonie van Leeuwenhoek | Pioneered practical microscopy; first to observe and describe bacteria and other microorganisms ("animalcules") |
| Jane Goodall | Pioneering long-term field studies of wild chimpanzee behaviour and social structure |
| Har Gobind Khorana | Indian-origin scientist; helped interpret the genetic code and its role in protein synthesis, Nobel Prize 1968 (see also the Nobel laureates table in the Physics part) |
Practice Recall: Match each of the twelve names above to their one-line discovery — then separately explain, in one sentence each, why Jenner and Fleming are both landmark figures in the history of fighting infectious disease, despite one working on prevention (vaccines) and the other on treatment (antibiotics); and why Ronald Ross's discovery is frequently paired with an Indian-context date (World Mosquito Day) despite Ross himself being British.