General Science — NDA General Knowledge
GK General Science is the biology-and-beyond half of NDA's science coverage — everything that isn't mechanics, heat, light, sound or electricity (Physics) and isn't reactions, elements or compounds (Chemistry). It is a closed set of facts about the human body, nutrition, disease, plants, cells, heredity, instruments, scientists and the environment — CBSE Class 9–10 general science, tested as pure recall under a four-mark, four-option, negative-marking clock. There is no derivation to fall back on here: either you know that Vitamin C deficiency causes scurvy and Vitamin A deficiency causes night blindness, or you guess and pay for it.
1. What NDA actually asks
Weightage: 10% of General Knowledge — tied with Current Events as the smallest of GK's six sub-areas. GK is Part B of the GAT paper: 100 of the GAT's 150 questions, worth 400 of its 600 marks. A 10% share of GK General Science works out to roughly 10 of the 100 GK questions — 40 of the 400 GK marks — behind Physics (25%), Geography (20%), History & Freedom Movement (20%) and Chemistry (15%). Every GAT question, English or GK, carries +4 for a correct answer and −1.3333 for a wrong one (1/3 of 4 marks); an unattempted question costs nothing.
General Science questions in NDA GK come in three recurring shapes:
- Factual recall — name the vitamin behind a deficiency disease, the organism that causes a named disease, the scientist behind a discovery, the organ that performs a given function.
- Structure-to-function matching — pair an organ, organelle, plant group or instrument with the single job it does, from a set of plausible-sounding neighbours.
- Correct-statement identification — four short statements about the same topic (blood groups, photosynthesis, a disease's transmission route), only one of which is scientifically accurate.
Nothing here goes beyond a CBSE Class 9–10 general science syllabus — this is the biology and applied-science a generalist officer is expected to know, not university-level physiology or genetics.
2. The human body — organ systems
Digestive system. Food is broken down mechanically and chemically along a single tube: mouth (saliva's amylase begins starch digestion) → oesophagus (moves food by peristalsis) → stomach (gastric juice's hydrochloric acid kills germs and activates pepsin, which digests proteins) → small intestine (the main site of digestion and absorption — bile from the liver, stored in the gallbladder, emulsifies fats; pancreatic juice from the pancreas supplies further enzymes; finger-like villi absorb the digested nutrients) → large intestine (absorbs water) → rectum → anus. The liver is the body's largest gland; the pancreas is unusual in being both a digestive gland (pancreatic juice) and a hormone gland (insulin and glucagon, which regulate blood sugar).
Respiratory system. Air travels nose → pharynx → larynx (voice box) → trachea (windpipe) → bronchi → bronchioles → alveoli, tiny air sacs where oxygen diffuses into the blood and carbon dioxide diffuses out — the actual site of gas exchange. The diaphragm, a dome-shaped muscle below the lungs, flattens on inhalation and relaxes on exhalation to drive breathing.
Circulatory system. The heart has four chambers — two upper atria (receive blood) and two lower ventricles (pump blood out). The right side handles deoxygenated blood (body → right atrium → right ventricle → lungs); the left side handles oxygenated blood (lungs → left atrium → left ventricle → rest of the body). Blood itself has four components: plasma (the liquid carrier), red blood cells/RBCs (carry oxygen via haemoglobin), white blood cells/WBCs (fight infection) and platelets (enable clotting). Karl Landsteiner discovered the ABO blood group system — O-negative is the universal donor (no A/B antigens to trigger a reaction), AB-positive is the universal recipient (no anti-A/anti-B antibodies in its plasma).
Nervous system. The cerebrum (the brain's largest part) handles voluntary actions, thought and memory; the cerebellum controls balance and coordination of muscular movement; the medulla oblongata controls involuntary actions — heartbeat, breathing, blood pressure. The neuron is the nervous system's structural and functional unit.
Skeletal system. The adult human skeleton has 206 bones, providing support, protection and (together with muscles) movement. The femur (thigh bone) is the longest bone in the body; the stapes, in the middle ear, is the smallest.
3. Health & nutrition
A balanced diet supplies all six nutrient classes in the right proportion: carbohydrates (primary energy source — rice, wheat, sugar), proteins (growth and tissue repair — pulses, eggs, meat), fats (concentrated energy store — oils, ghee), vitamins and minerals (regulatory functions), water, and fibre/roughage (aids digestion).
Vitamins and their deficiency diseases — a closed, frequently-tested list:
| Vitamin | Also known as | Deficiency disease | Common source |
|---|---|---|---|
| A | Retinol | Night blindness (xerophthalmia) | Carrot, milk, papaya |
| B1 | Thiamine | Beriberi | Whole grains, nuts |
| B2 | Riboflavin | Ariboflavinosis (cracked lips, sore throat) | Milk, eggs, green vegetables |
| B3 | Niacin | Pellagra | Meat, groundnut |
| B12 | Cobalamin | Pernicious anaemia | Meat, eggs, dairy |
| C | Ascorbic acid | Scurvy (bleeding gums) | Citrus fruits, amla |
| D | Calciferol | Rickets (children) / osteomalacia (adults) | Sunlight, fish oil |
| E | Tocopherol | Muscular weakness, infertility | Vegetable oils, nuts |
| K | Phylloquinone | Delayed blood clotting | Green leafy vegetables |
Protein-energy malnutrition produces two distinct, commonly-confused conditions in children: kwashiorkor (adequate calories but insufficient protein — causes oedema/swelling and a characteristic pot belly) and marasmus (an overall calorie-and-protein deficiency — causes severe wasting with no oedema). Beyond vitamins, iodine deficiency causes goitre (enlarged thyroid), and iron deficiency causes anaemia.
4. Common diseases — causes & prevention
Diseases are classified by their causative agent, which also fixes how they spread:
| Disease | Causative agent | Type | Spreads via |
|---|---|---|---|
| Tuberculosis (TB) | Mycobacterium tuberculosis | Bacterial | Airborne droplets |
| Cholera | Vibrio cholerae | Bacterial | Contaminated water/food |
| Typhoid | Salmonella typhi | Bacterial | Contaminated water/food |
| Tetanus | Clostridium tetani | Bacterial | Contaminated wounds |
| Common cold, influenza | Virus | Viral | Airborne droplets |
| Measles, chickenpox, mumps | Virus | Viral | Airborne droplets/contact |
| Polio | Poliovirus | Viral | Contaminated water (faecal-oral) |
| AIDS | HIV | Viral | Blood, body fluids |
| Rabies | Rabies virus | Viral | Bite of an infected animal |
| Malaria | Plasmodium (a protozoan) | Protozoan | Bite of a female Anopheles mosquito |
| Dengue | Dengue virus | Viral | Bite of an Aedes aegypti mosquito |
Communicable diseases (TB, cholera, common cold, malaria) spread from person to person or via a vector; non-communicable diseases (diabetes, cancer, hypertension) do not. Vaccination is prevention's front line: BCG guards against TB, OPV against polio, and DPT against diphtheria, pertussis and tetanus. Edward Jenner's smallpox vaccine (1796) was the world's first; smallpox itself has since been globally eradicated.
5. Plants — basic physiology & classification
Photosynthesis is how green plants make their own food: carbon dioxide and water, in the presence of sunlight and the pigment chlorophyll, combine inside the chloroplast to produce glucose and release oxygen — 6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂. It occurs only in green tissue, and only in the presence of light.
Respiration runs the reverse reaction — glucose combines with oxygen inside the mitochondria to release carbon dioxide, water and usable energy — and, unlike photosynthesis, happens continuously, day and night, in every living cell (plant and animal alike). Stomata, tiny pores on the leaf surface guarded by guard cells, are where a plant exchanges gases and loses water vapour (transpiration).
Plant classification splits first into non-flowering (cryptogams: algae, mosses and liverworts, ferns) and flowering/seed-bearing (phanerogams), which further split into gymnosperms (naked seeds, no fruit — pine, cycas) and angiosperms (seeds enclosed in a fruit). Angiosperms divide again into monocotyledons (one seed-leaf, parallel leaf venation, fibrous roots — wheat, maize, grass) and dicotyledons (two seed-leaves, net-like/reticulate venation, tap roots — gram, pea, mango).
6. Cell structure & genetics
The cell is the basic structural and functional unit of life — first observed and named by Robert Hooke in 1665, examining cork under a microscope; the cell theory (all living things are made of cells) was later formalised by Schleiden and Schwann. Prokaryotic cells (bacteria) have no true, membrane-bound nucleus; eukaryotic cells (plants, animals, fungi) do.
Key organelles: the nucleus houses the cell's genetic material (chromosomes/DNA); the mitochondria are the "powerhouse of the cell," generating energy through respiration; the chloroplast (plant cells only) is the site of photosynthesis; the ribosome builds proteins; the Golgi apparatus packages and dispatches them. The cell wall — rigid, made of cellulose — is present only in plant cells; the cell membrane encloses every cell, plant or animal.
Gregor Mendel, working with garden pea plants, formulated the basic laws of heredity — dominance, segregation and independent assortment — and is regarded as the father of genetics. DNA, the molecule that carries genetic instructions, was shown to have a double-helix structure by James Watson and Francis Crick in 1953. A human body cell carries 23 pairs of chromosomes (46 total); sex is determined by one pair — XX in females, XY in males — with the father's sperm supplying the deciding X or Y.
7. Instruments & scientists
Biology and medicine bring their own set of measuring instruments, distinct from the physics instruments (barometer, anemometer, seismograph, etc.) covered in the Physics chapter:
| Instrument | Measures / used for |
|---|---|
| Stethoscope | Heart and lung sounds |
| Microscope | Magnifying very small objects/cells |
| Endoscope | Viewing internal organs directly |
| Electrocardiograph (ECG) | Heart's electrical activity |
| Electroencephalograph (EEG) | Brain's electrical activity |
| Spirometer | Lung capacity/volume |
| Audiometer | Hearing acuity |
Famous scientists and discoveries relevant to GK General Science:
| Scientist | Known for |
|---|---|
| Edward Jenner | World's first vaccine — smallpox (1796) |
| Louis Pasteur | Germ theory of disease; pasteurisation; rabies vaccine |
| Robert Koch | Identified the bacteria causing TB, cholera, anthrax |
| Alexander Fleming | Discovered penicillin (1928), the first antibiotic |
| Charles Darwin | Theory of evolution by natural selection |
| Gregor Mendel | Laws of heredity — "father of genetics" |
| Robert Hooke | Discovered and named the cell (1665) |
| Watson & Crick | Discovered DNA's double-helix structure (1953) |
8. Environmental science
Pollution comes in several distinct forms: air pollution (vehicle and industrial emissions — CO, SO₂, oxides of nitrogen, particulate matter), water pollution (sewage, industrial effluents, and agricultural runoff that causes eutrophication — excess nutrients trigger algal blooms that deplete dissolved oxygen), soil pollution (pesticides, plastic waste) and noise pollution (measured in decibels).
Greenhouse gases — chiefly carbon dioxide, methane and CFCs — trap heat in the atmosphere, driving global warming; this is distinct from ozone layer depletion, where CFCs (chlorofluorocarbons, once common in refrigerants and aerosols) destroy stratospheric ozone (O₃), the layer that absorbs harmful UV-B radiation from the Sun. The two are frequently confused in GK questions but are different mechanisms with different gases doing the damage.
India holds four of the world's recognised biodiversity hotspots: the Himalaya, Indo-Burma, the Western Ghats & Sri Lanka, and Sundaland (via the Nicobar Islands). Conservation efforts include Project Tiger (launched 1973) and Project Elephant (launched 1992), the IUCN Red List/Red Data Book (which catalogues threatened and endangered species), and the Ramsar Convention, an international treaty protecting wetlands of global importance. In an ecosystem, energy flows from producers (green plants) to primary consumers (herbivores) to secondary/tertiary consumers (carnivores), with decomposers (bacteria and fungi) recycling nutrients back into the system.
Worked examples
Q1 (Organ function). Which organ produces bile, and where is it stored before use?
Show explanation
Solution. The liver produces bile; it is stored in the gallbladder and released into the small intestine to emulsify fats. A common trap swaps these two roles.
Q2 (Blood groups). Which blood group is known as the universal donor, and why?
Show explanation
Solution. O-negative — its red blood cells carry neither A nor B antigens, so they don't trigger an immune reaction in a recipient of any blood group.
Q3 (Deficiency disease). A sailor on a long voyage without fresh fruit develops bleeding gums and slow wound healing. Which vitamin deficiency is responsible?
Show explanation
Solution. Vitamin C (ascorbic acid) deficiency — scurvy. This is the textbook historical case that gave the disease its name; night blindness (the trap answer) is a Vitamin A deficiency, not Vitamin C.
Q4 (Correct-statement identification — photosynthesis vs respiration). Which of the following occurs continuously, day and night, in every living cell?
Show explanation
Solution. Respiration. Photosynthesis happens only in green tissue, and only in the presence of light; respiration runs at all times in all cells, plant and animal.
Q5 (Pathogen vs vector). Malaria is caused by which organism?
Show explanation
Solution. Plasmodium, a protozoan — transmitted by the bite of a female Anopheles mosquito, which is the vector, not the causative agent. Confusing the mosquito for the pathogen is a very common trap.
Q6 (Scientist matching). Who discovered penicillin, the first antibiotic?
Show explanation
Solution. Alexander Fleming, in 1928. A frequent trap offers Louis Pasteur, who is instead associated with the germ theory of disease and pasteurisation, not penicillin.
10. Common traps
- Swapping night blindness (Vitamin A) and scurvy (Vitamin C) — two of the most commonly tested deficiency diseases, and the easiest to mix up since both involve a single-letter vitamin name.
- Confusing kwashiorkor (protein deficiency with oedema/pot belly) and marasmus (overall calorie deficiency with severe wasting, no oedema) — both are childhood malnutrition disorders but with opposite physical presentations.
- Mistaking a disease's vector for its causative agent — the Anopheles mosquito spreads malaria but does not cause it; the actual pathogen is the protozoan Plasmodium. The same distinction applies to dengue (virus) and its Aedes aegypti vector.
- Assuming photosynthesis happens all the time, like respiration — photosynthesis requires light and occurs only in chlorophyll-bearing tissue; respiration runs continuously in every living cell, day and night.
- Mixing up mitochondria and chloroplasts — mitochondria (present in all eukaryotic cells) are the site of respiration/energy release; chloroplasts (plant cells only) are the site of photosynthesis. Only one of the two is exclusive to plants.
- Conflating the greenhouse effect and ozone layer depletion — the greenhouse effect (CO₂, methane trapping heat, causing global warming) and ozone depletion (CFCs destroying stratospheric O₃, letting in more UV) are two separate mechanisms, frequently tested as if interchangeable.
- Misattributing a discovery to the wrong scientist — Jenner (smallpox vaccine) vs Pasteur (germ theory, rabies vaccine, pasteurisation) vs Fleming (penicillin) is a favourite three-way trap; each did something genuinely different.
- Reversing universal donor and universal recipient — O-negative gives to everyone (no antigens to react against); AB-positive can receive from everyone (no antibodies to react with). The logic runs in opposite directions for donor and recipient.
11. Revision protocol
GK General Science rewards the same clean, memorised checklist that works for GK Physics — there is no problem-solving here, only a closed set of facts repeated across differently-worded questions. Rebuild the nine-vitamin deficiency table, the bacterial/viral/protozoan disease list with each pathogen's transmission route, the five organ systems' key functions, the monocot/dicot and gymnosperm/angiosperm splits, the eight-scientist discovery list, and the greenhouse-effect/ozone-depletion distinction from memory until each takes under five seconds to recall. At only 10% of GK, this chapter yields fewer raw marks than Physics or Geography, but its facts are self-contained flashcards with almost zero ambiguity — making it one of the fastest sub-areas to lock down cold in a single focused revision pass.
