General Science — Cells, Tissues, Human Organs, Balanced Diet & Major Discoveries
The biology part of the GAT is almost entirely about the human body and what it needs, which makes it the most intuitive section in the paper — you already live inside the subject matter. Questions cluster tightly around four things: the cell and its organelles, the organ systems, vitamins and deficiency diseases, and who discovered what. Deficiency diseases in particular are near-guaranteed marks, because there are only about eight of them and each maps to exactly one vitamin.
Human Organ Systems
| Organ / system | Key facts |
|---|---|
| Heart | Four chambers; beats ~72 times a minute; the left ventricle has the thickest wall because it pumps to the whole body |
| Blood | RBCs carry oxygen via haemoglobin and live ~120 days; WBCs fight infection; platelets clot. Universal donor O⁻, universal recipient AB⁺ |
| Lungs | Exchange happens in the alveoli; the diaphragm drives breathing |
| Liver | Largest gland in the body; makes bile; stores glycogen; detoxifies |
| Kidneys | Filter blood in nephrons — the functional unit; make urine |
| Skin | Largest organ; regulates temperature; makes vitamin D in sunlight |
| Skeleton | 206 bones in an adult (a newborn has ~300 that later fuse); femur is longest, stapes in the ear is smallest |
🎯 Why the pancreas appears in two chapters at once
The pancreas is both an exocrine gland (pouring digestive enzymes into the intestine) and an endocrine gland (releasing insulin and glucagon into the blood). That dual role is why it is called a mixed gland, and it is a standard question. Insulin lowers blood sugar, so its shortage causes diabetes mellitus — and the hormone was discovered by Banting and Best.- The thyroid needs iodine to make thyroxine; shortage causes goitre, which is why salt is iodised.
- The pituitary, the "master gland", sits at the base of the brain and controls other glands.
- Adrenaline from the adrenal glands is the "fight or flight" hormone — a fact with obvious relevance to a service exam.
- Digestion of starch begins in the mouth with salivary amylase, not in the stomach.
Balanced Diet, Vitamins & Deficiency Diseases
A balanced diet supplies carbohydrates and fats for energy, proteins for growth and repair, vitamins and minerals for regulation, plus roughage and water. Carbohydrates and fats are the energy foods; proteins are the body-building foods — 1 g of fat gives about 9 kcal against 4 kcal from carbohydrate or protein, which is why fat is the densest store.
| Vitamin | Chemical name | Deficiency causes |
|---|---|---|
| A | Retinol | Night blindness, xerophthalmia |
| B₁ | Thiamine | Beriberi |
| B₃ | Niacin | Pellagra |
| B₁₂ | Cyanocobalamin | Pernicious anaemia |
| C | Ascorbic acid | Scurvy — bleeding gums |
| D | Calciferol | Rickets in children, osteomalacia in adults |
| E | Tocopherol | Sterility, poor healing |
| K | Phylloquinone | Blood fails to clot |
🧠 Fat-soluble vitamins spell a word: A, D, E, K
Only A, D, E and K are fat-soluble and can be stored in the body; the B group and C are water-soluble and must be taken daily because the excess is excreted. That is why a single overdose of vitamin A can be toxic while excess vitamin C simply leaves in the urine. Also worth pairing: iron deficiency → anaemia, calcium → weak bones and teeth, iodine → goitre, fluorine excess → fluorosis.Major Scientific Discoveries & Inventions
| Discovery / invention | By |
|---|---|
| Laws of motion & gravitation | Isaac Newton |
| Theory of relativity | Albert Einstein |
| Penicillin | Alexander Fleming |
| Vaccination (smallpox) | Edward Jenner |
| Rabies vaccine, pasteurisation | Louis Pasteur |
| X-rays | W. C. Roentgen |
| Radioactivity / radium | Becquerel; Marie & Pierre Curie |
| Telephone | Alexander Graham Bell |
| Radio / wireless | Marconi (J. C. Bose's work preceded it) |
| Electric bulb | Thomas Edison |
| Aeroplane | Wright brothers |
| Circulation of blood | William Harvey |
| Raman effect | C. V. Raman (Nobel 1930) |
📖 Two accidents that changed medicine
Fleming returned from holiday in 1928 to find a mould had contaminated a dish of bacteria — and had killed them. That contaminated dish became penicillin, the first antibiotic. Roentgen, working with a cathode-ray tube in 1895, noticed a screen glowing across the room and could not name the rays, so he called them X — the mathematical symbol for the unknown. Facts attached to a story survive the exam hall; facts on a list often do not.Key takeaways
- Hooke discovered the cell; Brown the nucleus; mitochondria are the powerhouse.
- Plant cell has cell wall, chloroplasts and a large vacuole; animal cell has centrioles.
- Blood is a CONNECTIVE tissue, not a fluid tissue of its own type.
- Liver is the largest gland, skin the largest organ, and an adult has 206 bones.
- The pancreas is a MIXED gland — enzymes to the gut, insulin to the blood.
- Only A, D, E, K are fat-soluble and storable; B and C must be taken daily.
- Scurvy ← vitamin C, rickets ← D, night blindness ← A, poor clotting ← K.
- Fleming penicillin, Jenner vaccination, Roentgen X-rays, Harvey blood circulation.
Practice questions (8)
Attempt each one before opening the answer. Every explanation names the tempting wrong option as well as the right one, because that is where marks are lost.
The "powerhouse of the cell" is:
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Answer: C — Mitochondria
Mitochondria carry out cellular respiration and release energy as ATP. Ribosomes make protein, the Golgi body packages it, and the nucleus controls the cell.Which of these is present in a plant cell but ABSENT in an animal cell?
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Answer: B — Cell wall
The cellulose cell wall, chloroplasts and a large central vacuole are the three plant-only features. Mitochondria, nucleus and ribosomes are in both.The largest gland in the human body is the:
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Answer: C — Liver
The liver is the largest gland; the skin is the largest organ, which is the pair this question is usually set against. The pituitary is the smallest but is called the master gland.Scurvy is caused by the deficiency of:
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Answer: C — Vitamin C
Vitamin C (ascorbic acid) deficiency causes scurvy, marked by bleeding gums. Vitamin A shortage gives night blindness, B₁ beriberi and D rickets.Which group of vitamins is fat-soluble?
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Answer: B — A, D, E and K
A, D, E and K are fat-soluble and can be stored in the body, which is why an overdose of them can be toxic. B-complex and C are water-soluble and the excess is passed in urine.Insulin is secreted by the:
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Answer: B — Pancreas
The islets of Langerhans in the pancreas secrete insulin, which lowers blood glucose; its shortage causes diabetes mellitus. This dual endocrine-plus-exocrine role makes the pancreas a mixed gland.Blood is classified as which type of tissue?
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Answer: B — Connective
Blood is a connective tissue, along with bone, cartilage and ligaments, because it develops from the same embryonic layer and has cells suspended in a matrix — here the plasma.Penicillin, the first antibiotic, was discovered by:
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Answer: C — Alexander Fleming
Fleming found in 1928 that a Penicillium mould had killed bacteria on a contaminated dish. Jenner pioneered smallpox vaccination and Pasteur developed the rabies vaccine and pasteurisation.