- Questions on the human body appear in nearly every SSC, RRB and State PSC paper, mostly as one-line facts and matching pairs.
- An adult human has 206 bones; normal body temperature is about 37°C (98.6°F) and normal blood pressure about 120/80 mm Hg.
- Learn diseases by pathogen type — bacteria, viruses, protozoa, fungi — because exams ask "which of these is NOT a viral disease?".
Body Record-Holders
| Fact | Answer |
|---|---|
| Largest organ | Skin |
| Largest gland | Liver (it also stores glycogen and makes bile) |
| Largest / longest bone | Femur (thigh bone) |
| Smallest bone | Stapes, in the middle ear |
| Strongest muscle by force | Masseter (jaw) |
| Hardest substance | Tooth enamel |
| Master gland | Pituitary |
| Lifespan of red blood cells | About 120 days; they are made in the bone marrow and destroyed in the spleen and liver |
| Insulin | Made by beta cells of the islets of Langerhans in the pancreas; lack of it causes diabetes mellitus |
Blood Groups
The ABO system was discovered by Karl Landsteiner (1900–01). Group O negative is the universal donor (no A or B antigens on its red cells) and AB positive the universal recipient (no anti-A or anti-B antibodies in its plasma). If an Rh-negative mother carries an Rh-positive baby, her antibodies can harm a later Rh-positive pregnancy — a condition called erythroblastosis fetalis.
Bones (adult)206
Normal temperature37°C / 98.6°F
Normal BP120/80 mm Hg
Universal donorO negative
Largest glandLiver
RBC lifespan~120 days
Vitamins and Deficiency Diseases
| Vitamin | Chemical name | Deficiency disease | Sources |
|---|---|---|---|
| A | Retinol | Night blindness, xerophthalmia | Carrots, milk, liver |
| B1 | Thiamine | Beriberi | Whole grains, pulses |
| B3 | Niacin | Pellagra | Meat, groundnuts |
| B12 | Cobalamin | Pernicious anaemia | Animal foods only |
| C | Ascorbic acid | Scurvy (bleeding gums) | Amla, citrus fruits |
| D | Calciferol | Rickets in children, osteomalacia in adults | Sunlight on skin, fish oil |
| E | Tocopherol | Reproductive problems | Vegetable oils, nuts |
| K | Phylloquinone | Blood fails to clot properly | Green leafy vegetables |
Fat-soluble: A, D, E and K (stored in the body). Water-soluble: B group and C (must be taken regularly). Mineral deficiencies: iodine → goitre; iron → anaemia.
Diseases by Pathogen
| Pathogen | Diseases |
|---|---|
| Bacteria | Tuberculosis, cholera, typhoid, tetanus, diphtheria, leprosy, plague, whooping cough |
| Viruses | COVID-19, dengue, chikungunya, polio, rabies, measles, mumps, hepatitis, AIDS, influenza |
| Protozoa | Malaria (Plasmodium, spread by the female Anopheles mosquito), kala-azar (Leishmania, spread by sandflies), amoebic dysentery |
| Fungi | Ringworm, athlete's foot |
| Worms (helminths) | Filariasis (spread by Culex mosquitoes), roundworm infection |
Dengue and chikungunya are spread by the Aedes aegypti mosquito, which bites during the day.
Vaccines and Immunisation
- Edward Jenner developed the first vaccine, against smallpox, in 1796; smallpox was declared eradicated in 1980.
- Louis Pasteur made the rabies vaccine (1885) and developed pasteurisation.
- BCG protects against tuberculosis. Jonas Salk developed the injected polio vaccine and Albert Sabin the oral one.
- WHO certified India polio-free on March 27, 2014. Mission Indradhanush (2014) aims at full immunisation of children and pregnant women.
- Alexander Fleming discovered penicillin, the first antibiotic, in 1928. Antibiotics work against bacteria, not viruses.
- Odd one out: "Which is not a viral disease?" — typhoid, cholera or TB are the usual answers.
- Vitamin ↔ disease matching, often with chemical names (thiamine, ascorbic acid, calciferol).
- Vector questions: Anopheles → malaria, Aedes → dengue, Culex → filariasis, sandfly → kala-azar.
Q1. Scurvy is caused by a deficiency of:
✅ Answer: (c) Vitamin C
💡 Explanation: Vitamin C (ascorbic acid) deficiency causes scurvy, with bleeding gums.
Q2. Which of these diseases is caused by bacteria?
✅ Answer: (a) Typhoid
💡 Explanation: Typhoid is caused by Salmonella Typhi; the others are viral.
Q3. The universal donor blood group is:
✅ Answer: (b) O negative
💡 Explanation: O-negative red cells carry no A, B or Rh antigens.
Q4. Kala-azar is transmitted by:
✅ Answer: (d) Sandfly
💡 Explanation: Kala-azar (visceral leishmaniasis) is spread by sandflies.
Q5. The smallest bone in the human body is the:
✅ Answer: (a) Stapes
💡 Explanation: The stapes in the middle ear is the smallest bone.
🔁 Revise in 60 Seconds
- 206 bones; 37°C; 120/80; RBC life ~120 days.
- A night blindness, B1 beriberi, B3 pellagra, C scurvy, D rickets, K clotting.
- Bacterial: TB, cholera, typhoid, tetanus. Viral: dengue, polio, rabies, measles.
- Jenner smallpox (1796), Pasteur rabies (1885), Fleming penicillin (1928); India polio-free 2014.
📌 Prelims Traps to Avoid
- ✘ Malaria is caused by a protozoan, not a virus or bacterium.
- ✘ Antibiotics do not work against viral diseases such as flu or COVID-19.
- ✘ Vitamin D is made in the skin with sunlight; vitamin B12 comes almost only from animal foods.
Which vitamin deficiency causes night blindness?
Vitamin A (retinol). Severe deficiency can also cause xerophthalmia, a drying of the eye.
Which diseases are caused by protozoa?
Malaria (Plasmodium), kala-azar (Leishmania), amoebic dysentery (Entamoeba) and sleeping sickness (Trypanosoma).