Biology — Human Body and Health
Overview
Biology questions in UPSC Prelims test your understanding of the human body's basic functioning, common diseases, nutrition, and health-related government initiatives. This topic bridges pure science with current affairs — expect questions linking physiological concepts to recent health programmes, disease outbreaks, or nutritional schemes.
The key is understanding mechanisms (how vaccines work, why certain deficiencies cause specific symptoms) rather than memorising exhaustive lists. Questions frequently connect to schemes like Poshan Abhiyaan, Mission Indradhanush, or disease-specific programmes, making this a high-yield overlap area with governance and current affairs.
Key Concepts
- Cell as the basic unit: Human body comprises approximately 37 trillion cells; each cell contains nucleus (with DNA), mitochondria (energy production), ribosomes (protein synthesis), and cell membrane (selective permeability).
- Organ systems work in coordination: Digestive system breaks down food, circulatory system transports nutrients and oxygen, respiratory system exchanges gases, excretory system removes wastes, nervous system coordinates responses, endocrine system regulates through hormones.
- Genes carry hereditary information: DNA (deoxyribonucleic acid) contains genes; genes code for proteins; chromosomes are DNA packages (humans have 46 chromosomes — 23 pairs). Mutations cause genetic disorders.
- Immunity operates at multiple levels: Innate immunity (skin, mucus, white blood cells) provides immediate defence; adaptive immunity (antibodies, memory cells) provides specific, long-lasting protection.
- Communicable vs non-communicable diseases: Communicable diseases spread through pathogens (bacteria, viruses, parasites); non-communicable diseases (NCDs) like diabetes, cancer, heart disease arise from lifestyle, genetics, or environmental factors and are not transmissible.
- Vaccines train the immune system: Vaccines introduce weakened/inactivated pathogens or their components to stimulate antibody production without causing disease, creating immunological memory.
- Nutrition involves macro and micronutrients: Macronutrients (carbohydrates, proteins, fats) provide energy; micronutrients (vitamins, minerals) regulate body functions. Deficiencies cause specific disorders.
Formulas / Key Facts
Major Organ Systems and Functions
| System | Key Organs | Primary Function |
|---|---|---|
| Circulatory | Heart, blood vessels | Transport of oxygen, nutrients, hormones |
| Respiratory | Lungs, trachea, diaphragm | Gas exchange (O₂ in, CO₂ out) |
| Digestive | Stomach, intestines, liver, pancreas | Breakdown and absorption of food |
| Nervous | Brain, spinal cord, nerves | Control and coordination |
| Endocrine | Pituitary, thyroid, adrenals, pancreas | Hormone secretion and regulation |
| Excretory | Kidneys, ureters, bladder | Removal of metabolic wastes |
Important Vitamins and Deficiency Diseases
| Vitamin | Chemical Name | Deficiency Disease |
|---|---|---|
| A | Retinol | Night blindness, xerophthalmia |
| B1 | Thiamine | Beriberi |
| B12 | Cobalamin | Pernicious anaemia |
| C | Ascorbic acid | Scurvy |
| D | Calciferol | Rickets (children), osteomalacia (adults) |
| K | Phylloquinone | Delayed blood clotting |
Key Diseases and Causative Agents
| Disease | Pathogen Type | Agent | Transmission |
|---|---|---|---|
| Tuberculosis | Bacteria | Mycobacterium tuberculosis | Airborne droplets |
| Malaria | Parasite | Plasmodium (via Anopheles mosquito) | Vector-borne |
| Dengue | Virus | Dengue virus (via Aedes mosquito) | Vector-borne |
| Typhoid | Bacteria | Salmonella typhi | Contaminated water/food |
| COVID-19 | Virus | SARS-CoV-2 | Respiratory droplets, aerosols |
| Hepatitis B | Virus | HBV | Blood, body fluids |
Blood Groups and Compatibility
- ABO system: A, B, AB, O based on antigens on RBCs
- Rh factor: Positive (+) or Negative (−)
- Universal donor: O negative; Universal recipient: AB positive
Worked Examples
Example 1: A person suffers from prolonged bleeding even from minor cuts. Which vitamin deficiency is most likely responsible?
Solution: Vitamin K is essential for synthesis of clotting factors in the liver. Its deficiency leads to delayed coagulation and prolonged bleeding. Answer: Vitamin K deficiency.
Example 2: Which of the following diseases is caused by a virus? (a) Typhoid (b) Tuberculosis (c) Dengue (d) Cholera
Solution:
- Typhoid — caused by Salmonella typhi (bacteria)
- Tuberculosis — caused by Mycobacterium (bacteria)
- Dengue — caused by Dengue virus transmitted by Aedes mosquito
- Cholera — caused by Vibrio cholerae (bacteria)
Answer: (c) Dengue
Example 3: Statement I: Antibiotics are effective against viral infections. Statement II: Viruses lack cellular machinery and use host cells to replicate.
Solution: Statement I is false — antibiotics target bacterial structures (cell walls, ribosomes) absent in viruses. Statement II is true — this explains why antibiotics don't work on viruses. Antiviral drugs work differently by targeting viral replication mechanisms.
Common Mistakes
- Confusing vitamins with minerals → Vitamins are organic compounds (A, B, C, D, E, K); minerals are inorganic elements (iron, iodine, calcium, zinc). Iron deficiency causes anaemia, not a "vitamin deficiency."
- Mixing up vector and causative agent → Mosquito is the vector (carrier), not the pathogen. Plasmodium causes malaria; Anopheles mosquito only transmits it. Similarly, Aedes transmits dengue virus but doesn't cause the disease itself.
- Assuming all immunity is the same → Active immunity (vaccines, natural infection) involves body producing antibodies and lasts long. Passive immunity (mother's antibodies to infant, antiserum injections) provides ready-made antibodies and is temporary.
- Believing antibiotics work on all infections → Antibiotics only work against bacteria. Viral diseases (common cold, dengue, COVID-19) require antivirals or supportive treatment, not antibiotics.
- Confusing Type 1 and Type 2 diabetes → Type 1 is autoimmune (body attacks insulin-producing cells); Type 2 is lifestyle-related (insulin resistance). Type 2 accounts for 90–95% of diabetes cases.
Quick Reference
- RBC lifespan: approximately 120 days; produced in bone marrow; destroyed in spleen.
- Normal blood pressure: 120/80 mmHg (systolic/diastolic).
- Iodine deficiency: causes goitre (thyroid enlargement) and cretinism in children.
- Haemoglobin: iron-containing protein in RBCs; carries oxygen; normal range 12–16 g/dL.
- Insulin: hormone from pancreatic beta cells; regulates blood glucose; deficiency/resistance causes diabetes.
- Pulse Polio/Mission Indradhanush: government programmes for vaccination coverage — Oral Polio Vaccine (OPV) and Universal Immunisation Programme vaccines respectively.