Science & Technology
Life Science and Human Health
Cell and Human Body Systems
Cell structure and organelles, cell division, tissues and the human body systems (digestion, blood, heart, breathing, kidneys, nerves, hormones) for CGPSC.
Prerequisites
- Class 9–10 science vocabulary (cell, tissue, organ). Nothing beyond that is assumed.
- Life Science and Human Health: chapter overview for how the four topics fit together.
- Chemistry in Everyday Life helps with acids, enzymes and pH, which come up in digestion.
The Hook: A Blood Donation Camp in Raipur
Connect
Every year on 1 October (National Voluntary Blood Donation Day) colleges in Raipur and Bilaspur hold blood donation camps. A volunteer pricks your finger, drops your blood onto a white tile with three reagents and, within a minute, says “B positive”. Your blood pressure is checked (“120 by 80, fine”), you are asked if you had malaria recently, and your blood is sent to the blood bank at AIIMS Raipur.
In those ten minutes you met blood cells, antigens, the heart’s pumping cycle, the immune system and a parasite that lives inside red blood cells. Why can an O-negative donor give blood to almost anyone? What do “120/80” actually measure? This page answers these questions, starting from the cell.
Why it matters: General science in Prelims Paper I regularly asks one-line biology facts (“which organelle…”, “which gland…”, “which blood group…”). Mains P-IV (GS-II) asks short explanations of the same ideas, so learn them as facts plus a one-line reason.
The Cell (कोशिका): Unit of Life
| Milestone | Who and when |
|---|---|
| Cells first seen (in cork) and named | Robert Hooke, 1665 (Micrographia) |
| First living cells (bacteria, protozoa) seen | Antonie van Leeuwenhoek, 1670s |
| Nucleus described | Robert Brown, 1831 |
| Cell theory: all living things are made of cells | Schleiden (plants, 1838) and Schwann (animals, 1839) |
| “All cells arise from pre-existing cells” (omnis cellula e cellula) | Rudolf Virchow, 1855 |
| Double-helix structure of DNA | Watson and Crick, 1953 |
Prokaryotic vs eukaryotic cells
| Feature | Prokaryotic (bacteria, cyanobacteria) | Eukaryotic (plants, animals, fungi, protozoa) |
|---|---|---|
| Nucleus | No true nucleus; DNA lies in a region called the nucleoid | True nucleus bounded by a nuclear membrane |
| Membrane-bound organelles | Absent (no mitochondria, no ER, no Golgi) | Present |
| Ribosomes | Smaller (70S) | Larger (80S) in the cytoplasm |
| Size | Usually small (about 1–10 micrometres) | Usually larger |
Organelles and their jobs
| Organelle | Job | Exam tag |
|---|---|---|
| Cell membrane (plasma membrane) | Controls entry and exit of substances; selectively permeable | Made of lipids and proteins |
| Cell wall | Rigid outer layer for support | Plants (cellulose), fungi (chitin), bacteria; absent in animal cells |
| Nucleus (केंद्रक) | Holds DNA and controls the cell | “Control centre” |
| Mitochondria (माइटोकॉन्ड्रिया) | Aerobic respiration; makes energy as ATP | “Powerhouse of the cell”; have their own DNA and ribosomes |
| Chloroplast | Photosynthesis (contains chlorophyll) | Plants and algae only; also have their own DNA |
| Ribosomes | Protein synthesis | No membrane; found in prokaryotes too |
| Endoplasmic reticulum | Rough ER (with ribosomes) makes proteins; smooth ER makes lipids and detoxifies | Smooth ER is prominent in liver cells |
| Golgi apparatus | Packages, modifies and dispatches proteins; forms lysosomes | “Post office of the cell” |
| Lysosome | Contains digestive enzymes; breaks down waste and worn-out parts | “Suicide bag” |
| Vacuole | Storage, turgidity | Large central vacuole in plant cells; small or absent in animal cells |
| Centrosome (centrioles) | Helps form the spindle in cell division | Present in animal cells, generally absent in higher plants |
Plant cell vs animal cell in one line
Plant cells have a cell wall, chloroplasts and a large central vacuole. Animal cells lack all three but have centrioles. Mature mammalian red blood cells have no nucleus and no mitochondria, which is a favourite one-liner.
Cell division
| Feature | Mitosis | Meiosis |
|---|---|---|
| Where | Body (somatic) cells: growth, repair | Reproductive organs: forms gametes (sperm, egg) |
| Daughter cells | 2, identical to the parent | 4, genetically different |
| Chromosome number | Stays the same (diploid → diploid; 46 → 46 in humans) | Halved (diploid → haploid; 46 → 23) |
| Significance | Growth, wound healing; uncontrolled mitosis = cancer | Keeps chromosome number constant across generations; creates variation |
Humans have 46 chromosomes (23 pairs): 22 pairs of autosomes and one pair of sex chromosomes (XX female, XY male). The father’s gamete (X or Y) decides the sex of the child.
Tissues in one table
| Animal tissue | Examples |
|---|---|
| Epithelial (covering) | Skin surface, lining of the gut |
| Connective (support, link) | Blood, bone, cartilage, tendons (muscle to bone), ligaments (bone to bone), fat |
| Muscular | Skeletal (voluntary), smooth (involuntary, gut wall), cardiac (involuntary, never tires) |
| Nervous | Neurons (the longest cells in the body) and supporting cells |
Human Body Systems
graph LR
A["Digestive
food to nutrients"] --> B["Circulatory
blood carries nutrients, O2"]
C["Respiratory
O2 in, CO2 out"] --> B
B --> D["Excretory
kidneys filter waste"]
E["Nervous + Endocrine
control and coordination"] -.-> A
E -.-> B
E -.-> C
E -.-> D1. Digestive system (पाचन तंत्र)
| Part | What happens | Key enzyme / secretion |
|---|---|---|
| Mouth | Chewing; starch digestion begins | Salivary amylase (ptyalin): starch → maltose |
| Stomach | Churning; protein digestion begins | HCl (kills germs, makes the medium acidic), pepsin (proteins) |
| Liver | Makes bile (stored in the gall bladder) | Bile has no enzymes; it emulsifies fats |
| Pancreas | Pancreatic juice into the small intestine | Trypsin (proteins), lipase (fats), amylase (starch) |
| Small intestine | Most digestion and almost all absorption through finger-like villi | Intestinal juice completes digestion |
| Large intestine | Absorbs water; gut bacteria make some vitamins (e.g. vitamin K) | — |
The liver is the largest gland in the body. It stores glycogen, makes bile, detoxifies drugs and alcohol, and makes many blood proteins, including clotting factors.
2. Blood and circulation (रक्त परिसंचरण)
Blood is a fluid connective tissue: plasma (about 55%, mostly water) plus formed elements (about 45%).
| Component | Job | Facts |
|---|---|---|
| RBC (erythrocytes) | Carry O2 using haemoglobin (iron-containing) | Made in red bone marrow; life span about 120 days; destroyed mainly in the spleen (“graveyard of RBCs”); no nucleus in mammals |
| WBC (leucocytes) | Defence | Neutrophils (most numerous WBCs) and monocytes engulf germs; lymphocytes make antibodies and kill infected cells |
| Platelets (thrombocytes) | Blood clotting | Platelet count falls in dengue |
| Plasma | Carries nutrients, hormones, CO2, wastes | Contains clotting proteins (fibrinogen) and antibodies |
Clotting needs platelets, calcium ions, vitamin K and proteins such as fibrinogen. Haemophilia is an inherited (X-linked) clotting disorder, so it is seen mostly in males.
Blood groups
Karl Landsteiner discovered the ABO system (1900–01) and, with Wiener, the Rh factor (1940).
| 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 | All (universal recipient) |
| O | none | anti-A and anti-B | All (universal donor) | O only |
- Rh-negative people have no Rh antigen. If an Rh-negative mother carries an Rh-positive baby, her antibodies can attack the baby’s RBCs in a later pregnancy (erythroblastosis fetalis). An anti-D injection after delivery prevents this.
- Strictly, O-negative is the universal donor and AB-positive the universal recipient.
The heart (हृदय)
- Four chambers: two atria (receive blood) and two ventricles (pump blood). The left ventricle has the thickest wall because it pumps blood to the whole body.
- Double circulation: right side → lungs (pulmonary circulation); left side → body (systemic circulation).
- The heartbeat starts at the SA node, the heart’s natural pacemaker. A resting adult heart beats about 72 times a minute.
- Arteries carry blood away from the heart (thick walls, high pressure). Veins carry blood to the heart (valves stop backflow). Capillaries are where exchange happens.
- Exceptions: the pulmonary artery carries deoxygenated blood; the pulmonary vein carries oxygenated blood.
- Blood pressure “120/80 mmHg”: 120 is systolic (ventricles contracting), 80 is diastolic (ventricles relaxing). It is measured with a sphygmomanometer.
3. Respiratory system (श्वसन तंत्र)
- Air path: nose → pharynx → larynx (voice box) → trachea → bronchi → bronchioles → alveoli, the tiny air sacs where O2 and CO2 are exchanged by diffusion.
- Breathing is driven mainly by the diaphragm and rib muscles.
- Respiration (in the mitochondria) is different from breathing. Aerobic respiration gives far more ATP than anaerobic respiration. In hard exercise muscles respire anaerobically and lactic acid builds up, causing cramps.
- Carbon monoxide binds haemoglobin much more strongly than oxygen does, which is why a charcoal angithi in a closed room in winter can kill.
4. Excretory system (उत्सर्जन तंत्र)
- The kidneys filter blood. Their working unit is the nephron (about a million per kidney).
- Main nitrogenous waste in humans: urea, made in the liver and removed by the kidneys.
- Kidney stones are commonly calcium oxalate. Dialysis (artificial kidney) filters blood when the kidneys fail.
- ADH (antidiuretic hormone) makes the kidneys save water. Lack of ADH causes diabetes insipidus (large volumes of dilute urine), which is not the same as diabetes mellitus.
5. Nervous system (तंत्रिका तंत्र)
| Part | Function |
|---|---|
| Cerebrum | Largest part; thinking, memory, intelligence, voluntary actions, senses |
| Cerebellum | Balance, posture and coordination of movements (affected by alcohol) |
| Medulla oblongata | Involuntary functions: heartbeat, breathing, blood pressure, swallowing, vomiting |
| Hypothalamus | Body temperature, hunger, thirst; controls the pituitary |
| Spinal cord | Carries messages; centre for reflex actions (pulling the hand from a hot pan) |
The neuron is the structural and functional unit. Messages cross the gap between neurons (the synapse) as chemicals called neurotransmitters.
6. Endocrine system (अंतःस्रावी तंत्र)
Endocrine glands are ductless: they pour hormones directly into the blood.
| Gland | Hormone(s) | Deficiency / excess |
|---|---|---|
| Pituitary | Growth hormone and hormones that control other glands | “Master gland”. GH deficiency in childhood: dwarfism; excess: gigantism (children), acromegaly (adults) |
| Thyroid | Thyroxine (needs iodine) | Deficiency: goitre, cretinism (children), myxoedema (adults); excess: exophthalmic goitre |
| Parathyroid | Parathormone | Controls blood calcium |
| Pancreas (islets of Langerhans) | Insulin (beta cells) lowers blood sugar; glucagon (alpha cells) raises it | Lack of insulin or poor response to it: diabetes mellitus |
| Adrenal | Adrenaline (“fight or flight”), cortisol, aldosterone | Adrenaline is called the emergency hormone |
| Testes / ovaries | Testosterone / oestrogen and progesterone | Secondary sexual characters |
| Pineal | Melatonin | Sleep–wake rhythm |
| Thymus | Thymosin | T-lymphocyte maturation; shrinks after puberty |
The pancreas is both exocrine and endocrine: it sends digestive juice through a duct and hormones into the blood. Insulin was isolated by Banting and Best (1921).
7. Skeletal system and senses (quick facts)
- An adult has 206 bones. Longest: femur (thigh). Smallest: stapes (in the middle ear).
- Eye: the image forms on the retina. Rods handle dim light; cones handle colour. Lack of vitamin A affects rods, causing night blindness.
- Eye defects: myopia (near-sightedness, concave lens), hypermetropia (far-sightedness, convex lens), cataract (cloudy lens).
Analysis for Mains: Why Body-System Knowledge Matters for Public Health
- Anaemia is a blood problem with roots in nutrition (iron, folic acid, vitamin B12), infection (malaria, worms) and genetics (sickle cell disease). This one example links three topics of this chapter.
- Non-communicable diseases (diabetes, hypertension, heart and kidney disease) are disorders of the endocrine, circulatory and excretory systems. They now account for a large share of deaths in India, so screening for blood pressure and blood sugar is part of primary care at Ayushman Arogya Mandirs.
- Safe blood transfusion depends on correct grouping, Rh typing and screening for HIV, hepatitis B and C, syphilis and malaria. Thalassaemia and sickle cell patients in Chhattisgarh need repeated transfusions, so a strong blood-bank network matters to the state.
Memory Tricks
Organelle nicknames
Mitochondria = power plant, Ribosome = factory, Golgi = post office, Lysosome = suicide bag, Nucleus = control room. Mitochondria and chloroplasts are the only two organelles with their own DNA, the “two tenants with their own house keys”.
Blood groups
“O gives, AB takes.” O has no antigens to provoke the receiver; AB has no antibodies to attack the donor’s cells.
Arteries go Away
Arteries go Away from the heart. The two pulmonary vessels are the exceptions: the pulmonary artery still goes away from the heart, but its blood is deoxygenated.
Don’t Confuse
| This | vs | That |
|---|---|---|
| Mitosis: 2 identical diploid cells, growth | vs | Meiosis: 4 different haploid cells, gametes |
| Diabetes mellitus: insulin problem, sugar in urine | vs | Diabetes insipidus: ADH problem, large volume of dilute urine |
| Cerebellum: balance and coordination | vs | Medulla: heartbeat, breathing |
| Respiration: chemical process in mitochondria | vs | Breathing: physical movement of air |
| Tendon: muscle to bone | vs | Ligament: bone to bone |
| Bile: made by the liver, no enzyme, emulsifies fat | vs | Pancreatic lipase: the enzyme that actually digests fat |
| Universal donor: O− | vs | Universal recipient: AB+ |
Common Mistakes
MCQ traps
- “Bile contains enzymes that digest fat.” False. Bile only emulsifies fat. Lipase digests it.
- “Ribosomes are found only in eukaryotes.” False. Prokaryotes have ribosomes too (smaller, 70S).
- “All arteries carry oxygenated blood.” False. The pulmonary artery carries deoxygenated blood.
- “The mother decides the sex of the child.” False. The mother always gives an X. The father’s X or Y decides.
- “Thyroid is the master gland.” False. The pituitary is called the master gland. The thyroid is the largest endocrine gland, and the liver is the largest gland overall.
- “Mature human RBCs have a nucleus.” False. They lose it, which leaves more room for haemoglobin.
Practice
All questions below are original practice questions written in CGPSC style. They are not previous-year questions.
Level 1: Foundation
- The organelle known as the “suicide bag” of the cell is the ______.
- The natural pacemaker of the human heart is the ______.
- Which gland secretes both a digestive juice and a hormone?
Answers
- Lysosome.
- SA (sinoatrial) node.
- Pancreas (pancreatic juice through a duct; insulin and glucagon into the blood).
Level 2: Prelims MCQs
Q1. Consider the following statements:
- Mitochondria and chloroplasts contain their own DNA.
- Ribosomes are absent in prokaryotic cells.
- Mature mammalian red blood cells do not have a nucleus.
Which of the statements given above is/are correct?
- (a) 1 only
- (b) 1 and 3 only
- (c) 2 and 3 only
- (d) 1, 2 and 3
Answer and explanation
(b) 1 and 3 only. Mitochondria and chloroplasts have their own DNA and ribosomes. Statement 2 is wrong: prokaryotes do have ribosomes (70S), although they lack membrane-bound organelles. Mammalian RBCs lose their nucleus as they mature.
Q2. Match List I (Gland) with List II (Hormone or condition):
| List I | List II |
|---|---|
| A. Pituitary | 1. Goitre |
| B. Thyroid | 2. Acromegaly |
| C. Pancreas | 3. Emergency hormone |
| D. Adrenal | 4. Diabetes mellitus |
- (a) A-2, B-1, C-4, D-3
- (b) A-1, B-2, C-4, D-3
- (c) A-2, B-1, C-3, D-4
- (d) A-4, B-1, C-2, D-3
Answer and explanation
(a) A-2, B-1, C-4, D-3. Excess growth hormone from the pituitary in adults causes acromegaly. Thyroid problems (often iodine deficiency) cause goitre. Lack of insulin from the pancreas causes diabetes mellitus. The adrenal medulla releases adrenaline, the “fight or flight” or emergency hormone.
Q3. A person with blood group O-negative can safely donate red blood cells to persons of:
- (a) Group O only
- (b) Groups A and B only
- (c) Group AB only
- (d) All ABO groups, Rh-positive or Rh-negative
Answer and explanation
(d). O-negative RBCs carry neither A, B nor Rh antigens, so the recipient’s antibodies have nothing to attack. That is why O-negative is called the universal donor. (Option (a) describes who an O person can receive from.)
Q4. Which part of the human brain controls involuntary actions such as heartbeat and breathing?
- (a) Cerebrum
- (b) Cerebellum
- (c) Medulla oblongata
- (d) Hypothalamus
Answer and explanation
(c) Medulla oblongata. The cerebrum handles thinking and voluntary action, the cerebellum balance and coordination, and the hypothalamus temperature, hunger and thirst. The cerebellum is the usual distractor.
Q5. Which one of the following is not required for the clotting of blood?
- (a) Platelets
- (b) Calcium ions
- (c) Vitamin K
- (d) Insulin
Answer and explanation
(d) Insulin. Insulin regulates blood sugar. Clotting needs platelets, calcium ions, vitamin K-dependent clotting factors made in the liver, and fibrinogen.
Level 3: Mains Answer Writing
Q1. (60 words) Distinguish between mitosis and meiosis.
Model answer outline
- Mitosis: occurs in body cells; one division; two genetically identical diploid daughter cells; used for growth and repair. Uncontrolled mitosis leads to cancer.
- Meiosis: occurs in reproductive organs; two divisions; four haploid gametes that differ genetically; halves the chromosome number (46 → 23 in humans), so the number stays constant after fertilisation, and creates variation through crossing over.
Q2. (150–200 words) Explain the composition of human blood and the basis of ABO and Rh blood grouping. Why is blood grouping important in public health?
Model answer outline
- Intro: Blood is a fluid connective tissue: plasma (about 55%) and formed elements (about 45%).
- Body:
- RBCs (haemoglobin, O2 transport, about 120-day life), WBCs (defence), platelets (clotting); plasma carries nutrients, hormones, antibodies and fibrinogen.
- ABO grouping depends on A and B antigens on RBCs and the opposite antibodies in plasma (Landsteiner). O is the universal donor; AB the universal recipient.
- Rh factor (1940): an Rh-negative mother with an Rh-positive baby risks erythroblastosis fetalis in later pregnancies; anti-D injection prevents it.
- Public health: safe transfusion in accidents and childbirth (post-partum haemorrhage is a leading cause of maternal death); screening donated blood for HIV, hepatitis B and C, malaria and syphilis.
- Chhattisgarh angle: patients with sickle cell disease and thalassaemia need regular, safe transfusions, so blood banks and voluntary donation are vital in the state.
- Conclusion: Knowing blood biology underpins transfusion safety, maternal health and the management of inherited blood disorders.
Quick Revision Table
| Fact | Detail |
|---|---|
| Cell named | Robert Hooke, 1665 |
| Cell theory | Schleiden (1838), Schwann (1839); Virchow (1855) “cells from cells” |
| Powerhouse | Mitochondria (ATP) |
| Protein synthesis | Ribosomes |
| Suicide bag | Lysosome |
| Own DNA | Mitochondria, chloroplasts |
| Human chromosomes | 46 (23 pairs); sex decided by the father |
| Largest gland | Liver |
| Master gland | Pituitary |
| Largest endocrine gland | Thyroid (needs iodine) |
| Insulin / glucagon | Beta / alpha cells of islets of Langerhans; insulin isolated 1921 |
| RBC life span | About 120 days; graveyard: spleen |
| Universal donor / recipient | O− / AB+ |
| ABO / Rh discovery | Landsteiner (1900–01) / Landsteiner and Wiener (1940) |
| Pacemaker | SA node; about 72 beats/min at rest |
| BP 120/80 | Systolic / diastolic, mmHg |
| Kidney unit | Nephron; main waste urea (made in liver) |
| Balance | Cerebellum |
| Bones | 206; longest femur, smallest stapes |
Key Takeaways
Key Takeaways
- Learn each organelle with its job and nickname; plant cells add a cell wall, chloroplasts and a large vacuole.
- Mitosis keeps the chromosome number, meiosis halves it; humans have 46 chromosomes.
- Blood: RBC carry oxygen, WBC defend, platelets clot; O gives, AB takes; Rh incompatibility is prevented by anti-D.
- The heart has four chambers and a double circulation; pulmonary vessels are the exceptions to the artery–vein rule.
- Endocrine glands are ductless; know the deficiency disease of each hormone (goitre, diabetes, dwarfism).
What’s Next
- Nutrition and Deficiency Diseases — what the body needs to run these systems
- Communicable Diseases and Health Programmes — what goes wrong when germs invade
- Vaccines and Immunity — how the WBCs above defend the body
- Biotechnology — DNA, genes and their applications in medicine
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