Overview
Biology is the study of living organisms — their structure, function, growth, and evolution. TNPSC Group 4 biology covers cell biology, plant and animal kingdoms, human body systems, and diseases. These topics appear regularly in the science section.
The Cell — Basic Unit of Life
Discovery
- Robert Hooke (1665) — first observed cells in cork
- Schleiden and Schwann (1838–39) — proposed Cell Theory
- Cell Theory: All living things are made of cells; the cell is the basic unit of life; all cells arise from pre-existing cells
Cell Structure
| Organelle | Function |
|---|---|
| Nucleus | Control centre; contains DNA (genetic material) |
| Mitochondria | Energy production (ATP) — "Powerhouse of the cell" |
| Chloroplast | Photosynthesis (only in plant cells) — contains chlorophyll |
| Ribosome | Protein synthesis |
| Endoplasmic Reticulum | Transport within cell; rough ER has ribosomes |
| Golgi Apparatus | Packing and secretion of proteins |
| Vacuole | Storage; large central vacuole in plant cells |
| Cell Wall | Rigid outer layer in plant cells (cellulose) |
| Cell Membrane | Controls entry and exit of substances |
| Lysosomes | Digest waste — "suicide bags of the cell" |
Cell Types
- Prokaryotic — no true nucleus (e.g., bacteria)
- Eukaryotic — true nucleus with nuclear membrane (e.g., all plants and animals)
Classification of Living Organisms
Five Kingdoms (Whittaker, 1969)
| Kingdom | Examples | Key Feature |
|---|---|---|
| Monera | Bacteria, blue-green algae | No nucleus (prokaryotes) |
| Protista | Amoeba, paramecium, algae | Single-celled eukaryotes |
| Fungi | Mushroom, bread mold, yeast | Absorbs food; has cell wall (chitin) |
| Plantae | All green plants, trees | Photosynthesis; cell wall (cellulose) |
| Animalia | All animals | No cell wall; heterotrophic |
Plant Kingdom Quick Reference
| Group | Features | Examples |
|---|---|---|
| Algae | Aquatic, no roots/stem/leaves | Spirogyra, Chara |
| Bryophytes | Land plants, no vascular tissue | Moss, liverwort |
| Pteridophytes | Vascular, no seeds | Fern, Selaginella |
| Gymnosperms | Naked seeds (no fruit) | Pine, Cedar |
| Angiosperms | Seeds enclosed in fruit | All flowering plants |
Photosynthesis
Equation: 6CO₂ + 6H₂O + Sunlight → C₆H₁₂O₆ (glucose) + 6O₂
- Occurs in chloroplasts (contain green pigment chlorophyll)
- Raw materials: CO₂ (from air through stomata) + Water (from roots)
- Products: Glucose (food) + Oxygen (released into air)
- Light-dependent reactions occur in thylakoid; light-independent (Calvin cycle) in stroma
TNPSC Tip: Plants release oxygen during daytime (photosynthesis > respiration). At night, only respiration occurs, so they release CO₂.
Respiration
Aerobic Respiration (with oxygen): C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + Energy (ATP)
Anaerobic Respiration (without oxygen): Glucose → Lactic acid + Energy (in muscles during intense exercise) Glucose → Ethanol + CO₂ + Energy (in yeast — fermentation)
Human Body Systems
Digestive System
| Organ | Function |
|---|---|
| Mouth | Mechanical chewing; salivary amylase breaks starch |
| Stomach | HCl (kills bacteria); pepsin digests proteins |
| Small Intestine | Main digestion and absorption; bile from liver, pancreatic enzymes |
| Large Intestine | Water absorption; formation of faeces |
| Liver | Produces bile; detoxifies blood; stores glycogen |
| Pancreas | Produces insulin (controls blood sugar); digestive enzymes |
Circulatory System
- Heart — 4 chambers: 2 atria + 2 ventricles; pumps blood
- Blood components:
- Red Blood Cells (RBC) — carry oxygen (haemoglobin); no nucleus in mature RBC
- White Blood Cells (WBC) — immunity; fight infection
- Platelets — blood clotting
- Plasma — liquid component (~55% of blood)
- Blood groups — A, B, AB, O (ABO system); Rh factor (+/−)
- O negative = Universal donor; AB positive = Universal recipient
Respiratory System
- Air enters through nose → trachea → bronchi → bronchioles → alveoli
- Gas exchange occurs in alveoli (tiny air sacs in lungs)
- O₂ enters blood; CO₂ exits blood
Nervous System
- Brain — control centre; cerebrum (thinking), cerebellum (balance), medulla oblongata (breathing, heart rate)
- Spinal cord — connects brain to body; controls reflex actions
- Neurons — nerve cells; fastest signalling cells in the body
Excretory System
- Kidneys (2) — filter blood; remove urea, salts, excess water → urine
- Nephron = functional unit of kidney
- Liver — removes old RBCs; converts ammonia to urea
Skeletal System
- 206 bones in adult human body
- Smallest bone — Stapes (in ear)
- Largest bone — Femur (thigh bone)
- Joints: Ball-and-socket (hip, shoulder), Hinge (knee, elbow), Pivot (neck)
Reproduction
| Type | Description | Example |
|---|---|---|
| Asexual | One parent; no gametes | Binary fission (bacteria), budding (yeast), vegetative reproduction (plants) |
| Sexual | Two parents; gametes (sperm + egg) | Most animals, flowering plants |
Human Reproduction
- Male gamete = sperm; Female gamete = egg (ovum)
- Fertilisation → zygote → embryo → foetus
- Gestation period (humans) = 9 months (40 weeks)
Theory of Evolution
- Charles Darwin — Natural Selection (1859) — "survival of the fittest"
- Jean-Baptiste Lamarck — earlier theory (incorrect) — inheritance of acquired characteristics
- Gregor Mendel — Father of Genetics; discovered laws of heredity through pea plant experiments
DNA and Heredity
- DNA (Deoxyribonucleic Acid) — stores genetic information; located in nucleus
- Gene = segment of DNA that codes for a specific protein/trait
- Chromosome — humans have 46 chromosomes (23 pairs)
- XX = female; XY = male
Previous Year TNPSC Questions (Pattern)
1. Q: Powerhouse of the cell → Mitochondria 2. Q: Photosynthesis takes place in → Chloroplasts 3. Q: Functional unit of the kidney → Nephron 4. Q: Number of bones in adult human body → 206 5. Q: Universal blood donor → O negative 6. Q: Father of Genetics → Gregor Mendel 7. Q: Which organelle is called the suicide bag? → Lysosome 8. Q: Smallest bone in human body → Stapes
Frequently Asked Questions
The cell is the basic structural and functional unit of all living organisms. Robert Hooke discovered the cell in 1665 while examining cork under a microscope.