Biology — SSC CGL Study Notes

Overview

Biology questions in SSC CGL Tier 1 test your understanding of basic life science concepts that affect everyday life. Expect 4–6 questions from this section within the General Science portion. The exam focuses on practical, applied knowledge rather than detailed academic theory.

The four pillars are: **cell structure** (the building block), **human anatomy and physiology** (how our body works), **plant biology** (structure, nutrition, reproduction), and **diseases** (causes, symptoms, prevention). Most questions are direct factual recall — knowing which organelle does what, which vitamin prevents which disease, or which part of the plant performs photosynthesis. Avoid going too deep into biochemical pathways; stick to the "what" and "why" that matter for a generalist exam.

Success here comes from systematic coverage of common topics: digestive system, circulatory system, respiratory system, vitamins and deficiencies, photosynthesis, plant hormones, types of diseases (bacterial, viral, fungal), and basic cell organelles. A strong grasp of these fundamentals will cover 90% of exam questions.

Key Concepts

• **Cell** — the structural and functional unit of life. Prokaryotic cells (no nucleus, bacteria) vs eukaryotic cells (nucleus present, animals and plants).
• **Cell organelles** — each has a specific job: nucleus (genetic control), mitochondria (energy production), ribosomes (protein synthesis), chloroplasts (photosynthesis in plants), endoplasmic reticulum (transport), Golgi apparatus (packaging and secretion).
• **Human body systems** are interdependent: digestive (breaks down food), circulatory (transports nutrients and oxygen), respiratory (gas exchange), excretory (removes waste), nervous (coordination), endocrine (hormones).
• **Photosynthesis** in plants converts light energy into chemical energy (glucose) using chlorophyll, releasing oxygen as a by-product. Formula: Carbon dioxide + Water + Sunlight → Glucose + Oxygen.
• **Vitamins and minerals** are essential micronutrients. Deficiency diseases are high-yield: Vitamin A (night blindness), Vitamin C (scurvy), Vitamin D (rickets), Iodine (goitre), Iron (anaemia).
• **Diseases** fall into categories: infectious (caused by pathogens — bacteria, viruses, fungi, protozoa) and non-infectious (genetic, nutritional, lifestyle-related). Know mode of transmission and prevention.
• **Blood groups** (A, B, AB, O) and Rh factor are determined by antigens on red blood cells. Universal donor is O negative; universal recipient is AB positive.
• **Hormones** regulate body functions: insulin (blood sugar), adrenaline (fight-or-flight), thyroxine (metabolism), growth hormone (growth), testosterone and estrogen (reproductive functions).

Key Facts

1. **Cell wall** is present in plant cells (cellulose), absent in animal cells. Both have cell membrane. 2. **Mitochondria** are called the powerhouse of the cell because they produce ATP (energy currency). 3. **Human heart** has four chambers: two atria (upper) and two ventricles (lower). Right side pumps deoxygenated blood to lungs; left side pumps oxygenated blood to body. 4. **Largest organ** in the human body is skin (by area). Largest internal organ is liver. 5. **Blood pH** is slightly alkaline, around 7.4. Haemoglobin in RBCs carries oxygen. 6. **Photosynthesis occurs in chloroplasts**, mainly in leaf cells. Stomata (tiny pores) allow gas exchange. 7. **Vitamins A, D, E, K** are fat-soluble (stored in body). **Vitamins B-complex and C** are water-soluble (not stored, need regular intake). 8. **Malaria** is caused by Plasmodium parasite, transmitted by female Anopheles mosquito. **Dengue** is caused by a virus, transmitted by Aedes mosquito. 9. **Tuberculosis (TB)** is a bacterial disease affecting lungs, caused by Mycobacterium tuberculosis. It is airborne. 10. **Diabetes mellitus** results from insufficient insulin production (Type 1) or insulin resistance (Type 2), leading to high blood sugar. 11. **Transpiration** is loss of water vapour from plant leaves, which helps in water absorption from roots and cooling. 12. **Xylem** transports water and minerals from roots to leaves. **Phloem** transports food (sugars) from leaves to other parts.

Worked Examples

**Example 1: Cell Organelle Function** *Question:* Which organelle is responsible for protein synthesis in a cell? *Solution:* Ribosomes are the sites of protein synthesis. They read mRNA and assemble amino acids into proteins. Ribosomes may be free-floating in cytoplasm or attached to the endoplasmic reticulum (forming rough ER). *Answer:* Ribosomes.

**Example 2: Vitamin Deficiency** *Question:* A child suffers from weak bones and delayed tooth development. Which vitamin deficiency is likely? *Solution:* Weak bones and delayed dental development indicate calcium-related issues. Vitamin D helps in calcium absorption. Deficiency of Vitamin D in children causes rickets (soft, weak bones). *Answer:* Vitamin D.

**Example 3: Disease Transmission** *Question:* Cholera spreads through which route? *Solution:* Cholera is caused by the bacterium *Vibrio cholerae*. It spreads via the fecal-oral route — contaminated water and food. It is not airborne or vector-borne. *Answer:* Contaminated water (waterborne disease).

**Example 4: Plant Tissue** *Question:* Which plant tissue is responsible for upward transport of water? *Solution:* Xylem tissue consists of vessels and tracheids that conduct water and dissolved minerals from roots to stems and leaves, moving upward via transpiration pull. *Answer:* Xylem.

Common Mistakes

• **Confusing cell wall with cell membrane** → Cell wall is rigid, only in plants/bacteria. Cell membrane is semi-permeable, present in all cells.
• **Thinking all vitamins are stored in the body** → Only A, D, E, K are fat-soluble and stored. B and C are water-soluble, excreted if excess.
• **Mixing up xylem and phloem** → Remember: Xylem = water up (X for eXtra care with water), Phloem = food flow (Ph for Phood).
• **Assuming all diseases are caused by bacteria** → Many diseases are viral (dengue, polio, AIDS), fungal (ringworm), or protozoal (malaria). Antibiotics work only on bacteria, not viruses.
• **Forgetting chloroplasts are only in plant cells** → Animal cells do not photosynthesize and lack chloroplasts. Mitochondria are in both plant and animal cells.

Quick Reference

• **Nucleus** — controls cell activities, contains DNA.
• **Mitochondria** — ATP production (cellular respiration).
• **Chloroplast** — photosynthesis in plants.
• **Haemoglobin** — oxygen carrier in blood, iron-containing protein.
• **Insulin** — hormone regulating blood sugar, produced by pancreas.
• **Photosynthesis formula** — CO₂ + H₂O + Light → C₆H₁₂O₆ + O₂.
• **Deficiency diseases** — Night blindness (Vit A), Scurvy (Vit C), Rickets (Vit D), Beriberi (Vit B₁), Goitre (Iodine), Anaemia (Iron).
• **Disease types** — Bacterial (TB, cholera), Viral (dengue, polio), Fungal (ringworm), Protozoal (malaria).
• **Heart chambers** — 2 atria + 2 ventricles = 4 chambers.
• **Blood groups** — A, B, AB, O; universal donor O⁻, universal recipient AB⁺.

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**Study Tip:** Make a two-column table — one for human body systems (with organs and functions), another for diseases (with causative agent and transmission mode). Revise this table weekly. Practice previous-year biology questions to identify repeat patterns.