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. 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
- Cell wall is present in plant cells (cellulose), absent in animal cells. Both have cell membrane.
- Mitochondria are called the powerhouse of the cell because they produce ATP (energy currency).
- 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.
- Largest organ in the human body is skin (by area). Largest internal organ is liver.
- Blood pH is slightly alkaline, around 7.4. Haemoglobin in RBCs carries oxygen.
- Photosynthesis occurs in chloroplasts, mainly in leaf cells. Stomata (tiny pores) allow gas exchange.
- Vitamins A, D, E, K are fat-soluble (stored in body). Vitamins B-complex and C are water-soluble (not stored, need regular intake).
- Malaria is caused by Plasmodium parasite, transmitted by female Anopheles mosquito. Dengue is caused by a virus, transmitted by Aedes mosquito.
- Tuberculosis (TB) is a bacterial disease affecting lungs, caused by Mycobacterium tuberculosis. It is airborne.
- Diabetes mellitus results from insufficient insulin production (Type 1) or insulin resistance (Type 2), leading to high blood sugar.
- Transpiration is loss of water vapour from plant leaves, which helps in water absorption from roots and cooling.
- 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⁺.
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.