Zoology

Zoology — Study Notes for TNPSC Group IV

Overview

Zoology forms a crucial part of the General Science section in TNPSC Group IV, tested at SSLC standard. Questions typically focus on human anatomy and physiology, classification of animals, nutrition, and common diseases. This is a high-scoring area because concepts are straightforward and factual—memorisation combined with basic understanding yields easy marks.

The examiners favour questions on human body systems (especially circulatory, digestive, and nervous systems), vitamins and deficiency diseases, and communicable diseases. Mastering the key facts here gives you reliable marks with minimal calculation effort.

Students must focus on organ functions, disease-causative agents, and nutritional deficiencies. Visual memory helps—picture the heart's chambers, digestive tract sequence, or blood cell types as you study.

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Key Concepts

• Animal Kingdom Classification: Animals are classified into Invertebrates (without backbone—insects, worms, molluscs) and Vertebrates (with backbone—fish, amphibians, reptiles, birds, mammals). Humans belong to class Mammalia.
• Cell as Basic Unit: All living organisms are made of cells. Animal cells lack cell walls and chloroplasts (unlike plant cells). Key organelles include nucleus, mitochondria, ribosomes, and cell membrane.
• Human Organ Systems: The body has 11 major systems—digestive, circulatory, respiratory, nervous, excretory, skeletal, muscular, endocrine, reproductive, lymphatic, and integumentary (skin).
• Blood Composition: Blood contains plasma (55%) and formed elements (45%)—RBCs (carry oxygen), WBCs (fight infection), and platelets (clotting). Human blood groups are A, B, AB, and O based on antigens.
• Heart Function: The heart is a four-chambered muscular pump. Blood flow sequence: Body → Right Atrium → Right Ventricle → Lungs → Left Atrium → Left Ventricle → Body.
• Digestion Process: Mechanical and chemical breakdown of food. Digestion begins in mouth (saliva contains ptyalin enzyme), continues in stomach (pepsin, HCl), and completes in small intestine (bile, pancreatic juice).
• Nervous System Organisation: Central Nervous System (brain + spinal cord) and Peripheral Nervous System (nerves). Neurons are the functional units transmitting electrical impulses.
• Nutrition and Deficiency: Balanced diet includes carbohydrates, proteins, fats, vitamins, minerals, and water. Deficiency of specific nutrients causes specific diseases.

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Formulas / Key Facts

Human Body Quick Facts

Vitamins and Deficiency Diseases

Important Diseases and Causative Agents

Blood Facts

• Total blood volume in adult: ~5–6 litres
• Normal RBC count: 4.5–5.5 million/mm³
• Normal WBC count: 4,000–11,000/mm³
• Universal donor: O negative
• Universal recipient: AB positive
• Haemoglobin carries oxygen; iron is essential for its formation

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Worked Examples

Example 1: Vitamin Deficiency Question

Question: A child shows bow-shaped legs and weak bones. Which vitamin deficiency is responsible?

Solution:

• Step 1: Identify symptoms—bone deformities, weak bones in children
• Step 2: Recall vitamin functions—Vitamin D is essential for calcium absorption and bone formation
• Step 3: Deficiency of Vitamin D in children causes Rickets
• Answer: Vitamin D deficiency (Rickets)

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Example 2: Disease Vector Question

Question: Which mosquito spreads malaria?

Solution:

• Step 1: Malaria is caused by Plasmodium parasite
• Step 2: Vector (carrier) identification—Anopheles mosquito (female) transmits malaria
• Step 3: Distinguish from Aedes (dengue, chikungunya) and Culex (filariasis)
• Answer: Anopheles mosquito

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Example 3: Blood Circulation Path

Question: Trace the path of blood from lungs to body tissues.

Solution:

• Step 1: Oxygenated blood from lungs enters Left Atrium via pulmonary veins
• Step 2: Left Atrium contracts, blood enters Left Ventricle
• Step 3: Left Ventricle pumps blood through Aorta to body tissues
• Answer: Lungs → Pulmonary veins → Left Atrium → Left Ventricle → Aorta → Body

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Common Mistakes

• Confusing Rickets and Osteomalacia → Both are Vitamin D deficiency, but Rickets occurs in children (soft bones, bow legs) while Osteomalacia occurs in adults (bone pain, muscle weakness).
• Mixing up mosquito vectors → Anopheles = Malaria; Aedes = Dengue/Chikungunya; Culex = Filariasis. Remember: "A for Anopheles, A for malaria parasite (starts with 'P' but Anopheles carries it)."
• Confusing arteries and veins → Arteries carry blood away from heart (usually oxygenated except pulmonary artery); Veins carry blood towards heart (usually deoxygenated except pulmonary vein).
• Forgetting that small intestine is the main absorption site → Students often say stomach. Stomach mainly does digestion (protein breakdown); small intestine (especially ileum) absorbs nutrients through villi.
• Universal donor vs recipient confusion → O is donor ("O gives to all"), AB is recipient ("AB receives from all"). Memory trick: O = "Offer to all"; AB = "Accept from all, Both antigens."

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Quick Reference

• Largest organ: Skin; Largest gland: Liver; Largest bone: Femur (thigh)
• Smallest bone: Stapes (ear); Hardest substance in body: Tooth enamel
• RBC lifespan: 120 days; RBCs formed in: Bone marrow; Destroyed in: Spleen
• Normal body temperature: 37°C or 98.6°F
• Vitamin C deficiency = Scurvy (bleeding gums); Vitamin A deficiency = Night blindness
• Brain parts: Cerebrum (thinking), Cerebellum (balance), Medulla (involuntary actions)
• Communicable diseases spread by contact, air, water, or vectors; Non-communicable diseases (diabetes, cancer) do not spread person to person