Zoology
Study Notes for TNPSC Group II/IIA Prelims
Overview
Zoology covers the scientific study of animals — their classification, evolution, genetics, and physiology. For TNPSC Group II, this topic appears under General Science and tests your understanding of fundamental biological concepts rather than deep specialisation.
Questions typically focus on animal kingdom classification (phyla and their examples), basic genetics (Mendelian laws, chromosomes, DNA), evolutionary concepts (Darwin, natural selection), and human physiology (organ systems, blood, digestion). The examiners favour factual recall — knowing which animal belongs to which phylum, understanding dominant-recessive inheritance, or identifying functions of human organs.
Mastering this topic requires memorising classification tables, understanding genetic ratios, and knowing key physiological facts about the human body. Since many concepts overlap with Health and Nutrition topics, a solid foundation here helps across multiple question types.
Key Concepts
- Five Kingdom Classification: Animals belong to Kingdom Animalia, characterised by being multicellular, eukaryotic, heterotrophic organisms lacking cell walls.
- Phylum hierarchy: Animals are classified from Kingdom → Phylum → Class → Order → Family → Genus → Species. "King Philip Came Over For Good Soup" is a useful mnemonic.
- Vertebrates vs Invertebrates: Vertebrates possess a backbone (fish, amphibians, reptiles, birds, mammals); invertebrates lack one (insects, molluscs, worms). About 95% of animal species are invertebrates.
- Evolution through Natural Selection: Darwin's theory states that organisms with favourable variations survive and reproduce more successfully, passing traits to offspring over generations.
- Mendelian Genetics: Traits are inherited through discrete units (genes). Dominant alleles mask recessive ones. Monohybrid cross ratio is 3:1; dihybrid cross ratio is 9:3:3:1.
- DNA as genetic material: DNA (deoxyribonucleic acid) carries hereditary information. It has a double helix structure discovered by Watson and Crick (1953).
- Homeostasis: The human body maintains internal stability (temperature, pH, glucose levels) despite external changes — a fundamental physiological principle.
- Organ systems work together: Digestion provides nutrients, circulation transports them, respiration supplies oxygen, excretion removes wastes — all systems are interdependent.
Formulas / Key Facts
Animal Classification — Major Phyla
| Phylum | Key Feature | Examples |
|---|---|---|
| Porifera | Pore-bearing, no true tissues | Sponges |
| Cnidaria | Stinging cells (cnidocytes) | Jellyfish, coral, Hydra |
| Platyhelminthes | Flatworms, no body cavity | Tapeworm, Planaria |
| Nematoda | Roundworms, pseudocoelom | Ascaris, Hookworm |
| Annelida | Segmented worms | Earthworm, Leech |
| Arthropoda | Jointed legs, exoskeleton | Insects, crabs, spiders |
| Mollusca | Soft body, often with shell | Snail, octopus, oyster |
| Echinodermata | Spiny skin, water vascular system | Starfish, sea urchin |
| Chordata | Notochord present | Fish, birds, humans |
Genetics Facts
- Human chromosome number: 46 (23 pairs)
- Sex chromosomes: XX (female), XY (male)
- Genes are located on chromosomes
- Mutation: Sudden heritable change in DNA
Human Physiology Quick Facts
- Normal body temperature: 37°C (98.6°F)
- Normal heart rate: 72 beats per minute
- Blood groups: A, B, AB, O (based on antigens)
- Universal donor: O negative; Universal recipient: AB positive
- RBC lifespan: 120 days
- Largest organ: Skin; Largest internal organ: Liver
- Smallest bone: Stapes (ear); Largest bone: Femur (thigh)
Worked Examples
Example 1: Mendelian Inheritance
Question: In pea plants, tall (T) is dominant over dwarf (t). Cross a heterozygous tall plant (Tt) with a dwarf plant (tt). What is the phenotypic ratio of offspring?
Solution:
- Parent genotypes: Tt × tt
- Possible gametes: T, t from first parent; t, t from second
- Punnett square:
- Tt (tall), Tt (tall), tt (dwarf), tt (dwarf)
- Phenotypic ratio: 2 tall : 2 dwarf = 1:1
Example 2: Classification
Question: Which phylum does the housefly belong to? State one characteristic.
Solution:
- Housefly belongs to Phylum Arthropoda
- Characteristic: Jointed appendages and chitinous exoskeleton
- Additional: Insects have 3 body segments and 6 legs
Example 3: Human Physiology
Question: Which blood cells are responsible for immunity, and where are they produced?
Solution:
- White Blood Cells (WBCs/Leucocytes) provide immunity
- Produced in bone marrow (and mature in thymus for T-lymphocytes)
- Types include lymphocytes, neutrophils, monocytes
Common Mistakes
- Confusing arthropods with annelids → Arthropods have jointed legs and exoskeleton; annelids are segmented worms without jointed appendages. Remember: "Arthro" means joint.
- Mixing up genotype and phenotype → Genotype is the genetic makeup (Tt, TT); phenotype is the observable trait (tall, dwarf). The phenotype is what you see.
- Assuming all chordates are vertebrates → Not true. Amphioxus (Lancelet) is a chordate but not a vertebrate. Vertebrates are a subphylum within Chordata.
- Forgetting that O blood group has no antigens → Students often confuse antigens and antibodies. O group has no A or B antigens on RBCs but has both anti-A and anti-B antibodies in plasma.
- Thinking evolution means "survival of the strongest" → Darwin's theory is survival of the fittest, meaning best adapted to the environment — not necessarily physically strongest.
Quick Reference
- Arthropoda = largest phylum; includes insects, spiders, crabs — jointed legs + exoskeleton
- Monohybrid ratio 3:1; Dihybrid ratio 9:3:3:1 (F2 generation)
- Humans: 46 chromosomes, sex determined by father's sperm (X or Y)
- Blood group inheritance: A and B are codominant; O is recessive
- Haemoglobin in RBCs carries oxygen; iron deficiency causes anaemia
- Darwin's book: On the Origin of Species (1859) — natural selection theory