Quick Summary
The Zoology section of The Living World focuses on animal diversity, species concepts, biodiversity, and the mechanisms that generate and maintain variety in the animal kingdom. Natural selection and evolution provide the unifying framework. Key vocabulary from this chapter is used throughout the zoology syllabus.
Biodiversity
Definition: The variety and variability of life on Earth at all levels — genes, species, and ecosystems.
Levels of Biodiversity
| Level | Definition | Measure |
|---|---|---|
| Genetic diversity | Variation in genes within a species | Number of alleles, heterozygosity |
| Species diversity | Variety of species in an area | Species richness, evenness |
| Ecosystem diversity | Variety of ecosystems in a region | Number and types of ecosystems |
India's biodiversity:
- One of 12 mega-biodiversity nations
- 8.1% of world's species on 2.4% of land area
- Two biodiversity hotspots: Western Ghats and Eastern Himalaya
Species Concept
Biological Species Concept (Mayr, 1942)
A species = group of naturally interbreeding populations that are reproductively isolated from other groups.
Limitations: Cannot apply to asexual organisms; fossils; ring species.
Morphological Species Concept
Species defined by shared morphological (physical) characters — practical for identification.
Phylogenetic Species Concept
Smallest group sharing a common ancestor with unique derived characters.
Taxonomic Hierarchy (Animal)
Kingdom → Phylum → Class → Order → Family → Genus → Species
| Taxon | Human | Tiger |
|---|---|---|
| Kingdom | Animalia | Animalia |
| Phylum | Chordata | Chordata |
| Class | Mammalia | Mammalia |
| Order | Primates | Carnivora |
| Family | Hominidae | Felidae |
| Genus | Homo | Panthera |
| Species | sapiens | tigris |
Zoological Nomenclature (ICZN)
- Binomial system — Genus + species (e.g., Panthera tigris, Apis mellifera)
- Names italicised in print, underlined when handwritten
- Genus: capital letter; species: lowercase
- Author's name may follow (not italicised): Homo sapiens Linnaeus
Priority rule: The oldest validly published name for a taxon is the correct one.
Natural Selection and Evolution
Charles Darwin (1859): On the Origin of Species
Key Points of Darwinism
1. Overproduction: More offspring produced than can survive 2. Variation: Individuals differ in heritable traits 3. Struggle for existence: Competition for limited resources 4. Survival of the fittest: Best-adapted individuals survive and reproduce 5. Evolution: Gradual change in species over generations
Types of Natural Selection
| Type | Effect on population | Example |
|---|---|---|
| Directional | Shifts mean towards one extreme | Antibiotic resistance in bacteria |
| Stabilising | Favours average, eliminates extremes | Human birth weight |
| Disruptive | Favours extremes, eliminates average | Beak size in finches |
Adaptation
Definition: Heritable characteristics that increase an organism's fitness in its environment.
| Type | Example |
|---|---|
| Morphological | Streamlined body in fish |
| Physiological | Camel's urea conservation |
| Behavioural | Bird migration |
Convergent evolution: Unrelated species develop similar adaptations (e.g., wings of birds and bats). Divergent evolution: Related species develop different adaptations (Darwin's finches).
Important Questions
One Mark
- Who proposed the biological species concept?
- What is the full form of ICZN?
- Name two biodiversity hotspots of India.
- Define natural selection in one sentence.
Short Answer (3 marks)
- Explain the three levels of biodiversity with examples.
- What is the biological species concept? State two limitations.
- Distinguish between convergent and divergent evolution with examples.
Long Answer (5 marks)
- Describe Darwin's theory of natural selection with its key postulates.
- Explain the taxonomic hierarchy for the tiger (Panthera tigris) from Kingdom to Species.
Common Mistakes
- Biodiversity hotspots in India: Western Ghats AND Eastern Himalaya — students often name only one.
- Biological species concept excludes asexual organisms (bacteria, amoeba) — a common exam question.
- Survival of the fittest: "fittest" means best adapted to the environment, NOT strongest or largest.
- Convergent vs divergent: convergent = unrelated → similar; divergent = related → different (e.g., Darwin's finches).
Board Exam Tips
- Darwin's theory postulates (5 points) is a standard 5-mark question.
- Taxonomic hierarchy with human/tiger example appears as a 3-mark question.
- Biodiversity levels with examples is a reliable 3-mark question.
- NEET: Species concept, biodiversity hotspots, and types of natural selection appear regularly.