Biology / Botany / Zoology
Biology combines botany and zoology: cell biology, genetics, plant physiology, human physiology, reproduction, ecology, evolution and biotechnology. Answers are marked for correct terminology, labelled diagrams and causal explanation, not just names.
Core rules and concepts
- Cell biology: distinguish mitosis from meiosis by purpose, chromosome behaviour and product number.
- Genetics: use Punnett squares; separate genotype ratios from phenotype ratios; a test cross reveals an unknown genotype.
- Plant physiology: link photosynthesis and respiration to their sites, reactants, products and limiting factors.
- Human physiology: trace blood, filtrate or nerve impulses in the correct order.
- Ecology: energy decreases along a food chain; population growth may be exponential or logistic.
Worked example: monohybrid cross
Cross Tt × Tt for tall (T) dominant over dwarf (t). Gametes are T and t on each side. Offspring genotypes: TT : Tt : tt = 1 : 2 : 1. Phenotypes: tall : dwarf = 3 : 1. Reasoning: Tt individuals are tall because T is dominant, while only tt is dwarf. A test cross of Tt with tt would give 1 tall : 1 dwarf, confirming the heterozygote.
Traps that cost marks
- Mixing genotype and phenotype ratios.
- Drawing a diagram without labels or a caption.
- Describing 'adaptation' as a conscious choice rather than a selected trait.
- Confusing meiosis I and meiosis II events.
- Giving a name where the question asks for a function or sequence.