Biology: Cells, Genetics, Physiology and Ecology
Core concepts to master
Cell structure and organelle function, the differences between plant and animal cells, and the processes of diffusion, osmosis and active transport. Know photosynthesis and respiration as complementary processes with their equations and sites. Genetics requires Mendelian ratios, Punnett squares, the difference between genotype and phenotype, and the structure of DNA. Human physiology topics include circulation, respiration, digestion, excretion and the nervous system. Ecology covers food chains, energy flow, nutrient cycles and population dynamics.
Traps examiners set
- Confusing osmosis (water movement) with diffusion of solutes.
- Mixing up mitosis (identical daughter cells, growth) with meiosis (gametes, halving of chromosome number).
- Forgetting that photosynthesis consumes carbon dioxide while respiration releases it.
- Assuming dominant alleles are always the most common in a population.
- Ignoring the direction of blood flow or the site of a process when labelling.
Rule of thumb
When a genetics question gives parental phenotypes, convert to genotypes first, then draw the Punnett square; state the ratio as genotype and phenotype separately.
Worked example
Cross two heterozygous tall pea plants (Tt × Tt).
Offspring genotypes: TT, Tt, Tt, tt - a 1 : 2 : 1 ratio. Phenotypes: three tall to one short, so 75% tall. The recessive short plant appears only when both parents contribute t.
Practice habit
Learn processes as input–output pairs (what goes in, what comes out, where it happens); this answers most descriptive questions quickly.