Biology
Core concepts
Expect cell biology (organelles and their functions), transport across membranes, photosynthesis and respiration, genetics (Mendel, DNA, dominance), human body systems (circulatory, respiratory, digestive, nervous), and basic ecology (food chains, energy flow, ecosystems). Classification of living things and the characteristics of life also appear.
Common traps
- Mitochondria vs. chloroplasts: energy release vs. energy capture.
- Photosynthesis and respiration are not opposites in location - both occur in plants.
- Dominant vs. recessive ratios: a 3:1 phenotype ratio comes from a 1:2:1 genotype ratio in a monohybrid cross.
- Energy flow in food chains decreases at each level; only about 10% transfers.
- Osmosis direction: water moves toward higher solute concentration.
Worked example
Cross two heterozygotes Aa × Aa. Genotypes: 1 AA : 2 Aa : 1 aa; phenotypes 3 dominant : 1 recessive. Use a Punnett square to avoid errors.
Rule of thumb
When asked "where does X happen?", name the organelle or organ and one function; examiners award marks for the function, not just the name.