1. Cell Biology & Enzymes
- Plant vs Animal Cell: Plant cells contain cell walls, large central vacuoles, and chloroplasts; animal cells lack these structures.
- Enzyme Action: Enzymes are biological catalysts (proteins) that speed up chemical reactions without being consumed. Know how temperature and pH affect enzyme activity (denaturation at high temperatures).
2. Human Physiology & Homeostasis
- Excretion & Kidneys: Structure of the nephron (Bowman's capsule, glomerulus, loop of Henle). Ultrafiltration and selective reabsorption.
- Hormonal Control: Insulin lowers blood glucose; glucagon raises blood glucose. Both are produced in the pancreas.
3. Genetics & Monohybrid Crosses
Punnett Square Example (Genetics):
Scenario: Heterozygous tall plant (Tt) crossed with short plant (tt).
Genotypic Ratio: 50% Tt, 50% tt.
Phenotypic Ratio: 50% Tall, 50% Short (1 : 1).
Scenario: Heterozygous tall plant (Tt) crossed with short plant (tt).
Genotypic Ratio: 50% Tt, 50% tt.
Phenotypic Ratio: 50% Tall, 50% Short (1 : 1).
4. Ecology & Environmental Conservation
Understand food chains, food webs, pyramids of numbers vs pyramids of biomass, and the carbon/nitrogen cycles.
5. Paper 3 Practical Exam Advice
Practice testing for starch (Iodine solution turns blue-black), reducing sugars (Benedict's solution turns brick-red upon heating), and proteins (Biuret test turns purple/violet).