Biology: Cells, Systems, Genetics and Ecology
What the paper tests
Questions cover cell structure and division, the major organ systems (digestive, circulatory, respiratory, excretory, nervous), plant biology including photosynthesis, genetics and inheritance, and ecology with food chains and ecosystems.
Concepts to master
Plant cells have a cell wall, chloroplasts and a large vacuole; animal cells do not. Mitochondria release energy through respiration; chloroplasts carry out photosynthesis, which uses carbon dioxide and water with light to make glucose and oxygen. Mitosis produces identical body cells; meiosis produces gametes with half the chromosome number. In inheritance, genes occur in pairs, dominant alleles mask recessive ones, and a cross of two heterozygotes gives a 3:1 ratio. The blood circulates in a double circuit, and arteries carry blood away from the heart. In ecology, energy decreases at each trophic level, so food chains are short, and decomposers recycle nutrients.
Traps
Saying plants do not respire (they do, continuously); confusing arteries and veins by oxygen content rather than direction; mixing mitosis and meiosis products; and forgetting that energy, not biomass alone, is lost between trophic levels.
Rule of thumb
For genetics, draw a simple grid of parental alleles and read off genotypes and ratios. For system questions, trace the path of the substance step by step.
Worked example
Cross two heterozygous tall pea plants (Tt x Tt). Offspring genotypes are TT, Tt, Tt, tt, giving three tall to one short, a 3:1 phenotypic ratio.