CEnT-S biology
Biology is the third section: ten questions in twenty minutes, worth ten of the fifty-five marks. It is the section that rewards recall most directly. Where chemistry asks you to work something out, biology usually asks whether you know it, and the questions turn on matching a structure to what it does.
What the section covers
Biological molecules
The four classes of macromolecule and what distinguishes them. Lipids are the odd one out, since triglycerides are not polymers of a repeating monomer.
Cell structure
The differences between prokaryotic and eukaryotic cells, the organelles and their functions, and the features specific to plant cells. The distinction that matters is the absence of a true nucleus in prokaryotes: ribosomes, a plasma membrane and DNA are common to both, and a cell wall is shared with plants and fungi.
The cell cycle
Interphase, mitosis and meiosis. DNA is replicated in S phase, during interphase, not at the point where chromosomes first become visible. Meiosis produces four haploid cells through two divisions with no replication in between.
Genetics
Mendelian inheritance, dominant and recessive alleles, and reading a Punnett square. A cross between two heterozygotes gives one quarter showing the recessive phenotype and three quarters the dominant, and the two figures are easy to swap.
Photosynthesis and energy
The light-dependent and light-independent reactions, and the flow of energy through an ecosystem. Roughly a tenth of the energy at one trophic level reaches the next, so reaching secondary consumers means applying that transfer twice.
Ecology
Food chains and trophic levels, and the biotic interactions: mutualism, commensalism, competition, predation and parasitism. A parasite depends on its host staying alive, which is what separates it from a predator.
Human physiology
Tissues and the major organ systems. Arteries carry blood away from the heart; the pulmonary artery does so while carrying deoxygenated blood, which is why direction of flow rather than oxygen content is the reliable criterion.
What the section does not ask
There is very little calculation. Mendelian ratios and energy transfer between trophic levels are the two places arithmetic appears, and neither goes beyond simple fractions and powers of ten.
That makes biology the section where two minutes a question is most comfortable, and the one where a candidate short of time in an earlier section cannot make it up, because there is nothing to speed through.
Where marks are lost
Confident misconceptions. The oxygen released in photosynthesis comes from water, not from carbon dioxide, though carbon dioxide contains oxygen and is the more natural guess. Isotope labelling settled that question decades ago, and it appears as a distractor precisely because the wrong answer is so reasonable.
Reversing a proportion. Three quarters and one quarter both come out of the same Punnett square, and the question specifies which phenotype it wants.
Applying a transfer once instead of twice. Secondary consumers are two steps from the producers, so a single application of the ten per cent rule gives the figure for primary consumers.
Naming a related structure. The rough endoplasmic reticulum synthesises secretory proteins and the Golgi apparatus packages them, and a question about packaging has both on the page.
Practise the section
Ten original biology questions
Under the real twenty-minute limit, with every answer explained.
Start practice →