Biology: Cells, Genetics, Physiology, and Ecology
Biology in the Chiba Entrance Science exam tests cell structure and function, genetics, transport and physiology, ecology, and evidence for evolution. Questions often combine a diagram-free description with a prediction, so link each structure to its function and each cross to a probability.
Core rules
- The central dogma runs DNA → RNA → protein; transcription occurs in the nucleus in eukaryotes, and translation occurs on ribosomes.
- Diffusion moves substances down a concentration gradient; osmosis is water movement across a selectively permeable membrane.
- In Mendelian genetics, alleles segregate during meiosis, and independent assortment applies to genes on different chromosomes.
- Photosynthesis stores energy in glucose using light, CO2, and water; aerobic respiration releases energy from glucose using oxygen.
- In ecology, energy flows through trophic levels while matter cycles; only a fraction of energy passes to the next level.
Worked example
Two heterozygous pea plants (Tt × Tt) are crossed, where T is tall and t is short. Construct the gametes: each parent produces T and t with equal probability. The Punnett square gives TT, Tt, Tt, and tt in a 1:2:1 ratio. The probability of a short offspring, genotype tt, is 1/4. If 400 offspring are expected, the predicted number of short plants is 400 × 1/4 = 100. The tall phenotype would be expected in 300 offspring because TT and Tt both show the dominant trait.
Traps that cost marks
- Confusing genotype with phenotype, especially for carriers.
- Using the product rule when genes are linked and do not assort independently.
- Confusing mitosis with meiosis; meiosis halves chromosome number and creates variation.
- Reversing the direction of osmosis or diffusion.
- Assuming energy is recycled in an ecosystem when matter, not energy, cycles.