Biology - Mie Entrance Science
The Biology section spans cell structure and transport, enzymes, genetics, metabolism, homeostasis, and ecology. Questions often ask you to interpret described experiments and predict ratios or feedback outcomes, so link each fact to a mechanism.
Core rules
- Membranes: small nonpolar molecules diffuse; water moves by osmosis; ions and polar molecules need channels or carriers. Active transport uses ATP and can move against a gradient.
- Enzymes: lower activation energy, are not consumed, and are sensitive to pH and temperature; competitive inhibitors raise Km but not Vmax.
- Genetics: alleles segregate in meiosis; independent assortment applies to unlinked genes. A dihybrid AaBb × AaBb cross gives 9:3:3:1 phenotypes with complete dominance.
- Metabolism: photosynthesis stores energy in glucose; aerobic respiration yields more ATP than anaerobic pathways.
- Homeostasis: negative feedback reverses a deviation; positive feedback amplifies it, as in childbirth.
- Ecology: about 10% of energy transfers between trophic levels; pyramids of energy are always upright.
Worked example
A recessive genetic disease affects 1 in 2500 people in a population at Hardy–Weinberg equilibrium. Find the carrier frequency. q² = 1/2500, so q = 1/50 = 0.02 and p = 0.98. Carriers are 2pq = 2(0.98)(0.02) = 0.0392, about 3.9% - roughly 1 in 26 people.
Traps
- Confusing genotype with phenotype, especially for carriers of a recessive allele.
- Assuming dominant traits are always more common in a population.
- Reversing mitosis and meiosis: meiosis produces haploid gametes with recombination.
- Saying energy is “recycled” in ecosystems; matter cycles, while energy flows and is lost as heat.
- Treating correlation in an experiment as causation without a controlled comparison.