Life Sciences: Molecules to Populations
Scope
The Life Sciences paper spans biochemistry, molecular biology, genetics, cell and developmental biology, immunology, microbiology, plant physiology, ecology, evolution and biostatistics, so candidates must switch scales quickly.
Core molecular facts: semiconservative replication, DNA polymerase directionality (5′→3′ synthesis, leading versus lagging strands and Okazaki fragments), transcription and processing, the genetic code and its degeneracy, translation, and regulation via operons, promoters and epigenetics.
Biochemistry means enzyme kinetics (Michaelis–Menten, Lineweaver–Burk plots, inhibition types), bioenergetics and electron transport, glycolysis and the TCA cycle, and metabolic regulation.
Genetics and cell biology cover Mendelian and non-Mendelian inheritance, linkage and recombination, pedigree analysis, the cell cycle and checkpoints, apoptosis, signal transduction and the cytoskeleton.
Ecology and evolution test population growth models, Hardy–Weinberg equilibrium, species interactions, natural selection, genetic drift and speciation.
Traps
Treating Kₘ as a rate rather than a substrate concentration; forgetting that competitive inhibition raises apparent Kₘ but leaves Vₘₐₓ unchanged, while non-competitive inhibition lowers Vₘₐₓ; reversing 5′ and 3′ ends; counting chromatids as chromosomes; interpreting a non-significant p-value as proof of the null hypothesis; and confusing type I with type II error.
Worked example
If a recessive phenotype appears at frequency 0.04 in a Hardy–Weinberg population, then q² = 0.04, so q = 0.2 and p = 0.8; heterozygote frequency is 2pq = 0.32. Rule of thumb: always start from q² for the recessive trait, never from the phenotype of the dominant class.