Biology
The Biology domain of the ORELA Biology (NT316) exam assesses how well you connect molecular, cellular, organismal, and ecological ideas rather than recall isolated terms. Expect questions that ask you to interpret data, predict outcomes, and justify conclusions using biological mechanisms. Questions often combine a short scenario with a graph, table, or experimental setup, so practice extracting variables, controls, and conclusions.
Core rules and concepts
- Scientific inquiry: controlled experiments test one variable; correlation alone does not establish causation; sample size and replication affect confidence.
- Cell biology: membranes are selectively permeable; enzymes lower activation energy and are sensitive to pH, temperature, and substrate concentration; ATP links exergonic and endergonic reactions.
- Genetics: DNA → RNA → protein; meiosis creates genetic variation through crossing over and independent assortment; Mendelian ratios are predictions, not fixed outcomes in small samples.
- Evolution: natural selection acts on phenotypic variation; Hardy–Weinberg equilibrium describes allele frequencies only when mutation, migration, selection, and drift are absent and mating is random.
- Ecology: energy flows and matter cycles; trophic efficiency is roughly 10% between levels; population growth can be exponential or density-dependent.
- Homeostasis: feedback loops maintain internal stability; negative feedback reverses a change, while positive feedback amplifies it.
Worked example
In a population at Hardy–Weinberg equilibrium, 16% show the recessive phenotype. What fraction are carriers? q² = 0.16, so q = 0.4 and p = 0.6. Carrier frequency is 2pq = 2(0.6)(0.4) = 0.48, or 48%. The reasoning matters: 16% is the recessive genotype frequency, not q; carriers are heterozygous and therefore 2pq. This calculation assumes no selection, migration, mutation, or drift and random mating; if the scenario violates those assumptions, the estimate is not valid.
Traps that cost marks
- Treating q² as q, or reporting the recessive phenotype frequency as the allele frequency.
- Applying Hardy–Weinberg when selection, drift, or nonrandom mating is described.
- Confusing mitosis (growth/repair) with meiosis (gametes/variation).
- Ignoring experimental controls or inferring causation from observational data.
- Mixing energy flow (one-way) with matter cycling (recycled).
- Assuming all mutations are harmful or that evolution always produces perfect adaptation.
- Confusing species richness with species evenness.