Biology Content Domain
The ILTS Science: Biology (239) biology content domain samples the breadth of introductory college biology: molecular and cellular biology, genetics and inheritance, evolution and diversity, organismal physiology, and ecology. Because the state does not publish a subdomain breakdown, build fluency across those connected scales rather than memorizing isolated facts; questions often ask you to predict an outcome from a mechanism.
Core rules and concepts
- Structure determines function from macromolecules upward: phospholipid amphipathy creates bilayers, protein tertiary structure creates active sites, and surface-area-to-volume limits constrain cell size.
- Energy flows through coupled redox reactions. Photosynthesis oxidizes water and reduces CO2; aerobic respiration oxidizes glucose and reduces O2. ATP yield depends on proton-motive force, not direct substrate counting alone.
- Information flows DNA to RNA to protein, but regulation is the rule: operons, transcription factors, and epigenetic marks determine which proteins appear.
- Inheritance follows probability, not destiny. Segregation and independent assortment generate gamete frequencies; linkage and recombination modify expected ratios.
- Evolution is a change in allele frequencies across generations. Selection, drift, mutation, and migration act on variation; Hardy-Weinberg is a null model.
- Physiology maintains set points through negative feedback; positive feedback drives rapid, self-amplifying events such as action-potential depolarization.
- Ecology links population growth, community interactions, and nutrient cycling; energy is lost at each trophic transfer.
Worked example
In a population at Hardy-Weinberg equilibrium, an autosomal recessive disorder affects 1 in 10,000 newborns. What fraction are carriers? Affected genotype frequency equals q squared = 0.0001, so q = 0.01 and p = 0.99. Carrier frequency is 2pq = 2(0.99)(0.01) = 0.0198, about 1 in 50. The reasoning matters: 0.0001 is not q, and 0.0198 is not the disease frequency.
Traps that cost marks
Mixing up q and q squared is the classic Hardy-Weinberg error. Also watch for treating "fittest" as strongest rather than best reproductively suited to a given environment, confusing a testcross with a backcross, and treating correlation as causation in experimental-design questions. In cell transport, do not assume ATP is required for all movement: diffusion and facilitated diffusion are passive. In respiration calculations, track carbons and electron carriers, not just ATP totals.