Biology
Biology on the OAT tests molecular and cellular biology, genetics, microbiology, anatomy and physiology, evolution, and ecology. Questions reward mechanism and structure-function reasoning rather than isolated vocabulary.
Core rules
- DNA stores information; transcription makes RNA, and translation at ribosomes makes protein. A coding mutation may change protein sequence, while a silent mutation does not.
- Prokaryotes lack membrane-bound organelles; eukaryotes compartmentalize processes. Mitochondria and chloroplasts have double membranes and their own DNA.
- Mendelian ratios follow segregation and independent assortment. For independent events, multiply probabilities.
- Physiology emphasizes homeostasis, negative feedback, gradients, and exchange surfaces. Neurons use electrochemical gradients; kidneys use filtration, reabsorption, and secretion.
- Evolution is change in allele frequency; natural selection acts on phenotypes. Ecology links energy flow, nutrient cycling, population growth, and species interactions.
Worked example
Cross AaBb × AaBb with independently assorting genes. The probability of A_ is 3/4, and the probability of bb is 1/4. Product rule: 3/4 × 1/4 = 3/16.
Traps
Do not confuse transcription with translation; dominant does not mean more common; negative feedback opposes change; osmosis is water movement down its own potential gradient; correlation is not causation in ecology.