Biology
Biology in the FMRDA Medicine Admission exam assesses cell structure and transport, enzyme action, Mendelian and molecular genetics, human physiology, and basic ecology. Questions often combine recall with interpretation of experimental or pedigree data, so be ready to explain mechanisms rather than just label diagrams.
Cell and membrane biology
The fluid-mosaic model describes membranes as phospholipid bilayers with embedded proteins, cholesterol, and glycoproteins. Small nonpolar molecules diffuse directly; water moves by osmosis through aquaporins; ions and polar molecules need channels or carriers. Passive transport follows electrochemical gradients, while active transport uses ATP - for example, the Na+/K+ pump moves 3 Na+ out and 2 K+ in per ATP.
Enzymes and metabolism
Enzymes lower activation energy, not the equilibrium constant. Rate rises with substrate concentration until saturation (Vmax); Km is the substrate concentration at half-Vmax. Competitive inhibitors raise apparent Km without changing Vmax; noncompetitive inhibitors reduce Vmax. Temperature and pH extremes denature by disrupting bonds that maintain tertiary structure.
Genetics
Mendel's law of segregation predicts 3:1 phenotypic and 1:2:1 genotypic ratios in a monohybrid cross of heterozygotes. The law of independent assortment applies to genes on different chromosomes. Sex-linked recessive traits appear more often in males because they have one X. In pedigree analysis, affected males born to carrier mothers indicate X-linked recessive inheritance.
Worked example
Both parents are carriers of sickle-cell trait (Aa). What is the probability that their first two children are unaffected and their third child is affected? Each child: P(unaffected phenotype) = 3/4; P(affected) = 1/4. Independent events, so P = (3/4) × (3/4) × (1/4) = 9/64. The order matters; if the question asked for two unaffected and one affected in any order, use the binomial coefficient 3 × 9/64 = 27/64.
Traps that cost marks
- “Dominant” does not mean more common; it means expressed in heterozygotes.
- A carrier of a recessive allele is usually phenotypically unaffected but can pass the allele on.
- Osmosis is water movement toward higher solute concentration, not solute movement.
- In enzyme graphs, do not confuse increasing substrate with increasing enzyme concentration.
- In dihybrid crosses, multiply independent probabilities rather than adding them.