Biology
The MTTC Biology (017) “Biology” domain tests the integrated core of the life sciences: scientific inquiry, the chemistry of life, cell structure and function, energy transformations, molecular genetics, heredity, evolution, organismal diversity, and ecology. Questions typically ask you to apply a principle to a described experiment, data set, or scenario rather than recall an isolated fact, so connect each term to a mechanism.
Core rules and concepts
- Inquiry: Hypotheses must be testable and falsifiable; controlled experiments hold all but one variable constant, and correlation alone does not establish causation.
- Chemistry of life: Water’s polarity and hydrogen bonding explain cohesion, adhesion, and its role as a solvent. Know the monomers and bonds of carbohydrates, lipids, proteins, and nucleic acids.
- Cells: Prokaryotic versus eukaryotic organization, endosymbiotic theory, and membrane transport-simple diffusion, facilitated diffusion, osmosis, and active transport-are recurring targets.
- Enzymes: They lower activation energy, are not consumed, and denature at extreme temperature or pH; they do not change ΔG or the equilibrium position.
- Energy: Photosynthesis uses light reactions to make ATP and NADPH and the Calvin cycle (rubisco) to fix CO₂. Cellular respiration proceeds through glycolysis, the Krebs cycle, and oxidative phosphorylation, with ATP synthase driven by a proton gradient.
- Information flow: DNA replication is semi-conservative; transcription and translation follow the central dogma; mutations may be silent, missense, or nonsense.
- Genetics and evolution: Apply Mendelian probability, sex linkage, and non-Mendelian patterns; evolution is change in allele frequencies via selection, drift, mutation, and gene flow. Hardy–Weinberg describes a non-evolving population.
- Ecology: Energy flows through trophic levels (roughly 10% transfer), nutrients cycle, and populations grow exponentially or logistically.
Worked example
In a cross AaBb × AaBb with unlinked genes, what fraction of offspring is aabb? Treat each locus separately: Aa × Aa yields aa with probability 1/4; Bb × Bb yields bb with probability 1/4. Because the loci assort independently, multiply: 1/4 × 1/4 = 1/16. If the genes were linked, you could not multiply; you would need recombination frequencies or a testcross data set.
Traps that cost marks
“Dominant” does not mean more common. Osmosis moves water, not solute. Enzymes do not alter reaction free-energy change. Individuals do not evolve-populations do. The 10% rule is an average, not a fixed law.