Cell Biology, Genetics and Microbiology
Cell biology, genetics and microbiology tests structure–function relationships, inheritance ratios and safe handling of microorganisms. Diagrams and calculations both appear.
Cell structure and transport
Prokaryotes lack a membrane-bound nucleus; eukaryotes have organelles including mitochondria for respiration, chloroplasts for photosynthesis and ribosomes for protein synthesis. Diffusion, osmosis and active transport differ in whether energy and carrier proteins are required.
Enzymes and energy
Enzymes are biological catalysts; rate rises with temperature and substrate concentration until denaturation or saturation. Photosynthesis converts light energy to chemical energy; respiration releases it as ATP.
Cell division and genetics
Mitosis produces genetically identical diploid cells; meiosis produces four haploid gametes with crossing over and independent assortment. Monohybrid crosses use a Punnett square; a Tt × Tt cross gives 3 tall : 1 short.
Microbiology
Bacteria reproduce by binary fission; viruses require a host. Aseptic technique, sterilisation and correct incubation temperatures prevent contamination. Magnification = image size/actual size.
Worked example
In a Tt × Tt cross, gametes are T and t on both sides. Offspring are TT, Tt, Tt, tt: 3 tall to 1 short. The probability that a tall offspring is heterozygous is 2/3, because TT, Tt and Tt are the tall outcomes.
Traps
Using the wrong denominator in conditional probability, confusing magnification with actual size, and forgetting that meiosis halves the chromosome number.