Biology: Cell, Genetics, Physiology, and Ecology
Biology on SITEEE draws on cell biology, biomolecules, genetics, molecular biology, plant and human physiology, ecology, evolution, and biotechnology. Expect definition-based questions plus data interpretation: pedigrees, Punnett squares, enzyme graphs, and energy-flow diagrams.
Core rules and concepts
- Cell: prokaryotes lack a membrane-bound nucleus; mitochondria and chloroplasts have double membranes; plant cytokinesis uses a cell plate.
- Biomolecules: proteins are amino-acid polymers; enzymes lower activation energy without changing ΔG.
- Genetics: Mendelian monohybrid ratio 3:1; a test cross distinguishes homozygous dominant from heterozygous.
- Molecular biology: replication is semi-conservative; transcription makes RNA; translation uses mRNA codons and tRNA anticodons.
- Physiology: photosynthesis has light and Calvin cycles; aerobic respiration yields more ATP than anaerobic.
- Ecology: energy transfer between trophic levels is about 10%; Hardy-Weinberg uses p^2 + 2pq + q^2 = 1.
Worked example
Two carriers of an autosomal recessive condition marry. Each parent is Aa, where a is the disease allele. A Punnett square gives AA : Aa : aa = 1 : 2 : 1. The probability of an affected child (aa) is 1/4; the probability of a carrier child (Aa) is 2/4 = 1/2; the probability of an unaffected child is 3/4. If the condition were X-linked recessive, the carrier father would not exist in the same way, so identifying the inheritance pattern first is essential.
Traps
Calling a dominant allele 'more common'; confusing mitosis with meiosis; mixing transcription and translation; assuming Hardy-Weinberg equilibrium when selection, drift, or non-random mating is present; reading a pedigree without checking whether the trait is X-linked.