Biology: Cell Division, Genetics, Physiology, and Ecology
JENPAS-UG Biology covers cell structure, genetics, human physiology, plant physiology, and ecology. Questions reward precise definitions and pathway logic over rote lists.
Core rules and concepts
- Cell division: mitosis produces genetically identical diploid cells; meiosis has two divisions and produces four haploid cells, with variation from crossing over and independent assortment.
- Mendelian genetics: the law of segregation gives a 3:1 phenotype ratio and a 1:2:1 genotype ratio in a monohybrid cross of heterozygotes. A test cross reveals an unknown genotype.
- Human physiology: the SA node sets heart rate; glomerular filtration is followed by reabsorption in the proximal tubule. The oxygen dissociation curve shifts right with increased CO2, H+, or temperature.
- Photosynthesis: light reactions in the thylakoid produce ATP and NADPH; the Calvin cycle in the stroma fixes CO2 using RuBisCO.
- Ecology: energy transfer follows the 10% rule; logistic growth is dN/dt = rN(1 − N/K).
Worked example
In a monohybrid cross between two heterozygous tall pea plants (Tt × Tt), what fraction of offspring are tall? A Punnett square gives TT, Tt, Tt, tt. Three of four genotypes contain the dominant T allele, so the tall fraction is 3/4. If the question asks for homozygous tall, the answer is 1/4 - read the wording carefully.
Traps that cost marks
- Confusing mitosis with meiosis: meiosis produces four haploid cells, not two diploid cells.
- Mixing phenotype ratios with genotype ratios.
- Assuming a dominant allele is more common in the population.
- Confusing afferent and efferent arteriole effects on glomerular filtration.
- Forgetting that RuBisCO can act as an oxygenase in photorespiration.