KCET Biology - Ratios, Pathways, and Precise Wording
KCET Biology is 60 one-mark questions from first and second PUC (NCERT Class 11–12) Botany and Zoology. The section is memory-dense: nomenclature, pathways, hormone actions and genetic ratios. With no negative marking, attempting all 60 is worthwhile, but only if you read each stem carefully, because distractor options are often near-correct and differ by a single word.
Core rules to keep loaded
- Mendel: segregation concerns one gene, independent assortment two genes on different chromosomes; a test cross with a homozygous recessive tester reveals the gamete ratio directly.
- Photosynthesis: light reactions on thylakoid membranes, Calvin cycle in the stroma; RuBisCO fixes CO₂ and also binds O₂ during photorespiration.
- Human physiology: the SA node sets heart rhythm; the loop of Henle's counter-current mechanism builds the medullary osmotic gradient.
- Ecology: energy flows unidirectionally with roughly 10% transfer between trophic levels, whereas nutrients cycle.
- Biotechnology: restriction endonucleases cut palindromic sites; ligase seals the phosphodiester backbone.
Worked example
Cross TtRr with ttrr. The tester produces only tr gametes, so each offspring's phenotype equals the gamete contributed by the TtRr parent. Independent assortment gives TR, Tr, tR and tr in equal numbers, hence four phenotypes in a 1:1:1:1 ratio. If the two genes were linked, parental classes would exceed recombinants and the ratio would break down.
Traps that cost marks
Mitosis versus meiosis questions hinge on crossing over, which occurs only in prophase I of meiosis. Photorespiration happens in C3 plants, not C4. Homologous organs share ancestry; analogous organs share function only. Insulin lowers blood glucose while glucagon raises it, and option order is sometimes reversed. A gamete carries n chromosomes, but the zygote becomes 2n only after syngamy.