Generated by claude-sonnet-4-6 · 2026-06-15 06:52 · grounding rag
Model Answer
(a) Chromosomes are thread-like structures found in the nucleus of a cell, made up of DNA and proteins. They carry genes which transmit hereditary information from parents to offspring.
(b) In sexually reproducing organisms, gametes (sperm and egg) are formed by meiosis, which halves the chromosome number. When two gametes fuse during fertilisation, the original chromosome number is restored. This ensures that the DNA content remains constant in every generation of a species.
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Explanation
- (a) One mark — state what chromosomes are (location + composition). Mentioning DNA and genes earns the mark.
- (b) Two marks — the key concept is the meiosis–fertilisation cycle: meiosis halves the chromosome number (1 mark), fertilisation restores it (1 mark). Use correct terms: meiosis, gametes, fertilisation. No diagram is needed for 2 marks but mentioning haploid/diploid can strengthen the answer.