(a) A human body cell contains 46 chromosomes. State the number of chromosomes in a human sperm cell. [1]
(b) Give two differences between mitosis and meiosis. [2]
(c) Explain why it is important that gametes are haploid. [2]
- (a) 23(1)
- (b) any two from: mitosis produces two cells, meiosis four; mitosis produces diploid cells, meiosis haploid; mitosis produces genetically identical cells, meiosis genetically different cells; meiosis has two divisions, mitosis one — first difference (both sides needed)(1)
- (b) second difference(1)
- (c) at fertilisation two gametes fuse(1)
- (c) so the zygote is diploid / has 46 chromosomes / chromosome number stays the same each generation(1)
- Answer: (a) 23 (b) e.g. 2 vs 4 cells; diploid vs haploid; identical vs varied (c) fertilisation restores diploid number, keeping chromosome number constant
- Examiner tip: In (b) compare both processes in each point — 'meiosis makes four cells' alone is half a comparison.