[long_answer] When fertilisation does not occur in a human female, the thickened uterine lining is shed as menstruation. In a flowering plant, once fertilisation is complete, the ovary develops into a fruit and the ovules into seeds that are eventually dispersed. (i) Explain the biological events that trigger menstruation, and describe how the uterus prepares itself for the next reproductive cycle. (ii) Explain how fertilisation transforms the ovary and ovule, and why dispersal of seeds is important for the survival of the species. (iii) In what sense does each process — menstruation and seed dispersal — represent a 'reset' that prepares the organism for a future reproductive attempt?
Generated by claude-sonnet-4-6 · 2026-06-26 01:08 · grounding rag
Model Answer
(i) When the egg is not fertilised, it lives for about one day. Since no embryo is implanted, the thick, spongy uterine lining — which had been prepared to nourish a potential embryo — is no longer needed. It slowly breaks down and is shed through the vagina as blood and mucus. This is menstruation, lasting about two to eight days. After shedding, the uterus begins preparing its lining again for the next cycle.
(ii) After fertilisation in a flowering plant, the ovary develops into a fruit and the ovules develop into seeds. Dispersal of seeds is important because it prevents overcrowding around the parent plant, allows the species to colonise new areas, and improves the chances of survival and germination of offspring.
(iii) Both processes act as a 'reset': menstruation clears the uterine lining so it can rebuild and receive a future embryo, while seed dispersal ends one reproductive cycle and places new individuals in fresh environments, giving the species another opportunity to reproduce and survive.
Source: Chapter 7, Section 7.3.3(c) — What happens when the Egg is not Fertilised; Section 7.3.3(b) — Female Reproductive System
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Explanation
- Part (i): Examiners expect you to state that the unfertilised egg triggers breakdown of the thick uterine lining → shed as blood + mucus → cycle repeats. Mention the ~2–8 day duration for full marks.
- Part (ii): Key terms — ovary → fruit, ovules → seeds. For dispersal, give two reasons (no overcrowding + colonisation of new areas); one reason alone may cost a mark.
- Part (iii): This is a higher-order/application question. Link "reset" explicitly to preparing for the next attempt in both cases — don't just describe the process again. One clear sentence per process is enough.
- The source passages directly support (i) and the plant part of (ii); for dispersal benefits, use standard biology reasoning consistent with the chapter's theme of survival of the species.