A girl notices that the uterine lining builds up each month but breaks down and is shed if no fertilisation occurs. Explain WHY the uterine lining is built up in the first place, and what triggers its breakdown and shedding as menstruation.
Generated by claude-sonnet-4-6 · 2026-06-26 01:07 · grounding rag
Model Answer
The uterine lining builds up each month because the uterus prepares itself to receive and nourish a fertilised egg (embryo). The lining becomes thick, spongy, and richly supplied with blood to provide nutrition to the developing embryo if fertilisation occurs.
If the egg is not fertilised, it lives for only about one day. Since no embryo arrives, the thick lining is no longer needed. This triggers the lining to slowly break down and shed through the vagina as blood and mucus — a process called menstruation, lasting roughly two to eight days.
Source: Chapter 7, Section 7.3.3(b) and 7.3.3(c)
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Explanation
- Two parts to address: (1) why the lining builds up, and (2) what triggers breakdown → allocate roughly 1 mark each, with 1 mark for the term "menstruation" and its description.
- Key phrase examiners look for: "thick and spongy," "nourish the embryo," "egg not fertilised → lining not needed → sheds as blood and mucus."
- Don't just say "hormones change" — the passage grounds the trigger in the absence of fertilisation, so stick to that explanation.
- The word menstruation must appear for full credit.