A woman is trying to become pregnant. Her doctor explains that hormones control the monthly release of an egg from her ovaries. Explain how hormones in the menstrual cycle bring about ovulation and how this links to the role of gametes in reproduction.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Hormones released by the pituitary gland and ovaries control the menstrual cycle. One key event in the cycle is ovulation — the release of an egg from the ovary. Without ovulation, fertilisation cannot occur.
Model answer (5 marks)
1. The pituitary gland releases follicle‑stimulating hormone (FSH). 2. FSH stimulates a follicle in the ovary to grow and produce oestrogen. 3. The rising oestrogen causes a surge in luteinising hormone (LH) from the pituitary. 4. The LH surge triggers ovulation, causing the mature egg to be released from the follicle. 5. The released egg is a haploid gamete; when it fuses with a sperm gamete, fertilisation restores the diploid chromosome number and a zygote is formed.
Examiner tips
- Use the exact hormone names (FSH, LH) and the sequence of events; link the LH surge to ovulation; state that the egg is haploid and that fertilisation restores diploidy.
- Show the connection between hormone action and the role of gametes in producing a zygote.
Mark scheme (5 marks)
- A hormone (FSH) is released from the pituitary gland / a gland in the brain
- FSH stimulates the ovary to produce oestrogen / stimulates a follicle to develop in the ovary
- A surge in LH (luteinising hormone) triggers ovulation / causes the egg to be released from the ovary
- The egg released is a gamete / the egg is haploid / the egg contains half the number of chromosomes
- Fertilisation involves fusion of the egg gamete with a sperm gamete / fertilisation restores the diploid chromosome number / a zygote is formed with a full set of chromosomes
Key terms in this question
Related
- All OCR A-Level Biology B — Advancing Biology (H422) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
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