Human reproduction — Edexcel International GCSE Biology
The male and female reproductive systems, the menstrual cycle and its hormones, the placenta, amniotic fluid and secondary sexual characteristics.
Revision notes
5 short notes, in the order of the specification. Each one in short:
The male and female reproductive systems make gametes and bring them together for fertilisation. In males, the testes make sperm and testosterone, the prostate gland adds fluid to make semen, and the urethra carries semen out through the penis. In females, the ovaries make eggs, fertilisation usually happens in the oviduct, and the embryo implants in the uterus.
The menstrual cycle is a series of changes that repeats about every 28 days. Menstruation happens on days 1 to 5, the uterus lining is repaired and thickens until day 14, ovulation happens around day 14, and the lining is maintained. Oestrogen causes the repair and growth of the lining, and progesterone maintains it.
FSH and LH in the menstrual cycle
Biology onlyFSH and LH are hormones released by the pituitary gland that control the menstrual cycle with oestrogen and progesterone. FSH causes an egg to mature and stimulates the ovaries to make oestrogen. High oestrogen inhibits FSH and stimulates LH release, and LH causes ovulation around day 14. Progesterone then maintains the lining and inhibits FSH and LH.
The placenta is a disc-shaped organ that attaches the embryo to the uterus wall. Oxygen and nutrients diffuse from the mother's blood into the embryo's blood, and carbon dioxide and urea diffuse the other way, without the bloods mixing. Villi give a large surface area. Amniotic fluid in the amnion protects the embryo by absorbing shocks.
Secondary sexual characteristics are features that develop at puberty but are not directly part of the reproductive organs. In girls, oestrogen from the ovaries causes breasts to develop, hips to widen and the menstrual cycle to begin. In boys, testosterone from the testes causes facial hair, a deeper voice, muscle development and sperm production.
Exam questions
7 exam-style questions (22 marks), each with its mark scheme.
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15 cards: flip them, mark what you knew, and practise the rest.
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Quick check questions
Where are sperm made?
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In the testes.
What does oestrogen do in the menstrual cycle?
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It repairs and builds up the lining of the uterus.
What does progesterone do in the menstrual cycle?
Show answer
It maintains the lining of the uterus.
Biology only Which hormone causes ovulation?
Show answer
LH.
How does amniotic fluid protect the embryo?
Show answer
It absorbs shocks and cushions the embryo against knocks.
Frequently asked questions
What does FSH do in the menstrual cycle?
Biology only FSH, released by the pituitary gland, causes an egg to mature in an ovary and stimulates the ovaries to produce oestrogen. As oestrogen rises, it inhibits FSH and stimulates the release of LH, which causes ovulation. After ovulation, progesterone inhibits FSH and LH, so no more eggs mature.
What are the roles of oestrogen and progesterone in the menstrual cycle?
Oestrogen and progesterone are both made in the ovaries. Oestrogen causes the repair and growth of the uterus lining after menstruation. Progesterone maintains the thick lining, ready for a fertilised egg. If the egg is not fertilised, progesterone falls, the lining is no longer maintained and it breaks down in menstruation.
How does the placenta provide for the developing embryo?
The placenta lets substances pass between the mother's blood and the embryo's blood by diffusion, without the bloods mixing. Oxygen and nutrients such as glucose and amino acids diffuse into the embryo's blood, while carbon dioxide and urea diffuse into the mother's blood. Villi, thin walls and a good blood supply speed up diffusion.
Where does fertilisation happen in humans?
Fertilisation usually happens in the oviduct, the tube that carries the egg from the ovary to the uterus. Sperm are made in the testes, and eggs are made in the ovaries. Cilia lining the oviduct move the egg along, and the embryo then implants in the soft lining of the uterus.
What does testosterone do at puberty?
Testosterone, made by the testes, causes secondary sexual characteristics to develop in boys at puberty. Facial hair grows, the voice deepens, muscles develop and shoulders broaden, pubic and underarm hair grow, and sperm production begins. In girls, oestrogen from the ovaries causes the equivalent changes, such as breast development.
Written and checked against the Edexcel IGCSE Biology (4BI1) specification · Updated October 2026