Sexual reproduction in humans — Cambridge IGCSE Biology
The male and female reproductive systems, sperm and egg cells, fertilisation, implantation, and the fetus, placenta and umbilical cord.
Revision notes
3 short notes, in the order of the specification. Each one in short:
The male reproductive system makes and delivers sperm: the testes make sperm, the sperm ducts carry them to the urethra, the prostate gland adds fluid to make semen, and the penis places sperm in the vagina. In the female system, the ovaries release eggs, the oviducts carry them to the uterus, and the fetus develops in the uterus.
Fertilisation is the fusion of the nuclei from a male gamete (sperm) and a female gamete (egg cell), forming a zygote. Sperm are adapted with a flagellum to swim, many mitochondria to release energy, and enzymes in the acrosome to digest through the jelly coat. Egg cells have energy stores and a jelly coat that changes after fertilisation.
Implantation is when the embryo, a ball of cells, settles into the lining of the uterus; it then develops into a fetus. The placenta is where substances are exchanged between the mother's and the fetus's blood without them mixing. The umbilical cord connects the fetus to the placenta, and amniotic fluid protects the fetus from knocks.
Exam questions
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Quick check questions
Which part of the male reproductive system carries sperm from the testes to the urethra?
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The sperm duct.
Name the part of the female system where the fetus develops.
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The uterus.
What happens at fertilisation?
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The nucleus of a sperm fuses with the nucleus of an egg cell.
State the function of amniotic fluid.
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It protects the fetus from knocks and bumps.
Supplement Name two types of substance that can cross the placenta and harm a fetus.
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Pathogens and toxins.
Frequently asked questions
How are sperm cells adapted for their function?
Sperm cells have a flagellum that whips from side to side to move them towards the egg cell. They have many mitochondria, which release energy by aerobic respiration for the flagellum to move. Enzymes in the acrosome digest a way through the jelly coat around the egg cell so the sperm nucleus can enter.
Where does fertilisation happen in humans?
Fertilisation usually happens in the oviduct, the tube that carries the egg cell from the ovary to the uterus. The nuclei of a sperm and an egg cell fuse to form a zygote. The zygote divides to form an embryo, which travels to the uterus and implants into its lining.
What does the placenta do?
Supplement The placenta is where substances are exchanged between the mother's blood and the fetus's blood, mainly by diffusion, without the two bloods mixing. Oxygen and dissolved nutrients such as glucose and amino acids pass to the fetus. Carbon dioxide and urea pass from the fetus to the mother. Some pathogens and toxins can also cross.
How are egg cells adapted?
Egg cells have energy stores in the cytoplasm, which supply energy for the zygote and early embryo until it implants in the uterus. The jelly coat changes after one sperm has entered, so no other sperm can get in, and only one sperm nucleus fuses with the egg nucleus. Egg cells are much larger than sperm.
Written and checked against the Cambridge IGCSE Biology (0610) specification · Updated October 2026