If a man and a woman have sexual intercourse and do not want to produce a baby, they may use contraception. Explain how different methods of contraception prevent pregnancy.

Contraception refers to methods used to prevent pregnancy. They work through various biological mechanisms: - **Hormonal Methods (e.g., the Pill, patch, injection):** These contain hormones like oestrogen and progesterone. Their main function is to inhibit the pituitary gland from releasing FSH and LH. Without LH, ovulation (the release of an egg) does not occur. With no egg available, fertilisation is impossible. They also cause the mucus in the cervix to thicken, making it harder for sperm to swim through to the uterus. - **Barrier Methods (e.g., condoms, diaphragm):** These create a physical block. A male condom is worn on the penis and collects semen, preventing sperm from entering the vagina. A diaphragm is placed over the cervix, blocking sperm from entering the uterus. Their function is simply to prevent the sperm and egg from meeting. - **Intrauterine Methods (IUD/IUS):** An IUD is a small T-shaped device inserted into the uterus. A copper IUD releases copper ions which are toxic to sperm and also prevent a fertilised egg from implanting in the uterus wall. An IUS (hormonal IUD) releases progesterone, which thickens cervical mucus and thins the uterus lining, preventing implantation. - **Surgical Methods (Sterilisation):** These are permanent methods. A vasectomy in males involves cutting and sealing the sperm ducts, so sperm is not present in the ejaculated semen. Female sterilisation involves cutting or blocking the fallopian tubes, so the egg cannot travel from the ovary to the uterus, and sperm cannot reach the egg.