Reproduction in human beings

In the early teenage years, the body starts changing in new ways. This is puberty, when the reproductive organs begin to mature. In both boys and girls, new hair grows in the armpits and genital area, and the skin often becomes oily. Girls: breasts begin to grow and menstruation starts. Boys: hair grows on the face and the voice begins to crack. These changes are normal, and they happen at different times for different people.

The male system:

• the two testes make sperms and the hormone testosterone. They sit outside the body in the scrotum, because sperms need a temperature lower than body temperature;
• sperms travel along the vas deferens;
• the seminal vesicles and prostate add fluid that nourishes the sperms and helps them move;
• the urethra is a common passage for both sperms and urine.

The female system:

• the two ovaries release one egg each month;
• the egg travels down the oviduct (fallopian tube), where it may meet a sperm and be fertilised;
• the fertilised egg settles (implants) in the thick, blood-rich lining of the uterus and grows into an embryo;
• the placenta, a disc in the uterus wall, passes food and oxygen from the mother's blood to the embryo and takes away its wastes. A baby develops in about nine months.

Menstruation: every month the lining of the uterus thickens, ready to receive a fertilised egg. If the egg is not fertilised, the lining isn't needed. It breaks down slowly and leaves the body as blood and mucus. This happens roughly every month and lasts about two to eight days. It is a normal part of growing up, and everyone, boys included, should understand it.

Reproductive health. The book makes an important point: sexual maturity comes gradually, while the body is still growing, so being sexually mature does not mean the body or the mind is ready for sex or for bringing up children. Young people face many pressures, from friends and even family, and it is fine to take time and decide for yourself.

Some diseases spread through sexual contact: bacterial ones such as gonorrhoea and syphilis, and viral ones such as warts and HIV-AIDS. Using a condom helps prevent many of them to some extent.

Pregnancy makes big demands on a woman's body and mind, so ways to avoid it (contraception) have been developed:

Female foeticide is a serious wrong. Finding out a baby's sex before birth is banned by law in India, yet illegal abortions of girls continue in some places, and the child sex ratio is falling. For a healthy society, the female-male sex ratio must be maintained.