3. What is menstruation? Explain.
In the female body, the ova begin to mature with the onset of puberty (10 to 12 years of age). One of the ova matures and is released by the ovaries (once in 28-30 days). In this period, the wall of the uterus becomes thick so that it can receive the egg if it is fertilised leading to pregnancy in the female. If ovum is not fertilised, then the released egg and the thickened lining of the uterus along with its blood vessels are shed off. This causes bleeding in women. This process is known as menstruation.