CBSE Class 10 Science 2017 · Paper 531 · Question 15

(a) Every month an ovary releases an egg, and the uterus prepares to receive a fertilised egg: its lining becomes thick and spongy and richly supplied with blood, to nourish an embryo. If the egg is not fertilised, this lining is not needed. It slowly breaks down and comes out through the vagina as blood and mucus. This monthly flow is menstruation; it usually lasts about 2 to 8 days. (b) Sperm and ovum compared: (1) Size: the sperm is very small; the ovum is much larger. (2) Movement: the sperm is motile and swims with its tail; the ovum is not motile and has no tail. Other differences: the ovum stores food for the early embryo while the sperm has very little, and sperms are made in the testes while ova are made in the ovaries.