A, B and C are three common STDs. A and C are caused by bacteria whereas B is caused by a virus D. The virus D reduces the immunity of the infected person to such a low level that the person can die of even very mild diseases.

(a) What could A and C be?

(b) What is B?

(c) Name the virus D ?

(d) How can A, B and C be caused ?

(e) Out of A, B and C, which one does not have a definite cure as yet ?

A woman uses pills A as a method of birth control (or preventing pregnancy). The pills A stop the ovaries from releasing ovum into oviducts. Another woman uses pills B as a method of birth control. The pills B kill the sperms and prevent pregnancy.

(a) What do the pills A contain?

(b) What is the common name of pills A ?

(c) What do the pills B contain ?

(d) What is the common name of pills B ?

(e) What is the general name of these methods of birth control?

A woman uses a device X made of a common metal for preventing pregnancy. This device works by preventing the implantation of fertilised egg cell (or embryo) in the female organ Y.

(a) What are the two names of device X?

(b) Name the organ Y.

(c) Can this method of contraception protect a woman from acquiring a STD?

The germ cell A produced by a person X is round in shape and it fuses with another germ cell B having a long tail and produced by a person Y. The fusion of A and B produces a new cell C. The cell C divides repeatedly and grows inside the organ D of person X to form E in which the body features of the unborn baby are not much developed. E grows further 'to form Fin which the various body features of the unborn baby (like hands, legs, head, eyes, and ears, etc.) can be identified. F grows further and ultimately forms a baby. What are A, B, C, D, E and F ? Out of the two persons X and Y, which one is male and which one female?

Explain why, a human zygote is more likely to grow into an adult than a frog zygote.