Which part of the eye contains cells which are sensitive to light?

If sugar is detected in the urine of a person, name the disease he is suffering from.

Name two parts of the body which contain receptors of chemical stimuli.

What are the two main communications systems in an animal's body?

Which one term in each of the following includes the other three?

(a) thyroid, ductless gland, thymus, pituitary, ovary

(b) adrenalin, insulin, hormone, thyroxine, estrogen