What is meant by stimulus and reaction?
Stimulus is the change in the environment or environmental factors to to which the organism can respond or react. Theresponse shown by organisms towards or awaya stimulus is called reaction.
Hormones are called chemical messenger. Why?
We all know, hormones are the chemicals carried to all parts of the body through blood circulation to bring about the hormonious working of the body. So, hormones are called chemical messengers.