A stimulus is a detectable change in the internal or external environment of an organism that produces a response in the organism.
The ability to respond to stimuli increases the chances of survival for an organism. Those oragnisms that survive have a greater chance of raising offspring and of passing on their alleles to the next generation. Therefore there is a selection pressure favouring organisms with more appropriate responses.
stimulus -> receptor -> coodinator ->effector -> response
A taxis is a simple response whose direction is determined by the direction of the stimulus. Taxis are classified according to whether the movement is towards the stimulus…