A. Stimulus is the term used to describe what causes organisms to react to their environment. Stimulus is something that can provoke organisms to respond to the world around them. For example, if you put your hand on the stove, the stove is going to be the stimulus for you to get burned and move your hand from it because it will be to hot - that is going to be your reaction to the stimulus. Camouflage is a type of hiding mechanism, parasites are organisms, and homeostasis is equilibrium in an organism.