Which happened when an essential amino acid is missing from the diet

You need amino acids in your diet every day, since your body doesn't store excess amino acids consumed.  If essential amino acids are missing from your diet, your body will start breaking down muscle tissue to access the amino acids that is contains so they can use them elsewhere.

stimulus is a change in the environment that causes an organism to react. the response is the reaction to the stimulus. some examples of stimuli for zebras are drought, to many predators, and bad feeding grounds such as dead grass or plants. zebras respond to stimuli just like all other living organisms