Both deer and a tree react to changes in their external surroundings, them to maintain a constant internal enviornment. this statement describes

The answer to this question should be: homeostasis

An organism will try to maintain their environment to be as ideal as possible. One of the examples is temperature. This happened because the enzyme inside an organism has an ideal temperature and pH to work with. When the temperature is too low, the enzyme might stop working makes the organism lives in threat. In this case, the organism limb muscle might start to do unconscious contraction to produce heat.