chapter  1
Light and Eyes
Pages 22

All organisms, whether bacteria, oak trees, or whales, must be adapted to their environments if they are to survive and reproduce. The structure and physiology of organisms are not fixed at the start of life; to some extent, adjustments to changes in the environment can occur so as to “fine-tune” the organism’s adaptation. One way of achieving this is through the regulation of growth processes, as when plants grow so that their leaves face the strongest available light. Another way, which is much more rapid and is only available to animals, is movement of the body by contraction of muscles.