The answers that fit the blanks are small intestine and small intestine, respectively. Dipeptidases are enzymes which are produced by the <span>enterocytes found in the small intestines. These enzymes act in the villi of the small intestines. The function of this enzyme is to break down amino acids and turn it into dipeptides.</span>
In order for natural selection to take place we must have "variety in a population". This variety of traits is what allows natural selection to "pick" the most favorable traits.