After you swallow the first bite of your food, your stomach becomes active. Polypeptides in the ingested food stimulate the stomach to release acid and enzymes, which creates more polypeptides. This greater concentration of polypeptides stimulates the stomach to release even more acid and enzymes, which continues until the contents of the stomach pass into the next digestive chamber. This phenomenon is best explained by
◦ how evolution does not lead to a perfect animal form.
◦ the relationship between structure and function.
◦ positive feedback control.
◦ how different tissues form an organ.