Enzymes are catalysts for biological reactions, including one which we are all familiar with, digestion. When we consume foods we are asking our bodies to convert the form of the meal into a useful form.
We need to eat in order to gain energy but we also need other important substances such as proteins for the growth of our muscles as well as repair.
We often fail to remember that the food we eat was once inside other plants and animals. If we want to convert food into useful forms, we first need to break it down and then reform it. What this means is we need to digest our food and the mechanism by which we do that is through various digestive enzymes.
We digest large, stable molecules such as starch which is found in plants like rice, into smaller forms like maltose. In the case of starch, which is a polymer, we use amylase to break it down into maltose, which is a monomer. We consistently break down polymers into monomers and then re-form them with other enzymes such as glycogen synthase.
Part of the goal of breaking down molecules such as starch is to get the glucose it contains to our muscles where it can be used for respiration. This involves passing through the intestines via active transport and so the molecules are broken down into smaller, more soluble ones. Processing glucose through respiration and then excreting the waste products is part of the carbon cycle.