Each category represents one of the functions of proteins. Match each example with the appropriate function.

Explanation:

Homeostasis is the maintenance of internal environment of the cell with respect to the external environment. In the first statement, insulin is controlling the sugar level in the blood cells. Thus it is an example of homeostasis.

Collagen is an abundantly found protein in the mammals. It provides structural support to the connective tissues, bones, and muscles.

Pepsin is a digestive enzyme that breaks down proteins into respective amino acids. Our food normally have proteins which are thus degraded by the action of pepsin enzyme.

Immunoglobulin A or "IgA" is an antibody that play a vital role in immune/defense system. More precisely, it provides protection against viral and bacterial infections, e.g. influenza virus infection.

the answer is c) an oak tree