Final answer:
Proteins fulfill numerous roles in cells, including acting as enzymes, providing structural support, and participating in cell communication. Therefore, the answer to the question is that proteins can be used for all listed cellular roles.
Step-by-step explanation:
Proteins can be used for various cellular roles including biological catalysis, cell communication, and structural support. Thus, the correct answer to the student's question is D. All of these choices are correct.
Proteins such as enzymes act as catalysts that vastly speed up biochemical reactions within the cell, making processes like metabolism possible. Structural proteins, like collagen and keratin, provide the necessary support to cells and tissues, helping to maintain cell shape and integrity.
Moreover, proteins are involved in cell communication; they are part of the cell membrane components such as receptors and also serve as signaling molecules like hormones. Hemoglobin, as an example, is a protein that transports oxygen in the blood from the lungs to other parts of the body.