Final answer:
The key functions of protein in the body include structural support, enabling chemical reactions, and cellular communication, but proteins are not primarily an energy source.
The correct option that does not describe a key function of protein is option (d). Proteins are used for energy only when necessary, with the body preferring carbohydrates and fats for its energy needs.
Step-by-step explanation:
The key functions of protein in the body include a variety of roles such as providing structural material for the body, enabling chemical reactions as enzymes, and facilitating cellular uptake and communication through transport and signal proteins. However, proteins are not primarily considered a vital energy source, which is the correct option (d) that does not represent one of the key functions of protein. While proteins can be converted to glucose or triglycerides and used for energy when necessary, the body typically uses carbohydrates and fats for energy before using protein.
Proteins play a crucial role in growth and maintenance, acting as a major structural component of cells, especially muscle, skin, and hair. They also function in membranes, as hormones, and are necessary for the immune response, cellular repair, and the formation of blood cells. One specific example is the protein hemoglobin, which binds with oxygen to allow blood to carry oxygen from the lungs to cells throughout the body.
Therefore, the correct option that does not describe a key function of protein in the body is option (d), stating that proteins are a vital energy source as their primary role.