Which nutrient is primarily responsible for cellular growth and repair?

Proteins are primarily responsible for cellular growth and repair because they are made up of amino acids, which are the building blocks of tissues in the body. When cells need to grow, repair, or replace damaged parts, proteins play a crucial role in forming new cells and tissues. They are involved in various bodily functions, including the synthesis of enzymes and hormones, providing structural components for muscles and organs, and assisting in the immune response.

While carbohydrates and fats are essential for energy and overall health, they do not directly contribute to the structural components required for cell growth and repair in the way proteins do. Vitamins, on the other hand, are vital organic compounds that support various biochemical processes but do not provide the amino acids needed for building and repairing cells. Thus, proteins stand out as the nutrient that directly facilitates cellular growth and repair, making it the correct answer.