______ is essential for organ structure, nutrient transport and energy utilization.

The correct answer is phosphorus. Phosphorus plays a crucial role in several key biological processes, making it essential for organ structure, nutrient transport, and energy utilization in living organisms.

In terms of organ structure, phosphorus is a vital component of DNA and RNA, which are necessary for the growth, development, and repair of tissues. These molecules carry genetic information and are fundamental in forming the structures of cells.

When it comes to nutrient transport, phosphorus is involved in the formation of ATP (adenosine triphosphate), which is the primary energy carrier in cells. ATP is utilized in various metabolic processes, including the transport of nutrients across cell membranes.

Furthermore, phosphorus is an important constituent of phospholipids, which make up the cell membranes of organisms, thus contributing to the overall structure of organs and tissues.

While the other options, such as calcium, protein, and sulfur, have significant roles in biological processes, they do not encapsulate the combination of organ structure, nutrient transport, and energy utilization as effectively as phosphorus does. Calcium is critical for bone structure and muscle function, proteins serve as building blocks for the body's tissues and play roles in various functions, and sulfur is important in the formation of certain amino acids and enzymes. However,