What is the primary function of carbohydrates in living organisms?

The primary function of carbohydrates in living organisms is to act as energy sources and structural components. Carbohydrates are essential for providing energy to cells, as they can be broken down into glucose, which is then utilized in cellular respiration to produce ATP, the energy currency of the cell.

In addition to energy provision, carbohydrates also play a crucial role in the structural integrity of cells and organisms. For example, cellulose, a polysaccharide, is a major component of plant cell walls, providing strength and rigidity. Similarly, chitin serves a structural function in the exoskeletons of arthropods and the cell walls of fungi.

This dual role emphasizes the importance of carbohydrates not just in energy metabolism but also in maintaining the physical structure of biological systems. The other options, while important functions in their own right—such as storage of genetic information by nucleic acids, cellular communication facilitated by various signaling molecules, and protection against pathogens by immune responses—do not encapsulate the primary roles that carbohydrates play in the context of energy provisioning and structural function.