GED Science Practice

What is the primary function of a capillary?

1. an electrical device used to store electrical charge

2. long and slender with a very small internal diameter

3. unit of heat required to raise the temperature of water

4. one of the pair of tubes that branch off from the trachea and go into the lungs

The correct answer is: long and slender with a very small internal diameter

The primary function of a capillary relates to its unique structure, which is characterized by being long and slender with a very small internal diameter. This design is crucial for its role in the circulatory system, where capillaries serve as the sites for the exchange of gases, nutrients, and waste between blood and surrounding tissues. The narrowness of capillaries allows blood to flow slowly, facilitating the delivery of oxygen and the removal of carbon dioxide and metabolic byproducts effectively. In addition, the thin walls of capillaries, composed of a single layer of endothelial cells, enable efficient diffusion of substances. The extensive network of capillaries also ensures that all cells in the body are within close proximity to a blood supply, promoting effective nutrient and gas exchange. This structural characteristic aligns directly with the primary function of capillaries in the body’s circulatory system.