Cells need oxygen to make energy. Oxygen-rich blood is transported to tissues. When the oxygen is dropped off, it needs to move through structures that are small and thin. Which vessels allow for oxygen movement into the tissues?

Capillaries have very thin walls, allowing oxygen to diffuse from the blood into nearby tissues. Arteries carry blood away from the heart, and veins return blood to the heart; neither is the main site of oxygen exchange. The correct choice is capillaries.

AI-written and checked against the verified answer.