Final answer:
The exchange of materials such as oxygen, nutrients, and waste occurs across the thin, single-layered walls of capillaries, the smallest blood vessels, via diffusion.
Step-by-step explanation:
The exchange of oxygen, nutrients, and waste materials takes place across capillary walls. Capillaries are the smallest blood vessels and have walls consisting of a single layer of epithelial cells, which makes them well-suited for the exchange of substances between the blood and the surrounding tissues. As blood flows through capillaries, substances like water, oxygen, glucose, other nutrients, and waste products such as carbon dioxide can pass quickly and easily through these thin walls.
This process is primarily facilitated by diffusion, which is the dominant mechanism in this exchange. Furthermore, proteins and other large solutes cannot typically leave through the capillary walls, thus, about 85% of the plasma that does leave the capillaries diffuses back near the venules. The remaining plasma enters the interstitial fluid and can be absorbed by the lymphatic system.