Which vessels allow diffusion of oxygen and nutrients across their cell layers?

Capilleries

Explanation:

Capillaries are the places where the exchange of substances between blood and surrounding tissues occurs. Substance exchange can occur between and through the cells that make up the vessel wall. The pores present in some types of blood capillaries also act as transfer sites. It is noteworthy that the permeability of these vessels varies from one body region to another. In summary, we can say that it is the capillaries that allow the diffusion of oxygen and nutrients through their cell layers.

Blood capillaries are vessels of the cardiovascular system that are characterized by their small caliber.