Final answer:
Capillaries are the blood vessels where gas and nutrient exchange occurs, as they are the smallest vessels that allow individual cells to pass and facilitate the exchange of oxygen and nutrients.
Step-by-step explanation:
The type of blood vessel that is the site of gas and nutrient exchange is the capillary. Capillaries are the smallest blood vessels in the body, and they are where individual blood cells pass and exchanges such as the diffusion of oxygen and nutrients occur. This exchange is vital for delivering nutrients to tissues and removing waste products. Arteries carry oxygenated blood away from the heart, veins carry deoxygenated blood back to the heart, and lymphatic vessels are involved in the immune response and the transport of lymph fluid, not gas exchange.