AP BIOLOGY

Detailed explanation-1: -ALVEOLI are the very small air sacs where the exchange of oxygen and carbon dioxide takes place. CAPILLARIES are blood vessels in the walls of the alveoli. Blood passes through the capillaries, entering through your PULMONARY ARTERY and leaving via your PULMONARY VEIN.

Detailed explanation-2: -How do oxygen and carbon dioxide cross capillary walls? Oxygen diffuses down its concentration gradient (from high to low concentration) from the capillary into the interstitial fluid; carbon dioxide diffuses down its concentration gradient from the interstitial fluid into the capillary.

Detailed explanation-3: -Capillaries-these are the sites of gas exchange between the tissues. Veins-these return “oxygen poor” blood to the heart, except for the vein that carries blood from the lungs.

Detailed explanation-4: -What do capillaries do? Capillaries complete the circulatory system by connecting arteries to veins: Arteries carry oxygen-rich blood from the heart to your organs. Veins help the body remove low-oxygen blood and waste.