AP BIOLOGY

Detailed explanation-1: -The alveoli are covered by a rich blood supply of capillaries-this provides a diffusion gradient for oxygen to move into the blood and carbon dioxide to move into the lungs. The alveoli are also highly folded, meaning there is a high surface area: volume ratio for gas exchange.

Detailed explanation-2: -The walls of the alveoli share a membrane with the capillaries. That’s how close they are. This lets oxygen and carbon dioxide diffuse, or move freely, between the respiratory system and the bloodstream.

Detailed explanation-3: -Adaptations of the alveoli: Moist walls-gases dissolve in the moisture helping them to pass across the gas exchange surface. Permeable walls-allow gases to pass through. Extensive blood supply-ensuring oxygen rich blood is taken away from the lungs and carbon dioxide rich blood is taken to the lungs.

Detailed explanation-4: -Alveoli are adapted for their function in gas exchange due to their small size and consequent large surface area, as well as their extremely thin walls. Clusters of alveoli lie at the end of bronchioles in the lungs, which are small air passages that branch off of larger airways called bronchi.

Detailed explanation-5: -a) The alveoli wall (and the capillary wall) is only one cell thick so there is only a short distance over which diffusion takes place (short diffusion pathway) so there is a faster rate of diffusion of oxygen from alveoli into the blood.