AP BIOLOGY

Detailed explanation-1: -Diffusion is a type of passive transport, where molecules move from high concentration to low concentration. This means that the concentration of oxygen in the air must be higher than it is in the blood. The concentration of carbon dioxide is also different between the alveolar air and the blood of the capillary.

Detailed explanation-2: -Because the CO2 is of a higher concentration in the cell than in the blood passing by, this gas continually diffuses out of the cell. It too is small and uncharged so it can pass through cell membranes easily. These movements require no energy (in the form of ATP) on behalf of the cell.

Detailed explanation-3: -Facilitated diffusion. Some molecules, such as carbon dioxide and oxygen, can diffuse across the plasma membrane directly, but others need help to cross its hydrophobic core. In facilitated diffusion, molecules diffuse across the plasma membrane with assistance from membrane proteins, such as channels and carriers.

Detailed explanation-4: -CO2 diffuses down its pressure gradient, moving out of the capillaries and entering the alveoli. Oxygen and carbon dioxide move independently of each other; they diffuse down their own pressure gradients.

Detailed explanation-5: -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. Oxygen molecules attach to red blood cells, which travel back to the heart.