Question

which statements explain the gas exchange that happens at the alveoli? check all that apply.
carbon dioxide moves from the air in the alveoli to the blood.
carbon dioxide moves from the blood to the air in the alveoli.
the capillaries that surround the alveoli exchange both carbon dioxide and oxygen.
the capillaries that surround the alveoli exchange only oxygen.
oxygen is absorbed by the blood in the capillaries that surround the alveoli.
oxygen is the air we breathe out when we exhale.

Explanation:

• Gas exchange at alveoli: Carbon dioxide moves from blood (high - concentration in blood) to alveolar air (low - concentration in alveolar air) by diffusion.
• Capillaries around alveoli: They exchange both carbon dioxide (from blood to alveoli) and oxygen (from alveoli to blood). Oxygen is absorbed by the blood in these capillaries (as it moves from high - concentration in alveoli to low - concentration in blood).
• Incorrect statements: Carbon dioxide does not move from alveolar air to blood (it's the opposite). Capillaries around alveoli do not exchange only oxygen (carbon dioxide is also exchanged). Oxygen is not what we breathe out (we breathe out carbon dioxide, nitrogen, and a small amount of oxygen which is less than the inhaled amount).

Answer:

• B. Carbon dioxide moves from the blood to the air in the alveoli.
• C. The capillaries that surround the alveoli exchange both carbon dioxide and oxygen.
• E. Oxygen is absorbed by the blood in the capillaries that surround the alveoli.