The movement of oxygen from the alveoli to the blood in the pulmonary capillaries depends on: A) facilitated transport by way of the hemoglobin molecule. B) active transport of oxygen from an area of lower concentration to an area of higher concentration. C) diffusion of oxygen from an area of higher concentration to an area of lower concentration. D) osmosis of the H₂O molecule across the respiratory membrane, where oxygen dissociates from hydrogen.

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Quizplus · Accepted Answer

Oxygen moves from an area of higher concentration (in the alveoli) to an area of lower concentration (in the pulmonary capillaries) through diffusion, which does not require a transport protein or an input of energy. Hemoglobin does assist in carrying oxygen in the bloodstream, but it does not facilitate the movement of oxygen from the alveoli to the pulmonary capillaries. Active transport, which requires energy input, moves substances from an area of lower concentration to an area of higher concentration, which is the opposite of the direction that oxygen moves in this process. Osmosis, which is the movement of water across a membrane from an area of lower concentration to an area of higher concentration, does not apply to the movement of oxygen in the respiratory system.

The Movement of Oxygen from the Alveoli to the Blood