Question

question 9 (1 point) learning goal 3: explain where gas exchange occurs and how it takes place.

Explanation:

Gas exchange occurs in the alveoli of the lungs (and also in tissues at the capillary - tissue interface). In the lungs, oxygen from the inhaled air diffuses across the thin walls of the alveoli and the surrounding capillaries into the bloodstream, while carbon dioxide diffuses from the blood in the capillaries into the alveoli to be exhaled. At the tissue level, oxygen diffuses out of the capillaries into the body's cells, and carbon dioxide (a waste product of cellular respiration) diffuses from the cells into the capillaries to be transported back to the lungs. This diffusion is driven by concentration gradients: oxygen moves from an area of higher concentration (in the alveoli or blood) to an area of lower concentration (in the blood or cells), and carbon dioxide moves from an area of higher concentration (in cells or blood) to an area of lower concentration (in blood or alveoli).

Answer:

Gas exchange occurs in the alveoli of the lungs (and at tissue - capillary interfaces). In the lungs, $O_2$ diffuses from alveoli to blood, $CO_2$ from blood to alveoli (driven by concentration gradients). At tissues, $O_2$ diffuses from blood to cells, $CO_2$ from cells to blood, also via concentration - gradient - driven diffusion.