Question

movement of gas molecules (oxygen and carbon dioxide) between the air in the lungs and the blood or between the blood and the tissues is by which process?
phagocytosis
filtration
active transport
diffusion

Explanation:

Phagocytosis is cell eating of pathogens; filtration uses pressure to separate substances; active transport requires energy to move substances against a gradient. Diffusion is the passive movement of molecules from an area of higher concentration to lower concentration, which is how oxygen and carbon dioxide move between lungs/blood and blood/tissues down their concentration gradients.

Answer:

Diffusion