Biology

The correct answer is: D.By diffusion

Oxygen typically moves in and out of cells by diffusion. Since oxygen is a small, nonpolar molecule, it can easily pass through the lipid bilayer of the cell membrane without the need for energy or transport proteins. Oxygen moves from areas of higher concentration (such as in the lungs or blood) to areas of lower concentration (inside the cells) as part of the process of cellular respiration. Similarly, oxygen moves out of cells when its concentration inside the cell becomes higher than in the surrounding environment.<...