How do single-celled organisms typically obtain oxygen for cellular respiration?

Learn about simple diffusion: Simple diffusion is the passive movement of molecules from an area of higher concentration to an area of lower concentration. Oxygen molecules naturally diffuse across the cell membrane of single-celled organisms because the concentration of oxygen is typically higher in the surrounding environment than inside the cell.

Rule out other options: Active transport through protein pumps requires energy and is typically used for moving molecules against their concentration gradient, not for oxygen uptake. Specialized respiratory organs are absent in single-celled organisms, and cilia are not used for absorbing oxygen.