Oxygen gas molecules diffusing across a cell’s plasma membrane is an example of passive transport.
Passive transport refers to the movement of substances across a cell membrane without the need for energy input from the cell. In the case of oxygen molecules, they move from an area of higher concentration (outside the cell) to an area of lower concentration (inside the cell) until equilibrium is reached. This process occurs naturally due to the random motion of molecules and continues as long as a concentration gradient exists.
Cells require oxygen for cellular respiration, a process that produces energy. Therefore, the diffusion of oxygen into the cell is crucial for its survival and function.