Diffusion refers to which process in the context of oxygen in water?

• A. The transport of oxygen by bacteria
• B. The mechanical mixing of water to release oxygen
• C. The movement of oxygen from higher to lower concentrations until equilibrium
• D. The chemical reaction consuming oxygen

Answer: (C)

Diffusion is the movement of dissolved substances from a region of higher concentration to a region of lower concentration until equilibrium is reached. In water, oxygen diffuses from areas where it’s more concentrated (near the air-water interface or where photosynthesis adds O2) to areas where it’s depleted, driven by random molecular motion, and it does not require energy input. This process explains how oxygen distributes within a body of water over time.

The other ideas aren’t diffusion: oxygen being transported by bacteria refers to consumption or transfer related to microbial activity, not the passive spreading of molecules. Mechanical mixing is a form of physical agitation that speeds up distribution but is not diffusion itself. A chemical reaction consuming oxygen describes a reaction changing the chemical state rather than the spread of oxygen molecules.