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Ion transport mechanisms are ways by which ions move across cell membranes. These mechanisms include diffusion, ion channels, and ion pumps. Let's describe each briefly: 1. Diffusion: The movement of ions from an area of high concentration to an area of low concentration until equilibrium is reached. No energy input is required for this process. 2. Ion channels: These are protein structures embedded in the cell membrane that allow specific ions to pass through due to concentration differences. Ion channels also function without the need for energy input. 3. Ion pumps: These are also protein structures embedded in the cell membrane that actively transport ions against their concentration gradient. They require energy in the form of ATP to function.

Based on the descriptions of each transport mechanism, we can conclude that ion pumps are the only transport mechanism that requires ATP for its functioning. Diffusion and ion channels do not require energy input as they rely on the concentration gradient to facilitate ion movement.

The ion pump transport mechanism requires ATP for the active transport of ions against their concentration gradient.