Which factors affect the rate of diffusion?

• A. Temperature only.
• B. Temperature, concentration gradient, surface area, and membrane permeability.
• C. Gravity only.
• D. Pressure only.

Answer: (B)

The rate of diffusion is driven by four main factors: how steep the concentration gradient is, how much kinetic energy the particles have, how much surface area is available for crossing, and how permeable the membrane is to the substance. A larger concentration gradient means a stronger push for molecules to move from where they are plentiful to where they are scarce, speeding up diffusion. Higher temperature gives particles more kinetic energy, so they move and mix faster. A bigger surface area of the membrane provides more opportunity for particles to cross, increasing the overall rate. Greater membrane permeability means the membrane allows particles to pass through more easily, directly boosting diffusion speed.

Gravity doesn’t play a meaningful role in diffusion across membranes, and while pressure can influence gas diffusion in some contexts, it isn’t the broad factor governing diffusion rates in this typical cellular scenario. That’s why the combination of temperature, concentration gradient, surface area, and membrane permeability best explains how diffusion rate is controlled.