In passive transport, how does increasing temperature affect the rate of diffusion of small molecules across a solution or membrane (assuming no phase change and constant concentration gradient)?

• A. It increases the diffusion rate because higher temperature increases molecules' kinetic energy and random motion.
• B. It stops diffusion by eliminating the concentration gradient.
• C. It decreases the diffusion rate because higher temperature increases viscosity in most aqueous solutions.
• D. It has no effect on diffusion rate because diffusion depends only on the concentration gradient.

Answer: (A)

Verified step by step guidance

1. Understand that passive transport, specifically diffusion, is the movement of molecules from an area of higher concentration to an area of lower concentration without energy input.
2. Recall that the rate of diffusion depends on factors such as the concentration gradient, the permeability of the membrane, and the kinetic energy of the molecules involved.
3. Recognize that temperature is directly related to the kinetic energy of molecules: as temperature increases, molecules move faster and collide more frequently.
4. Apply this knowledge to diffusion: higher molecular kinetic energy at increased temperatures leads to faster movement across the membrane or solution, thus increasing the diffusion rate.
5. Note that the concentration gradient remains constant in this scenario, so the increase in diffusion rate is due solely to the increased molecular motion from the higher temperature.