Which of the following is least likely to increase the rate of diffusion across a cell membrane?

• A. Decreasing the size of diffusing molecules
• B. Increasing membrane permeability
• C. Decreasing the temperature
• D. Increasing the concentration gradient

Answer: (C)

Verified step by step guidance

1. Understand the concept of diffusion: Diffusion is the movement of molecules from an area of higher concentration to an area of lower concentration. The rate of diffusion is influenced by factors such as temperature, molecule size, concentration gradient, and membrane permeability.
2. Analyze the effect of molecule size: Smaller molecules diffuse faster because they encounter less resistance when moving through the membrane. Decreasing the size of diffusing molecules would increase the rate of diffusion.
3. Evaluate the role of membrane permeability: Increasing membrane permeability allows molecules to pass through the membrane more easily, which would increase the rate of diffusion.
4. Examine the impact of temperature: Temperature affects the kinetic energy of molecules. Higher temperatures increase molecular movement, speeding up diffusion. Conversely, decreasing the temperature reduces molecular movement, slowing down diffusion.
5. Consider the concentration gradient: A steeper concentration gradient (greater difference in concentration between two areas) increases the rate of diffusion because molecules move more rapidly to equalize the concentrations.