The rate of diffusion of a substance across the plasma membrane depends on which of the following factors?

• A. The size of the cell
• B. The concentration gradient of the substance
• C. The type of organelles present in the cell
• D. The amount of ATP available

Answer: (B)

Verified step by step guidance

1. Understand that diffusion is the movement of molecules from an area of higher concentration to an area of lower concentration.
2. Identify that the rate of diffusion is primarily influenced by the concentration gradient, which is the difference in concentration of the substance across the membrane.
3. Recognize that a steeper concentration gradient (a larger difference in concentration) will result in a faster rate of diffusion.
4. Acknowledge that other factors like the size of the molecules, temperature, and the permeability of the membrane can also affect diffusion, but the concentration gradient is the most direct factor.
5. Conclude that the size of the cell, the type of organelles, and the amount of ATP do not directly affect the rate of diffusion of a substance across the plasma membrane.