Which of the following statements correctly compares simple diffusion and facilitated diffusion?

• A. Facilitated diffusion only occurs in prokaryotic cells, while simple diffusion occurs in all cells.
• B. Both simple and facilitated diffusion require energy input from ATP.
• C. Facilitated diffusion requires membrane proteins, while simple diffusion does not.
• D. Simple diffusion can move substances against their concentration gradient, but facilitated diffusion cannot.

Answer: (C)

Verified step by step guidance

1. Step 1: Begin by understanding the concepts of simple diffusion and facilitated diffusion. Simple diffusion is the passive movement of molecules from an area of high concentration to an area of low concentration, directly across the phospholipid bilayer, without the need for membrane proteins. Facilitated diffusion, on the other hand, also moves molecules down their concentration gradient but requires the assistance of membrane proteins such as channel or carrier proteins.
2. Step 2: Evaluate the first statement: 'Facilitated diffusion only occurs in prokaryotic cells, while simple diffusion occurs in all cells.' This statement is incorrect because both simple diffusion and facilitated diffusion occur in all types of cells, including prokaryotic and eukaryotic cells.
3. Step 3: Evaluate the second statement: 'Both simple and facilitated diffusion require energy input from ATP.' This statement is incorrect because neither simple diffusion nor facilitated diffusion requires energy input. Both processes are passive and rely on the concentration gradient to drive the movement of molecules.
4. Step 4: Evaluate the third statement: 'Facilitated diffusion requires membrane proteins, while simple diffusion does not.' This statement is correct because facilitated diffusion relies on specific membrane proteins to transport molecules across the membrane, whereas simple diffusion does not require any proteins and occurs directly through the lipid bilayer.
5. Step 5: Evaluate the fourth statement: 'Simple diffusion can move substances against their concentration gradient, but facilitated diffusion cannot.' This statement is incorrect because neither simple diffusion nor facilitated diffusion can move substances against their concentration gradient. Both processes are passive and only move substances down their concentration gradient.