Which feature is shared by both facilitated diffusion and active transport across a cell membrane?

• A. Both allow only water molecules to pass through the membrane.
• B. Both require the use of membrane proteins to transport substances.
• C. Both require direct input of cellular energy (ATP).
• D. Both move substances against their concentration gradient.

Answer: (B)

Verified step by step guidance

1. Understand the key terms: Facilitated diffusion is a passive transport process that moves substances down their concentration gradient with the help of membrane proteins, while active transport moves substances against their concentration gradient and requires energy input (ATP).
2. Identify the shared feature: Both facilitated diffusion and active transport involve the use of membrane proteins to transport substances across the cell membrane.
3. Eliminate incorrect options: Facilitated diffusion does not require ATP, so the option 'Both require direct input of cellular energy (ATP)' is incorrect. Facilitated diffusion also does not move substances against their concentration gradient, so the option 'Both move substances against their concentration gradient' is incorrect.
4. Clarify the role of water: Neither facilitated diffusion nor active transport is limited to transporting only water molecules, so the option 'Both allow only water molecules to pass through the membrane' is incorrect.
5. Conclude the correct answer: The shared feature is that both facilitated diffusion and active transport require the use of membrane proteins to transport substances.