Which of the following statements is true?

• A. Ion channels allow ions to cross the cell membrane against their concentration gradients.
• B. All cells have an equilibrium potential, which is a difference in electrical charges across their plasma membrane.
• C. Concentration gradients of proteins across the plasma membrane represent potential energy.
• D. None of the listed responses is correct.
• E. Ion channels are selectively permeable, permitting only certain ions to pass.

Answer: (E)

Verified step by step guidance

1. Step 1: Understand the function of ion channels. Ion channels are proteins that create specific pathways for charged ions to pass through the cell membrane. They are selectively permeable, meaning they allow certain ions to pass based on factors like size and charge.
2. Step 2: Analyze the statement about ion channels allowing ions to cross against their concentration gradients. Ion channels typically facilitate passive transport, allowing ions to move down their concentration gradient, not against it.
3. Step 3: Consider the concept of equilibrium potential. The equilibrium potential is the electrical potential difference across the membrane at which there is no net flow of a particular ion. It is related to the concentration gradient of ions, not proteins.
4. Step 4: Evaluate the statement about concentration gradients of proteins. Proteins generally do not move across the plasma membrane to create concentration gradients; instead, ions do. The movement of ions across the membrane can create potential energy.
5. Step 5: Review the correct answer provided. Ion channels are indeed selectively permeable, allowing only certain ions to pass through, which aligns with the correct answer given in the problem.