Which of the following does not accurately describe a channel or a carrier?

• A. Channel – open to both sides of the membrane simultaneously.
• B. Carrier – open to one side of the membrane at a time.
• C. Carrier – requires a conformation change to complete function.
• D. Channel – not selective for molecules that move through it.

Answer: (D)

Verified step by step guidance

1. Understand the basic function of channels and carriers in cell membranes. Channels are proteins that form pores in the membrane, allowing specific molecules or ions to pass through by diffusion. Carriers, on the other hand, bind to specific molecules and undergo a conformational change to transport them across the membrane.
2. Recognize that channels are typically selective, meaning they allow only certain molecules or ions to pass through based on size, charge, or other properties. This selectivity is crucial for maintaining cellular homeostasis.
3. Identify that carriers are also selective and require a specific binding interaction with the molecule they transport. This interaction often triggers a conformational change in the carrier protein, allowing the molecule to be transported across the membrane.
4. Analyze the statement 'Channel – not selective for molecules that move through it.' This statement is incorrect because channels are generally selective for the molecules they transport, contrary to what the statement suggests.
5. Conclude that the statement 'Channel – not selective for molecules that move through it' does not accurately describe a channel, as channels are indeed selective for the molecules they allow to pass through.