Questions: How is facilitated diffusion in axons similar to active transport?

Solution Steps

The question asks for similarities between facilitated diffusion and active transport within axons. We need to evaluate each option to see if it applies to both.

Facilitated diffusion does _not_ require ATP; it moves substances down their concentration gradient. Active transport _does_ require ATP to move substances against their concentration gradient. Thus, this option is incorrect.

Facilitated diffusion moves substances _down_ their concentration gradient. Active transport moves substances _against_ their concentration gradient. Thus, this option is incorrect.

Sodium-potassium pumps are a specific example of _active transport_. Facilitated diffusion utilizes various protein channels and carriers but not sodium-potassium pumps. Therefore, this is incorrect.

Both facilitated diffusion and active transport rely on membrane proteins to move substances across the cell membrane. In facilitated diffusion, these proteins are channels or carriers that facilitate the movement of substances down their concentration gradients. In active transport, these proteins are pumps that use energy to move substances against their concentration gradients.

Final Answer: The correct answer is D. They are both carried out by proteins embedded in the axon membrane.