What allows sodium and potassium ions to diffuse down their electrochemical gradient across the cell membrane?

• A. Ion channels
• B. Active transport pumps
• C. Exocytosis
• D. Endocytosis

Answer: (A)

Verified step by step guidance

1. Understand the concept of electrochemical gradients: These gradients are created by differences in ion concentration and electrical charge across a cell membrane.
2. Identify the role of ion channels: Ion channels are proteins that create specific pathways for charged ions to pass through the cell membrane.
3. Recognize that ion channels allow passive transport: This means ions move down their electrochemical gradient without the need for energy input.
4. Differentiate from active transport: Active transport pumps require energy to move ions against their gradient, which is not the case here.
5. Clarify that exocytosis and endocytosis are not involved: These processes are for moving large molecules or particles in and out of the cell, not for ion diffusion.