Question

exam lesson name: the cell and its processes
exam number: 700942rr
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question 19 of 20 :
select the best answer for the question.

1. why is active transport necessary for the sodium-potassium pump to work?

○ a. it allows sodium and potassium to move against their concentration gradient.
○ b. all channel movement requires active transport to equalize the cell.
○ c. the sodium would never leave a cell while potassium can move against the gradient.
○ d. the potassium would never leave a cell while sodium can move against the gradient.

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Explanation:

To determine the answer, we analyze the sodium - potassium pump and active transport:

1. Recall the concept of active transport: Active transport is the movement of molecules across a cell membrane from a region of lower concentration to a region of higher concentration (against the concentration gradient), and it requires energy.
2. Analyze the sodium - potassium pump: The sodium - potassium pump moves 3 sodium ions out of the cell and 2 potassium ions into the cell. Sodium ions are moving from an area of lower concentration outside the cell to higher concentration inside the cell (initially, but the pump moves them out against their concentration gradient), and potassium ions are moving from an area of lower concentration inside the cell to higher concentration outside the cell (the pump moves them in against their concentration gradient). So, the sodium - potassium pump needs active transport because it moves sodium and potassium against their concentration gradients.
3. Evaluate the options:

• Option A: This option correctly states that active transport allows sodium and potassium to move against their concentration gradient, which is the reason the sodium - potassium pump needs active transport.
• Option B: Not all channel movement requires active transport. For example, ion channels can allow for passive transport (like in facilitated diffusion). Also, the goal of the sodium - potassium pump is not to equalize the cell (in fact, it helps maintain the electrochemical gradient), so this option is incorrect.
• Option C: Sodium can leave the cell through the sodium - potassium pump (with active transport), and potassium also moves against its gradient (into the cell) via the pump, so this statement is incorrect.
• Option D: Potassium is moved into the cell (against its gradient) and sodium is moved out of the cell (against its gradient) by the pump, so this statement is incorrect.

Answer:

A. It allows sodium and potassium to move against their concentration gradient.