The sodium-potassium pump moves sodium and potassium ions across the plasma membrane by:

Options

A. facilitated transport
B. active transport
C. cotransport
D. endocytosis

Explanation

**Step-by-Step Solution:**

1. **Understanding the Sodium-Potassium Pump**: The sodium-potassium pump is a vital membrane protein that helps maintain the concentration gradients of sodium (Na⁺) and potassium (K⁺) ions across the plasma membrane of cells.

2. **Ion Movement**: The pump specifically moves three sodium ions out of the cell and two potassium ions into the cell. This process is essential for various cellular functions, including maintaining osmotic balance and electrical excitability in neurons.

3. **Energy Requirement**: The movement of these ions against their concentration gradients (from low to high concentration) requires energy. This energy is derived from ATP (adenosine triphosphate), which is the primary energy currency of the cell.

4. **Type of Transport**: Since the sodium-potassium pump requires energy to move ions against their concentration gradients, it is classified as an active transport mechanism. Active transport differs from passive transport, where substances move along their concentration gradient without the use of energy.

5. **Carrier Proteins**: The sodium-potassium pump utilizes specific proteins known as carrier proteins. These proteins facilitate the transport of ions by undergoing conformational changes that allow the ions to be moved across the membrane.

6. **Conclusion**: Based on the above information, the sodium-potassium pump moves sodium and potassium ions across the plasma membrane primarily through active transport.

**Final Answer**: The sodium-potassium pump moves sodium and potassium ions across the plasma membrane by **active transport**.

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