The correct answer to the question is:
d. active transport.
Explanation:
1. Active transport is a process in which molecules or ions move across a cell membrane from an area of lower concentration to an area of higher concentration, requiring energy input to drive this movement against the concentration gradient.
2. The sodium-potassium pump is a specific example of active transport in cells. It actively transports sodium ions out of the cell and potassium ions into the cell against their respective concentration gradients.
3. In this process, the sodium-potassium pump uses energy in the form of ATP (adenosine triphosphate) to pump sodium and potassium ions across the cell membrane, maintaining the cell's electrochemical gradient.
4. Unlike passive transport processes such as facilitated diffusion, where molecules move along the concentration gradient without energy input, active transport mechanisms like the sodium-potassium pump play a crucial role in maintaining cellular homeostasis and proper functioning.
