Question

The $Na^+$/$K^+$ pump is present in the plasma membrane of mammalian cells where it
A. Expels potassium from the cell.
B. Expels sodium and potassium from the cell.
C. Pump sodium into the cell.
D. Expels sodium from the cell.

Answer 1

Hint: The sodium and potassium move against the concentration gradient. It is found in cell membranes and is present in all cellular life. It helps in maintaining the cell potential and cellular volume.

Complete Answer:
The plasma membrane is semi-permeable in nature. It facilitates the transport of ions and molecules across the cell. The molecules and ions are transported by the help of protein channels and protein pumps.
Mechanism of $Na^+$/$K^+$ pump- This process takes place against the concentration gradient. This pump utilises energy.
- 3 sodium ions bind to the carrier protein/pump.
- A phosphate from the ATP is utilised by the pump, the pump changes its shape and expels sodium out of the cell.
- 2 potassium ions bind to the pump and are transferred into the cell.
- Phosphate is released and the pump regains its original shape.

Thus the correct answer is (D). The $Na^+$/$K^+$ pump is present in the plasma membrane of mammalian cells where it expels sodium out of the cell.

Note: Sodium and potassium are needed for the body for proper functioning. It helps in maintaining the blood and fluid volume in the body. A person suffers from high blood pressure when he consumes too much sodium and less potassium.