Question

In plant cells, the principal ion that is electrogenically pumped across membranes in plasmamembrane and tonoplast is:

• A. $\text{Mg}^{2+}$
• B. $\text{K}^+$
• C. $\text{Ca}^{2+}$
• D. $\text{H}^+$

Hint:

In animal cells, the principal electrogenic pump is the $\text{Na}^+/\text{K}^+$-ATPase.
In plants, fungi, and bacteria, the equivalent primary pump is always the $\text{H}^+$-ATPase.

Answer 1

The Correct Option is D

Step 1: Understanding the Concept:
Electrogenic pumps are primary active transporters that hydrolyze ATP to pump ions across biological membranes, establishing an electrochemical gradient.

Step 2: Detailed Explanation:
In plant cells, the proton ($\text{H}^+$) is the primary ion used to establish membrane potential and drive secondary active transport.
At the plasma membrane, P-type $\text{H}^+$-ATPases pump protons out of the cytoplasm into the extracellular space.
At the vacuolar membrane (tonoplast), V-type $\text{H}^+$-ATPases and $\text{H}^+$-pyrophosphatase (V-PPase) pump protons from the cytoplasm into the vacuole.
These activities maintain a proton-motive force that drives the uptake of nutrients, sugars, and other ions against their concentration gradients.

Step 3: Final Answer:
The principal ion electrogenically pumped across the plasma membrane and tonoplast is the proton ($\text{H}^+$).