Question

The membrane protein channels or pores controlling the selective movement of water are

• A. Aquaporins
• B. Channel proteins
• C. Carrier proteins
• D. Transport proteins

Hint:

Aquaporins are the "water plumbing system" of the cell. Discovered by Peter Agre (who won the 2003 Nobel Prize), they allow water to cross membranes up to 10-fold faster than simple diffusion, while keeping the cell's ion balance intact.

Answer 1

The Correct Option is A

Step 1: Understanding the Concept:
While water molecules can slowly diffuse directly through the lipid bilayer of cell membranes (simple diffusion), the rate is insufficient to support rapid physiological processes like cell expansion, stomatal movement, and root water uptake.
Plants utilize specialized transmembrane channels to facilitate rapid, regulated water transport.

Step 2: Detailed Explanation:
Aquaporins (A): These are a family of highly conserved, water-selective channel proteins embedded in the plasma membrane (plasma membrane intrinsic proteins, PIPs) and tonoplast (tonoplast intrinsic proteins, TIPs).
They form narrow pores that allow the rapid, single-file movement of water molecules along osmotic or hydrostatic gradients while completely blocking the passage of ions and larger polar molecules.
Their activity is tightly regulated by gating mechanisms (such as phosphorylation and pH changes) to control cellular water balance.
While aquaporins are a subset of channel proteins, they are the specific membrane channels dedicated to selective water transport.
General channel proteins (B), carrier proteins (C), and transport proteins (D) are broader categories that transport various ions, sugars, and organic solutes, rather than selectively facilitating water transport.

Step 3: Final Answer:
The membrane channels controlling the selective movement of water are Aquaporins, which corresponds to option (A).