Q.Which one of the following is a Carrier Protein?

Symport is a carrier protein — it binds two solutes and, by undergoing a conformational change, moves both across the membrane in the same direction; porins and aquaporins are channel proteins, not carriers.

Cell membrane transport proteins fall into two broad structural classes:

1. Channel proteins — form a continuous, water-filled pore through the membrane. Solutes simply diffuse through the open pore without the protein changing shape. Porins (found in the outer membrane of Gram-negative bacteria, mitochondria and chloroplasts) and aquaporins (water-specific channels) both belong here.
2. Carrier (transporter) proteins — do NOT form an open pore. Instead, the carrier binds the solute on one side of the membrane, undergoes a conformational change, and releases the solute on the other side. Carrier-mediated transport is classified by how many solutes move and in which direction:
   • Uniport — one solute moves alone. …