C. A passive transporter. Aquaporins are integral membrane proteins that form pores in the membrane of biological cells. Aquaporin proteins form complexes that span the membrane and water moves through these channels passively in response to osmotic gradients.Aquaporins selectively conduct water molecules in and out of the cell, while preventing the passage of ions and other solutes. Solution C. A passive transporter. Aquaporins are integral membrane proteins that form pores in the membrane of biological cells. Aquaporin proteins form complexes that span the membrane and water moves through these channels passively in response to osmotic gradients.Aquaporins selectively conduct water molecules in and out of the cell, while preventing the passage of ions and other solutes..