Concept:Water moves across kidney cell membranes by osmosis, which is the movement of water from a region of higher water concentration to lower water concentration through a semi-permeable membrane.Explanation:In the kidneys, water is reabsorbed from the filtrate back into the blood.This movement of water occurs through a semi-permeable membrane, from where water is more concentrated to where it is less concentrated.This process is called osmosis.Answer:C. osmosis