Peter Agre (1949- present) was awarded half the 2003 Nobel Prize in Chemistry for revealing the molecular basis for the movement of water into and out of cells. He was able to isolate a protein in the cell membrane that he later discovered to be a water channel, which had been discussed by scientists since the mid-1800s. With colleagues, he studied the response of cells with and without the channel when placed in a water solution. The cells with the channel swelled up as water flowed in, while those lacking the channel remained the same size. Agre named the channel aquaporin. Researchers subsequently discovered a whole family of water channels in animals, plants, and bacteria. Two different aquaporins were later found to play a major role in the mechanism by which human kidneys concentrate urine and return the extracted water to the blood.