A human kidney cell has 2 x 105 aquaporin monomers in its plasma membrane. If water molecules flow through the cell membrane at 5 x 108 per aquaporin tetramer per second and the volume of the kidney cell is 5 x 10-11, ml, how long will it take for the kidney cell to reduce its water volume by ½? (Avogadro’s number = 6.02 x 1023 Density of H2O = 103 gL-1)