. (a) According to Fick's law , the diffusion of a solute across a cell membrane is given by ′ () = [ − ()], ⋯ ⋯ ⋯ ⋯ ⋯ ⋯ ⋯ ⋯ ⋯ (1) where is the area of the cell membrane, is the volume of the cell, () is the concentration inside the cell at time , is the concentration outside the cell, and is a constant. If 0 represents the concentration of the solute inside the cell when = 0, then it can be shown that () = (0 − ) − + ⋯ ⋯ ⋯ ⋯ ⋯ ⋯ ⋯ (2) (i) Use the last result to find ′(). (ii) Substitute back into Equation (1) to show that (2) is indeed the correct antiderivative of (1). [8] (b) If the rate of excretion of a bio-chemical compound is given by () = 0.02 −0.02 , the total amount excreted by time (in minutes) is (). (i) Find an expression for () (ii) If 0 units are excreted at time = 0, how many units are excreted in 15 minutes?