Two routes into a cell

An artificial cell takes up solute Z through a saturable transporter and a passive leak. The initial uptake is J = Jmax C/(K + C) + kC, with external concentration C, negligible internal Z, Jmax = 12 units/min, K = 2 mmol/L and k = 1 unit min⁻¹ per mmol/L. A selective blocker removes transporter activity but leaves the leak unchanged. All measurements use identical membrane area. A graph of blocked uptake against C is a straight line through the origin; unblocked uptake bends towards a line parallel to it.