Glycerol enters some cells by simple diffusion and other cel

Glycerol enters some cells by simple diffusion and other cells through a carrier protein, On the plot below, indicate which line represents passive diffusion and which represents diffusion through a channel. Why do the rates of the two processes differ at low substrate concentration? Why do the rates of the two processes differ at high substrate concentration?

Solution

a) A is diffusion through channel and B is passive diffusion

b) At low substrate concentration, rate of transport differs in both A and B. Because passive diffusion is always at the steady state rate but diffusion through channel depends on number of channels opened so its rate is higher.

c) At high substrate concentration, rate of transport in passive diffusion maintains its steady state rate so it gradually increases along with substrate concentration. But in diffusion through channel, as the substrate concentration increases, there will be saturation state that is the channels will be overcrowded to handle such concentration.