A scientist who is studying passive movement of chemicals across the cytoplasmic membrane of Salmonella enterica serotype Typhi measures the rate at which two chemicals diffuse into a cell as a function of external concentration. The results are shown in the following figure. Chemical A diffuses into the cell more rapidly than does B at lower external concentrations, but the rate levels off as the external concentration increases. The rate of diffusion of chemical B continues to increase as the external concentration increases.
a. How can you explain the differences in the diffusion rates of chemicals A and B?
b. Why does the diffusion rate of chemical A taper off?
c. How could the cell increase the diffusion rate of chemical A?
d. How could the cell increase the diffusion rate of chemical B?