Graphs A and B depict two ways of determining how molecules

Graphs A and B depict two ways of determining how molecules (in this case, molecules (X, Y, Z)can gain entry into a cell: (A)Increase the extracellular concentration (Co) of the molecule and measure flux and (B) keep Co constant and measure the intracellular concentration (Ci) of the molecule over time until equilibrium is reached. Which molecule enters by simple diffusion? explain? Which of the molecules enters by facilitated diffusion? explain? Which molecule enters by active transport? explain?

Solution

(a) The molecule Z enters the cell by simple diffusion.

The reason is that, as the extra-cellular concentration (Co) is increased, the flux also increases exponentially. In simple diffusion, the transport of molecules is from a region of high concentration to a region of low concentration. Therefore, as the concentration is increased in the exterior of cell, the flux increases and since it is a passive transportation process, no energy is expended.

(b) The molecule X enters the cell by facilitated diffusion.

The reason is that, when the extracellular concentration is kept constant, the intracellular concentration (Ci) increases with time until the Co equals Ci. Facilitated diffusion is similar diffusion but with the need of proteins to help in the process.

(c) The molecule Y enters the cell by active transport.

The reason is that, even when the extracellular concentration is not increased, the Ci increases ith the help of energy driven active transport process.