Orange dye moves independently of purple dye.Concentration gradients exist that drive diffusion of both dyesThere is a net movement of orange dye from side A to side B.Purple dye moves only from side B to side A.
There is no net movement of purple dye.
The Correct Answer and Explanation is:
Correct Answer:
There is no net movement of purple dye because the concentration of purple dye is equal on both sides, even though individual purple dye molecules continue to move from side B to side A and vice versa.
Explanation (300+ words):
Diffusion is the movement of molecules from an area of higher concentration to an area of lower concentration. This process continues until there is an equilibrium, meaning the molecules are evenly distributed across the space available. Importantly, diffusion is passive—it does not require energy—and it relies entirely on the concentration gradient of a substance.
In the situation described, we have two different dyes: orange and purple. Each dye diffuses independently, meaning the movement of one does not affect the movement of the other. This is typical in biological and chemical systems where different substances follow their own concentration gradients.
We are told that:
- The orange dye is moving from side A to side B, which suggests a higher concentration on side A and a lower concentration on side B.
- The purple dye is moving only from side B to side A, but overall, there is no net movement.
“No net movement” means that while individual molecules of purple dye may still be moving back and forth, the total amount of purple dye on each side stays the same. This occurs when the concentration of purple dye is the same on both sides—an equilibrium has been reached. In such a state, random molecular motion still happens, but the rate of movement in each direction is equal, canceling each other out.
Thus, the presence of equal concentration explains why there is no net movement of purple dye. Even though molecules still move (as molecules always have kinetic energy), they do so equally in both directions, leading to dynamic equilibrium.
This principle is crucial in physiology, particularly in how gases like oxygen and carbon dioxide diffuse across membranes in the lungs, or how nutrients move into and out of cells.