Question

Does diffusion occur in only one direction, or can one substance diffuse in one direction, and a second substance diffuse in the opposite direction? What is your evidence? Give specific examples. What determines the direction of diffusion?

Answer 1

Interesting one!! Yes, diffusion occurs only in one direction; i.e. from a region of high concentration to one of lower concentration. All the substances will always diffuse from a region of their higher concentration to one of their lower concentration.

Let me give you answer to your last question before giving the examples and the answer is Concentration Gradient. Yes, it is only concentration gradient which determines the direction of diffusion. A concentration gradient is a just a region of space over which the concentration of a substance changes and substances will naturally move down their gradients, from an area of higher to an area of lower concentration.

Now, let me come to the examples, in our daily life we see many examples of diffusion, as well as in our body, in many reactions, diffusion is taking place.

One example I will give you, its very simple, and you see daily in your life, Suppose you take a beaker full of normal water, then you add some droplets of red dye into it, then what you see, that within less than a minute, the whole water becomes red, it is due to diffusion, that the molecules of red dye move towards their low concentration from their high concentration.

Now another example is from our body itself, Oxygen inhaled into our body diffuses through the lungs and into the bloodstream. The oxygen is then transported throughout the body. Carbon dioxide is the waste gas produced by respiration. Carbon dioxide diffuses from body tissues into the bloodstream and is exhaled via the lungs.

The figures are attached with the answer to make you understand better.

Hope this answer helps you, Thanks.