To understand the working and functioning of molecules in the body, it is very important to first understand some terms in this topic.

Solute: These are those substances that are dissolved in any liquid.

Solvent: The liquid in which solute is dissolved is called solvent.

Hypotonic solution: When solute in the solution is in low amount than solvent, it’s called hypotonic solution.

Hypertonic solution: when solute in the solution is in high amount than solvent, it’s called hypertonic solution.

Isotonic solution: when both solute and solvent are in equal amount, it’s called isotonic solution.

After learning these terms well, it would be easy to understand the complete topic. There are several components that are essential for living cell. It can be thus figured out that these materials are not necessarily present in the cell, most of the time they are present outside the cell. This separation is due to the presence of semi permeable membrane that checks the entry and exists of molecule. Therefore, in such cases diffusion takes place where exchange of materials in and out of the cell occurs. Diffusion is the movement of molecules form higher to lower concentration.

In case of diffusion, when liquid is left untouched, the molecules move form high to low concentration but at the same time there are also lots of molecules in high concentration region and hence this results in net flow of molecule balancing both the sides and equalizing the concentration of both the side. Hence it is the random motion that increases the entropy of the complete system and works in accordance with the second law of thermodynamics.

The process of diffusion is important for small molecules that are needed by the cell. Diffusion can be of different types:

1. Simple diffusion: In this case the diffusion is completely simple where molecules move form high to low concentration.

2. Facilitated diffusion: In this case, substances that fail to normally diffuse to the other side by simple process, use protein channels for this process. Hence, the only difference is the involvement of protein channels.

It cannot be said that molecule does not move from low concentration to high concentration, yes molecule do move but the process requires expenditure of energy. In case of diffusion, there is no energy involved. Therefore, when we talk about free movement of molecules it goes along the concentration gradient that is from higher to lower till equilibrium is established.

Let’s see this in a better way with the example: if we have two lakes or pond side by side, one having less water and the other with more water, both with equal slopes followed by a small path for water flow between them, it can be clearly noticed that water from higher volume moves to that of lower ones. Same is the case in cell, like that in case with sodium and potassium ion where influx of sodium ion occurs and out fluxes of potassium ion, in order to balance ion in both side of the cell.

Therefore, in order to balance both side energy favors on high to low concentration, and hence molecules generally move form high to low concentration. If we talk about low to higher concentration, generally no such process takes place but in case if it does then energy is used that helps in transfer of molecules from low to high concentration.

This topic is included in science and also all its branches because it is very important for students to understand the movement of molecules because it is the part of biological system which covers the real world.

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