Osmosis and Diffusion – Definitions, Function

In nature, we often observe several phenomena which support the evidence for the processes of osmosis and diffusion. The movement in and outside the cells are identified as osmosis and diffusion. Ever wondered why the raisins become a puffball when left in the water or why your skin becomes wrinkled when you’re swimming for longer hours?

These daily-life examples show how osmosis takes place right in front of our eyes. Osmosis refers to the process wherein the particles move from the areas of lower concentration in the presence of a semi-permeable membrane to the areas of higher concentration.

Diffusion is also one of the prominent processes happening right in front of our eyes on a daily basis. You spray perfume in one corner of the room and the smell traverse to all the corners of the room. How a drop of food colouring diffuses into the water and how the tea is brewed by keeping the tea bag in hot water for a few minutes is an example of the diffusion process taking place in our daily life. Diffusion is the process wherein the particles move from the areas of higher density to the areas of lower density.

Osmosis

Osmosis is the cell movement wherein in the presence of a semipermeable membrane, the particles move from the areas of low density to the ones with higher concentrations. The phenomenon was deeply studied for the first time in 1877 by German plant physiologist Wilhelm Pfeffer. The term osmose (now osmosis) was coined for the first time by a British chemist Thomas Graham but the study was very less accurate as it talked about leaky membranes.

In the presence of a permeable membrane, the particles will move from the low concentration solutions to more concentrated solutions to dilute the solution on the other side of the membrane by a greater percentage. This movement can be stopped by applying pressure on the solution, called osmotic pressure. The membrane should be a living cell in order for the osmosis process to take place.

Diffusion

The process of diffusion refers to the cell movement wherein the particles move from the areas of higher concentration to the areas of lower concentration. The characteristic that sets apart diffusion from osmosis is that the diffusion does not require the presence of a membrane to kick-start the procedure.

The procedure of diffusion was identified in the 19th century, though it is said the artisans and blacksmiths were inducing the diffusion process since millennia to build objects. Diffusion in science was inspired by the studies conducted by Thomas Graham (diffusion in gases and saltwater),  Robert Brown’s Brownian motion which was also worked upon by Albert Einstein and Marian von Smoluchowski.

Points of Differences

Movements

Osmosis

In the case of Osmosis, the fluids move from the solutions with low concentrations towards the solutions with high concentrations. The difference in the concentration of the solute molecules on either side of the membrane leads to the different clusters of free molecules on either side of the membrane. On the side with a higher concentration,  the free water molecules strike the membrane creating pores from which the movements take place. These movements can be stopped through osmotic pressure.

Diffusion

In the case of diffusion, the particles move from the solutions with a higher concentration to the areas with a lower concentration to equalize the concentrations. The movement is continued up to the time equilibrium is reached. The process is induced by the random movement of particles. The difference between the concentration of the solutions is termed the concentration gradient. It has been identified that if this difference is bigger, the movement of diffusion is faster.

Presence of Membrane

Osmosis

The process of osmosis requires the presence of a semi-permeable membrane. The membrane plays a very important role in the process of osmosis. The membrane is selectively permeable, which allows the movement of selective molecules in and outside the cell structure. The membrane is two-layered made up of phospholipid and protein molecules along with the chains of fatty acids. The membrane can self-repair any minor harm imposed and it should be noted that any severe damage will make the cell deteriorate.

Diffusion

Usually, the diffusion of molecules does not require the presence of a membrane. As mentioned about the concentration gradient, every molecule has its own concentration gradient which is independent of the others and diffuse according to their own concentration gradient. There is a type of diffusion termed facilitated diffusion in which the molecules need the help of the plasma membrane to cross the threshold. These molecules do have their own independent concentration gradient, however, due to them being charged, the molecules are not able to diffuse on their own.

Examples

Osmosis

1. Swelling up of raisins when left in water.
2. Soil absorbing the water.
3. Wrinkling up of the skin due to prolonged exposure to water.
4. Shrinking of potato in a sugar solution.
5. Swelling up of red blood cells when placed in freshwater.

Diffusion

1. Spreading up of perfume smell from one corner of the room to other.
2. Cigarette smoke flaring up on the environment.
3. The brewing of tea through tea bags.
4. Disappearing carbon dioxide bubbles from the soda bottle when left open.

Conclusion

The movements in cells are identified as osmosis and diffusion. Osmosis is the movement from the lower concentration areas to higher concentration areas and diffusion is the movement from the higher concentration areas to the lower concentration areas.