Diffusion is the net movement of ions and/or molecules from the area of high concentration to a lower concentration area.

Diffusion only occurs in liquid and gas. Solid particles are packed together which is why excess molecules cannot pass through it.

The best example of diffusion is found in your kitchen. You probably have noticed that the smell of your cooked food reaches your room. What happens is that the food particles which have evaporated from your food due to intense heat has spread across the air in your kitchen creating a high concentration of food particles in the kitchen. According to the nature of such particles it travels to places which have low concentration of the food particles. This process occurs in seconds.

In Liquid, you can test such process by adding a liquid food color on to a clean glass of water. You shouldn’t mix it with spoon as it will only speed up the process and ruin the experiment. The food color will slowly spread across the water and turn the whole solution blue in a matter of 24 hours. What happens is that the colored particles move and try to reach the low concentration area where the color has changed yet.

Comparing Liquid with Gas:

In gas the process of diffusion is much faster compared to liquid. This is because of their properties. Gas has large spaces in between its molecules allowing the molecules to roam freely.

Liquid, however, has small spaces between its molecules. Resulting in a bit of delay before other particles pass through.


Osmosis involves water particles. It is the process of water molecules passing through a partially permeable membrane from a diluted solution to the concentrated solution.

For example; When you pour a sucrose solution, which has 10% sucrose in it, in one end of the U-tube and pour a sucrose solution which has 5% of sucrose in the other and divide the solutions with a partially permeable membrane, you will notice that osmosisthe 10% sucrose solution will rise. The 5% sucrose solution will decrease. This happens because the 5% sucrose solution has more water particles compared to the other solution.

This may seem a little complex but you will understand it when you try it practically.

Water Potential:

This is simple. You can understand this by using the U-tube example. The side with more water molecules which is the diluted sucrose solution that solution has the high water potential. Meaning it has higher potential to move to the other side of the partially permeable membrane than the lower potential side.

You can also define osmosis with this.

Osmosis is the net movement of the water molecules from a solution with high water potential to the solution with lower water potential.

Diffusion and Osmosis in Living Organisms:

Such processes occur in our bodies as well. Cells in our bodies have a partially permeable membrane that lets in molecules. The molecules which diffuse through mostly are food particles which have been cut to very small sizes by the enzymes in the digestive system. The mitochondria break the particles down to extract energy which strengthens the living organism.

Osmosis is used by the cells to dispose the wast products in form of urea and sweat etc.

Hypo tonic, Isotonic and Hyper tonic solutions:

Isotonic solution:

When a solution and a cell have the same amount of water molecules that solution is called isotonic solution.

                                                                                          Hyper tonic solution:

Tonic2When a solution has more concentration of water molecules compared to the cell it is hypertonic with respect to the cell.

Hypo tonic solution:

When the concentration of water molecules in a solution is lower compared to the the cell it is hypo tonic with the respect to the cell.

Cells in the Hyper tonic solution:


Animal cells in such solutions:

In a solution with low water molecules (hypo tonic solution) the animal cell will expand as the water molecules in the cytoplasm will try to escape and it will burst.

In a solution with a high water molecules (hyper tonic solution) the animal cell will shrivel as the water molecules would enter the cell and damage the plasma membrane causing it to shrivel.

In an isotonic solution no change will occur.

Plant cells in such solutions:

In a hypo tonic solution the water molecules in the plant cell would try to burst out. The cell wall would not allow the cell to burst making it turgid.

In a hyper tonic solution the water molecules in the solution would try to enter the cell but the cell wall won’t allow it, making it plasmolyzed.

No change occurs in isotonic solution.

Active Transport:

When a cell absorbs substances from a lower concentrated solution though the cell has a higher concentration of such substances than the outside solution. This process is called active transport.

Concentration Gradient:

To understand all this you should use the concentration gradient graph.
singlebargraph2As you can see in the case of diffusion the particles move from the higher concentration gradient to the low concentration gradient.

In active transport the absorption occurs against the concentration gradient. Particles move from low concentration gradient to the high concentration gradient.

With this I conclude today’s article.


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