Saturday, March 5, 2016



You have learnt earlier that plants survive if water, minerals ans others nutrients are provided to them. In this lesson, we will learn how these substances enter the plant cell. To understand this we have to understand the terms diffusion and ‘osmosis’ and the processes associated with them.

We will do a simple experiment to understand the process of diffusion. Take a beaker full of water and carefully add two or three crystals of copper sulphate or potassium permanganate.
When the crystals settle down on the bottom of beaker, leave it on the table and do not distrub this and Watch it from time to time and record the changes in the colour of water.
The crystals starts dissolving in water. The water around the crystals will appear dark in colour. As time progress, all the wter in the beaker becomes coloured- initially pale in colour and slowly all the water in the beaker becomes uniformly coloured.
Let us now understand the changes that have taken place.
When the permanganate crystal settles at the bottom of the beaker, a small amount of water comes in contact with the surface of crystal. This water dissolves permanganate and results in the formation of a 
concentrated solution of the salt at the point. 
This is the reason for the appearance of small dark coloured spot at the bottom of the beaker in the intial stages.
From this spot, the molecules of permanganate move away and get dispered all over the water in the beaker. As this goes on, rest of the water becomes coloured.
As the concentration of dissolved permanganate increase, the colour of water also becomes darker. Finally, after along time, all the molecules of permanganate are uniformly distrusted in the water and water in the beaker becomes uniformly coloured.
From this experiment we cleared that:
1. All the molecules in a solution are in a state of       continuous motion.
2. They move randomly in all the directions.
3. Molecules move from higher concentration to         lower concentration.
4. this movement from higher to lower                  

    concentration occurs till the concentration    
    becomes equal at both the points..

The process of movement of molecules or ions from appoint of high concentration to a point of low concentration till the concentration at both the points become equal is called diffusion.
We have not supplied and additional energy for the movement of the molecules. The energy required for the movement of molecules comes from the kinetic energy of the molecules its self. The process of diffusion occurs nor only in water but also in air.
The process of diffusion occurs not only in water but also in air. This is commonly amounts in the bottle is opened- molecules responsible for perfume are in the air amounts in the bottle while there are no perfume molecules in the air surrounding the bottle. Hence , perfume molecules diffuse through air to all the areas in the room.
Diffusion is physical process and no external energy is required for the movement of molecule by diffusion.


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