Osmosis and Diffusion!! Yeah!

OSMOSIS AND DIFFUSION

Definition

Osmosis is the passage of water from a region of high water concentration through a semi-permeable membrane to a region of low water concentration.

The definition contains three important statements:

1. Osmosis is the passage of water from a region of high water concentration through a semi-permeable membrane to a region of low water concentration.
2. Osmosis is the passage of water from a region of high water concentration through a semi-permeable membrane to a region of low water concentration.
3. Osmosis is the passage of water from a region of high water concentration through a semi-permeable membrane to a region of low water concentration.

Explanation

First the definition of osmosis:

1. Semi-permeable membranes are very thin layers of material (cell membranes are semi-permeable) which allow some things to pass through them but prevent other things from passing through.
   
   Cell membranes will allow small molecules like Oxygen, water, Carbon Dioxide, Ammonia, Glucose, amino-acids, etc. to pass through. Cell membranes will not allow larger molecules like Sucrose, Starch, protein, etc. to pass through.
2. A region of high concentration of water is either a very dilute solution of something like sucrose or pure water. In each case there is a lot of water: there is a high concentration of water.

3.      A region of low concentration of water is a concentrated solution of something like sucrose. In this case there is much less water.

Diffusion refers to the process by which molecules intermingle as a result of their kinetic energy of random motion.

Consider two containers of gas A and B separated by a partition.

The molecules of both gases are in constant motion and make numerous collisions with the partition. If the partition is removed as in the lower illustration, the gases will mix because of the random velocities of their molecules.

In time a uniform mixture of A and B molecules will be produced in the container.

The tendency toward diffusion is very strong even at room temperature because of the high molecular velocities associated with the thermal energy of the particles.

Diffusion and Osmosis are both types of PASSIVE TRANSPORT - that is, no energy is required for the molecules to move into or out of the cell.