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How are diffusion and osmosis different?

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  • Diffusion:

    • Diffusion is the transport of the gasses from the region of higher concentration to the region of lower concentration.

    • The gases that are to be transported in and out of the cell are oxygen and carbon dioxide. Oxygen is required to generate energy by cellular respiration and carbon dioxide is the product of cellular respiration.

    • Thus, the concentration of CO2 increases inside the cell and that of O2 decreases.

    • When the concentration of CO2 becomes more inside the cell as compared to outside, it voluntarily moves out of the cell.

    • At the same time, the concentration of O2 decreases inside the cell and it is been more outside the cell causing the voluntary movement of O2 inside the cell. This is how the diffusion of gases takes place.

  • Osmosis:

    • Osmosis is the movement of water from the region of high concentration of water to the region of low concentration.

    • The plasma membrane allows the movement of the water molecules in and out of the cell at the same time.

    • The movement of water also depends on the substances dissolved in the water. If more substances are dissolved on one side of the membrane than the other side, then water moves towards the region where there are more dissolved substances.

    • Hypotonic solution: When the cell is kept in a solution containing less dissolved substances as compared to that inside the cell, the rate of movement of the water from inside the cell to the outside is less than the rate of movement of water from outside to inside the cell. This results in an increase in the volume of cell solution and the cell swells. This phenomenon is called endosmosis and the solution outside the cell is called a hypotonic solution.

    • Isotonic solution: When the cell is kept in a solution containing equally dissolved substances as compared to that inside the cell, the rate of movement of the water from inside the cell to the outside is equal to the rate of movement of water from outside to inside the cell. This results in no change in the volume of cell solution. The solution outside the cell is called an isotonic solution.

    • Hypertonic solution: When the cell is kept in a solution containing more dissolved substances as compared to that inside the cell, the rate of movement of the water from inside the cell to the outside is more than the rate of movement of water from outside to inside the cell. This results in a decrease in the volume of cell solution and the cell shrinks. This phenomenon is called exosmosis and the solution outside the cell is called a hypertonic solution.

    • The examples of osmosis are: Movement of water in the unicellular freshwater organisms; Absorption of water by the cells of the root from the soil.

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