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Osmosis in the plant cell


As stated above, if two solutions remain separated by a semipermeable membrane, water flows from the most dilute to the most concentrated solution. This diffusion of the solvent is called osmosis.

When a plant cell is in a hypotonic environment, it absorbs water. Unlike the animal cell, it does not break, because it is coated with cell wall or cellulosic membrane, which is fully permeable but has limited elasticity, restricting the increase in cell volume. Thus, water entry into the cell does not depend solely on the osmotic pressure difference between the extracellular medium and the intracellular medium (mainly the osmotic pressure of the vacuolar juice, liquid present within the vacuole of the plant cell).

It also depends on the counter pressure exerted by the cell wall. This pressure is known as turgor pressure, or resistance of the cellulosic membrane to water entering the cell.

Osmosis in the plant cell It depends on the osmotic pressure (PO) exerted by the vacuole solution, which is also called the internal suction of the vacuole (Si). We may call the osmotic pressure or internal suction of the vacuole the force of water entering the plant cell.

As water enters the plant cell, the cellulosic membrane undergoes deformation and begins to exert force against water entering the plant cell.

This force of resistance to water entering the plant cell is called Turgor or Turgescence pressure (PT) or cellulosic membrane resistance (M).

This turgidity of water entering the plant cell may be called the water output force of the plant cell.

The difference between the inlet and outlet forces of the plant cell water is called the DPD diffusion pressure difference or cellular suction (Sc).

Thus we have:

DPD = PO - PT

or

Sc = Si - M