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Plant Cell Osmosis: vital to the plant's existence.
Introduction
All cells are lined with a membrane. A feature of this membrane that confers the ability to keep the cell alive is selectivity. The cell membrane, including plant cells, is semipermeable. It is crossed by water molecules. Also, glycoproteins are carrier elements that let some solutes pass, but not others.
If a plant cell is in a medium more diluted than its interior, water flows from that medium into the cell. We call this process osmosis.
Is the cell wall or cellulosic membrane, which is covering the cell membrane of plant cells, also semipermeable? No, the cell wall is entirely permeable. That is, the cell wall does not restrict the flow of water or solutes.
Main features and how it occurs
Plant cell osmosis does not occur in an uncoordinated manner. Otherwise, the inside of the cell would be flooded with water or dehydrated so that both situations would result in biochemical problems. Two processes need to work well:
1 - Does the cell wall maintain its elastic limit
Although basically composed of cellulose, the cell wall has a certain elasticity. The wall exerts a force contrary to the pressure exerted by the water entering the cell: the turgor pressure (PT). This pressure limits the entry of more water.
2 - The osmotic pressure of the vacuole in operation
Plant cells have organelles called vacuoles, which, among other functions, participate in osmotic control of the cell. Vacuoles contain an internal fluid and this exerts a force called Osmotic Pressure (PO). It creates a pressure for water to enter the plant cell.
Calculation of force difference
There is a difference between the inlet and outlet water pressures of the plant cell. It is known as Diffusion Pressure Difference (DPD), can be expressed in number and calculated mathematically. The formula for its calculation is:
DPD = PO - PT
Curiosity
Some plants face prolonged drought but do not wither. The vacuoles in their cells accumulate low molecular weight compounds. These compounds allow minimal water to enter cells and keep them turgid.
