Plasmolysis

Plant cells are eukaryotes, composed of specialized cellular organelles that differ in several fundamental factors from Animal cell. Plant cells usually consist of a thick cell wall that functions by holding them upright and also prevents from losing their shape. The plasma membrane, cytoplasm and all other cell organelles function together to keep the plant active. The vacuoles, a  fluid-filled membrane-bound organelle, located within the cytoplasm holds the water in the plant cell. In certain conditions,  plant cells do not get a sufficient amount of water or there is a severe loss of water from the cell. This results in the total shrinkage of the plant cell and the phenomenon are called plasmolysis.

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Table of Contents

What is Plasmolysis?

Plasmolysis is defined as the process of contraction or shrinkage of the protoplasm of a plant cell and is caused due to the loss of water in the cell. Plasmolysis is one of the outcomes of osmosis and rarely occurs in nature.

The word Plasmolysis was generally derived from a Latin and Greek word plasma – The mould and lusis meaning loosening.

Stages of Plasmolysis

The complete process of Plasmolysis take place in three different stages:

  1. Incipient plasmolysis: It is the first stage of the Plasmolysis. In this stage, water starts flowing out of the cell; initially, the cell shrinks in volume and cell wall become detectable.
  2. Evident plasmolysis: It is the second stage of the Plasmolysis. In this stage, the cell wall has reached its limit of contraction and cytoplasm gets detached from the cell wall attaining the spherical shape.
  3. Final plasmolysis: It is the third and the final stage of the Plasmolysis. In this stage, the cytoplasm will be completely free from the cell wall and remains in the centre of the cell.

How do Water Pass through the Cell Membranes?

During the process of Plasmolysis within the plant cell, the cell membrane separates the interiors of the cell from the surrounding. It permits the movement of water molecules, ion and other selective particles across the membrane and stops others. Water molecules travel in and out of the cell across the cell membranes and the water flow is a necessary consequence that enables cells to fetch water.

Plasmolysis

Demonstration of Plasmolysis in peels of the Rheo plant

The process of Plasmolysis can be easily demonstrated in the lab by placing a living cell in a strong salt solution. When the plant cells are placed in the concentrated salt solution, because of osmosis, water from the cell sap moves out. Therefore, the water travels through the cell membrane into the neighbouring medium. Finally, the protoplasm separates from the cell and assumes a spherical shape.

Normally, for this experiment Tradescantia or Rheo plant cell, Elodea plants or onion epidermal cells are used, because they have coloured sap which can be easily observed and identified under the microscope.

Types of Plasmolysis

There are two different types of plasmolysis and this classification is mainly based on the final structure of the cytoplasm.

Concave Plasmolysis

During the concave plasmolysis, both the cell membrane and protoplasm shrink away and begins to detach from the cell wall, which is caused due to the loss of water. Concave plasmolysis is a reversible process and it can be revised by placing the cell in a hypotonic solution, which helps calls to regain the water back into the cell.

Convex plasmolysis

During the convex plasmolysis, both the cell membrane and protoplasm lose so much water that they completely get detach from the cell wall. Later, the cell wall collapses and results in the destruction of the cell. Alike concave plasmolysis, convex plasmolysis cannot be reversed, and this happens when a plant wilts and dies from lack of water. This type of plasmolysis is more complex compared to convex plasmolysis.

Examples of Plasmolysis

Plasmolysis is more common and happens in extreme cases of water loss. Some real-life examples of Plasmolysis are:

  • Shrinkage of vegetables in hypertonic conditions.
  • Blood cell shrinks when they are placed in the hypertonic conditions.
  • During extreme coastal flooding, ocean water deposits salt onto land.
  • Spraying of weedicides kills weeds in lawns, orchards and agricultural fields. This is due to the natural phenomena-Plasmolysis.
  • When more amount of salt is added as the preservatives for food like jams, jellies, and pickles. The cells lose water due to higher concentration outside and become less conducive to support the growth of microorganisms.

Also read: Osmosis

Deplasmolysis

When the plasmolysed cell is placed in a hypotonic solution, (the solution in which solute concentration is less than the cell sap), the water travels into the cell due to the higher concentration of water outside the cell. Then the cell swells and becomes turgid. This is known as deplasmolysis.

When the living cells are placed in isotonic solution(both solutions have an equal amount of solute particles), the water does not flow within or outside. Here, the water passes in and out of the cell and in an equilibrium state, and Therefore, the cells are called as flaccid.

To know more about Plasmolysis and other Biology related concepts@ BYJU’S Biology

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