What is known as plasmolysis?

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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 an example of the results 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.

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

1. Incipient plasmolysis: It is the initial stage of the plasmolysis, during which, water starts flowing out of the cell; initially, the cell shrinks in volume and cell wall become detectable.
2. Evident plasmolysis: It is the next stage of the plasmolysis, during which, 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, during which 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 allows 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.

Demonstration of Plasmolysis in Rheo plant

The process of plasmolysis can be easily explained in the laboratory 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.

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. Similar to 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 complicated compared to convex 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

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.

Stay tuned with  BYJU’S Biology to learn more in detail about plasmolysis and other related concepts.

Plasmolysis is when plant cells lose water after being placed in a solution that has a higher concentration of solutes than the cell does. This is known as a hypertonic solution. Water flows out of the cells and into the surrounding fluid due to osmosis. This causes the protoplasm, all the material on the inside of the cell, to shrink away from the cell wall. Severe water loss that leads to the collapse of the cell wall can result in cell death. Since osmosis is a process that requires no energy on the part of the cell and cannot be controlled, cells cannot stop plasmolysis from taking place.

Osmosis is responsible for the occurrence of plasmolysis. Osmosis is a special type of diffusion that occurs when water flows into or out of a membrane such as a cell’s plasma membrane. It occurs based on the type of solution that a cell is in. A solution is a mixture that contains a fluid, or solvent (usually water), and a solute that is dissolved in the solvent. When a cell is placed into a hypertonic solution, there is a higher concentration of solutes outside the cell, so water flows out of the cell to balance the concentration on both sides of the membrane. Since plasmolysis is the loss of water from a cell, it occurs when a cell is in a hypertonic solution. Conversely, when a cell is placed into a hypotonic solution, there is a lower solute concentration outside the cell than inside, and water rushes into the cell. In an isotonic solution, solute concentrations are the same on both sides, so there is no net gain or loss of water.

Plant cells fare best in hypotonic solutions. This is because when plant cells are full of water, they push against each other to form the basic support structure for the plant and allow it to stand upright. Plant calls full of water are known as turgid cells; they exert turgor pressure on each other. The cells’ rigid cell wall keeps them from bursting. Unlike plant cells, animal cells do not have a cell wall in addition to their cell membrane. When animal cells are placed in a hypotonic solution and too much water rushes in, they will lyse, or burst. They fare best in isotonic solutions instead.

This figure shows a plant cell in different types of solutions:

Concave plasmolysis is a process that can usually be reversed. During concave plasmolysis, the protoplasm and the plasma membrane shrink away from the cell wall in places due to the loss of water; the protoplasm is then called protoplast once it has started to detach from the cell wall. Half-moon-shaped “pockets” form in the cell as the protoplast peels from the surface of the cell wall. This can be reversed if the cell is placed in a hypotonic solution, which will cause water to rush back into the cell.

Convex plasmolysis is more severe than concave plasmolysis. When a cell undergoes complex plasmolysis, the plasma membrane and protoplast lose so much water that they completely detach from the cell wall. The cell wall collapses in a process called ctyorrhysis. Convex plasmolysis cannot be reversed, and results in the destruction of the cell. Essentially, this is what happens when a plant wilts and dies from lack of water.

Plasmolysis happens in extreme cases of water loss, and does not happen very often in nature. Plants have a couple mechanisms to protect against water loss. Stomata, which are small holes on the underside of a plant’s leaves, close to help keep water in the plant. Plants also naturally produce wax that is another defense against water loss.

Although plasmolysis more commonly happens in a laboratory setting, it can happen in real-life settings as well. For example, during periods of extreme coastal flooding, ocean water deposits salt onto land. Too much salt causes the water to flow out of any plants on the affected land, killing them. Chemical weedicides are also used to kill unwanted plants through plasmolysis. This same process is also used when a lot of salt and/or sugar is added to preserve food and make jams, jellies, and pickles. The cells lose water and become less conducive to the growth of microorganisms such as bacteria, allowing these food items to be preserved.

• Osmosis – Process by which water diffuses across a membrane to balance out the solute concentration on either side of the membrane.
• Cell wall – Found in plant and fungi cells, a tough layer surrounding the outside of the cell that provides structural support.
• Ctyorrhysis – Permanent and irreversible collapse of the cell wall due to too much water being lost through plasmolysis.
• Protoplasm – The material comprising the inside of the cell; it is called protoplast when it separates from the cell wall through plasmolysis.

1. In what type of solution does plasmolysis occur?
A. Hypertonic
B. Isotonic
C. Hypotonic

A is correct. In a hypertonic solution, water flows out of plant cells through osmosis, and this causes the protoplast to detach partially or fully from the cell wall.

2. What mechanisms do plants use to defend themselves against plasmolysis?
A. The plants’ stomata close to help keep water inside.
B. The plants produce wax that keep water inside.
C. The plants pump water into their cells through reverse osmosis.
D. Both A and B

D is correct. Stomata and wax are two defenses that plants have for maintaining enough water in their cells. Osmosis happens without any energy or control on the part of the cell, so the cell cannot reverse the process.

3. What type of solution is best for plant cells?
A. Hypertonic
B. Isotonic
C. Hypotonic

C is correct. Plant cells do best in a hypotonic solution because water flows into the cells and allows them to have full turgor pressure. In an isotonic solution, the cells are not as turgid as they could be since there is no net gain or loss of water, and the plant begins to droop. In a hypertonic solution, water flows out of the cells, and plasmolysis occurs.