In order to gain an understanding of plasmolysis in a plant cell or a plasmolysed cell, one needs to know the definition of plasmolysis, examples, importance, types, processes, and causes. This article elaborates more on these.
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Plasmolysis definition in biology
Plasmolysis in plant cells is defined as the constriction of a eukaryotic cell caused by protoplast shrinkage when exposed to a hypertonic solution.
What is plasmolysis?
Plasmolysis is the process whereby the protoplasm of a plant cell shrinks away from its cell wall.
Plasmolysis occurs due to water molecules diffusing to their concentration gradient, causing plants to lose water. However, in animal cells, the net efflux of water causes the cells to wrinkle, but the existence of the cell wall in plant cells prevents them from becoming wrinkled like the animal cells.
- When blood cells are exposed to hypertonic circumstances, they shrivel.
- The dumping of salts onto land by ocean water during significant coastal flooding.
- Plasmolysis causes the killing of weeds after the application of weedicides on lawns, orchards, and agricultural areas.
- When a higher level of salt is used as a preservative in foods such as jams, jellies, and pickles. Because of the increased concentration outside, the cells lose water and become less favorable to microbe development.
- When vegetables shrink in hypertonic environments.
The above mentioned are some of the examples of plasmolysis in our daily life.
What causes plasmolysis?
Plasmolysis is caused by water loss which causes protoplasmic shrinkage, resulting in holes between the cell wall and plasma membrane. This water loss can be caused by a change in the solute concentration in the environment of the cell.
Process of plasmolysis
- Incipient plasmolysis
- Evident plasmolysis
- Final plasmolysis
The above listed are the 3 stages or processes involved in plasmolysis.
This is the first stage of plasmolysis and it occurs when water begins to flow out of the cell. Initially, the cell shrinks in volume and the cell wall becomes detectable.
This is the next stage of plasmolysis in which the cell wall reaches its limit of contraction and the cytoplasm separates from the cell wall, forming a spherical shape.
This is the third and final stage of plasmolysis, in which the cytoplasm is completely free of the cell wall and remains in the cell’s center.
The cell membrane separates the interiors of the plant cell from the surrounding environment during the Plasmolysis process. It allows water molecules, ions, and other selective particles to pass through the membrane while preventing others from doing so. Water molecules travel in and out of cells across cell membranes, and water flow is a necessity that allows cells to obtain water.
Plasmolysis can be easily demonstrated in the laboratory by immersing a living cell in a strong salt solution. When plant cells are immersed in a concentrated salt solution, osmosis causes water from the cell sap to escape. As a result, water passes through the cell membrane and into the surrounding medium. Finally, the protoplasm separates from the cell and takes on the shape of a sphere.
Onion cell plasmolysis
Normally, in conducting such experiments, Tradescantia or Rheo plant cells, Elodea plants (known as elodea plasmolysis experiment), or onion epidermal cells (known as the onion cell plasmolysis experiment) are used because they have colored sap that can be easily observed and identified under the microscope. The video below elaborates on the onion plasmolysis.
Types of plasmolysis
- Concave plasmolysis
- Convex plasmolysis
The two types of plasmolysis are distinguished primarily by the final structure of the cytoplasm.
Concave plasmolysis is a typically reversible process. The loss of water during concave plasmolysis causes the protoplasm and plasma membrane to shrink away from the cell wall. The protoplasm is then referred to as protoplast once it has begun to detach from the cell wall. As the protoplast peels from the surface of the cell wall, half-moon-shaped “pockets” form in the cell. This can be reversed by immersing the cell in a hypotonic solution, which causes water to rush back into the cell. In the event of concave plasmolysis, they create concave pockets.
When a cell undergoes convex plasmolysis, the plasma membrane and protoplast lose so much water that they detach from the cell wall completely. Leading to a state of ctyorrhysis ( a process by which the cell wall collapses). Convex plasmolysis is irreversible and results in the cell’s destruction. This is essentially what happens when a plant wilts and dies due to a lack of water. The severity of convex plasmolysis is greater than that of concave plasmolysis. In the case of convex plasmolysis, they form a whole sphere.
Importance of plasmolysis
The partial separation of the protoplasm from the cell wall indicates that the plant needs to correct the situation, which prompts the plant to take in water from the roots and prevent further water loss via the stomatal mechanism.
Deplasmolysis is a process that occurs when a plasmolyzed cell is immersed in a hypotonic solution (a solution with a lower solute concentration than the cell sap), water enters the cell due to the higher concentration of water outside the cell. The cell then swells and becomes turgid. Deplasmoylsis is referred to as reverse plasmolysis in plants and it only happens when the cell is undergoing concave plasmolysis and not convex plasmolysis.
Plasmolysis and osmosis
The occurrence of plasmolysis is caused by osmosis. Osmosis is a type of diffusion that occurs when water flows into or out of a membrane, such as the plasma membrane of a cell. It depends on the type of solution in which a cell is immersed. When a cell is immersed in a hypertonic solution, the concentration of solutes outside the cell increases, causing water to flow out of the cell to balance the concentration on both sides of the membrane.
Because plasmolysis is defined as the loss of water from a cell, it occurs when the cell is immersed in a hypertonic solution. When a cell is immersed in a hypotonic solution, the solute concentration outside the cell is lower than the solute concentration inside, and water rushes into the cell. Solute concentrations are the same on both sides of an isotonic solution, so there is no net gain or loss of water.
Plasmolysis and flaccidity
Plasmolysis is defined as the shrinking of protoplasm as a result of exposure to a hypertonic environment. Flaccidity is the loss of turgor caused by a lack of net water movement between the plant cell and the isotonic surrounding environment. Flaccidity is similar to plasmolysis in that it causes the plant to wilt by losing cell turgor. Both of these conditions can be restored to normal plant cell turgor by hypo tonicizing the solution surrounding the cell. However, a flaccid cell is one that is neither turgid (swollen) nor plasmolyzed (shrunk).
Plasmolysis and turgidity
The osmotic movements of water influence both plasmolysis and turgidity because there is a difference between the water potentials and solute concentrations in the two solutions. Turgidity in cells refers to a swollen state caused by a high fluid (water) content. A plant cell, for example, is normally turgid due to protoplasm turgor pressure. This explains why plants can remain rigid and upright in the face of sunlight. Plasmolysis, on the other hand, causes the plant cell to lose water and thus turgor.
Differences between plasmolysis and turgidity
This is also known as exosmosis which is the process by which cells lose water (i.e. net water efflux)
Also known as endosmosis which is the process by which cells absorb water (i.e. net water influx)
As the protoplasm and plasma membrane pull away from the cell wall, the cell shrinks.
As the protoplasm and plasma membrane press against the cell wall, the cell swells.
This happens when the cell is immersed in a hypertonic solution.
This happens when the cell is in a hypotonic solution.
The turgor pressure falls.
The turgor pressure is increasing.
Plants wilt as a result of this.
Plant rigidity and uprightness are the end results.
Plasmolysis and cytolysis
Plasmolysis differs from another type of lysis known as cytolysis. Cytolysis is the bursting of a cell as a result of an excessive influx of water. This happens when the cell is exposed to a hypotonic solution, causing water to diffuse into the cell until the volume capacity exceeds the capacity of the cell membrane. The result of too much water inside the cell causes cell bursting or cytolysis. A good example of cytolysis occurs when red blood cells burst due to an excessive influx of water. But this does not happen in a plant cell due to the presence of cell wall and turgor pressure.
Because of differences in osmotic pressures, both plasmolysis and cytolysis are influenced by the osmotic movement. Water enters the cell during cytolysis due to the hypotonic environment, whereas water exits the cell during plasmolysis due to the hypertonic environment. As a result, it appears that cytolysis is the inverse of plasmolysis.
FAQ on plasmolysis in a plant cell
What is the relationship between plasmolysis and crenation?
Both crenation and plasmolysis have to do with the shrinking of cells as a result of the loss of water from the cells. The only difference is that crenation is a term used for only animal cells while plasmolysis is used for plant cells.
Why can’t plasmolysis occur in animal cells?
Because animal cells lack cell walls, plasmolysis does not occur in them. Rather the term for animal cells is crenation.
Can plasmolysis be reversed?
Yes, plasmolysis can be reversed when there is only a shrinking of the cell wall. But if the cell wall totally collapses a process known as ctyorrhysis, then plasmolysis becomes irreversible.
What is the opposite of plasmolysis?
The opposite of plasmolysis is known as deplasmolysis and it occurs when the cell is placed in a hypotonic solution whereby it can take in water to become turgid.
What are the stages of plasmolysis?
The three stages of plasmolysis are listed below.
1. Incident plasmolysis
2. Evident plasmolysis
3. Final plasmolysis
Does plasmolysis also occur in animal cells?
No, it doesn’t because there is no cell wall in animal cells.
What is the definition of plasmolysis in biology?
Plasmolysis in plant cells is defined as the process in which plant cells lose water in a salt solution (hypertonic solution).