PLASMOLYSIS: CHARACTERISTICS, PHASES AND TYPES - BIOLOGY - 2025

The plasmolysis is the process of contraction or retraction of the protoplasm of the plant cell due to loss of water in the cell. This process is one of the results of osmosis. It occurs when the concentration of the external environment contains a greater number of dissolved molecules and less water per unit volume compared to the cellular liquid.

Then the semi-permeable membrane lets water molecules flow freely, increasing the flow to the outside, so the concentration of the vacuole must equal the concentration of the external environment, reducing it due to the loss of water. The cell membrane is reduced and separated from the cell wall.

Finally the cell membrane wall is separated because the cell plasmolyses. If during this process the plant does not get water to fill the vacuole so that the cell can regain its turgor, the plant will most likely die.

What is plasmolysis?

Cell anatomy

To understand plasmolysis, it is necessary to previously refer to the anatomy of a plant cell. Each cell is made up of a plasma membrane, a cytoplasm inside, and protecting this structure, a cell wall basically composed of cellulose.

All major parts of the cell work together to keep the plant active. The vacuole is found in the cytoplasm that contains the water in the plant cell.

The cell or plasma membrane separates the interior of the cell from the wall, allowing the passage of water molecules, ions or some particles through the membrane and preventing the passage of others.

Water molecules travel in and out of the cell through cell membranes. This flow is a necessary consequence that allows cells to obtain water.

When cells do not receive enough water, plasmolysis occurs, the plasma membrane and cytoplasm contract and separate from the cell wall, causing the entire plant to contract.

Phases of plasmolysis

The wilting of plants observed under conditions of water scarcity is an indication of plasmolysis of cells. There are three stages in plasmolysis: early plasmolysis, overt plasmolysis, and final plasmolysis.

1- Incipient plasmolysis

In the incipient phase of plasmolysis, the first sign of shrinkage of cell wall content is detected. In a turgid cell, with the right amount of water, the plasma membrane squeezes the cell wall and is in total contact with it.

When this cell is kept in a hypertonic solution, water begins to move out of the cell. Initially there will be no effect on the cell wall. But as the water continues to be lost, the cell contracts in volume.

Still, the plasma membrane maintains its contact with the cell wall due to its elastic capacity. As the water outflow continues, the plasma membrane reaches its yield point and tears away from the cell wall at the ends, maintaining contact in other regions. This is the first stage of plasmolysis.

2- Obvious plasmolysis

In this second phase, the cell, under hypertonic conditions, continues to lose water in the external environment and is further reduced in volume. The plasma membrane tears completely from the cell wall and contracts.

3- Final plasmolysis

As exosmosis continues, contraction of the cell and cytoplasm reaches the minimum limit and no further contraction in volume is possible.

The cytoplasm is completely detached from the cell wall, reaching a spherical shape and remaining in the center of the cell.

Types of plasmolysis

Based on the final form of the cytoplasm, final plasmolysis is divided into two types: concave plasmolysis and convex plasmolysis.

Concave plasmolysis

During concave plasmolysis, the protoplasm and plasma membrane contract and separate from the cell wall due to loss of water. The protoplasm transforms into a protoplast once it has begun to separate from the cell wall.

This process can be reversed if the cell is placed in a hypotonic solution, which will cause the water to flow back into the cell.

Convex plasmolysis

Convex plasmolysis, on the other hand, is more serious. When a cell undergoes complex plasmolysis, the plasma membrane and protoplast lose so much water that they completely separate from the cell wall.

The cell wall collapses in a process called cytorrisis. Convex plasmolysis cannot be reversed and leads to cell destruction. Essentially, this is what happens when a plant withers and dies from lack of water.

Osmosis, plasmolysis and turgor

Osmosis is the passage of water through a semi-permeable membrane from an area where the water has a higher concentration (having fewer solutes) to an area where it has a lower concentration (having more solutes).

In cells, the semipermeable membrane is the cell or plasma membrane, which cannot normally be seen. However, when the wall and membrane separate, the cell membrane becomes visible. This process is plasmolysis.

In their usual state, plant cells are in a state of turgor. Thanks to the turgor, the nutrient solutions move between the cells, helping the plants to stay upright and preventing them from sagging.

Deplasmolysis

In the laboratory, osmosis can be experienced by placing a living cell in a saline solution, which will cause the cell sap to move. The concentration of water inside the cell will be higher than outside the cell.

Therefore, the water travels through the cell membrane to the neighboring medium. Finally, the protoplasm separates from the cell and assumes a spherical shape, producing plasmolysis.

When a plasmolyzed cell is placed in a hypotonic solution (a solution in which the solute concentration is lower than the cell sap), water travels to the cell due to the higher concentration of water outside the cell.

The cell then swells and regains its turgor again. This process of recovering the normal turgor of a plasmolyzed cell is known as deplasmolysis.

References

1. S. Beckett. "Biology: A Modern Introduction". Oxford University Press (1986) England.
2. "Osmosis" Recovered from: "The cell: fundamental unit" in: sites.google.com.
3. "Plasmolysis" in: Biology Dictionary. Recovered from: biologydictionary.net.
4. "Plasmolysis" (Jun. 2016) in: Byju's byjus.com.
5. Bhavya, "What is plasmolysis?" in: Preservative articles. Recovered from: preservearticles.com.
6. Stadelmann "Plasmolysis and deplasmolysis". Methods in Enzymology. Volume 174, 1989 Ed. Elvesier. Available online 29 Nov. 2003 Science Direct Recovered from: sciencedirect.com.
7. Stadelmann "Chapter 7 Evaluation of Turgidity, Plasmolysis, and Deplasmolysis of Plant Cells" in: Methods in Cell Biology, Volume 2 Retrieved from: sciencedirect.com.
8. Müller. "Plasmolysis" in: Plant Physiology Laboratory Manual IICA Library Venezuela. Recovered from: books.google.es.