Key Difference – Osmosis vs Plasmolysis
Particles move from a region of higher concentration to a region of lower concentration passively until an equilibrium is achieved between two regions. This process is known as diffusion and it happens spontaneously in all environments. Osmosis is a special version of diffusion in which water molecules move from a higher water potential to a lower water potential across a semipermeable membrane. During osmosis, cells undergo different states which reflect the net movement of water molecules. Plasmolysis is a state which occurs when a plant cell is placed in a hypertonic solution and it loses water molecules from its cytoplasm to outside solution. Due to the water loss, cytoplasm contracts inside and cell membrane detaches from the cell wall. At this moment the cell is known as a plasmolyzed cell. This is the key difference between osmosis and plasmolysis.
CONTENTS
1. Overview and Key Difference
2. What is Osmosis
3. What is Plasmolysis
4. Side by Side Comparison – Osmosis vs Plasmolysis
5. Summary
What is Osmosis?
Osmosis is a process in which water molecules move from a high concentration to a low concentration across a semipermeable membrane until the water potential becomes equal on both sides. In other words, osmosis refers to a process in which water molecules moves from a high water potential area to a low water potential area via a semipermeable membrane until both areas reach the same osmotic potential. It is a biological process important for solute distribution in cellular environments.
Cells have a semipermeable membrane called cell membrane. Solute and other molecules transport across the cell membrane by osmosis. It is a type of a selective diffusion which happens from high water potential to low water potential spontaneously.
Figure 01: Osmosis
What is Plasmolysis?
Plant cells have cell walls outer to cell membranes. The cell wall is a rigid structure which decides the shape of the plant cell. When molecules enter or exit the cytoplasm, it undergoes changes. However, cell wall resists these changes. In a normal state, cytoplasm and cell membrane remain intact with the cell wall of a plant cell. When a plant cell is placed in a hypertonic solution which has a higher solute concentration and a low water concentration compared to the cytoplasm of the cell, water molecules move out from the cell to the outside solution via osmosis. Cytoplasm shrinks inside due to the water loss. Cell membrane detaches cell wall together with the cytoplasm. This process is known as plasmolysis and the cell is known as plasmolyzed cell as shown in figure 02.
If a plasmolyzed cell is placed in a hypotonic solution, it can convert back to the normal state.
Figure 02: Plasmolysis, turgid and flaccid states of a plant cell
What is the difference between Osmosis and Plasmolysis?
Osmosis vs Plasmolysis |
|
| Osmosis is defined as a process in which water molecules move from high concentration to low concentration across a semi permeable membrane. | Plasmolysis is a state in which a plant cell is placed in a hypertonic solution and the cell cytoplasm loses its water and shrinks. |
| Water Movement | |
| Water moves from higher concentration to lower concentration. | Water moves from cytoplasm to outside hypertonic solution. |
| Types | |
| Endosmosis and exosmosis are two types of osmosis shown by cells. | Plasmolysis and deplasmolysis are two types of states shown by cells. Plasmolysis occurs due to exosmosis. |
Summary – Osmosis vs Plasmolysis
Osmosis is a biological process which describes the movement of water molecules (solvent molecules) from a high concentration to a low concentration across a semi-permeable membrane. When water molecules enter a cell via the cell membrane by osmosis, it is known as endosmosis and when the water molecules exit the cell via cell membrane by osmosis, it is known as exosmosis. Osmosis occurs in almost every type of cells including plant cells. When water exits from a plant cell, cytoplasm contracts and reduces its volume. Cell membrane loses its contact with the cell wall. This state is known as plasmolysis. Plasmolysis occurs due to the exo-osmosis of the cells. This is the difference between osmosis and plasmolysis.
References:
1. Ray, Peter M. “On the Theory of Osmotic Water Movement.” Plant Physiology. U.S. National Library of Medicine, Nov. 1960. Web. 17 Apr. 2017
2. Lang, Ingeborg, Stefan Sassmann, Brigitte Schmidt, and George Komis. “Plasmolysis: Loss of Turgor and Beyond.” MDPI. Multidisciplinary Digital Publishing Institute, 26 Nov. 2014. Web. 17 Apr. 2017.
Image Courtesy:
1. “OSC Microbio 03 03 Plasmolysi” By CNX OpenStax – (CC BY 4.0) via Commons Wikimedia