The main difference between turgor pressure and osmotic pressure is that osmotic pressure is the minimum pressure required to be applied to the solution to prevent the inward flow of its pure solvent across a semi-permeable membrane, whereas turgor pressure is the pressure inside the cell that pushes the plasma membrane against the cell wall of the plant cell.
Pressure is simply the continuous physical force exerted on or against an object perpendicularly per unit area by something in contact with it. It is a scalar quantity, which means it has a magnitude and no direction. Pressure is exerted by or on solids, liquids, and gases. Moreover, there are different types of pressure. For example, gauge pressure, absolute pressure, differential pressure, vacuum pressure, liquid pressure, atmospheric pressure, osmotic pressure, and turgor pressure.
Key Areas Covered
1. What is Turgor Pressure
– Definition, Function, Importance
2. What is Osmotic Pressure
– Definition, Function, Importance
3. Difference Between Turgor Pressure and Osmotic Pressure
– Comparison of Key Differences
Key Terms
Turgor Pressure, Osmotic Pressure
What is Osmotic Pressure
Osmotic pressure is the minimum pressure that must be applied to a solution to halt the flow of solvent molecules through a semi-permeable membrane. This pressure is dependent on the concentration of the solute particles in the solution. Moreover, osmotic pressure is a colligative property.
Osmosis is the movement of a solvent from a place of low concentration of solute to a place of high concentration of solute through a semi-permeable membrane. It is also the minimum amount of pressure to nullify the process of osmosis. Also, the more water or solute that moves across the membrane, the higher the osmotic pressure. In fact, this osmotic pressure depends on the temperature and the behavior of the solution in water or a relevant solvent.
Figure 1: Osmosis
When the concentrations of substances are different in two areas and have contact with each other, the random motion of particles will cause the substance to diffuse until the solution is uniform throughout the whole area. This motion of particles can cause the total volume of water on each side of the membrane to change. Then at a certain point, it reaches an equilibrium. Finally, the side with more molecules of water may end up with much more water.
We can observe the process of osmotic pressure in many plant parts. Osmotic pressure also causes some issues. For example, the decrease in external osmotic pressure causes water influx, swelling, and even lysis.
Calculation of Osmotic Pressure
We can calculate osmotic pressure using the formula:
π = iCRT,
where π is the osmotic pressure, C is the molar concentration of the solute in the solution, i is Van’t Hoff factor, R is the universal gas constant, and T is the temperature. But this equation is only applicable to solutions having ideal behaviour.
What is Turgor Pressure
Turgor pressure is the pressure within the cells that pushes the plasma membrane against the cell wall. It is generated through an inflow of water into cells by osmosis across a selectively permeable membrane. Furthermore, maintaining turgor pressure needs energy. We can commonly find turgor pressure in plant cells. Turgor pressure plays an important role in many different processes. It is associated with processes such as signalling, responding to stimuli, flowering, responding to stresses, and cell growth. One of the best and most common examples of turgor pressure is the opening and closing of stomata by guard cells in the leaf epidermis.
Figure 2: Stomata Opening
(1-Epidermal cell 2-Guard cell 3-Stoma 4-K+ ions 5-Water 6-Vacuole)
Sometimes, turgor pressure also occurs in organisms with cells having cell walls. Animal cells, on the contrary, try to avoid turgor pressure as they do not have cell walls that protect them from over expanding of the cells and lysing of cells.
Difference Between Turgor Pressure and Osmotic Pressure
Definition
Osmotic pressure is the minimum pressure that is required to be applied on the solution to prevent the inward flow of its pure solvent across a semi-permeable membrane. In contrast, turgor pressure is the pressure inside the cell that pushes the plasma membrane against the cell wall of the plant cell.
Occurrence
Moreover, osmotic pressure occurs across a semi-permeable membrane, whereas turgor pressure occurs within the cell.
Affecting Factors
The number and type of solutes present can affect osmotic pressure, while the concentration of solutes within the cell and the surrounding environment can affect turgor pressure.
Importance
Osmotic pressure is important in maintaining the balance of fluids in cells and organisms, while turgor pressure is important for maintaining plant stiffness and rigidity and also plant growth.
Conclusion
Pressure is force (perpendicular ) acting per unit area of something. There are different types of pressure, including osmotic and turgor pressure. Osmotic pressure is the minimum pressure a solution needs to prevent the inward flow of its pure solvent across a semi-permeable membrane. On the other hand, turgor pressure is the pressure inside the cell that pushes the plasma membrane against the cell wall of the plant cell. Thus, this is the main difference between turgor pressure and osmotic pressure.
Reference:
1. “Osmotic Pressure.” Byju’s.
2. “Turgor Pressure – An Overview.” Science Direct.
Image Courtesy:
1. “Osmosis diagram” By KDS4444 – Own work (CC0) via Commons Wikimedia
2. “Stoma Opening Closing” By Lmackay2013 – Own work (CC BY-SA 3.0) via Commons Wikimedia
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