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Q5(c):
Differentiate between the following:
(c) Osmotic Pressure and Osmotic Potential
Solution :
Theoretical Foundation & Definitions
In plant physiology, the movement of water across semi-permeable membranes is governed by the thermodynamic potential of water. The terms Osmotic Pressure and Osmotic Potential are related but distinct in sign and physical definition.
Step 1: Defining Osmotic Pressure ($\Psi_\pi$)
Osmotic Pressure is defined as the external pressure that must be applied to a solution to prevent the inward flow of water across a semi-permeable membrane. [Per the definition of Van't Hoff’s law of osmotic pressure].
- It is always a positive value.
- It represents the pressure equivalent of the solute concentration.
- Mathematical notation: $\Pi = iCRT$, where $i$ is the Van't Hoff factor, $C$ is molar concentration, $R$ is the gas constant, and $T$ is absolute temperature.
Step 2: Defining Osmotic Potential ($\Psi_s$)
Osmotic Potential, also known as Solute Potential ($\Psi_s$), is the component of water potential that is due to the presence of solute molecules. [Per the Water Potential Equation: $\Psi_w = \Psi_s + \Psi_p$].
- It is always a negative value (or zero for pure water).
- It quantifies the reduction in the free energy of water caused by solutes.
- Relation to Osmotic Pressure: $\Psi_s = -\Pi$.
Step 3: Comparative Analysis
| Feature | Osmotic Pressure ($\Pi$) | Osmotic Potential ($\Psi_s$) |
|---|---|---|
| Sign | Always positive ($+$) | Always negative ($-$) |
| Definition | The pressure required to stop osmosis. | The effect of solutes on water potential. |
| Relationship | $\Pi = -\Psi_s$ | $\Psi_s = -\Pi$ |
Step 4: Visualization of Osmotic Dynamics
Figure: Semi-permeable membrane allowing water flux toward the solution side, identifying the site where osmotic pressure/potential is measured.
Final Solution: Osmotic pressure is the positive pressure applied to stop osmosis, whereas osmotic potential is the negative contribution of solutes to the total water potential; they are numerically equal but opposite in sign ($\Psi_s = -\Pi$).
More Questions from Class 11 Biology Transport in Plants EXERCISES
- Q1: What are the factors affecting the rate of diffusion?
- Q2: What are porins? What role do they play in diffusion?
- Q3: Describe the role played by protein pumps during active transport in plants.
- Q4: Explain why pure water has the maximum water potential.
- Q5(a): Differentiate between the following: (a) Diffusion and Osmosis
- Q5(b): Differentiate between the following: (b) Transpiration and Evaporation
- Q5(d): Differentiate between the following: (d) Imbibition and Diffusion
- Q5(e): Differentiate between the following: (e) Apoplast and Symplast pathways of movement of water in plants.
- Q5(f): Differentiate between the following: (f) Guttation and Transpiration.
- Q6: Briefly describe water potential. What are the factors affecting it?
- Q7: What happens when a pressure greater than the atmospheric pressure is applied to pure water or a solution?
- Q8(a): (a) With the help of well-labelled diagrams, describe the process of plasmolysis in plants, giving appropriate examples.
- Q8(b): (b) Explain what will happen to a plant cell if it is kept in a solution having higher water potential.
- Q9: How is the mycorrhizal association helpful in absorption of water and minerals in plants?
- Q10: What role does root pressure play in water movement in plants?
- Q11: Describe transpiration pull model of water transport in plants. What are the factors influencing transpiration? How is it useful to plants?
- Q12: Discuss the factors responsible for ascent of xylem sap in plants.
- Q13: What essential role does the root endodermis play during mineral absorption in plants?
- Q14: Explain why xylem transport is unidirectional and phloem transport bi-directional.
- Q15: Explain pressure flow hypothesis of translocation of sugars in plants.
- Q16: What causes the opening and closing of guard cells of stomata during transpiration?
CBSE Solutions for Class 11 Biology Transport in Plants
Chapters in CBSE - Class 11 Biology
- The Living World
- Biological Classification
- Plant Kingdom
- Animal Kingdom
- Morphology of Flowering Plants
- Anatomy of Flowering Plants
- Structural Organisation in Animals
- Cell – The Unit of Life
- Biomolecules
- Cell Cycle and Division
- Mineral Nutrition
- Photosynthesis
- Respiration in Plants
- Plant Growth and Development
- Digestion and Absorption
- Breathing and Exchange of Gases
- Body Fluids and Circulation
- Excretory Products and Elimination
- Locomotion and Movement
- Neural Control and Coordination
- Chemical Coordination and Integration
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