Osmosis and Plasmolysis
Explains the process of osmosis, its types (endosmosis, exosmosis), and the phenomenon of plasmolysis in plant cells.
What is Osmosis and Plasmolysis?
The net movement of solvent molecules through a selectively permeable membrane from a region of higher solvent concentration (lower solute concentration, higher water potential) to a region of lower solvent concentration (higher solute concentration, lower water potential).
Key formula / rule: Water Potential
Key points
- Define osmosis and its types.
- Explain the process of plasmolysis and deplasmolysis.
- Differentiate between endosmosis and exosmosis.
- Understand the role of water potential in osmosis.
Common exam trap
Confusing osmosis with diffusion (osmosis is specific to solvent movement across a semipermeable membrane).
Definitions
- Term
Osmosis
- Meaning
The net movement of solvent molecules through a selectively permeable membrane from a region of higher solvent concentration (lower solute concentration, higher water potential) to a region of lower solvent concentration (higher solute concentration, lower water potential).
- Term
Semipermeable Membrane (SPM)
- Meaning
A membrane that allows solvent molecules to pass through but restricts the passage of solute molecules.
- Term
Plasmolysis
- Meaning
The process in plant cells where the protoplasm shrinks and pulls away from the cell wall due to the loss of water by osmosis.
- Term
Turgor Pressure
- Meaning
The pressure exerted by the protoplast against the cell wall when water enters the cell, causing it to swell.
- Term
Water Potential (Ψw)
- Meaning
The potential energy of water per unit volume relative to pure water. It determines the direction of water movement.
- Term
Solute Potential (Ψs)
- Meaning
The potential energy associated with dissolved solutes. It is always negative or zero.
- Term
Pressure Potential (Ψp)
- Meaning
The potential energy associated with positive pressure. It is usually positive in turgid plant cells.
Learning objectives
Define osmosis and its types.
Explain the process of plasmolysis and deplasmolysis.
Differentiate between endosmosis and exosmosis.
Understand the role of water potential in osmosis.
Relate osmosis and plasmolysis to plant cell behavior in different solutions.
Formulae
- Name
Water Potential
- Note
Ψw is water potential, Ψs is solute potential, Ψp is pressure potential.
- Expression
Ψw = Ψs + Ψp
- Name
Solute Potential
- Note
i is van't Hoff factor, C is molar concentration, R is ideal gas constant, T is absolute temperature. This is a theoretical calculation, often Ψs is given.
- Expression
Ψs = -iCRT
Prerequisites
Diffusion
Cell structure (cell wall, cell membrane, protoplasm)
Concentration gradients
Solvent and solute concepts
Common mistakes
Confusing osmosis with diffusion (osmosis is specific to solvent movement across a semipermeable membrane).
Not understanding the direction of water movement based on solute concentration or water potential.
Incorrectly applying the terms turgid, flaccid, and plasmolyzed.
Forgetting the formula for water potential (Ψw = Ψs + Ψp).
Assuming that plasmolysis is reversible without qualification (it is reversible if not prolonged).
Keywords
Osmosis
Plasmolysis
Endosmosis
Exosmosis
Semipermeable membrane
Water potential
Solute potential
Pressure potential
Turgor pressure
Flaccidity
Turgidity
Hypertonic
Hypotonic
Isotonic
Deplasmolysis
Practice preview
Which of the following statements is TRUE regarding osmosis?…
easy
Plasmolysis occurs when a plant cell is placed in a solution that is:…
easy
The water potential of a solution is affected by:…
medium