The Question is from neet-botany plant-physiology , and it was created by the author K SURESH KUMAR

Question

A plant cell is placed in a solution, and its volume initially increases.  After a while, the volume increase stops. Which of the following BEST explains why the volume stopped increasing?

K SURESH KUMAR · Accepted Answer

## CORE INFORMATION
✓ **Answer**: D
## CONCEPT FRAMEWORK
 **Primary Concept**: Osmosis and Turgor Pressure in Plant Cells
 **Related Topics**: Water potential, osmotic pressure, cell wall, cell membrane
 **Prerequisites**: Understanding of osmosis, semi-permeable membranes, and the structure of plant cells.
## SOLUTION PATHWAY
**Given Information**:
  A plant cell is placed in a solution.
  The cell's volume initially increases, then stops.
**Method & Steps**:
 1. Osmosis: Water moves across a semi-permeable membrane from a region of high water potential (low solute concentration) to a region of low water potential (high solute concentration).
  Reasoning: Initially, the water potential outside the cell is higher than inside, causing water to enter the cell via osmosis.
  Formula/Rule:  Water potential ($Ψ$) is influenced by solute potential ($Ψ_s$) and pressure potential ($Ψ_p$):  $Ψ = Ψ_s + Ψ_p$ 
 2. Turgor Pressure: As water enters the plant cell, the cell swells. The cell wall resists this swelling, creating turgor pressure ($Ψ_p$).
  Working: Turgor pressure pushes against the cell wall, increasing the cell's internal pressure.
  Key Point: The cell wall provides structural support and prevents the cell from bursting.
 3. Equilibrium: The volume increase stops when the turgor pressure inside the cell equals the osmotic pressure of the external solution. At this point, there is no net movement of water.
  Result:  The system reaches equilibrium.
  Verification:  The net water movement becomes zero when the water potential inside and outside the cell are equal.
 ## OPTION ANALYSIS
A :x: The cell membrane is flexible and can stretch significantly before reaching its maximum capacity. This isn't the primary reason for the volume increase stopping.
B :x: The cell doesn't absorb all the available water; it stops when equilibrium is reached. The solution still contains water.
C :x: The cell wall is responsible for providing structural support but does not become impermeable to water.
D ✓: This option correctly identifies the equilibrium point where turgor pressure balances the osmotic pressure, resulting in no further net water movement into the cell.
 ## LEARNING AIDS
 **Common Mistakes**:
  1. Confusing osmosis with diffusion: Osmosis is the movement of water across a semi-permeable membrane, while diffusion is the movement of any substance from high to low concentration.
  How to avoid: Clearly define osmosis and its conditions.
  2. Ignoring the role of the cell wall: The cell wall is crucial in plant cells, providing resistance and preventing lysis.
  How to avoid: Understand the structure and function of the cell wall in maintaining turgor pressure.
 **Quick Tips**:
  1. Remember the concept of water potential and its components to understand the driving force behind osmosis.
  2. Visualize a plant cell in different solutions (hypotonic, isotonic, hypertonic) to understand the water movement and resulting changes in volume.

K SURESH KUMAR · Answer

The cell membrane reached its maximum stretching capacity.

K SURESH KUMAR · Answer

All available water in the solution was absorbed by the cell.

K SURESH KUMAR · Answer

The cell wall became impermeable to water.

K SURESH KUMAR · Answer

The correct Option is "Turgor pressure reached equilibrium with the external solution's osmotic pressure."

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