IGCSE Biology Paper-2: Specimen Questions with Answers 149 - 149 of 203

Question 149

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Question

MCQ▾

Which diagram shows the appearance of a plant cell several minutes after it has been placed in a hypertonic solution?

Choices

Choice (4)
a.
A plant cell several minutes
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b.
A plant cell several minutes
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c.
A plant cell several minutes
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d.
A plant cell several minutes
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Answer

d.

Explanation

Plasmolysis

  • If a living plant cell is placed in a highly concentrated solution (i. e. The shrinkage of the protoplast of a living cell from its cell wall due to exosmosis under the influence of a hypertonic solution is called plasmolysishypertonic solution), water comes out of the cell due to exosmosis, through the plasma membrane. The loss of water from the cell sap causes shrinkage of the protoplast away from the cell wall in the form of a round mass in the centre. “. ”
  • The stage of plasmolysis, when the protoplast just begins to contract away from the cell wall is called incipient plasmolysisevident plasmolysis. The stage when the cell wall has reached its limit of contraction and the protoplast has detached from cell wall attaining spherical shape is called . In a plasmolysed cell, the space between the contracted protoplast and the cell wall remains filled with external solution. If a cell with incipient plasmolysis is placed in a hypertonic solution, it will show more plasmolysis.
  • If a plasmolysed cell is placed in pure water or hypotonic solution, endosmosis takes place. The protoplast attains its original shape and the cell regains its original size. “The swelling up of a plasmolysed protoplast due to endosmosis under the influence of a hypotonic solution or water is called deplasmolysis”. Deplasmolysis is possible only immediately after plasmolysis otherwise the cell protoplast becomes permanently damaged.
  • Leaf of Tradescantia is used for demonstration of plasmolysis in laboratory. The value of TP becomes zero at the time of limiting plasmolysis and below zero during incipient and evident plasmolysis.
Leaf of Tradescantia

Leaf of Tradescantia

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