Question

With rise in turgidity, wall pressure will
a. Decrease
b. Increase
c. Fluctuate
d. Remain unchanged

Answer 1

Hint: The plant cell when placed in pure water, swells but does not burst. It is because of the negative osmotic potential of the vacuolar solution, water will move into the cell and cause the plasma lemma to be pressed against the cell wall. The actual pressure that develops i.e. the pressure responsible for pushing the membrane against the cell wall is called turgor pressure.

Complete answer:
- When water enters the living cell, a pressure is developed within the cell due to turgidity. The hydrostatic pressure that develops on the cell wall inside the cell because of endosmosis is called turgor pressure.
- The cell wall being rigid exerts an equal pressure in the opposite direction which is called the wall pressure.
- As a result of this interplay of forces, the plant cell under these conditions is said to be turgid.
- When the wall pressure equals the turgor pressure then the entry of water into the cell stops and at this stage the water potential of the cell is equal to that of its environment.
- Thus a stage of dynamic equilibrium sets in with no net movement. However an equal exchange of water molecules can occur across the cell.
- In a hypertonic solution, the protoplasm shrinks and leaves the cell wall which makes the cell flaccid.

Hence, the correct answer is option (B).

Note: Plants live and grow normally due to turgidity in cells and turgidity in plants which depends upon osmosis. The rigidity of plant organs is maintained by turgidity caused due to endosmosis. For example leaves remain erect and expanded and do not wilt due to turgidity.