Answer:
(a) Plasmolysis occurs when
water moves out of the cell and the cell membrane of a plant cell shrinks away
from its cell wall. This occurs when the cell is kept in a solution that is
hypertonic (has more solutes) to the protoplasm. Water moves out from the cell
through diffusion causes the protoplasm to shrink away from the -walls. In such
situation, cell becomes plasmolysed.
When the cell is placed in an isotonic solution. There is
not flow of. water towards the inside or outside. If the external solution
balances the osmotic pressure of the cytoplasm, it is said to be isotonic. When
the water flow into the cell and out of the cells are in equilibrium the cell
is called flaccid.
(b) When the plant cell is
kept in a solution having high water potential (hypotonic solution or diluite
solution as compared to cytoplasm), water diffuses into the cell causing the
cytoplasm to build up a pressure against the wall, called turgor pressure. The
pressure exerted by the protoplasts due to entry of water against the rigid
walls is called pressure potential *Fp. Because of the rigidity of the cell
wall, the cell does not rupture. This turgor pressure is ultimately responsible
for enlargement of cells.
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