`star` Plasmolysis
`star` Imbibition


● The `color{violet}"behaviour"` of the plant cells (or tissues) with regard to `color{violet}"water movement"` depends on the `color{violet}"surrounding solution"`.

● If the `color{violet}"external solution balances"` the `color{violet}"osmotic pressure"` of the cytoplasm, it is said to be `color{Brown}"isotonic"`. If the `color{violet}"external solution"` is more dilute than the `color{violet}"cytoplasm"`, it is `color{Brown}"hypotonic"` and if the external solution is `color{violet}"more concentrated"`, it is `color{Brown}"hypertonic"`.

● `color{violet}"Cells swell"` in hypotonic solutions and `color{violet}"shrink"` in hypertonic ones.

● `color{Brown}"Plasmolysis"` occurs when `color{violet}"water moves out"` of the cell and the `color{violet}"cell membrane"` of a plant cell `color{violet}"shrinks away"` from its cell wall.

● This occurs when the `color{violet}"cell (or tissue)"` is placed in a solution that is `color{violet}"hypertonic"` (has more solutes) to the protoplasm.

● `color{violet}"Water moves out"`; it is first lost from the `color{violet}"cytoplasm"` and then from the `color{violet}"vacuole"`.

● The `color{violet}"water when drawn"` out of the cell through `color{violet}"diffusion"` into the `color{violet}"extracellular (outside cell)"` fluid causes the `color{violet}"protoplast"` to shrink away from the walls.

● The cell is said to be `color{violet}"plasmolysed"`.

● The `color{violet}"movement of water"` occurred across the membrane moving from an area of `color{violet}"high water potential"` (i.e., the cell) to an area of `color{violet}"lower water potential"` outside the cell.

● When the cell (or tissue) is placed in an `color{violet}"isotonic solution"`, there is `color{violet}"no net flow"` of water towards the `color{violet}"inside or outside"`.

● If the `color{violet}"external solution balances"` the osmotic pressure of the cytoplasm it is said to be `color{violet}"isotonic"`.

● When `color{violet}"water flows"` into the cell and `color{violet}"out of the cell"` and are in `color{violet}"equilibrium"`, the cells are said to be `color{Brown}"flaccid"`.

● The process of `color{violet}"plamolysis"` is usually `color{violet}"reversible"`.

● When the cells are placed in a`color{violet}"hypotonic solution"` (higher water potential or dilute solution
as compared to the cytoplasm), `color{violet}"water diffuses into"` the cell causing the cytoplasm to build up a `color{violet}"pressure against the wall"`, that is called `color{Brown}"turgor pressure"`.

● The pressure `color{violet}"exerted by the protoplasts"` due to entry of water against the `color{violet}"rigid walls"` is called `color{Brown}"pressure potential"` p..

● Because of the `color{violet}"rigidity of the cell wal"`l, the cell does `color{violet}"not rupture"`.

● This `color{violet}"turgor pressure"` is ultimately responsible for `color{violet}"enlargement and extension"` growth of cells.


● `color{Brown}"Imbibition"` is a special type of `color{violet}"diffusion"` when water is absorbed by solids – `color{Brown}"colloids"` – causing them to `color{violet}"enormously increase"` in volume.

● The `color{Brown}"classical examples"` of imbibition are absorption of water by `color{violet}"seeds and dry wood"`.

● The pressure that is `color{violet}"produced by the swelling"` of wood had been used by prehistoric man to `color{violet}"split rocks and boulders"`.

● If it were not for the `color{violet}"pressure"` due to imbibition, `color{violet}"seedlings"` would not have been able to `color{violet}"emerge out"` of the soil into the open; they probably would not have been able to `color{violet}"establish"`!

● Imbibition is also `color{violet}"diffusion"` since water movement is along a `color{violet}"concentration gradient"`; the seeds and other such materials have `color{violet}"almost no water"` hence they absorb water easily.

● `color{violet}"Water potential gradient"` between the `color{Brown}"absorbent and the liquid"` imbibed is essential for imbibition.

● In addition, for any substance to `color{violet}"imbibe any liquid,"` `color{Brown}"affinity"` between the `color{violet}"adsorbant and the liquid"` is also a pre-requisite.