(i) In animals, water moves into different parts of the body under the effect of the process of osmosis.

(ii) Stretching of leaves, flower, etc., is also controlled by osmosis.

(iii) Osmosis helps in rapid growth of the plants and germination of seeds.

(iv) Different movements of plants such as opening and closing of flowers etc, are controlled by osmosis.

When egg is placed in mineral acid solution outershell of egg dissolves. Egg is now removed and placed in hypertonic solution. Size of egg get reduced and egg shrivels due to osmosis. Egg is now placed in a bottle with narrow neck. Finally on adding hypotonic solution egg regain its shape due to osmosis.

Diagramatically it can be represented as

Certain compounds when dissolved in suitable solvents either dissociate or associate. e.g., ethanoic acid dimerises in benzene due to H -bonding, while in water, it dissociates and forms ions.

As a result the number of chemical species in solution increases or decreases as compared to the number of chemical species of solute added to form the solution.

Since, the magnitude of colligative property depends on the number of solute particles, it is expected that the molar mass determined on the basis of colligative properties will either higher or lower than the expected value or the normal value and is called abnormal molar mass.

In order to account for the extent of dissociation or association of molecules in solution, van't Hoff introduced a factor, $i$, known as the van't Hoff factor.

$$\begin{aligned} & i= \frac{\text { expected molar mass }}{\text { abnormal molar mass }}=\frac{\text { observed colligative property }}{\text { calculated colligative property }} \\ & \\ &=\frac{\text {total number of moles of particles after association or dissociation}}{\text { total number of moles of particles before association or dissociation}} \\ & \end{aligned}$$