Excessive use of chemical fertilisers causes shrivelling of the roots and wilting of the plant, because the

ANS:C - osmotic pressure of the soil water becomes higher than that of the plant sap.

Excessive use of chemical fertilizers causes shriveling of the roots and wilting of the plant because the osmotic pressure of the soil water becomes higher than that of the plant sap. Explanation:

1. Osmotic Pressure: Osmotic pressure refers to the pressure exerted by the solvent (in this case, water) as it moves across a semi-permeable membrane to equalize concentration gradients. In the context of plants, osmotic pressure plays a crucial role in water uptake and nutrient absorption from the soil.
2. Effect of Excessive Fertilizer: When chemical fertilizers are applied excessively to the soil, particularly those containing soluble salts such as nitrogen, phosphorus, and potassium, the concentration of salts in the soil solution increases significantly.
3. High Salt Concentration: The increased salt concentration in the soil solution leads to a higher osmotic pressure surrounding the roots compared to the osmotic pressure within the plant's cells (plant sap). As a result, water from the plant's root cells moves outwards into the soil, driven by osmosis.
4. Root Dehydration: The loss of water from the root cells to the soil causes the roots to become dehydrated and shrink. Shrinking roots are less effective in absorbing water and nutrients from the soil, leading to wilting of the plant and overall reduced plant health.
5. Symptoms of Damage: The symptoms of damage due to excessive fertilizer application include wilting of leaves, yellowing or browning of leaf margins (leaf burn), stunted growth, and ultimately, plant death if the stress persists.