Question

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

• A. Osmotic pressure of the soil water becomes less than that of the plant sap
• B. Soil becomes too alkaline
• C. Osmotic pressure of the soil water becomes higher than that of the plant sap
• D. Soil becomes too acidic

Hint:

Water always travels toward areas with a higher salt/solute concentration. Over-fertilizing makes the soil saltier than the root interior, pulling water out of the plant and causing it to dehydrate and wilt.

Answer 1

The Correct Option is C

Concept: Osmosis is the spontaneous net movement of solvent water molecules through a semi-permeable membrane from a region of lower solute concentration (lower osmotic pressure) to a region of higher solute concentration (higher osmotic pressure).

Step 1: Analyzing the soil environment after over-fertilization.
Chemical fertilizers contain highly concentrated, soluble inorganic salts (such as ammonium nitrate, potassium chloride, and urea). Applying an excessive amount of these chemicals significantly increases the concentration of dissolved ion solutes in the surrounding soil moisture.

Step 2: Evaluating the osmotic pressure shift.
This high solute concentration increases the osmotic pressure of the soil water, making it hypertonic relative to the fluid inside the plant root cells (the plant sap). Because water naturally flows toward regions of higher osmotic pressure, moisture is drawn *out* of the root cells and into the soil. This process, known as exosmosis, causes cellular plasmolysis. The loss of turgor pressure causes the roots to shrivel and the plant to wilt, an effect commonly referred to as "fertilizer burn." This matches option (3).