Give biological explanations for the following:
Plants growing in fertilized soil are often found to wilt if the soil is not adequately watered.
Topic: Wilting in over-fertilised soil
Answer
The fertiliser makes the soil solution HYPERTONIC — more concentrated than the cell sap of the root hairs. Water therefore passes OUT of the root hairs by EXOSMOSIS instead of entering them. The cells lose their turgor, become FLACCID and PLASMOLYSED, the plant can no longer absorb water, and it WILTS.
The reason must trace the OSMOTIC DIRECTION, since that is the whole mechanism: concentrated outside means water moves OUT.
Use the technical terms — HYPERTONIC, EXOSMOSIS, FLACCID, PLASMOLYSIS. They are what the examiner looks for.
WHY WATERING HELPS: adding water DILUTES the soil solution, restoring it to hypotonic, so that water can once again enter the root hairs by endosmosis.
This is a good example of a question that applies OSMOSIS — from a different chapter — to a practical agricultural problem. Farmers call it FERTILISER BURN.