Excessive use of fertilisers in agricultural fields reduces the yield of crops. Justify the statement.

1. Excess fertiliser makes the soil solution HYPERTONIC — more concentrated than the root cell sap. Water is then drawn OUT of the root hairs by exosmosis instead of being absorbed, so the plant wilts and may die. This is called fertiliser burn.
2. Repeated heavy use makes the soil ACIDIC, destroys its texture and kills the earthworms and useful soil micro-organisms that maintain fertility, so the land becomes progressively less productive.

The word JUSTIFY means give reasons, so the answer must explain a MECHANISM rather than simply assert that fertilisers are harmful.

THE FIRST REASON is the one examiners want, because it applies osmosis — a concept from a different chapter — to a practical problem. Too much fertiliser reverses the osmotic gradient the root depends on, so the very substance meant to feed the plant dehydrates it.

A third point if the question allows: excess fertiliser is washed into ponds and rivers, where it causes EUTROPHICATION — an explosion of algal growth that blocks light and, as the algae die and decompose, strips the water of oxygen and kills the fish.