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ICSE Question Bank
2019Q1(c)(iii)Absorption by Roots – The Processes Involved
ReasoningHard1 mark
1(c)

Give suitable biological reasons for the following statements:

Root hairs become flaccid and droop when excess fertilizers are added to the moist soil around them.

Topic: Excess fertiliser and root hairs

Previous-year question practice database

Answer

Exam answer

The excess fertiliser makes the soil solution HYPERTONIC — more concentrated than the cell sap of the root hairs. Water therefore passes OUT of the root hair cells by EXOSMOSIS instead of entering them. The cells lose their turgor, become FLACCID and PLASMOLYSED, and the root hairs droop.

Explanation

The reason must trace the OSMOTIC direction, since that is the whole mechanism: concentrated outside means water moves OUT.

This is a fine example of a question that applies OSMOSIS — from a different chapter — to a practical agricultural problem. The very substance meant to feed the plant ends by dehydrating it, a condition farmers call FERTILISER BURN.

Use the terms: HYPERTONIC, EXOSMOSIS, FLACCID, PLASMOLYSIS. They are what the examiner is looking for.

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