Biological termEasy1 mark
1(a)
Name the following:
The process by which root hairs absorb water from the soil.
Topic: Osmosis
Previous-year question practice database
Answer
Exam answer
OSMOSIS.
Explanation
Water enters the root hair by OSMOSIS — the movement of water from a region of higher water concentration (the dilute soil solution) to one of lower water concentration (the more concentrated cell sap), through the SELECTIVELY PERMEABLE plasma membrane.
THE GRADIENT IS WHAT MATTERS: the cell sap of the root hair is HYPERTONIC to the soil water, so water moves inward. If the soil were more concentrated — as after excess fertiliser — the flow would reverse and the plant would wilt.
Note that MINERALS are absorbed differently, by ACTIVE TRANSPORT against the gradient, using energy from ATP. Water by osmosis, minerals by active transport.
More from Absorption by Roots – The Processes Involved
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