Root hair

Each root hair is one long cell of the root's outer skin, the epidermis. It pushes out between soil particles and touches the thin film of water around them. Inside it is a large vacuole full of cell sap. Three features suit it to its job:

• Root hairs are many and long, so they give a large surface area.
• The cell wall is thin, so water passes through easily.
• The cell sap is more concentrated than soil water, so water enters by osmosis.

A small example

Soil water is a weak solution. The cell sap in a root hair is stronger. So water moves into the root hair by endosmosis. From there it passes from cell to cell until it reaches the xylem at the centre of the root.

Where marks go

The 2024 ICSE Biology paper asked for two adaptations of roots for taking in water. The marking scheme took any two of the three features above. The same paper asked for the name of "unicellular outgrowths from the epidermis of roots". CISCE's report on the 2024 ICSE Biology paper names "rootlets" as an incorrect answer.

The ICSE 2027 specimen paper tests the direction of the difference. Its correct pair is a large surface area and a higher concentration of cell sap. A lower concentration is one of the wrong options.

About the author

Deepti Sardana

Founder Member & Academic Lead

An IIT alumna (M.Sc., M.Phil.) with over 25 years in teaching, child psychology and learning assessment. As Academic Lead at EduBrahma, she leads the method TRUtesting uses to find where and why a child loses marks.

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