BiologyICSE Class 10 · Absorption by Roots

Root Hair, Absorption of Water and Ascent of Sap (ICSE Class 10 Biology)

Updated 15 October 2026 · Fact-checked

A root hair is a long single-celled outgrowth of a root epidermal cell. Its thin wall, huge surface area and concentrated cell sap let soil water enter by osmosis. Water then passes cell to cell through the cortex, endodermis and pericycle into the xylem, and rises up the stem by root pressure, cohesion, adhesion and, mainly, transpiration pull.

Understand Root Hair, Water Absorption and Ascent of Sap

Where absorption happens. Behind the root tip lies the root-hair zone, covered with thousands of fine hairs. This zone, not the older parts of the root, absorbs most of the water and minerals.

Structure of a single full-grown root hair. A root hair is one cell: a tubular outgrowth of an epidermal cell (it is not a separate cell or a branch of the root).

Cell wall: thin, made of cellulose on the inside with an outer layer of pectin that is sticky and helps the hair cling to soil particles; no cuticle.
Plasma membrane: selectively permeable, just inside the wall.
Cytoplasm: a thin lining layer, with the nucleus usually near the tip of the hair.
Large central vacuole containing cell sap, more concentrated than soil water.

Characteristics that make roots suitable for absorbing water (expected points for the 2024 paper).

Feature	How it helps
Root hairs very numerous and long	huge surface area in contact with soil water
Thin, freely permeable wall, no cuticle	water passes easily
Cell sap more concentrated than soil water	water enters by osmosis (endosmosis)
Hairs grow between soil particles and stick to them	close contact with the water film
Selectively permeable plasma membrane	lets water in, keeps cell sap in
Roots branch and spread widely	reach water deep and far

Path of water from soil to xylem. Soil water → root hair (osmosis) → cortex cells, cell to cell (each inner cell has slightly more concentrated sap than the one outside it) → endodermis → pericycle → xylem of the root. Once water reaches the xylem it travels up the stem to the leaves.

Minerals. Minerals are absorbed as ions dissolved in soil water, partly by diffusion but mostly by active transport, which uses energy (ATP) from respiration to move ions against their concentration gradient. This is why well-aerated soil, which lets roots respire, helps mineral uptake.

Root pressure. Water entering the root by osmosis builds up a pressure in the root xylem that pushes water some way up the stem. Evidence: water oozes from the cut end of a stem cut close to the ground. Root pressure alone is small and cannot lift water to the top of tall trees.

Ascent of sap and the forces behind it. The upward movement of water and dissolved minerals through the xylem is called the ascent of sap. The forces (a general idea only, as the syllabus says):
1. Root pressure: a push from below.
2. Capillarity: water rises in very narrow tubes such as xylem vessels.
3. Cohesion: water molecules attract one another, so the water in a vessel forms an unbroken column.
4. Adhesion: water molecules are attracted to the walls of the xylem, which helps hold the column up.
5. Transpiration pull (the main force): as leaves lose water vapour through stomata, water is drawn out of the xylem in the leaf; because of cohesion the whole column is pulled up from the roots, like drinking through a straw.

Flow chart. Soil water → root hair (osmosis) → cortex → endodermis → pericycle → root xylem → stem xylem (root pressure, cohesion, adhesion, transpiration pull) → leaf veins → mesophyll → evaporates through stomata.

Experiment to show conduction of water through xylem. Place a young balsam plant (or a white-flowered shoot) with its cut end in water coloured with eosin or red ink, in sunlight. After a few hours the veins of the leaves turn red. A thin transverse section of the stem viewed under a microscope shows only the xylem stained red. Conclusion: water rises through the xylem.

Draw-and-label checklist: root hair. Neighbouring epidermal cells in a row; one epidermal cell with a long tubular outgrowth reaching between soil particles; film of soil water round the particles; labels: cell wall, plasma membrane, cytoplasm, nucleus, vacuole with cell sap, soil particle, water film.

Root Hair, Water Absorption and Ascent of Sap: key facts

Root adaptations for absorption: Root hairs very large surface area
Wall thin, permeable, no cuticle
Cell sap more concentrated than soil water
Hairs cling to soil particles; Any two make the 2-mark answer.
Path of water: Soil water
Root hair
Cortex
Endodermis
Pericycle
Xylem; Learn as a sequence; ICSE asks for it in order.
Forces in the ascent of sap: Root pressure push from below
Capillarity rise in narrow tubes
Cohesion water to water
Adhesion water to xylem wall
Transpiration pull main pull from the leaves; Cohesion and adhesion are often swapped.
Water versus mineral uptake: Water: by osmosis, passive, no energy | Mineral ions: mostly active transport, against gradient, uses ATP; Active and passive transport in brief, per syllabus.

Root hairs	very large surface area
Wall	thin, permeable, no cuticle
Cell sap	more concentrated than soil water
Hairs	cling to soil particles

Root pressure	push from below
Capillarity	rise in narrow tubes
Cohesion	water to water
Adhesion	water to xylem wall
Transpiration pull	main pull from the leaves

How to answer Root Hair, Water Absorption and Ascent of Sap questions

ICSE asks for root adaptations, the path of water, labelled root hair diagrams, the forces of ascent of sap and the eosin experiment, often from a picture of a tree or a set-up.

1For adaptations, give the feature and its use: 'numerous root hairs give a large surface area'.
2For the path, write each tissue in order with arrows; do not skip endodermis and pericycle.
3For a tree diagram, name the process at each part: roots absorption, stem ascent of sap, leaves transpiration.
4Define cohesion and adhesion with 'between water molecules' and 'between water and the xylem wall'.
5For the experiment, give set-up, observation (only xylem stained red) and conclusion.

Root Hair, Water Absorption and Ascent of Sap in real life

The idea, met in an everyday situation. Answer the question in your own words, then compare with the model answer. The one-line hook is what to remember.

Why transplanting needs a ball of soil

Suppose a gardener pulls a marigold seedling out of a nursery bed roughly, shakes the soil off and replants it. Another seedling is lifted with a ball of moist soil round its roots. By evening the first plant has drooped badly.

Why did the first seedling wilt, and how does the ball of soil help?

Try it first, then show the solutionSolution

Most water is absorbed by the delicate root hairs just behind the root tip.
Pulling and shaking tears off many root hairs, so the surface for absorption falls sharply.
Leaves keep losing water by transpiration, so cells become flaccid and the plant wilts.
The soil ball protects the root hairs and keeps them in contact with soil water.

Answer: Root hairs were damaged, so absorption could not keep up with transpiration; the soil ball protects them.

Memory hook: No hairs, no water.

Tricks to remember Root Hair, Water Absorption and Ascent of Sap

Short memory aids. Say each one aloud once, then use it on a question the same day.

Some Real Clever Elephants Push eXtra
Soil, Root hair, Cortex, Endodermis, Pericycle, Xylem.
Use it when: The path of water in order.
CO-hesion = CO-workers
Cohesion is water sticking to fellow water molecules; ADhesion is water ADhering to the wall.
Use it when: Not swapping the two forces.
Straw in a glass
The leaf sips at the top of the straw (transpiration pull); the column follows because it does not break (cohesion).
Use it when: Explaining the main force of ascent of sap.

Root Hair, Water Absorption and Ascent of Sap: solved examples

Ordered from board level to HOTS. Try each one before you open the solution.

Example 1: Two root adaptations · 2 marks · Short answerBoard level

Give two features of the root-hair zone that make it efficient at taking in water from the soil, and say how each helps. (The 2024 paper asked for root adaptations of this kind.)

Try it first, then show the solutionSolution

Numerous long root hairs give a very large surface area for absorption (1 mark).
The cell sap of root hairs is more concentrated than soil water, so water enters by osmosis; or thin walls without cuticle (1 mark).

Answer: Large surface area from root hairs; concentrated cell sap (or thin walls).

Example 2: Path of water · 1 mark · Very short answerBoard level

Arrange in the correct sequence the parts through which water passes from the soil to the stem: pericycle, root hair, xylem, cortex, endodermis.

Try it first, then show the solutionSolution

Root hair → cortex → endodermis → pericycle → xylem.

Answer: Root hair, cortex, endodermis, pericycle, xylem.

Example 3: Phenomena in a tree · 3 marks · Short answerHarder board level

In a picture of a tree, part (a) is the root, (b) the trunk and (c) the leaves. Name the phenomenon taking place at each part with respect to water. (A similar tree picture was asked in 2025.)

Try it first, then show the solutionSolution

(a) Absorption of water by root hairs by osmosis (endosmosis) (1 mark).
(b) Ascent of sap through the xylem (1 mark).
(c) Transpiration, which creates the transpiration pull (1 mark).

Answer: (a) Absorption by osmosis; (b) ascent of sap; (c) transpiration.

Example 4: Cohesion, adhesion and pull · 3 marks · Short answerHarder board level

A coconut palm about 20 m tall keeps its crown of leaves supplied with water on a hot day. Explain the part played by transpiration pull, cohesion and adhesion in lifting the water.

Try it first, then show the solutionSolution

Transpiration from leaves removes water from the xylem at the top, creating a pull (1 mark).
Cohesion between water molecules keeps the column in the xylem unbroken, so the whole column moves up (1 mark).
Adhesion of water to the xylem walls holds the column and stops it falling back (1 mark).

Answer: Transpiration pulls; cohesion keeps the column continuous; adhesion holds it to the walls.

Example 5: Eosin experiment · 3 marks · Case-basedHOTS / competency

Suppose a student keeps a white carnation stem in red ink for six hours and finds red streaks in the petals. (a) Which tissue carried the ink? (b) How would you confirm it? (c) Why must the stem be cut under water before the experiment?

Try it first, then show the solutionSolution

(a) Xylem (1 mark).
(b) Cut a thin transverse section of the stem and see under a microscope that only the xylem is stained red (1 mark).
(c) Cutting in air lets air bubbles enter the xylem and break the water column, which would block the rise of water (1 mark).

Answer: (a) Xylem. (b) T.S. shows only xylem stained. (c) To prevent air bubbles breaking the water column.

Example 6: Waterlogged soil · 2 marks · Short answerHOTS / competency

Plants in waterlogged soil often show mineral deficiency even though water is plentiful. Explain.

Try it first, then show the solutionSolution

Waterlogging drives air out of the soil, so roots get little oxygen and respiration slows (1 mark).
Mineral ions are taken up mainly by active transport, which needs energy (ATP) from respiration, so uptake falls (1 mark).

Answer: Lack of oxygen reduces respiration and so the energy for active uptake of minerals.

Where students lose marks in Root Hair, Water Absorption and Ascent of Sap

The slips examiners see most often, and what to write instead.

Mistake: Vague adaptations
Answers such as 'roots are long' or 'roots are strong' miss the expected points: large surface area of root hairs, concentrated cell sap, thin walls.
Do this: Name the root hair feature and say how it helps absorption.
Usually costs: 1-2 marks.
Mistake: Not naming the three phenomena in a tree
CISCE examiners' comments (2025): on a picture of a tree, candidates failed to identify absorption of water at the roots, ascent of sap in the stem and transpiration at the leaves.
Do this: Learn the triple: roots absorb, stem conducts, leaves transpire.
Usually costs: 1-3 marks.
Mistake: Calling the root hair multicellular
A root hair is a single epidermal cell with an extended wall, not a group of cells.
Do this: Write 'unicellular outgrowth of an epidermal cell'.
Usually costs: 1 mark.

Exam tips

Write the path of water with arrows and no gaps.
In the eosin experiment state the T.S. observation: only xylem stained.
Keep cohesion (water to water) and adhesion (water to wall) definitions word-perfect.
Say 'transpiration pull is the main force' whenever ascent of sap is asked.

Practice questions on Root Hair, Water Absorption and Ascent of Sap

Write each answer on paper first. Open the hint only if you are stuck, and the answer only when you have finished.

Q1 · 1 mark · MCQBoard level
A root hair is an outgrowth of:
(a) cortex cell (b) epidermal cell (c) endodermis (d) pericycle
Hint
Outermost layer.
Answer
(b) epidermal cell.
Q2 · 1 mark · Very short answerBoard level
Name the main force responsible for the ascent of sap in tall trees.
Hint
Comes from the leaves.
Answer
Transpiration pull.
Q3 · 2 marks · Short answerHarder board level
Define root pressure. Give one piece of evidence for it.
Hint
Cut stem near the ground.
Answer
Root pressure is the pressure developed in the root xylem due to the continuous entry of water by osmosis. Evidence: sap oozes out of a stem cut close to the ground.
Q4 · 2 marks · Short answerHarder board level
Distinguish between cohesion and adhesion.
Hint
Like and unlike molecules.
Answer
Cohesion is the attraction between water molecules themselves, keeping the column unbroken. Adhesion is the attraction between water molecules and the walls of the xylem.
Q5 · 2 marks · Short answerHarder board level
Why is the cell sap of a root hair kept more concentrated than the soil water? What would happen if the soil water became more concentrated?
Hint
Direction of osmosis.
Answer
So that water enters the root hair by osmosis (endosmosis). If the soil solution became more concentrated (hypertonic), water would leave the root hair by exosmosis and the plant would wilt.
Q6 · 3 marks · Short answerHarder board level
Draw a neat diagram of a single full-grown root hair among soil particles and label: cell wall, cytoplasm, nucleus, vacuole, soil particle.
Hint
One cell, tubular outgrowth.
Answer
Diagram: epidermal cell extended into a long tube between soil particles; thin wall; cytoplasm lining the wall; nucleus near the tip; large vacuole; soil particles with water films. All five labels correctly placed.
Q7 · 1 mark · Assertion-reasonHarder board level
Assertion (A): A root treated with a poison that stops respiration soon stops taking up potassium ions from the soil.
Reason (R): Mineral ions are taken in by active transport using energy from respiration.
(a) (A) is true and (R) is false.
(b) (A) is false and (R) is true.
(c) Both (A) and (R) are true, and (R) is the correct explanation of (A).
(d) Both (A) and (R) are true, but (R) is not the correct explanation of (A).
Hint
What supplies the energy for uptake against the gradient?
Answer
(c).
Q8 · 3 marks · Case-basedHOTS / competency
Read and answer.
Suppose two identical potted plants are watered equally. Plant X is kept in a sunny, breezy spot and plant Y in a still, dark cupboard. Each stem is then cut near the soil, and a tube is fixed to measure water rising from the cut stump.
(a) Which force alone pushes water up the stumps? (1)
(b) Which plant, before cutting, was raising water faster through its xylem? Why? (1)
(c) Why can this force alone not explain water reaching the top of a 30 m tree? (1)
Hint
Stumps have no leaves.
Answer
(a) Root pressure. (b) Plant X, because sun and wind increase transpiration and so the transpiration pull. (c) Root pressure is small and lifts water only a short height; the main force in tall trees is transpiration pull aided by cohesion and adhesion.

Test your recall

Answer in your head or on paper first, then open the card. Pulling an answer out of memory makes it stick far better than re-reading.

1.Is a root hair one cell or many?Show answer
One cell: an outgrowth of an epidermal cell.
2.Which layer lies just outside the xylem in the path of water?Show answer
The pericycle.
3.What is the ascent of sap?Show answer
The upward movement of water and dissolved minerals through the xylem.
4.By which process are most mineral ions absorbed?Show answer
Active transport.
5.Which dye is used to show conduction through xylem?Show answer
Eosin (or red ink).

Root Hair, Water Absorption and Ascent of Sap: frequently asked questions

Why do only young roots absorb water?

Root hairs grow only in the zone just behind the root tip. Older roots lose their hairs and develop corky layers that let little water through.

Is root pressure enough to raise water in tall trees?

No. It is small; the main force is transpiration pull, helped by cohesion, adhesion and capillarity.

Do I need the detailed cohesion-tension theory for ICSE?

No. The syllabus asks for a general idea of cohesive and adhesive forces and transpiration pull.

What is the difference between active and passive transport?

Passive transport moves substances along their concentration gradient without energy, as in osmosis. Active transport moves them against the gradient using energy from respiration.