Absorption by Roots Class 10 ICSE — Selina Chapter 4
Absorption by roots class 10 ICSE is the Selina Biology Chapter 4 topic that explains how plants take up water and minerals from the soil. It covers osmosis, diffusion, imbibition, plasmolysis, active transport, and the forces that raise sap upward. Roots fix the plant in the soil, but their most important function is absorbing water and mineral nutrients and conducting them into the stem.
Download Absorption By Roots the Processes Involved Class 10 ICSE Biology Chapter 4 PDF
Download the Absorption By Roots the Processes Involved Class 10 ICSE Biology chapter PDF from the Selina Concise textbook to revise offline or print for practice. It is the full chapter as printed in the book — 18 pages, 12 sections, 49 questions.
What is inside Chapter 4
18 pages · 12 sections · 49 exercise questions
| Section | Title |
|---|---|
| 4.1 | ABSORPTION BY THE ROOTS |
| 4.2 | NEED OF WATER AND MINERALS FOR PLANTS |
| 4.3 | CHARACTERISTICS OF ROOTS FOR ABSORBING WATER |
| 4.4 | ABSORPTION AND CONDUCTION OF WATER AND MINERALS |
| 4.4.1 | Imbibition |
| 4.4.2 | Diffusion |
| 4.4.3 | Osmosis and osmotic pressure |
| 4.4.4 | Active Transport |
| 4.4.5 | Turgidity and Flaccidity (Plasmolysis) |
| 4.6 | IMPORTANCE OF ROOT-HAIRS AND THE UPWARD MOVEMENT OF ABSORBED WATER AND MINERALS |
| 4.7 | SOME EXPERIMENTS ON ABSORPTION AND CONDUCTION OF WATER IN THE PLANTS. |
| 4.8 | FORCES CONTRIBUTING TO ASCENT OF SAP |
- PROGRESS CHECK: 4 questions
- PROGRESS CHECK: 5 questions
- PROGRESS CHECK: 1 questions
- PROGRESS CHECK: 4 questions
- REVIEW QUESTIONS: 35 questions
4.1 ABSORPTION BY THE ROOTS
The roots perform two jobs in a plant. They fix the plant in the soil, giving it support. More importantly, they absorb water and mineral nutrients from the soil.
Roots conduct these absorbed substances into the stem. From there, they reach the leaves, flowers, and fruits. Without this absorption, the plant cannot photosynthesise, transport food, or stay stiff. This is why the chapter calls absorption a life-supporting function.
Every other process in this chapter depends on this basic job. Once you see absorption as the roots’ main function, the rest of the chapter falls into place.
4.2 NEED OF WATER AND MINERALS FOR PLANTS
Water is a constituent of protoplasm. It also serves four purposes inside the plant body:
- Photosynthesis: Water is a raw material for making glucose in green leaves.
- Transpiration: Water passes out as vapour, cooling the plant and producing a suction force.
- Transportation: Dissolved substances move upward as mineral salts and downward as sugars.
- Mechanical stiffness: Water provides turgidity, the fully distended state that keeps tissues stiff.
Mineral nutrients reach the plant through the roots from the soil. Some are absorbed as salts such as nitrates, phosphates, and sulphates. Others enter simply as ions, including potassium, calcium, magnesium, and chlorine. These elements build cell constituents and help the cell synthesise compounds and enzymes. In the Class 10 ICSE syllabus, you are expected to state these four uses of water and give examples of mineral salts and ions.
4.3 CHARACTERISTICS OF ROOTS FOR ABSORBING WATER
Three characteristics let roots draw water from the soil.
- Enormous surface area. Rootlets and root hairs create a huge absorbing surface. Botanist H.J. Dittmer (1937) measured a four-month-old rye plant. Its aggregate root length was about 600 km. It had over 14 billion root hairs, with a total hair length exceeding 10,000 km.
- Concentrated cell sap. Root hairs contain cell sap at a higher concentration than the surrounding soil water. This difference sets up osmosis, which pulls water inward.
- Thin walls. Root hairs have a thin, permeable cell wall and a thin, semi-permeable cell membrane. The wall lets water and dissolved substances pass freely. The membrane lets water molecules pass but blocks larger salt molecules.
Notice the distinction. The cell wall is permeable. The cell membrane is semi-permeable. Confusing these two is a frequent exam error. The thin membrane is the real secret of water absorption by roots.
4.4 ABSORPTION AND CONDUCTION OF WATER AND MINERALS
The entire mechanism of absorbing water and minerals from the soil by the roots, its movement through the root thickness, and its upward conduction through the stem results from five phenomena. Each plays a specific role.
- Imbibition starts the process when dry tissues take up water by surface attraction.
- Diffusion moves molecules along concentration gradients.
- Osmosis drives water across semi-permeable membranes.
- Active transport carries ions against the gradient.
- Turgidity and flaccidity create the pressure changes that push sap upward.
Keep this list in mind as a roadmap. The next sections explain each phenomenon in turn. Once you see how each force contributes, the whole mechanism becomes clear. This section exists to orient you before the details follow.
4.4.1 Imbibition
Imbibition is the absorption of water by surface attraction in living or dead plant cells. Substances made of cellulose or protein are hydrophilic, meaning they have a strong affinity for water. They imbibe water or moisture and swell up.
Dry seeds and wooden doors are everyday examples. Both swell on contact with water or moist air. During germination, imbibitional pressure builds up and ruptures the seed coat. This pressure is also an important force in the ascent of sap.
The force is real and measurable. Soaked gram seeds in a pit underground can swell enough to push a heavy idol upward. This is the ‘biological trick’ described in the textbook. It shows how much force imbibition generates. The seeds absorb moisture from the ground, swell, and push the earth above them.
4.4.2 Diffusion
Diffusion is the free movement of molecules of a substance from a region of higher concentration to a region of lower concentration. The two regions must be in direct contact. No membrane is involved.
The textbook shows this with a simple activity. Place a sugar cube, a dye tablet, or a potassium permanganate crystal in one corner of a beaker of water. The substance slowly dissolves and spreads. Eventually, the molecules distribute uniformly throughout the water. Stirring hastens the process and gives a homogeneous solution faster.
Diffusion applies to gases and solutions. It works over considerable distances, unlike osmosis. The molecules move freely in all directions with no obstacle in their path. This free movement continues until the concentration is uniform throughout the liquid.
4.4.3 Osmosis and osmotic pressure
Osmosis is the movement of water molecules from a region of higher water concentration to a region of lower water concentration through a semi-permeable membrane. Only water molecules move across the membrane. The solute stays on its own side.
With reference to a cell, osmosis can be inward or outward. Endosmosis is the inward movement of water when the surrounding solution is less concentrated. It tends to swell the cell. Exosmosis is the outward movement when the surrounding solution is more concentrated. It causes the cell to shrink.
The thistle funnel experiment demonstrates osmosis. Suppose a thistle funnel holds 25 mL of 10% sugar solution, sealed with cellophane, and sits in a beaker of pure water. After two hours, the funnel level rises roughly 2 cm. The beaker water stays unsweet. Replace the cellophane with a rubber sheet, and the level stays flat. The rise comes from water crossing the membrane, not from sugar moving out.
Three conclusions follow. Water from the beaker passed through the cellophane into the funnel. Sugar did not pass out. The cellophane acted as a selectively permeable membrane, allowing water but not sugar molecules.
Tonicity describes the relative concentration of solutions on either side of a membrane. An isotonic solution matches the cell contents, so there is no net movement. A hypotonic solution has lower solute concentration, so water enters by endosmosis. A hypertonic solution has higher solute concentration, so water leaves by exosmosis.
Osmotic pressure is the minimum pressure needed to prevent pure solvent from passing into a solution across a semi-permeable membrane. Simply put, it measures a solution’s tendency to take in water by osmosis.
| Feature | Diffusion | Osmosis |
|---|---|---|
| Distance | Gases and liquids diffuse over considerable distances | Water moves only a short distance |
| Molecules that move | Solute or solvent molecules | Only water molecules |
| Speed | Rapid in gases, slow in solutions | Slow process |
| Direction | High to low concentration | Low concentration (more water) to high concentration (fewer water molecules) |
| Membrane needed | Not required | Semi-permeable membrane required |
4.4.4 Active Transport
Active transport is the passage of a substance from lower to higher concentration, opposite to diffusion, using cell energy through a living cell membrane. The energy comes from ATP.
Root cells need active transport for certain ions. Nitrates, sulphates, potassium, zinc, and manganese are more concentrated inside root cells than outside. These ions cannot pass easily through the cell membrane by diffusion. The high internal concentration is maintained deliberately. It builds osmotic pressure for absorbing water.
So the roots ‘forcibly’ carry these ions inward, against the gradient. This requires energy from the cell. Passive transport is different. It is simply diffusion, meaning free movement from higher to lower concentration with no energy input.
Common mistakes students make in this ICSE chapter:
- Roots absorb water by osmosis. They absorb minerals by active transport. Confusing the two is a frequent error.
- The cell wall is permeable. The cell membrane is semi-permeable. Do not swap these.
- Diffusion needs no membrane. Osmosis always needs a semi-permeable membrane.
- Endosmosis swells the cell. Exosmosis shrinks it.
4.4.5 Turgidity and Flaccidity (Plasmolysis)
Every living plant cell is in contact with fluids. Root hairs are surrounded by soil water. These cells are subject to osmosis. Water continues to enter as long as the cell sap is more concentrated than the surrounding fluids.
When a cell can take no more water, it is fully distended. This state is turgidity. The pressure of the cell contents on the cell wall is turgor pressure. The wall presses back on the contents with wall pressure.
When a living cell is placed in a strong hypertonic solution, such as 5% salt solution, the cytoplasm shrinks. The plasma membrane withdraws from the cell wall. This shrinkage is plasmolysis. The cell becomes limp, or flaccid. If the cell returns to water before it dies, its protoplasm swells again. This recovery is deplasmolysis.
| Feature | Turgid cell | Flaccid cell |
|---|---|---|
| Cell state | Fully distended, wall rigid and stretched | Cell contents shrunken, cell limp |
| Plasma membrane | Presses against the cell wall | Withdrawn from the cell wall |
| Water content | Maximum, cannot take more | Water lost by exosmosis |
| Cause | Water entered by endosmosis | Water left by exosmosis |
| Example | Fresh leaf cells | Cell kept in 5% salt solution |
Turgor plays five roles in plant life:
- Rigidity of soft tissues. Leaves wilt when transpiration exceeds absorption, then recover in the evening.
- Pushing through hard ground. Mushrooms and seedlings push up through soil. Roots can even crack walls.
- Building root pressure. Water rises from a cut stem, a phenomenon called bleeding.
- Opening and closing stomata. Guard cell turgor controls the stomatal aperture.
- Turgor movements. The sensitive plant Mimosa pudica droops when touched because cells at the pulvinus lose water.
Root pressure is the pressure developed in the roots by cell-to-cell osmosis. It helps push sap upward through the stem. Guttation occurs when excess root pressure forces water out as drops at leaf margins in tomato, grass, banana, and ferns.
One edge case deserves attention. The textbook reports that fresh grapes in a fully saturated sugar solution did not shrink, even after a week. Student Wasiya Fargana repeated the experiment and got the same result. The grapes shrank only slightly in saturated common salt solution. The outer grape skin is probably impermeable to sugar solution. So the classic claim that grapes shrink in strong sugar does not always hold.
4.6 IMPORTANCE OF ROOT-HAIRS AND THE UPWARD MOVEMENT OF ABSORBED WATER AND MINERALS
Water absorption happens through root hairs. A root hair contains cell sap with a higher concentration of salts than the outside soil water. This difference sets off osmosis, and outside water diffuses into the root hair.
From the cell bearing the root hair, water passes to adjoining cells one after another. It finally enters the xylem vessels. The turgidity acquired by the cells helps push water upward through the xylem.
Mineral elements take a different route. They are absorbed by active transport, often as ions rather than salts. The dilute solution of water and mineral salts travels up through the xylem to reach the leaves for food manufacture.
4.7 SOME EXPERIMENTS ON ABSORPTION AND CONDUCTION OF WATER IN THE PLANTS.
Four experiments in this chapter prove how roots absorb water and how xylem and phloem conduct it.
Experiment 1: Roots absorb water. Take two test tubes filled with water. Put a young leafy plant, such as balsam, with its roots intact into one tube. Add a few drops of oil to prevent evaporation. Mark the water levels. The tube with the plant shows a falling level over a day or two. The tube without the plant stays unchanged. This proves the roots absorbed the water.
Experiment 2: Xylem conducts water upward. Place a washed balsam plant in a beaker of eosin solution, a pink dye. Keep the roots submerged for 3-4 hours. Then cut transverse sections of the root, stem, and leaves. The xylem vessels appear stained red. This proves water travels upward through the xylem.
Experiment 3: Xylem, not phloem, conducts water. Take two leafy shoots cut under water to prevent air bubbles. In one shoot, remove a 3 cm outer ring of phloem, keeping the xylem intact. In the other, remove the central xylem, keeping the phloem. After two days, the first shoot’s leaves stay turgid. The second shoot’s leaves wilt. Water travels through the deeper xylem.
Experiment 4: Phloem conducts food downward. Girdle a woody stem by cutting a ring through the phloem and cambium, but not the xylem. Sap oozes from the cut margin. A bulge forms above the ring. The part below stops growing. This proves food moves downward through the phloem.
4.8 FORCES CONTRIBUTING TO ASCENT OF SAP
Four forces raise sap upward in plants.
- Root pressure. This builds enough force to push sap in the xylem up to a certain height. It may be enough for herbaceous plants.
- Capillarity. The narrow diameter of xylem vessels raises water to fill the vacuum left by transpiration. The narrower the tube, the higher the water rises.
- Transpiration pull. Water lost from leaves pulls more water up. Cohesion keeps a continuous column through the stem.
- Adhesion. Water sticks to cell surfaces. When leaf cells lose water, more water is drawn from below. This is important in tall trees such as pines, which lack enough root pressure.
Cohesion is the molecular attraction by which the particles of a body are united throughout its mass. The downward movement of food in the phloem is simpler. It flows down mainly because of gravity.
For absorption by roots class 10 ICSE, remember that all four forces work together. No single force raises sap to the top of a tall tree. Guttation, the loss of water droplets from leaf margins, is treated further in the next chapter on Transpiration. You can find it in our ICSE Class 10 Transpiration chapter guide.
What to practise from Absorption by Roots Class 10 ICSE
This ICSE chapter has two kinds of exercise blocks. The PROGRESS CHECK blocks appear four times through the chapter. The REVIEW QUESTIONS block ends the chapter.
- PROGRESS CHECK (4 questions): Root functions, water needs, and root characteristics.
- PROGRESS CHECK (5 questions): Diffusion, osmosis, and active transport.
- PROGRESS CHECK (1 question): Turgor terms, naming the states and pressures.
- PROGRESS CHECK (4 questions): The absorption and conduction experiments.
- REVIEW QUESTIONS (35 questions): Split into multiple choice, very short answer, short answer, and structured or application type.
The question types map to specific sections of the chapter.
- MCQs test definitions. Expect questions on imbibition, plasmolysis, turgidity, and semi-permeable membranes.
- Very short answers test term recall. Guttation, endosmosis, and bleeding appear often.
- Short answers test differences. Plasmolysis versus deplasmolysis, turgor pressure versus wall pressure, and guttation versus bleeding are common.
- Structured questions test diagrams. The thistle funnel experiment, the root hair cell, and the potato cube experiment are favourite topics.
For the full syllabus structure, check the official CISCE website and our ICSE Class 10 Biology chapter list.
Absorption by Roots Class 10 ICSE frequently asked questions
What is the difference between osmosis and diffusion in absorption by roots class 10 ICSE?
Diffusion is the free movement of molecules from higher to lower concentration when two regions are in direct contact, with no membrane involved. Osmosis is the movement of only water molecules through a semi-permeable membrane, from a region of more water molecules to fewer. Diffusion works over considerable distances for gases and liquids. Osmosis moves water only over a short distance and always needs a semi-permeable membrane.
Why does a plant cell become plasmolysed in a hypertonic solution and how is it reversed in Class 10 ICSE Biology?
A hypertonic solution has a higher solute concentration than the cell sap. Water leaves the cell by exosmosis. The cytoplasm shrinks, and the plasma membrane withdraws from the cell wall. This shrinkage is plasmolysis. If the cell returns to water before it dies, water re-enters, the protoplasm swells, and the cell regains its turgid state. This recovery is deplasmolysis.
How do root hairs absorb water and minerals differently in this ICSE chapter?
Root hairs absorb water by osmosis because their cell sap is more concentrated than the surrounding soil water. Minerals enter by active transport, which uses cell energy to carry ions such as nitrates and potassium against their concentration gradient. Confusing these two processes is a common error in this chapter.
What are the four forces that contribute to the ascent of sap in Class 10 ICSE?
Root pressure pushes sap upward through the xylem, enough for herbaceous plants. Capillarity, the narrow diameter of xylem vessels, raises water to fill the vacuum left by transpiration. Transpiration pull draws water up because cohesion keeps a continuous column. Adhesion makes water stick to cell surfaces, drawing more water from below. Downward movement of food in the phloem is driven mainly by gravity.
Why do potato cubes placed in water become firm but turn soft in sugar solution in Class 10 ICSE?
In water, the potato cells take in water by endosmosis. The cells become turgid, so the cubes feel firm and slightly larger. In concentrated sugar solution, the cells lose water by exosmosis. They become flaccid, so the cubes turn soft and shrink slightly. The process being tested is osmosis.
Reference: ICSE Class 10 Biology textbook material, chapter 4: Absorption By Roots the Processes Involved — CISCE-aligned.