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Chapter 4

Absorption by Roots — The Process Involved

Class 10 - Selina Concise Biology Solutions


Multiple Choice Type

(Select the most appropriate option in each case)

Question 1

Absorption of water by the plant cells by surface attraction is called:

  1. Diffusion
  2. Osmosis
  3. Imbibition ✓
  4. Endosmosis

Question 2

A plant cell placed in a certain solution got plasmolysed. What was the kind of solution?

  1. Isotonic sugar solution
  2. Hypotonic salt solution
  3. Hypertonic salt solution ✓
  4. Isotonic salt solution

Question 3

The state of a cell in which the cell wall is rigid and stretched by the increase in volume due to the absorption of water is called

  1. Flaccidity
  2. Turgidity ✓
  3. Capillarity
  4. Tonicity

Question 4

Which one of the following is a characteristic NOT related with the suitability of the roots for absorbing water?

  1. Tremendous surface area
  2. Contain cell sap at higher concentration than the surrounding soil water
  3. Root hairs have thin cell walls
  4. Grow downward into the soil ✓

Question 5

Movement of molecules of a substance from the region of their higher concentration to the region of their lower concentration without the involvement of a separating membrane, is called:

  1. Osmosis
  2. Diffusion ✓
  3. Active transport
  4. Capillarity

Question 6

Osmosis and diffusion are the same except that in osmosis there is

  1. a freely permeable membrane
  2. a cell wall in between
  3. a selectively permeable membrane in between ✓
  4. an endless inflow of water into a cell

Question 7

The highest water potential (capacity to move out to higher concentrated solution) is that of

  1. Pure water ✓
  2. 10% salt solution
  3. Honey
  4. 50% sugar solution

Question 8

The space between the cell wall and plasma membrane in a plasmolysed cell is filled with

  1. isotonic solution
  2. hypotonic solution
  3. hypertonic solution
  4. water ✓

Question 9

What is responsible for guttation?

  1. Osmotic pressure
  2. Root pressure ✓
  3. Suction pressure
  4. Capillarity

Question 10

The most appropriate characteristic of a semi-permeable membrane is that

  1. it has minute pores
  2. it has no pores
  3. it allows the solute to pass through but not the solvent
  4. it allows a solvent to pass through freely but prevents the passage of the solute ✓

Very Short Answer Type

Question 1

Name the following:

(a) The condition of a cell placed in a hypotonic solution.

(b) The process by which intact plants lose water in the form of droplets from leaf margins.

(c) The process by which water enters root hairs.

(d) The tissue concerned with upward conduction of water in plants.

(e) The term for the inward movement of solvent molecules through the plasma membrane of a cell.

(f) The process by which molecules distribute themselves evenly within the space they occupy.

(g) The pressure which is responsible for the movement of water molecules across the cortical cells of the root.

Answer

(a) Turgidity

(b) Guttation

(c) Osmosis

(d) Xylem

(e) Endosmosis

(f) Diffusion

(g) Root pressure

Question 2

Give the equivalent terms for the following:

(a) Pressure exerted by the cell contents on the cell wall.

(b) The condition in which the cell contents are shrunken.

(c) Loss of water through a cut stem.

Answer

(a) Turgor pressure

(b) Flaccidity

(c) Bleeding

Question 3

Complete the following statements:

(a) Hypotonic solution is one in which the solution kept outside the cell has .......... solute concentration than inside the cell.

(b) Active transport is one in which the ions outside the roots move in by utilising ........... .

(c) The bending movements of certain flowers towards the sun and the sleep movements of certain plants at night are examples of .......... .

Answer

(a) Hypotonic solution is one in which the solution kept outside the cell has lower solute concentration than inside the cell.

(b) Active transport is one in which the ions outside the roots move in by utilising energy from the cell.

(c) The bending movements of certain flowers towards the sun and the sleep movements of certain plants at night are examples of turgor movements.

Question 4

Fill in the blanks by choosing the correct alternative from those given in brackets.

(a) When placed in a more concentrated solution, the cell contents will .......... (shrink / swell up).

(b) The pressure by which the .......... molecules tend to cross the semi-permeable membrane is called osmotic pressure. (salt / water)

(c) Active transport is in a direction .......... to that of diffusion. (opposite / same)

Answer

(a) When placed in a more concentrated solution, the cell contents will shrink.

(b) The pressure by which the water molecules tend to cross the semi-permeable membrane is called osmotic pressure.

(c) Active transport is in a direction opposite to that of diffusion.

Question 5

Match the items in column I with those in column II Column I | Column II ---------|------------- (a) Xylem | (i) semi-permeable (b) Phloem | (ii) permeable (c) Cell membrane | (iii) downward flow of sap (d) Root pressure | (iv) upward flow of water (e) Cell wall | (v) guttation

Answer

Column IColumn II
(a) Xylem(iv) upward flow of water
(b) Phloem(iii) downward flow of sap
(c) Cell membrane(i) semi-permeable
(d) Root pressure(v) guttation
(e) Cell wall(ii) permeable

Short Answer Type

Question 1

Differentiate between the following :

(a) Plasmolysis and Deplasmolysis

(b) Turgor Pressure and Wall Pressure

(c) Hypotonic and Hypertonic solution

(d) Turgidity and Flaccidity

Answer

(a) Difference between Plasmolysis and Deplasmolysis

PlasmolysisDeplasmolysis
It refers to the shrinkage of the cytoplasm and withdrawal of the plasma membrane from the cell wall caused due to the withdrawal of water when placed in a hypertonic solution.Deplasmolysis is the recovery of a plasmolysed cell when it is placed in water, wherein the cell's protoplasm again swells up due to the re-entry of water.
In Plasmolysis, the cell becomes flaccid.In Deplasmolysis, the cell becomes turgid.

(b) Difference between Turgor pressure and Wall pressure

Turgor PressureWall Pressure
Turgor pressure is the pressure of the cell contents on the cell wall.Wall pressure is the pressure exerted by the cell wall on the cell content.
It helps keeps plant stems erect, keeps leaves expanded, involve in opening and closing of stomata, etc.It helps maintain the structure of cells and the plant.
It acts towards the outside from the cell.It acts towards the inside of the cell.

(c) Difference between Hypotonic and Hypertonic solution

Hypotonic SolutionHypertonic Solution
The solution outside the cell has a lower solute concentration than the fluids inside the cell.The solution outside the cell has higher solute concentration than the fluids inside the cell.
Endosmosis occurs as the water molecules move into the cell.Exosmosis occurs as the water molecules move out from the cell.
When placed in Hypotonic Solution, the cell slightly enlarges or even bursts.When placed in Hypertonic Solution, the cell shrinks in size and loses shape.

(d) Difference between Turgidity and Flaccidity

TurgidityFlaccidity
It is the state of a cell in which the cell wall is rigid and stretched by an increase in the volume of vacuoles due to the absorption of water.It is the condition in which the cell content is shrunken and the cell is not tight.
It occurs when the cell is placed in a Hypertonic solution.It occurs when the cell is placed in an Isotonic solution.
It is caused by Endosmosis.It is caused by both Endosmosis and Exosmosis.
Water moves into the cell.Water moves out of the cell.

Question 2

Mention whether the following statements are true (T) or false (F). Correct the false statements by altering the last word only.

(a) Addition of salt to pickles prevents the growth of bacteria because they turn turgid.

Answer

False
Corrected statement — Addition of salt to pickles prevents the growth of bacteria because they turn flaccid.

(b) Cells that have lost their water content are said to be deplasmolysed.

Answer

False.
Corrected statement — Cells that have lost their water content are said to be plasmolysed.

(c) Xylem is the water conducting tissue in plants.

Answer

True.

(d) The protoplasm shrinks, when a cell is kept in hypotonic solution.

Answer

False.
Corrected statement — The protoplasm shrinks, when a cell is kept in hypertonic solution.

(e) The cell wall of the root cell is a differentially permeable membrane.

Answer
False.
Corrected statement — The cell wall of the root cell is a permeable membrane.

Question 3

Mention whether the following statements are true (T) or false (F) and give explanation in support of your answer.

(a) Guttation is another name for bleeding in plants.

Answer

False.
Reason — Guttation is the process by which drops of water appear along leaf margins due to excessive root pressure whereas bleeding is the loss of cell sap through a cut stem.

(b) Soaked seeds burst their seed coats.

Answer

True.
Reason — Imbibition is a phenomenon by which the living or dead plant cells absorb water by surface attraction. Substances which are made up of cellulose or proteins are hydrophilic(strong affinity for water). They imbibe water or moisture and swell up due to imbibition and endosmosis. Hence, the force generated by the water thus absorbed is strong enough to make the seed coats burst.

(c) If the phloem of a twig is removed keeping the xylem intact, the leaves of a twig wilt.

Answer

False.
Reason — The leaves of the twig remain turgid since its xylem is intact and xylem is responsible for water conduction in plants.

(d) Guttation in plants occurs maximum at mid-day.

Answer

False.
Reason — Guttation is the exudation of drops of xylem sap on the tips of leaves and occurs due to excessive root pressure. It is maximum when root pressure is maximum which occurs in the early mornings or at night. This is because during these times, transpiration is very low and water absorption is very high.

(e) Raisins when submerged in water swell up due to endosmosis.

Answer

True Reason — When raisins are submerged in water, concentration of solute inside the raisins is more than the concentration of water. Water acts as a Hypotonic solution for raisins due to which endosmosis occurs. As raisins absorb water due to endosmosis, they swell up.

Descriptive Type

Question 1

Give two examples of turgor movements in plants.

Answer

Two examples of turgor movements in plants.

(i) The rapid dropping of the leaves of the sensitive plant Mimosa pudica, is an outstanding example of turgor movement. If one of the leaves is touched, even lightly, the leaflets fold up and within 2 to 3 seconds, the entire leaf droops. If the leaf is touched somewhat strongly, the wave of folding and drooping spreads from the stimulated leaf to all neighbouring leaves.

(ii) Turgor movements are found in insectivorous plants whose leaves close up to entrap a living prey. When the insect comes in contact with the leaf, it loses its turgor hence closing the leaves of the plant.

Question 2

Define the following terms:

(a) Imbibition

(b) Diffusion

(c) Osmosis

(d) Osmotic pressure

(e) Active transport

(f) Tonicity

(g) Root pressure

Answer

(a) Imbibition — Imbibition is a phenomenon by which the living or dead plant cells absorb water by surface attraction. Its the passive absorption of water by substances such as cellulose (in cell wall) and starch.

(b) Diffusion — Diffusion is the free movement of molecules of a substance from the region of their higher concentration to the region of their lower concentration when the two are in direct contact.

(c) Osmosis — Osmosis is the movement of water molecules from their region of higher concentration (dilute solution or with a lower solute concentration) to their region of lower concentration (concentrated solution or with a higher solute concentration) through a semi permeable membrane.

(d) Osmotic pressure — Osmotic pressure is the minimum pressure that must be exerted to prevent the passage of the pure solvent into the solution when the two are separated by a semi-permeable membrane.

(e) Active transport — Active transport is the passage of a substance from its lower to higher concentration through a living cell membrane using energy from the cell.

(f) Tonicity — Relative concentration of the solutions that determine the direction and extent of diffusion is called tonicity.

(g) Root pressure — The upward flow of water due to heavy pressure from the roots is called root pressure. Thus, it is one of the forces to raise water up through the stem into the leaves.

Question 3

Give reasons for the following:

(a) If you sprinkle some common salt on grass growing on a lawn, it is killed at that spot.

(b) If you uproot a plant from the soil, its leaves soon wilt.

(c) It is better to transplant seedlings in a flower-bed in the evening and not in the morning.

(d) A plant cell when kept in a hypertonic salt solution for about 30 minutes turns flaccid.

(e) Potato cubes when placed in water become firm and increase in size.

Answer

(a) When common salt is sprinkled on grass growing in lawn, the common salt acts as a hypertonic solution for the grass. The cells of grass start losing water, grass becomes flaccid and Plasmolysis occurs causing the protoplasm to go away from the cell wall. This creates gaps between the membrane and the cell wall. Grass cells shrink completely and ultimately get killed.

(b) If a plant is uprooted, the leaves continue losing water by transpiration, but there is no more water absorbed by the roots. This does not allow the compensation for the loss of water by transpiration hence the leaves of the uprooted plant wilt soon.

(c) Transplantation in the evening helps the seedlings to adjust for a longer time during the night (cooler temperatures) because the quantity of water absorbed exceeds the loss of water through transpiration. Therefore, it is better to transplant seedling in a flower bed in the evening and not in the morning.

(d) When a plant cell is kept in a hypertonic salt solution, it starts losing water due to Plasmolysis. As the solution outside the cell has higher solute concentration than the fluids inside the cell so exosmosis occurs. In 30 minutes, the plant cell will lose its distended appearance, the cytoplasm will shrink and the plasma membrane will withdraw from the cell wall causing the plant cell to turn flaccid.

(e) Potato cubes contain excess of salts and sugars as compared to the water in which the cubes are placed. Hence, due to endosmosis, water from the surrounding enters the potato cubes making them firm and increasing their size.

Question 4

Explain the mechanism of the closing and opening of the stomata.

Answer

The closing and opening of the stomata depends on the turgidity of the guard cells. Each guard cell has a thicker wall on the side facing the stoma and a thin wall on the opposite side. Guard cells contain chloroplasts. As a result of the synthesis of glucose during photosynthesis and some other chemical changes, the osmotic pressure of the contents of the guard cells increases and they absorb more water from the neighbouring cells, thus becoming turgid. Due to turgor, the guard cells become more arched outwards and the aperture between them widens, thereby opening the stoma. At night or when there is shortage of water in the leaf, the guard cells turn flaccid and their inner rigid walls become straight, thus closing the stomatal aperture.

Question 5

What is transpirational pull? How is it caused?

Answer

As water is lost from the leaf surface by transpiration, more water molecules are pulled up due to the tendency of water molecules to remain joined i.e. cohesion. This produces a continuous column of water throughout the stem which is known as 'transpiration pull'. A negative pressure or tension is produced in the xylem that pulls the water from the roots and soil. Transpirational pull is an important force which causes the ascent of sap.

Structured / Application / Skill Type

Question 1

A leaf cell of a water plant was placed in a liquid other than pond water. After sometime, it assumed a shape as shown below:

A leaf cell of a water plant was placed in a liquid other than pond water. After sometime, it assumed a shape as shown. Give the term for the state of the cell it has acquired. Name the structure which acts as a selectively permeable membrane. Absorption by Roots, Concise Biology Solutions ICSE Class 10.

(a) Give the term for the state of the cell it has acquired.

(b) Name the structure which acts as a selectively permeable membrane.

(c) Comment on the nature (tonicity) of the liquid surrounding the cell.

(d) Name any one feature of this plant cell which is not present in an animal cell.

(e) Redraw in the space provided, the diagram of the cell if it is soon placed in ordinary water for some time.

Answer

(a) Flaccid cell

(b) Plasma membrane

(c) The liquid surrounding the cell is hypertonic solution. It has higher solute concentration outside the cell than the fluids inside the cell.

(d) Cell wall

(e) The cell will become turgid as follows:

A  turgid leaf cell of a water plant placed in ordinary water for some time. Absorption by Roots, Concise Biology Solutions ICSE Class 10.

Question 2

The diagram given below represents an experimental set-up to demonstrate a certain process. Study the same and answer the questions that follow:

The diagram given below represents an experimental set-up to demonstrate a certain process. Study the same and answer the questions that follow. Name the process. Define the above named process. What would you observe in the experimental set-up after an hour or so? What control experiment can be set up for comparison? Absorption by Roots, Concise Biology Solutions ICSE Class 10

(a) Name the process.

(b) Define the above named process.

(c) What would you observe in the experimental set-up after an hour or so?

(d) What control experiment can be set up for comparison?

(e) Keeping in mind the root-hair, cell and its surroundings, name the parts that correspond to (1) concentrated sugar solution (2) parchment paper and (3) water in the beaker.

(f) Name any other material that can be used instead of parchment paper in the above experiment.

(g) Mention any two advantages of the process to the plants.

Answer

(a) Osmosis

(b) Osmosis is the movement of water molecules from their region of higher concentration (dilute solution or with a lower solute concentration) to their region of lower concentration (concentrated solution or with a higher solute concentration) through a semi permeable membrane.

(c) After an hour or so, the level of sugar solution in the thistle funnel will rise and the level of water in the beaker will drop slightly.

(d) As a control, take another thistle funnel with plain water filled in it and suspend it in another beaker also containing water. Again mark the level on its stem.

(e) The corresponding parts are mentioned below:

  1. Concentrated sugar solution → Cell sap (of higher concentration than that of the surrounding water) within the root hair.
  2. Parchment paper → Cell membrane of root hair.
  3. Water in the beaker → Water in soil.

(f) The other substance that can be used instead of parchment paper in the above experiment is cellophane paper or animal bladder.

(g) Advantages of the osmosis process are —

  1. It controls the absorption of water by root hairs from the soil.
  2. It controls opening and closing of stomata during transpiration through its regulation of the turgidity of guard cells.

Question 3

The diagram below represents a layer of epidermal cells showing a fully grown root hair. Study the diagram and answer the questions that follow:

The diagram below represents a layer of epidermal cells showing a fully grown root hair. Study the diagram and answer the questions that follow. Name the parts labelled A, B, C and D. The root hair cell is in a turgid state. Name and explain the process that caused this state.  Mention one distinct difference between the parts labelled A and B. Draw a diagram of the above root hair cell as it would appear when a concentrated solution of fertilizers is added near it. Absorption by Roots, Concise Biology Solutions ICSE Class 10.

(a) Name the parts labelled A, B, C and D.

(b) The root hair cell is in a turgid state. Name and explain the process that caused this state.

(c) Mention one distinct difference between the parts labelled A and B.

(d) Draw a diagram of the above root hair cell as it would appear when a concentrated solution of fertilizers is added near it.

Answer

(a) The parts labelled A, B, C and D are:

  • A → Cell wall
  • B → Cell membrane
  • C → Cytoplasm
  • D → Nucleus

(b) Root hairs are the extensions of the outer (epidermal) cells of the root. Absorption of water by the root is by means of root hairs. A root hair contains cell sap which has a higher concentration of salts as compared to the outside soil water. A root hair gets turgid because of the absorption of water from the surrounding. Absorption of water by root hair is achieved by the process of osmosis. The concentration of water in the surrounding is more than that of the interior of the cell; this causes the water from the surrounding to move in because of endosmosis.

(b) A root hair gets turgid because of the absorption of water from the surrounding. Absorption of water by root hair is achieved by the process of Osmosis. Root hairs contain cell sap which has a higher concentration of salts as compared to the outside soil water. This causes the water from the surrounding to move in because of endosmosis and in the process the root hair gets turgid.

(c) The cell wall of a root hair is freely permeable and allows both salt and water to pass through whereas the cell membrane of a root hair is semi-permeable and does not allow large dissolved salt molecules to pass through.

(d) Below is the diagram of the root hair cell as it would appear when a concentrated solution of fertilizers is added near it:

The diagram below represents a layer of epidermal cells showing a fully grown root hair. Study the diagram and answer the questions that follow. Name the parts labelled A, B, C and D. The root hair cell is in a turgid state. Name and explain the process that caused this state.  Mention one distinct difference between the parts labelled A and B. Draw a diagram of the above root hair cell as it would appear when a concentrated solution of fertilizers is added near it. Absorption by Roots, Concise Biology Solutions ICSE Class 10.

Question 4

Study the diagram given below and answer the questions that follow:

Study the diagram and answer the questions that follow. Name the process being studied in experiment. Explain the process. Why is oil placed over water? What do we observe with regard to the level of water when this set up is placed in bright sunlight, humid conditions, windy day? Mention any three adaptations found in the roots of the plant which enable them to carry out the process mentioned. Absorption by Roots, Concise Biology Solutions ICSE Class 10.

(a) Name the process being studied in the above experiment.

(b) Explain the process mentioned in (a) above

(c) Why is oil placed over water?

(d) What do we observe with regard to the level of water when this set up is placed in (1) bright sunlight (2) humid conditions (3) windy day?

(e) Mention any three adaptations found in the roots of the plant which enable them to carry out the process mentioned in (a).

Answer

(a) The process of absorption of water by plant roots through osmosis is being studied here.

(b) Absorption of water by the root is by means of root hairs. A root hair contains cell sap which has a higher concentration of salts as compared to the outside soil water. This difference sets of osmosis and the outside soil water diffuses into the root hair. From the cell bearing root hair, water continues to pass to adjoining cells one after another to finally enter the xylem vessels. The turgidity acquired by the cells in the process also helps to push the water upwards through the xylem vessels.

(c) The surface of water is covered with oil to prevent any loss of water by evaporation.

(d) Roots absorb water and hence, the level of water in set up A falls down. Since the surface of water was covered with oil, there will be no effect of factors such as bright sunlight, humid conditions and windy day on the given set up. Hence, the level of water.

(d) Below are the observations with regard to the level of water for the different situations:

  • Bright Sunlight — When this set up is placed in bright sunlight, the water level in the test tube is seen to be less when compare to its initial marking as the rate of transpiration is very high.
  • Humid Conditions — When this set up is placed in humid conditions, the water level in the test tube decreases from its initial mark, but at a very slow rate as the rate of transpiration is reduced.
  • Windy Day — When this set up is placed in windy day the rate of transpiration highly increases thus the level of the water in the test tube is seen to decrease fast from its initial marking.

(e) Adaptations in plants to foster the process of absorption of water by plant roots:

  1. Large surface area provided by rootlets and root hairs.
  2. Root hairs contain cell sap at a higher concentration than that of the surrounding water
  3. Root hairs with thin walls.

Question 5

Three cylinders of potato were carefully dried on a blotting paper and weighed. Each piece weighed 3 grams. Each one was placed in the beaker as shown below:

Three cylinders of potato were carefully dried on a blotting paper and weighed. Each piece weighed 3 grams. Each one was placed in the beaker. After 48 hours, which potato cylinder would be the heaviest? The movement of which substance is mainly responsible for the weight change in the potato cylinders? Name and define the process which is responsible for the movement of substance mentioned in answer. Write specific names of the processes which occur in beakers B and C. Would there be any difference in the weight of the potato cylinder in beaker A after 48 hours? Give reason. Absorption by Roots, Concise Biology Solutions ICSE Class 10.

Answer the following questions:

(a) After 48 hours, which potato cylinder would be the heaviest?

(b) The movement of which substance is mainly responsible for the weight change in the potato cylinders?

(c) Name and define the process which is responsible for the movement of substance mentioned in answer (b).

(d) Write specific names of the processes which occur in beakers B and C [kinds of processes defined in answer (c)].

(e) Would there be any difference in the weight of the potato cylinder in beaker A after 48 hours? Give reason.

Answer

(a) After 48 hours, Cylinder B kept in distilled water will be the heaviest as distilled water will act as a hypotonic solution for Potato Cylinder. The Potato Cylinder will absorb distilled water from the beaker through the process of endosmosis and its weight will increase.

(b) Movement of water between potato cylinders and beakers is mainly responsible for the weight change in the potato cylinders.

(c) The physical process which is responsible for the movement of substance mentioned in answer (b) is Osmosis. Osmosis is the movement of water molecules from their region of higher concentration to their region of lower concentration through a semi-permeable membrane.

(d) The process that takes place in beaker B is osmosis, which is diffusion of water across the membrane of the potato slice cells. Plasmolysis occurs in beaker C as the potato shrinks due to hypotonic solution of 20% sucrose solution.

(d) Beaker B → Endosmosis
     Beaker C → Exosmosis

(e) There will be no change in the weight of the potato cylinder in beaker A because it is kept in air. As there is no movement of water between potato cylinder and beaker so no significant change in the weight of the potato cylinder is observed in beaker A.

Question 6

The figure given below is a diagrammatic representation of a part of the cross-section of the root in the root hair zone. Study the same and then answer the questions that follow:

The figure is a diagrammatic representation of a part of the cross-section of the root in the root hair zone. Study the same and then answer the questions that follow. Name the parts indicated by guidelines 1 to 5. Is the root hair cell unicellular or multicellular? Explain what would happen to the root hair cell if some fertilizer is added to the soil close to it. Name the process responsible for the entry of water molecules from the soil into A1 and then into A2. What pressure is responsible for the movement of water in the direction indicated by arrows? How is this pressure set up? Absorption by Roots, Concise Biology Solutions ICSE Class 10.

(a) Name the parts indicated by guidelines 1 to 5.

(b) Is the root hair cell unicellular or multicellular?

(c) Explain what would happen to the root hair cell if some fertilizer is added to the soil close to it.

(d) Name the process responsible for the entry of water molecules from the soil into A1 and then into A2.

(e) What pressure is responsible for the movement of water in the direction indicated by arrows?

(f) How is this pressure set up?

Answer

(a) Below are the parts indicated by guidelines 1 to 5:

  • 1 → Root hair cell
  • 2 → Soil particles
  • 3 → Xylem vessel
  • 4 → Cortex cells
  • 5 → Vacuole

(b) Root hair cell is unicellular.

(c) When fertilizers are added to the moist soil close to the root hair cell, it will form a hypertonic solution, resulting the protoplasm to shrink. The plasma membrane withdraws itself from the cell wall. Hence, the root hair also becomes limp or flaccid.

(d) Osmosis.

(e) Root pressure.

(f) Root pressure is built up due to cell-to-cell osmosis in the root tissue. As one turgid cell presses the next cell, the force of the flow of water increases inwards.

Question 7

Study the experimental setup in the figure and then answer the questions that follow.

Study the experimental setup in the figure and then answer the questions that follow. What phenomenon is being studied by this setup? Explain the phenomenon mentioned in (a) above. What is meant by semipermeable membrane? What will you observe in the setup after about half an hour? Give a reason for your answer. Absorption by Roots, Concise Biology Solutions ICSE Class 10.

(a) What phenomenon is being studied by this setup?

(b) Explain the phenomenon mentioned in (a) above.

(c) What is meant by 'semipermeable membrane'?

(d) What will you observe in the setup after about half an hour? Give a reason for your answer.

Answer

(a) Osmosis phenomenon is being studied by this setup.

(b) Osmosis is the movement of water molecules from their region of higher concentration (dilute solution or with a lower solute concentration) to their region of lower concentration (concentrated solution or with a higher solute concentration) through a semi permeable membrane.

(c) A semipermeable membrane is a membrane which allows the passage of molecules selectively. It allows a solvent such as water molecules to pass through it freely but prevents the passage of the solute (sugar or salt molecules in solution).

(d) Water molecules will continue to pass from 5% sucrose solution to 10% sucrose solution through the semipermeable membrane due to osmosis. This will continue till the concentration of water molecules becomes the same in both ends of the setup.

Question 8

A candidate in order to study the process of osmosis has taken 3 potato cubes and put them in 3 different beakers containing 3 different solutions. After 24 hours, in the first beaker the potato cube increased in size, in the second beaker the potato cube decreased in size and in the third beaker, there was no change in the size of the potato cube. The following diagram shows the result of the same experiment.

A candidate in order to study the process of osmosis has taken 3 potato cubes and put them in 3 different beakers containing 3 different solutions. After 24 hours, in the first beaker the potato cube increased in size, in the second beaker the potato cube decreased in size and in the third beaker, there was no change in the size of the potato cube. Give the technical terms of the solutions used in the beakers 1, 2 and 3. Absorption by Roots, Concise Biology Solutions ICSE Class 10.

(a) Give the technical terms of the solutions used in the beakers 1, 2 and 3.

(b) In beaker 3, the size of the potato cube remains the same. Explain the reason in brief.

(c) Write the specific features of the cell sap of root hairs which helps in absorption of water.

(d) What is osmosis?

(e) How does a cell wall and a cell membrane differ in their permeability?

Answer

(a) Solution 1 → Hypotonic solution
     Solution 2 → Hypertonic solution
     Solution 3 → Isotonic solution

(b) In beaker 3, the solution present is an isotonic solution, i.e. the relative concentration of water molecules and solutes is the same in the solution as well as inside the cell. There is no movement of water molecules across the cell membrane. Hence, the size of potato cube remains the same.

(c) The cell sap of root hair has a higher concentration of salts as compared to the outside soil water.

(d) Osmosis is the movement of water molecules from their region of higher concentration (dilute solution or with a lower solute concentration) to their region of lower concentration (concentrated solution or with a higher solute concentration) through a semi permeable membrane.

(e) The cell wall is freely permeable. It allows the movement of water molecules and dissolved substances freely in and out of the cell. The cell membrane is semi permeable. It allows water molecules to pass through but not the larger molecules of the dissolved salts.

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