Chapter 4 : Absorption by Roots : The Processes Involved - Selina Solutions for Class 10 Biology ICSE

Biology is one of the crucial subjects in ICSE Class 10. ICSE Class 10 Biology speaks about the cell as the basic unit of life, genes, and evolution and deals with how living organisms interact with the environment, including the behavior of living beings. TopperLearning is one of the premier online platforms which helps students of ICSE Class 10 to study various concepts in Biology.

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Chapter 4 - Absorption by Roots : The Processes Involved Excercise Ex. 1

Question 1

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

a) Diffusion

b) Osmosis

c) Imbibition

d) Endosmosis
Solution 1
c) Imbibition
Question 2

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

a) Isotonic sugar solution

b) Hypotonic salt solution

c) Hypertonic salt solution

d) Isotonic salt solution
Solution 2
c) Hypertonic 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

a) Flaccidity

b) Turgidity

c) Capillarity

d) Tonicity
Solution 3
b) Turgidity
Question 4

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

a) Tremendous surface area

b) Contain cell sap at higher concentration than the surrounding water

c) Root hairs have thin cell walls

d) Grow downward into the soil
Solution 4
d) 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:

a) Osmosis

b) Diffusion

c) Active transport

d) Capillarity
Solution 5
b) Diffusion
Question 6

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

a) a freely permeable membrane

b) a cell wall in between

c) a selectively permeable membrane in between

d) an endless inflow of water into a cell

Solution 6

c) a selectively permeable membrane in between

Question 7

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

a) Pure water

b) 10% salt solution

c) Honey

d) 50% sugar solution
Solution 7
a) Pure water
Question 8

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

a) isotonic solution

b) hypotonic solution

c) hypertonic solution

d) water
Solution 8
d) water
Question 9

What is responsible for guttation?

a) Osmotic pressure

b) Root pressure

c) Suction pressure

d) Capillarity
Solution 9
b) Root pressure
Question 10

The most appropriate characteristic of semi-permeable membrane is that

a) it has minute pores

b) it has no pores

c) it allows the solute to pass through but not the solvent

d) it allows a solvent to pass through freely but prevents the passage of the solute
Solution 10
d) it allows a solvent to pass through freely but prevents the passage of the solute
Question 11
Name the following:

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

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

(c) 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.
Solution 11
(a) Turgidity

(b) Guttation

(c) Osmosis

(d) Xylem

(e) Endosmosis

(f) Diffusion

(g) Root pressure
Question 12

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.

Solution 12

(a) Turgor pressure

(b) Flaccidity

(c) Bleeding

Question 13

Complete the following statements:

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

(b) Active transport is one in which the ions outside the roots move in with expenditure of energy __________.

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

Solution 13

(a) the fluids inside

(b) from the region of their lower concentration outside to the region of their higher concentration inside

(c) turgor movements

Question 14

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)

Solution 14

(a) shrink

(b) water

(c) opposite

Question 15

Match the terms in column I 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

 

Solution 15

 

 

Column I

Column 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

 

Question 16
Differentiate between the following :

(a) Plasmolysis and deplasmolysis

(b) Turgor pressure and wall pressure

(c) Guttation and bleeding

(d) Turgidity and flaccidity
Solution 16

(a)


Plasmolysis

Deplasmolysis

1. 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.

2. In Plasmolysis, the cell becomes flaccid.

1.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.

2. In deplasmolysis, the cell becomes turgid.

(b)

Turgor pressure

Wall 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.

(c)


Guttation

Bleeding

Guttation is the process by which drops of water appear along leaf margins due to excessive root pressure.

Bleeding is the loss of cell sap through a cut stem.

(d)


Turgidity

Flaccidity

1. It is the state of a cell in which the cell cannot accommodate any more water and it is fully distended.

1. It is the condition in which the cell content is shrunken and the cell is not tight.

 

Question 17

What is the difference between flaccid and turgid? Give one example of flaccid condition in plants.

Solution 17

The cell is said to be turgid when the plant cell wall becomes rigid and stretched by an increase in the volume of vacuoles due to the absorption of water when placed in hypotonic solution. On the other hand, the cell is said to be flaccid when the cell contents get shrunken when the cell is placed in hypertonic solution and the cell is no more tight. Flaccidity is the reverse of turgidity.

Example Weeds can be killed in a playground by sprinkling excessive salts around their base.

Or


A plant cell when immersed in hypertonic solution like salt solution for about 30 minutes will become flaccid or limp.

Question 18

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.

Solution 18

(a) Common salt when sprinkled on the grass causes the Plasmolysis of grass cell ultimately leading them to death. Hence, if we sprinkle some common salt on grass growing on a lawn, it is killed at the spot.

(b) If a plant is uprooted, the leaves continue losing water by transpiration, but there is no more water absorbed 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 causes stress to the seedlings. If the seedlings are transplanted in the morning, they would have to immediately bear the additional stress of excessive transpiration occurring during the hot afternoon. 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) In a hypertonic solution, the solution outside the cell has higher solute concentration than the fluids inside the cell. Therefore, water flows out from the plant cell due to exosmosis. The cytoplasm shrinks and the plasma membrane withdraws away from the cell wall and this the cell becomes flaccid. Hence a plant cell when kept in a hypertonic salt solution for about 30 minutes turns 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 19
Mention whether the following statements are true (T) or false (F) and give explanation in support of your answer.

(a) Plasmolysis is reverse of deplasmolysis.

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

(c) Soaked seeds burst three seed coats

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

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

(f) Dry seeds when submerged in water swell up due to endosmosis.
Solution 19
(a) True.

Plasmolysis occurs due to outflow of water from the cell when placed in hypertonic solution due to which the cytoplasm shrinks away from the cell wall. On the other hand, deplasmolysis is the result of the re-entry of water into the plasmolysed cell when placed in hypotonic solution due to which the protoplasm again swells up pressing tight against the cell wall.

(b) False.

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.

(c) False.

There is only one seed coat in a seed.

(d) False.

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

(e) False.

Guttation 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.

(f) False.

Dry seeds when submerged in water swell up due to imbibitions. On contact with water dry seeds imbibe water and swell up.
Question 20
Give two examples of turgor movements in plants.
Solution 20
Examples of turgor movements in plants:

(i) In Mimosa pudica, a sensitive plant, the stimulus of touch leads to loss of turgor at the base of the leaflets and at the base of the petioles called pulvinus. This causes the folding and drooping of leaves of the plant.

(ii) The leaves of insectivorous plants close up to entrap a living prey. When the insect come in contact with the leaf, it loses it turgor hence closing the leaves of the plant.

(iii) The bending movements of certain flowers towards the sun.

(Any two)
Question 21
Explain the mechanism of the closing and opening of the stomata.
Solution 21
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 22
Concentration of mineral nutrient elements is higher inside the root-hairs than in the surrounding soil. How do roots take them in from the soil?
Solution 22
If the concentration of mineral nutrient elements is higher inside the root-hairs than in the surrounding soil, then roots take them in from the soil by 'active transport'. In active transport, the mineral ions are forcibly carried from the surrounding soil i.e. the region of their lower concentration into the roots i.e. the region of their higher concentration through the cell membrane by expenditure of energy. This energy is supplied by the cell in the form of ATP.
Question 23
Explain how soaked seeds swell up and burst their seed coats.
Solution 23
When soaked in water, the seeds swell up due to imbibition and endosmosis. During these two processes water enters the cell. Due to endosmosis, at some point, the seed coat is unable to bear the turgor pressure and hence, the seed coat bursts.
Question 24
Leaves of the sensitive plant wilt and droop down on a slight touch. What mechanism brings about this change?
Solution 24
Leaves of the sensitive plant wilt and droop down on a slight touch due to turgor movement. Petiole of sensitive plant is held up by turgid pulvinus tissue. The stimulus of touch leads to loss of turgor at the base of the leaflets and at the base of the petioles i.e. pulvinus. The cells of the lower side of pulvinus lose water and the petiole collapses. This causes the wilting and drooping of the leaves.

Question 25
What is transpirational pull? How is it caused?
Solution 25
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.

Question 26
The following diagram represents a plant cell after being place in a strong sugar solution.



Guidelines 1 to 5 indicate the following:

(1) Cell Wall

(2) Strong Sugar Solution

(3) Protoplasm

(4) Large Vacuole

(5) Nucleus



(a) What is the state of the cell shown in the diagram?

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

(c) If the cell had been placed in distilled water instead of strong sugar solution, which feature would not have been seen?

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

Solution 26
(a) The cell is flaccid i.e. it is plasmolysed.

(b) Plasma Membrane

(c) Plasmolysis would not occur and flaccidity would not be seen i.e. the protoplasm would not have shrunken away from the cell wall.

(d) Cell Wall is absent in animal cell.
Question 27
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) Give the term for the state of the cell it has acquired.

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

(c) Redraw in the space provided, the diagram of the cell if it is soon placed in ordinary water for some time.
Solution 27
(a) Flaccid Cell

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

(c)


Question 28

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

  

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.

Solution 28

a.  

A - Cell wall

B - Cell membrane

C - Cytoplasm

D - Nucleus

 

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. 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.

 

c.  

Cell wall

Cell membrane

The cell wall of a root hair is freely permeable and allows both salt and water to pass through.

The cell membrane of a root hair is semi-permeable and does not allow large dissolved salt molecules to pass through.

 

d.  

  

Question 29
Two potato cubes each 1 cm3 in size, were placed separately in two containers (A and B), the container A having water and the other (B) containing concentrated sugar solution. After 24 hours when the cubes were examined, those placed in water were found to be firm and had increased slightly in size and those placed in concentrated sugar solution were found to be soft and somewhat decreased in size. Use the above information to answer the questions that follow:

(a) Account for the firmness and increase in the size of the potato cubes placed in water.

(b) Account for the softness and decrease in size of the potato cubes which were placed in sugar solution.

(c) Name and define the physical process being investigated in this experiment.
Solution 29
(a) Water is hypotonic to the potato cells, due to which endosmosis occurs and water enters the potato cells. The protoplasm swells up pressing tight against the cell wall. The cells are fully distended i.e. turgid. This causes the firmness and increase in the size of the potato cubes when placed in water.

(b) Sugar solution is hypertonic to the potato cells, due to which exosmosis occurs and water flows out of the potato cells. The potato cell loses its distended appearance, the cytoplasm shrinks and the plasma membrane withdraws from the cell wall. The cells become limp or flaccid. This causes the softness and decrease in size of the potato cubes when placed in sugar solution.

(c) The process being investigated is osmosis. Osmosis is the diffusion of water molecules across a semi-permeable membrane from a more dilute solution (with a lower solute concentration) to a less dilute solution (with a higher solute concentration).
Question 30

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



(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 plants to foster the process mentioned in (a) above

Solution 30

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

(b) A root-hair contains cell sap which contains higher concentration of salts as compared to outside soil water. This difference sets off osmosis and outside water diffuses into the root-hair. From the cell bearing root-hair, water passes into adjoining cells one after another to finally the xylem vessels.

(c) The surface of water was 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  

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

  • Large surface area provided by rootlets and root hairs
  • Root hairs containing cell sap at a higher concentration than that of the surrounding water
  • Root hairs with thin walls
Question 31
Show by a series of diagrams, the change which a plant cell will undergo when placed in

(a) Hypertonic salt solution and

(b) Hypotonic salt solution.

Solution 31
(a)



(b)

Question 32

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

  

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

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

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

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

Solution 32

(a) Osmosis

(b) Osmosis is the movement of water molecules from their region of higher concentration (dilute solution) to their region of lower concentration (concentrated solution) through a semipermeable 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 33

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) 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 hair which helps in absorption of water.

(d) What is osmosis?

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

Solution 33

(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 cubes remains the same.

(c) The cell sap of root hair has a higher concentration of solute than the surrounding water.

(d) Osmosis is the diffusion of water molecules across a semi-permeable membrane from the region of dilute solution (i.e. a lower solute concentration) to the region of concentrated solution (i.e. a higher solute concentration).

(e) The cell wall is freely permeable to all substances, while the cell membrane is selectively permeable and allows only certain substances to enter or exit the cell.

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