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

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

Solution A.1
c) Imbibition
Solution A.2
c) Hypertonic salt solution
Solution A.3
b) Turgidity
Solution A.4
d) Grow downward into the soil
Solution A.5
b) Diffusion
Solution A.6

c) a selectively permeable membrane in between

Solution A.7
a) Pure water
Solution A.8
d) water
Solution A.9
b) Root pressure
Solution A.10
d) it allows a solvent to pass through freely but prevents the passage of the solute
Solution B.1
(a) Turgidity

(b) Guttation

(c) Osmosis

(d) Xylem

(e) Endosmosis

(f) Diffusion

(g) Root pressure
Solution B.2

(a) Turgor pressure

(b) Flaccidity

(c) Bleeding

Solution B.3

(a) the fluids inside

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

(c) turgor movements

Solution B.4

(a) shrink

(b) water

(c) opposite

Solution B.5

 

 

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

 

Solution C.1

(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.

 

Solution C.2

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

 

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

 

(c) True.

 

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

 

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

Solution C.3

(a) 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.

 

(b) False. There is only one seed coat in a seed.

 

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

 

(d) 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.

 

(e) True.

Solution D.1
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)
Solution D.2

(a) Imbibition: Imbibition is a phenomenon by which the living or dead plant cells absorb water by surface attraction.

 

(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 to their region of lower 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. 

Solution D.3

(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.

Solution D.4

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.

Solution D.5

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.

Solution E.1

(a) Flaccid cell

 

(b) Plasma membrane

 

(c) The liquid 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:

  

Solution E.2

(a) Osmosis

(b) 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).

(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) For control experiment, the beaker will contain the water. At the same time, instead of the sugar solution; the thistle funnel with the cellophane paper tied on its mouth and inverted in the beaker will also contain water.

(e)

(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) cellophane paper, egg membrane, animal bladder (any one)

(g)

(i) The roots of plants absorb water and minerals from surrounding soil due to osmosis.

(ii) Osmosis allows plants to absorb water from the soil which helps plants to keep cells alive in roots, stems and leaves.

(iii) Osmosis is also important in the opening and closing of stomata which is an important feature for the processes like transpiration and photosynthesis. (Any two)

Solution E.3

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.  

  

Solution E.4

(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
Solution E.5

(a) Cylinder B: In distilled water.

 

(b) When the potato cube is placed in water, the water starts entering the potato cube thus causing an increase in its size and due to pressure of cell contents on the cell wall, there appears a firmness in the wall of the cube.

 

(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.

 

(e) The weight of the potato cylinder in beaker A will be less as compared to initial phase after 48 hours due to loss of water to the surroundings through plasmolysis. 

Solution E.6

(a) 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) Osmotic pressure.

 

(f) Osmotic pressure is set up due to difference in osmotic gradient.

Solution E.7

(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.

Solution E.8

(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.