Class 10 SELINA Solutions Biology Chapter 4 - Absorption by Roots : The Processes Involved
Absorption by Roots : The Processes Involved Exercise Ex. 1
(a) Turgor pressure
(d) Active transport
(d) Pure water
(b) Cell membrane
(g) Root pressure
(a) Turgor pressure
(a) Hypotonic solution is one in which the solution kept outside the cell has lower solute concentration than the fluids inside the cell.
(b) Active transport is one in which the ions outside the roots move in with expenditure of energy from the region of their lower concentration outside to the region of their higher concentration inside.
(c) The bending movements of certain flowers towards the sun and the sleep movements of certain plants at night are examples of turgor movements.
(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.
(iv) upward flow of water
(iii) downward flow of sap
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.
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.
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.
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.
(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.
(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.
(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.
(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.
Examples of turgor movements in plants: (Any two)
(i) In the sensitive plant Mimosa pudica, 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 the leaves of the plant.
(ii) The leaves of insectivorous plants close up to entrap a living prey. When the insect comes in contact with the leaf, the leaf loses its turgor, hence closing the plant leaves.
(iii) The bending movements of certain flowers towards the sun and the sleep movements of the leaves of certain plants at night are also due to turgor movements.
(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.
(a) Common salt, when sprinkled on the grass, causes the plasmolysis of grass cells, ultimately resulting in their death.
(b) If a plant is uprooted, the leaves continue losing water by transpiration, but the roots absorb no more water. This does compensate for the water loss 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 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 seedlings in a flower bed in the evening and not in the morning.
(d) In a hypertonic solution, the solution outside the cell has a 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 from the cell wall; thus, 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 salts and sugars compared to the water in which the cubes are placed. Hence, due to endosmosis, water from the surroundings enters the potato cubes, making them firm and increasing their size.
The four main forces which contribute to the ascent of sap (upward movement of water and minerals) are root pressure, capillarity, transpirational pull and adhesion.
a) Root pressure- It builds up sufficient force to push the sap in the xylem vessels up to a certain height and may be enough for herbaceous plants.
b) Capillarity- It causes the water from a lower level to rise in order to fill the vacuum created due to water loss from transpiration from the leaves. Greater the diameter of a tube, greater will be the height of water rising in it, exerting a force known as the capillary force.
c) Transpirational pull- As water evaporates from the leaf surface, more water molecules are drawn up due to the tendency of water molecules to remain connected, resulting in a continuous column of water through the stem.
d) Adhesion- When the leaf cells lose water during transpiration, it causes the water to adhere to the surface of the cells, attracting more water molecules from below. This pulling power generated by the leaves is especially essential in tall plants such as pines with insufficient root pressure.
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.
(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:
(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.
(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) Advantages of osmosis: (Any two)
(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.
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.
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.
(a) The process of water absorption by plant roots through osmosis is being studied here.
(b) A root hair contains cell sap, which contains a higher concentration of salts than 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 the water was covered with oil to prevent water loss by evaporation.
(d) Below are the observations for the level of water under different situations:
(1) Bright sunlight — When this set-up is placed in bright sunlight, the water level in the test tube decreases as compared to its initial marking as the rate of transpiration is very high.
(2) 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.
(3) Windy day — When this set-up is placed on a 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:
- 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
(a) Cylinder B: In distilled water.
(b) When the potato cube is placed in water, the water starts entering it, thus causing an increase in its size, and due to the pressure of cell contents on the cell wall, there appears to be firmness in the wall of the cube.
(c) The physical process responsible for the movement of substances 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 in beaker B is osmosis, which is the diffusion of water across the membrane of the potato slice cells. Plasmolysis occurs in beaker C as the potato shrinks due to the hypotonic solution of 20% sucrose solution.
(e) After 48 hours, the weight of the potato cylinder in beaker A will be less than in the initial phase due to the water loss to the surroundings through plasmolysis.
(a) (i) Root hair, Xylem vessel, Soil particles, Cortex respectively
(b) (iii) Osmosis
(c) (ii) Adhesive force
(d) (iv) Cohesive force
(e) (iii) Guttation
(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.
(a) (iv) Cytoplasm, Cell wall and Vacuole respectively
(b) (iii) Wall pressure
(c) (iii) Turgor pressure
(d) (ii) Osmotic pressure
(e) Plasmolysed plant cell