Absorption by Roots — The Process Involved

A is True and R is False.

Explanation
Soil is the storehouse of different essential minerals but for photosynthesis, plant absorb Carbon dioxide from air.

A is False and R is True.

Explanation
Diffusion is the process of free movement of liquid as well as gas molecules.

A is False and R is True.

Explanation
Translocation of prepared food material in plants always occurs through the phloem tissue in both upward and downward directions.

Both A and R are True.

Explanation
Active transport does not occur through a non-living semi-permeable membrane because it requires energy (ATP) which can only be provided by living membrane.
Active transport moves molecules against their concentration gradient, from an area of lower concentration to an area of higher concentration, which requires energy input.

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.

(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 (solute or solvent, gas, liquid) from the region of their higher concentration to the region of their lower concentration when the two are in a 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.

(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 plasmolysed.

(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.

The four main forces which contribute to the ascent of sap are:

1. Root pressure — Root pressure builds up sufficient force to push the sap in the xylem vessels up to a certain height and may be enough for herbaceous plants.
2. Capillary force — Capillarity (narrow diameter) of xylem vessels causes the water from a lower level to rise to fill up the vacuum created by the loss of water due to transpiration from the leaves. Narrower the diameter of a tube, greater will be the height of water rising in it exerting a force called capillary force.
3. Transpiration pull — As the 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 (cohesion), and thus to produce a continuous column of water through the stem.
4. Adhesion — It causes the water to stick to the surface of cells thus drawing more water molecules from below when the leaf cells lose water during transpiration. This pulling force (or suction force) provided by the leaves is important for tall trees.

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.

Turgor pressure

Reason — Turgor pressure is the pressure applied by the cell contents on the wall of cell.

Hypertonic

Reason — The concentration of solutes in hypertonic solution is more than the cell sap. When a cell is kept in such solution, water moves out of the cell and it shrinks.

Active transport

Reason — Active transport involves use of energy as such transport is against the gradient.

Pure water

Reason — Water potential is the capacity of water to move out to higher concentrated solution. It is maximum for pure water.

Deplasmolysis

Reason — When plasmolysed cell is kept in a hypotonic solution, it absorbs water and gets fully distended.

Transpiration

Reason — Transpiration (loss of water through plant surface) creates a suction force called transpiration pull. It works with root pressure due to which the roots absorb water.

Imbibition

Reason — Substances which are made up of cellulose or proteins are hydrophilic. They can imbibe water due to surface attraction.

Cell membrane

Reason — Cell membrane is semi-permeable due to its structure. It allows entry of some substances and prevent the movement of some other materials.

Plasmolysis

Reason — Adding salt to the pickle increases the concentration of solute outside the cells of bacteria. This results in movement of water outwards from the cell and thus bacteria gets killed.

Manometer

Reason — Manometer is the instrument to measure root pressure.

P - Endosmosis, Q - Exosmosis

Reason — Plant cell P is placed in water, so the concentration of water molecules inside the cell is less than the surrounding, hence water molecules enter the cell causing the cell to swell up. Plant cell Q is placed in sugar solution, so the concentration of water molecules inside the cell is more than the surrounding, hence water will move out of the cell and as a result it will shrink.

The three primary functions of root are:

1. Fixes the plant in soil giving it support.
2. Absorbs water and mineral nutrient from soil.
3. Conducts absorbed water and mineral to stem.

Plants need water for:

1. Photosynthesis
2. Transpiration
3. Transportation
4. Mechanical stiffness

The mineral nutrients are used by plants in formation of cell and cell organelles as well as in synthesis of various compounds and enzymes.

Three main characteristics of the roots that enable them to draw water from the soil are:

1. Surface area of roots is enormous.
2. Root hairs contain cell sap, of a higher concentration than that of the surrounding water.
3. Root hairs have thin walls.

(i) False
Corrected Statement — Diffusion is the free movement of molecules of a substance (solute or solvent, gas, liquid) from the region of their higher concentration to the region of their lower concentration when the two are in a direct contact.

(ii) True

(iii) True

(iv) False
Corrected Statement — Endosmosis may cause bursting of a cell.

(v) True

(vi) False
Corrected Statement — In an experiment on osmosis, if external pressure is applied on a dilute solution, more water will pass into the concentrated solution.

The solution is a hypotonic solution i.e., concentration of solute in it is less than that of cell sap. A cell when kept in hypotonic solution swells and finally bursts due to endosmosis.

Active transport needs involvement of energy.

Yes, we can call diffusion as passive transport as it occurs according to concentration gradient i.e., from higher concentration of solute to lower concentration. It does not involve any energy expense.

(i) Turgid

(ii) Turgor Pressure

(iii) Flaccid

(iv) Deplasmolysed

(v) Root pressure

Oil was added over water in the test tubes to avoid the loss of water due to evaporation.

Coloured eosin solution in water was taken to stain xylem vessel in order to show that there is upward movement of absorbed water.

The xylem is located deeper and the phloem is relatively superficial in location.

The stem below the ring stopped growing and even slightly decayed because its food supply was cut. After girdling, the lower portion of stem remains alive for few days due to stored food in it but later it stops to grow.

(a) Difference between Plasmolysis and Deplasmolysis

(b) Difference between Turgor pressure and Wall pressure

(c) Difference between Hypotonic and Hypertonic solution

(d) Difference between Turgidity and Flaccidity

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

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

(c) True

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

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

(a) 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) True
Reason — The seeds and grains swell up when soaked in water due to imbibition and endosmosis. The force generated by water thus absorbed is strong enough to make the seeds coats burst.

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

(d) 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) 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.

(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) 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.

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

• 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. 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:

(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.

(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.

(a) Root hair, Xylem vessel, Soil particles, Cortex respectively.

(b) Osmosis

(c) Adhesive force

(d) Cohesive force

(e) Guttation

(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.

(a) Cytoplasm, Cell wall and Vacuole respectively.

(b) Wall pressure

(c) Turgor pressure

(d) Osmotic pressure

(e) Labelled diagram of a plasmolysed plant cell is given below :

(a) Turgidity

(b) Guttation

(c) Osmosis

(d) Xylem

(e) Endosmosis

(f) Diffusion

(g) Root pressure

(a) Turgor pressure

(b) Flaccidity

(c) Bleeding

(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.

(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.