Absorption of Roots

(a) The root cap acts as a protective tissue.

(b) The apparatus used to demonstrate osmosis is called osmometer.

(c) Osmosis is the diffusion of water molecules only.

(a) Exosmosis

(b) Imbibition

(c) Osmosis

(i) Vascular tissues, i.e., xylem and phloem.

(ii) Root pressure

(iii) Turgidity

(iv) Bleeding (exudation)

(v) Isotonic solution

Five important roles of water and other minerals in plants are:

1. Water acts as a medium for the transportation of dissolved substances from roots to the upper parts of the plant.
2. Water is used as a raw material in photosynthesis for the synthesis of glucose.
3. Water provides turgidity, giving mechanical stiffness to plant tissues.
4. A large quantity of water is given out as vapour during transpiration and helps in maintaining the plant's temperature.
5. Minerals act as building blocks for many compounds and serve as constituents of cells, cell organelles and enzymes synthesised by the plant.

Absorption of water and minerals occurs by the processes of imbibition, diffusion, osmosis and active transport.

Upward conduction of water and minerals occurs by root pressure, capillary force (capillarity) and transpiration pull, aided by the cohesive and adhesive forces of water molecules.

hypertonic

Reason — In a hypertonic solution the concentration of solutes is more than that of the cell sap. When a cell is kept in such a solution, water moves out of the cell by exosmosis, so the cell shrinks in size and loses its shape.

xylem tissue

Reason — Xylem conducts water and dissolved minerals upward in the plant. The coloured eosin solution rises up through the xylem, so the xylem tissue gets stained pink.

Endosmosis

Reason — The clown fish is a saltwater fish whose body fluids are hypertonic to freshwater. In the freshwater aquarium (hypotonic surrounding), water enters its body cells by endosmosis, causing the cells to swell and burst, which leads to its death.

hypertonic solution

Reason — During plasmolysis the cell is kept in a hypertonic solution. As the cell wall is freely permeable, this outside hypertonic solution passes in and fills the space created between the cell wall and the shrunken plasma membrane.

Turgor pressure exceeds wall pressure.

Reason — Wall pressure normally balances turgor pressure and prevents further entry of water. If turgor pressure exceeds the wall pressure, the wall can no longer resist the outward push of the cell contents and the cell may burst.

root hair, cortical cells, vascular cells

Reason — Water first enters the root hair by osmosis, then passes from cell to cell through the cortical cells and finally reaches the vascular (xylem) cells.

(A) is false and (R) is true.

Explanation — Diffusion is the movement of molecules from the region of their higher concentration to the region of their lower concentration, so the Assertion is false. Diffusion is a passive process that does not require energy, so the Reason is true.

Tap water

Reason — Tap water is hypotonic to the cell sap of a plasmolysed cell. Water re-enters the cell by endosmosis, the protoplasm swells back to its original position and the cell becomes turgid. This recovery is called deplasmolysis.

Active transport

Reason — Active transport is the movement of substances against the concentration gradient (from lower to higher concentration) through a living membrane, and this requires energy in the form of ATP supplied by the cell.

B and C

Reason — Osmosis involves the net movement of water (solvent) molecules only, not solute molecules, so statement A is wrong. Osmosis occurs across a semi-permeable membrane (B) and its inward or outward direction depends on the concentration of the surrounding solution (C).

Pectin

Reason — The cell wall of a root hair is made up of two layers — the outer layer is composed of pectin and the inner layer is composed of cellulose.

Turgor pressure

Reason — The hydrostatic pressure exerted by the cell sap (cell contents) on the cell wall is called turgor pressure.

Root pressure

Reason — The continuous inward movement of water by cell to cell osmosis makes the cortical cells turgid, and they force water into the xylem. This develops a pressure in the roots called root pressure.

Hypertonic

Reason — In a hypertonic solution, water moves out of the cell by exosmosis. The protoplasm shrinks and the plasma membrane withdraws from the cell wall, so the cell becomes plasmolysed.

Xylem

Reason — Xylem is the tissue that conducts water and dissolved minerals upward. The coloured eosin solution rises through the xylem, so the pink colour is distinctly seen in the xylem.

Conducts water and minerals in leaves

Reason — Xylem is the water-conducting tissue of the plant. It carries water and dissolved minerals upward from the roots to the stem and leaves.

Hypertonic, Exosmosis

Reason — In the figure the protoplasm has shrunk and withdrawn from the cell wall, showing that the cell has lost water. This happens when the cell is placed in a hypertonic solution, in which water moves out of the cell by exosmosis.

(A) is true and (R) is false.

Explanation — A turgid cell is in a balanced state because no more water can enter it. However, in a turgid cell the turgor pressure and wall pressure are equal but act in opposite directions, not in the same direction. Hence the Reason is false.

Deplasmolysis

Reason — The inward movement of water molecules (endosmosis) into a plasmolysed cell makes the protoplasm swell back to its original position. This recovery is called deplasmolysis.

P - Imbibition, Q - Osmosis

Reason — During absorption of water, imbibition first helps in the uptake of soil water by the root hair, and then osmosis draws water into the root hair because its cell sap is of higher concentration than the surrounding soil water.

plasmolysis and flaccidity

Reason — A 5% salt solution is hypertonic to the cell sap. Water moves out of the cell by exosmosis, the cell becomes flaccid and its protoplasm shrinks away from the cell wall, i.e., it gets plasmolysed.

Raj and Sonu

Reason — Roots absorb water and minerals from the soil (Raj) and fix the plant firmly to the soil, giving mechanical support (Sonu). Conduction of food is done by phloem, not roots, so Lata is wrong, and roots do not carry out photosynthesis, so Abhay is wrong.

Plasmolysis

Reason — The common salt makes the soil solution hypertonic to the grass cells. Water moves out of the cells by exosmosis, the cells become plasmolysed, and the grass wilts and dies.

Osmosis

Reason — The plant absorbed water from the soil through its roots by osmosis, which supported its growth. The pot without a plant had no root hairs to absorb water, so no such change was seen.

Active Transport - Requires energy to move substances from low to high concentration; Passive Transport - Moves substances from high to low concentration without energy.

Reason — Active transport moves substances against the gradient, i.e., from lower to higher concentration, and needs energy (P). Passive transport moves substances along the gradient, i.e., from higher to lower concentration, without using energy (Q).

(i) Osmosis

(ii) Phloem

(iii) Xylem

(iv) Endosmosis

(v) Plasmolysis

(vi) Osmosis

(vii) Diffusion

(a) (i) osmosis

(b) (ii) rises

(c) (iii) water

(d) (iv) sugar (solute)

(e) (v) water

(i) Xylem — Conducts water and dissolved minerals upward from the roots to the stem and leaves.

(ii) Phloem — Conducts (translocates) the prepared food from the leaves to other parts of the plant.

(iii) Root hairs — Absorb water and minerals from the soil.

(iv) Stomata — Help in the exchange of gases and in transpiration (loss of water vapour).

(v) Thylakoids — Contain chlorophyll and are the site of the light reactions of photosynthesis, trapping light energy.

(i) Soil water → Root hair → cortical cells → Xylem

(ii) Epidermis → Cortex → Endodermis → Xylem

(i) False
Corrected Statement — Deplasmolysis is reverse of plasmolysis.

(ii) False
Corrected Statement — Dry seeds when soaked in water, swell up due to imbibition.

(iii) True

(iv) False
Corrected Statement — A plant cell placed in hypertonic solution gets plasmolysed.

(v) False
Corrected Statement — The cell wall of the root hair is a permeable membrane.

(vi) False
Corrected Statement — The cell sap of root hair is hypertonic.

(vii) False
Corrected Statement — Freshwater fish when placed in hypertonic salt solution lose water and shrink.

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

Imbibition is the phenomenon in which living or dead plant cells, in their dry or semi-dry state, absorb water by surface attraction (surface tension).

Turgor pressure is the hydrostatic pressure exerted by the cell sap (cell contents) on the cell wall.

Ascent of sap is the upward movement of water and dissolved minerals absorbed by the roots, through the xylem, to the stem and leaves of the plant.

Turgidity is the state of a cell in which the cell wall is rigid and stretched by the increase in the volume of vacuoles due to the absorption of water, so that the cell cannot accommodate any more water.

Active transport is the movement of substances through the cell membrane of living cells from their lower to higher concentration (against the concentration gradient) using metabolic energy (ATP).

Differences between Turgidity and Flaccidity are:

Differences between Plasmolysis and Deplasmolysis are:

Differences between Hypotonic solution and Hypertonic solution are:

Differences between Turgor pressure and Wall pressure are:

Sprinkled salt makes the soil solution hypertonic to the grass cells. Water moves out of the cells by exosmosis, the cells become plasmolysed and flaccid, and the grass is killed at that spot.

Potato cubes contain a higher concentration of salts and sugars than the water around them. Water enters the cubes by endosmosis, making the cells turgid, so the cubes become firm and increase in size.

Resins are made of hydrophilic substances that absorb water by surface attraction. Due to this imbibition of water, they swell up when kept in water.

Sea water is hypertonic to the body fluids of a freshwater fish. Water moves out of its body cells by exosmosis, causing it to lose water and become dehydrated, so it cannot survive in sea water.

Excess soluble fertilisers make the soil solution hypertonic to the root hair cell sap. Water moves out of the root hairs by exosmosis, they become plasmolysed and can no longer absorb water, so the plant wilts and begins to die.

Cold water is hypotonic to the cell sap of the wilted leaves. Water enters the cells by endosmosis, making them turgid, so the leaves become crisp and firm again.

Much salt makes the surroundings hypertonic to microorganisms present in the pickle. Water moves out of their cells by exosmosis, causing plasmolysis and inhibiting their growth, so the pickle is preserved.

Excess fertilizers make the moist soil solution hypertonic to the root hair cell sap. Water moves out of the root hairs by exosmosis, so they lose their turgidity, become flaccid and droop.

The labelled diagram of the plasmolysed cortical cell is shown below, with the cytoplasm (shrunken protoplasm), the hypertonic solution (in the space between the cell wall and the plasma membrane) and the plasma membrane marked.

The significance of osmosis is as follows:

1. It helps in the absorption of water and minerals by the roots from the soil.
2. It develops turgidity and thus maintains turgor pressure in plant cells, which keeps the plant firm and erect.
3. It allows the movement of water from one cell to another, thereby ensuring the flow of water and minerals throughout the plant.
4. It regulates the opening and closing of stomata through its control of the turgidity of guard cells.

(i) Utility of plasmolysis — Plasmolysis is used to kill weeds growing in lawns. It is also used in the preservation of food items such as pickles and jams, where a high concentration of salt or sugar plasmolyses and kills the bacteria, preventing their growth.

(ii) Active transport — Active transport is the movement of substances (salts or ions) through the cell membrane of living cells from their lower to higher concentration, i.e., against the concentration gradient. It requires metabolic energy in the form of ATP supplied by the cell.

Two manifestations of root pressure are:

1. Bleeding — When the stem of a well-watered plant is cut close to the ground, the cell sap oozes out from the cut end due to root pressure. This exudation of sap from an injured or cut part of the plant is called bleeding.

2. Guttation — Due to excess root pressure, drops of water are given out along the margins of the leaves of certain plants, especially in the early morning. This loss of water in the form of liquid drops is called guttation.

(i) Freshwater is hypotonic to the body fluids of a marine fish. Water enters the body cells of the fish by endosmosis, causing the cells to swell and finally burst, which leads to the death of the fish.

(ii) The pressure that develops inside the cells of the fish is turgor pressure (osmotic pressure).

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

The semi-permeable membrane present in a plant cell is the cell membrane (plasma membrane).

(i) A neat, labelled diagram of a root hair is shown below.

(ii) Root hairs contain cell sap which has a higher concentration than the surrounding soil water. This difference in concentration sets up osmosis, due to which water is drawn into the root hairs from the soil.

(i) (a) Cell A — Turgid
(b) Cell B — Plasmolysed

(ii) (a) Cell A — water
(b) Cell B — strong sugar solution

(iii) (a) Cell A — when the soil has plenty of water, i.e., the soil water is hypotonic to the cell sap, so the root hair absorbs water and becomes turgid.
(b) Cell B — when the soil has an excess of salts or fertilizers, i.e., the soil solution is hypertonic to the cell sap, so the root hair loses water and becomes plasmolysed.

(iv) Root pressure is responsible for the movement of water from the root hair cell to the xylem of the root. It is set up when water absorbed by osmosis passes from cell to cell, making the cortical cells turgid; these turgid cells then force their water content into the xylem, developing root pressure.

(v) Transpiration pull helps in the upward movement of water through the xylem.

(i) Osmosis

(ii) Osmosis is the net movement of water molecules from their region of higher concentration (dilute solution with lower solute concentration) to their region of lower concentration (concentrated solution with higher solute concentration) through a semi-permeable membrane. Here, water from the beaker passes through the membrane into the concentrated sugar solution in the thistle funnel.

(iii) After about 10 minutes, the level of the sugar solution in the thistle funnel will rise.

(iv) The sugar solution is hypertonic.

(v) The sugar solution represents the cell sap of the plant cell.

(i) Capillary water

Reason — Capillary water is held in the small spaces between soil particles and is readily available for absorption by plant roots.
Mineral water is drinking water containing dissolved minerals. Cell sap is the fluid present inside plant cells, not in the soil. Water vapour is present in the air spaces of the soil.

(ii) Turgid

Reason — In a hypotonic solution, water enters the plant cell by endosmosis, making the cell turgid.
Flaccid cell has lost some water. Plasmolysis occurs in a hypertonic solution when water leaves the cell. Cell swells and becomes turgid in a hypotonic solution.

(iii) Endosmosis

Reason — Water enters the root hair cells from the soil by endosmosis, a type of osmosis in which water moves into the cell through a selectively permeable membrane.
Exosmosis is the movement of water out of the cell.Guttation is the loss of liquid water from leaf margins through hydathodes. Transpiration is the loss of water vapour from the aerial parts of the plant.

(iv) Wall pressure

Reason — As water enters the plant cell, the cell sap exerts turgor pressure on the cell wall. In response, the cell wall exerts an equal and opposite pressure called wall pressure, balancing the turgor pressure.
Osmotic pressure is the minimum pressure required to prevent osmosis. Active pressure is not a recognized biological term related to plant cells. Atmospheric pressure is the pressure exerted by the surrounding air.