Revision: Plant Physiology >> Absorption by Roots: The Processes Involved Biology (English Medium) ICSE Class 10 CISCE

The transport of water with dissolved minerals from the root to other aerial parts like stem and leaves, against gravity, is called translocation or ascent of sap.

The diffusion pressure of pure solvent (pure water) is always more than the diffusion pressure of the solvent in a solution. The difference between the diffusion pressure of the pure solvent and that of the solvent in solution is called the Diffusion Pressure Deficit (DPD) or Suction Pressure (SP).

The cell wall is thick and rigid, exerts a counter pressure on the cell sap. This is called Wall pressure (W. P).

It is the actual hydrostatic pressure developed inside a cell as a result of the entry of water into it.

Imbibition is a phenomenon in which living or dead plant cells absorb water by surface attraction.

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

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.

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

Example: Perfume fills a whole room.

The relative concentration of the solutions that determines the direction and extent of diffusion is called tonicity.

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.

A hypertonic solution is a solution that has a higher concentration of solutes (such as salt or sugar) compared to the inside of a cell.

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.
or
Osmotic pressure of a solution is a measure of its tendency to take in water by osmosis.

Relative concentration of the solutions that determines the direction and extent of diffusion is called tonicity.

The intermolecular force of attraction between two molecules of the same material is called the cohesive force.

Example: The force of attraction between two water molecules.

Active transport is the passage of a substance (salt or ion) from its lower to higher concentration through a living cell membrane using energy from the cell. [Active transport is in a direction opposite to that of diffusion.]

Active transport is the passage of a substance (salt or ion) from its lower to higher concentration through a living cell membrane using energy from the cell. Active transport is in a direction opposite to that of diffusion.

Active absorption is a physiological process in which a substance (such as water, mineral ions, or nutrients) is taken up by a cell or organism against a concentration gradient, requiring the expenditure of metabolic energy.

Passive transport is nothing different from diffusion "Passive" refers to requiring no input of energy. There is a free movement of molecules from their higher concentration to their lower concentration. 

Plasmolysis is the process in which the cytoplasm shrinks and the plasma membrane pulls away from the cell wall due to the loss of water when a plant cell is placed in a concentrated solution.

or

Plasmolysis is the contraction of cytoplasm from the cell wall caused due to the withdrawal of water when placed in a strong (hypertonic) solution. 

Flaccidity is the condition of a cell when it becomes limp due to plasmolysis, and the plasma membrane is no longer pressed tightly against the cell wall. It is the reverse of turgidity.

or

Flaccidity is the condition in which the cell content is shrunken and the cell is no more "tight'. The cell is then said to be flaccid. 

The pressure of the cell contents on the cell wall is called turgor pressure.

A cell is said to be turgid when it is fully distended by the maximum intake of water and can no longer accommodate more water.

Turgidity is the condition in which a cell becomes fully swollen with water, exerting pressure on the cell wall.

or

Turgidity is the state of a cell in which the cell wall is rigid and stretched by an increase in the volume of vacuoles due to the absorption of water. The cell is then said to be turgid. 

The pressure exerted by the cell wall on the cell content is called wall pressure.

The pressure developed in the roots due to cell-to-cell osmosis that helps push water upward through the xylem is called root pressure.

During the absorption of water, the continuous flow of water develops hydrostatic pressure in the living cells of the root. This is called root pressure.

The loss of water in the form of tiny droplets from the tips or edges of leaves, especially during early morning, due to high root pressure is called guttation.

1. Water forms a part of protoplasm and is vital for various physiological processes in plants.
2. Photosynthesis requires water as a raw material for glucose synthesis in green leaves.
3. Transpiration removes excess water, cools the plant, and helps in creating a suction force for water movement.
4. Transportation of minerals from roots to shoots and sugars from leaves occurs in a water solution.
5. Mechanical stiffness is maintained by water in plant cells through turgidity.
6. Minerals are absorbed by roots as salts or ions and are crucial for cell structure, organelles, and enzyme synthesis.

1. Large Surface Area: Numerous root hairs and rootlets greatly increase surface area for absorption.
2. High Cell Sap Concentration: Root hair cell sap has a higher solute concentration than surrounding soil water, aiding osmosis.
3. Thin Cell Wall: The thin, permeable cell wall allows the easy movement of water and dissolved substances.
4. Semi-permeable Membrane: Allows selective entry of water molecules while restricting larger solutes.
5. Efficient Osmosis: These features together enable roots to absorb water effectively through osmosis.

• Imbibition is the swelling of hydrophilic colloids by the adsorption of water. The adsorbing substance is imbibant and the liquid adsorbed is imbibate.
• Root hair cell walls (pectin + cellulose) are hydrophilic colloids, enabling water absorption by imbibition.
• Water is tightly adsorbed without forming a solution, and the process stops at equilibrium (moves along the concentration gradient).
• Examples - soaking of seeds, swelling of raisins, kneading of flour.

• Diffusion - movement of molecules from higher to lower concentration due to kinetic energy; continues till equilibrium is reached.
• Diffusion Pressure (DP) is proportional to the number of diffusing particles. Pure water always has more DP than a solution.
• DPD (Diffusion Pressure Deficit) = DP of pure solvent − DP of solvent in solution. Coined by B.S. Meyer (1938); now called water potential. It is the "thirst" of a cell to absorb water.
• Diffusion is important for absorption of water & minerals, gas exchange, water conduction, and food transport in plants.
• Facilitated diffusion — passive movement of hydrophilic solutes via carrier proteins (aquaporins & ion channels); needs a concentration gradient but no energy.

• Osmotic Pressure (OP) is the pressure required to stop osmosis - i.e., the pressure needed to prevent solvent molecules from entering the cell through a semipermeable membrane. It has a positive value.
• Key equation - DPD = OP − TP (since TP = WP, also written as DPD = OP − WP). In a flaccid cell, TP = 0, so DPD = OP. In a turgid cell, DPD = 0, so TP = OP.
• Importance of Turgor Pressure (TP) - keeps cells stretched, supports non-woody tissues, is essential for cell enlargement during growth, maintains cell shape, and helps in the opening and closing of stomata.
• Importance of Osmosis - responsible for absorption of water into roots, maintains cell turgidity, facilitates cell-to-cell water movement, and offers resistance to drought and frost.
• Osmosis also causes drooping of leaflets in the "Touch Me Not" plant (Mimosa pudica) and helps in cell-to-cell movement of water in plant tissues.

• Meaning: Plasmolysis is the shrinkage of the protoplast due to loss of water when a plant cell is placed in a hypertonic solution (exosmosis).
• Cell Changes: The protoplast shrinks and moves away from the cell wall, forming a gap filled with the external solution, and the cell becomes flaccid.
• Turgor Pressure: In a plasmolysed cell, turgor pressure (TP) becomes zero.
• Deplasmolysis: When the plasmolysed cell is placed in a hypotonic solution, water enters (endosmosis), and the cell becomes turgid again; this process is called deplasmolysis.