Revision: Plant Physiology >> Transport in Plants Biology (Theory) ISC (Science) ISC Class 11 CISCE

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.

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.]

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

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

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. 

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. 

• 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.

• 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.