Revision: Transportation in Plants Biology ICSE ICSE Class 8 CISCE

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.

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.

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

• 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.