Absorption by Roots – Transpiration
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Plants lose huge quantity of water through transpiration. The excessive water loss has to be replaced or else the plants will wilt. In multicellular land plants, absorption of water occurs mainly through roots by diffusion, osmosis etc.
- Water. Universal solvent needed for all the important life activities. It is the major source of protoplasm.
- Root Hairs. Multicellular land plants absorb water form the soil by root hairs. These are unicellular outgrowth of roots. Plants absorb water mainly by diffusion, osmosis, imbibition etc.
- Imbibition. The process by which hydrophilic substance absorbs water.
- Diffusion. The movement of molecules of a substance from their higher concentration to their lower concentration. The rate of diffusion of molecules is proportional to their kinetic energy, size, the density of the medium, etc.
- Osmosls. The diffusion of water (solvent) from their region of higher concentration to their lower concentration through a semi-permeable membrane.
- Semi-permeable Membrane. A membrane which allows the passage of molecules selectively e.g., plasma membrane, cellophane paper, egg membrane etc.
- Osmotic Pressure (O.P.). The pressure developed in a solution when it sis separated from pure water by semi-permeable membrane.
- Turgor Pressure (T.P.). The pressure which develops in a osmotic system due to osmotic entry of water into it.
- Wall Pressure (W.P.). The pressure exerted by the cell wall over the protoplast of a fully turgid cell.
- Turgidity. The condition in which the cells are fully distended due to osmotic entry of water into it and the cell is called turgid.
- Flaccidity. The condition in which a cell loses water from its cytoplasm and the cell is called flaccid.
- Plasmolysis. The shrinkage of protoplasm when a cell is placed in a hypertonic solution.
- Deplasmolysis. The recovery of the protoplasm when a plasmolysed cell is placed in a hypotonic solution. When the turgor pressure becomes equal to osmotic pressure, the cell stops absorbing water.
- Tonocity. It is external osmotic environment of a cell.
- Hypotonic. In this condition the solution outside the cell has lower solute concentration than the cell sap.
- Hypertonic. In this condition the solution outside the cell has higher solute concentration than the cell sap.
- Isotonic. Relative concentration of water molecules and the solute on either side of the cell membrane is equal.
There are two types of water absorption-passive and active absorption.
- Passive Absorption. The movement of substances into root cells by simple diffusion without using energy.
- Active Absorption. The uptake of mineral ions against the concentration gradient by using energy stored in the ATP molecules.
- Root Pressure. The pressure which develops in the cortical cells of root pushes the water and minerals into the xylem vessels.
Distinguish between the following pairs:
- Plasmolysis and deplasmolysis.
- Osmotic pressure and turgor pressure.
- Endosmosis and exosmosis
- Diffusion and osmosis.
- Active absorption and passive absorption.
- Flaccid and turgid conditions.
- Osmosis and plasmolysis.
- Hypertonic and hypotonic solution.
- Xylem and phloem.
|1.||It takes place when a cell is kept in a hypertonic solution.
Shrinkage of protoplast.
Cells becomes flaccid.
|It takes place when a cell is placed in a hypotonic solution.
Swelling of protoplast
Cells become turgid.
|2.||Osmotic Pressure||Turgor Pressure|
|It develops due to osmotic entry of water in a cell.
It helps in the absorption of water.
|It is the pressure exerted by the cell contents on the cell wall.
It helps the plant in keeping erect.
|It occurs when a cell is placed in a hypotonic solution.
Water moves into the cell.
|It occurs when a cell is placed in a hypertonic solution.
Water moves out of the cell.
|Movement of the molecules of solute or solvent.
Occurs with or without a semi-permeable membrane.
|Movement of water or solvent.
Semi-permeable membrane is needed.
|5.||Active absorption||Passive Absorption|
|It takes place from lower concentration to higher concentration.
Cell energy from ATP required.
|It takes place from higher concentration to lower concentration.
Cell energy not required.
|It is a condition when a cell is placed in a hypertonic solution.
Water is lost form the plant due to exosmosis.
|It happens when a cell is placed in hypotonic solution.
Water enters into a cell due to endosmosis.
|It is the movement of water from its higher concentration to its lower concentration through a semi-permeable membrane.||It is the shrinkage of urotoplasm when a cell is placed in a hypertonic solution.|
|8.||Hypertonic solution||Hypotonic Solution|
|A solution whose concentration is more than the cells sap.
Its osmotic pressure is more.
|A solution whose concentration is less than the cell sap.
Its osmotic pressure is less.
|Helps in the conduction of water and minerals.
It is a dead tissue.
|Helps in the transport of prepared food.
It is a living tissue.