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Diffusion
1. Diffusion refers to the process by which molecules of matters move from high concentration towards the low concentration.
2. For example, when a sugar cube is dropped in a glass of water the particles of sugar mixes up in the water as they move from higher concentration of sugar cube towards the lower concentration of water.
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Uniport, symport and antiport
1. Uniport transports one solute at a time across the membrane.
2. Symport transports the solute and a co-transported solute at the same time in the same direction in or out of the cell.
3. Antiport transports the solute in or out and the co-transported solute at the same time in the opposite direction across the membrane. One comes in and the other goes out of the cell or vice-versa.
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Osmosis
Osmosis is the diffusion of water molecules from a region of higher water potential to that of lower water potential through a semi-permeable membrane.
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Diffusion and osmosis
The difference between diffusion and osmosis are as follows:
| Diffusion | Osmosis |
| Diffusion is the transport of gases or dissolved substances in solution from a region of high concentration to a region of low concentration when the two are in direct contact. | Osmosis is the transport of water through a semi-permeable membrane from a solution of low concentration to a solution of high concentration. |
| Diffusion does not require a semipermeable membrane. | Osmosis requires a semipermeable membrane. |
| Liquids and gases can diffuse over considerable distance. | Water is transported only over a short distance. |
| Diffusion mainly depends on the presence of other particles. | Osmosis mainly depends on the number of solute particles dissolved in the solvent. |
| Rapid in gases, but slow in solutions. | Slow process. |
| Transport from high or low concentration along a gradient. | Transport water from a solution of low concentration to that of high concentration. |
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Water potential
1. It is the difference in the free energy or chemical potential per unit molar volume of water in a system and that of pure water at the same temperature and pressure.
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Osmotic or solute potential
1. Osmotic or solute potential is the decrease in the chemical potential of pure water due to the presence of solute particles in it.
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Pressure potential
1. Pressure potential is the pressure which develops in an osmotic system due to osmotic entry or exit of water from it.
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Transpiration
1. Transpiration is the evaporative loss of water from the aerial parts (leaves and stem) of the plant.
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Absorption of water through cells
1. Water is absorbed by the roots and it is transported through the xylem.
2. The cells of the roots absorb the water by the process of osmosis.
3. Osmosis is the absorption of water from the higher concentration of solute to the lower concentration through the semipermeable membrane.
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Transportation of food and other substances
1. Excess of food is taken into the storage organs like roots, fruits and seeds.
2. This process is known as translocation and it takes place through phloem in upward as well as downward directions.
3. In flowering season, sugar stored in the roots or stem is translocated to the buds for growing them into flowers.
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Root pressure
1. Root pressure is the pressure developed in the roots due to the inflow of water, brought about due to the alternate turgidity and flaccidity of the cells of the cortex and the root hair cells, which helps in pushing the plant sap upwards.
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Imbibition
1. Imbibition is a phenomenon by which the living or dead plant cells absorb water by surface attraction.
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Plasmolysis and Deplasmolysis
1. Plasmolysis is the withdrawal of water from a plant cell by osmosis if placed in a strong (hypertonic) solution resulting in contraction of cytoplasm away from cell walls.
2. Deplasmolysis is the reversal of plasmolysis when a plasmolysed cell is placed in water (before the cell is dead).
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