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Means of Transport in Plants
The transport of materials in and out of the cells is carried out by diffusion and active transport in plants.
The movement of molecules in liquid and solids from a region of higher concentration to a region of their lower concentration without the utilization of energy is called diﬀusion. This is a passive process.
Active transport utilizes energy to pump molecules against a concentration gradient. Active transport is carried out by membrane bound proteins. These proteins use energy to carry substances across the cell membrane hence they are often referred to as pumps. These pumps can transport substances from a low concentration to a high concentration (‘uphill’ transport).
Osmosis is the movement of solvent or water molecules from the region of higher concentration to the region of lower concentration through a semi-permeable membrane. This process is carried out till an equilibrium is reached. Osmosis is the passive movement of water or any other solvent molecules.
It occurs when water moves out of the cell and resulting in the shrinkage of cell membrane away from the cell wall.
Imbibition is a type of diffusion in which a solid absorbs water and gets swelled up. eg. absorption of water by seeds and dry grapes. If it were not for imbibition, seedlings would not have been able to emerge out of the soil.
Demonstration of Osmosis
A thistle funnel whose mouth is covered with a semipermeable membrane, is fi lled with sucrose solution. It is kept inverted in a beaker containing
water. The water will diff use across the membrane due to osmosis and raise the level of the solution in the funnel.
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