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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