TRANSPORT IN PLANTS

Transport over a longer distance proceeds through the vascular system is called translocation. In
rooted plants, transport in xylem is unidirectional from roots to the stems. Organic and mineral nutrients
undergo multidirectional transport.
The molecule of any substance move away from their higher concentration to their lower concentration,
this process is called diffusion. In facilitated diffusion special proteins help to move substances across
membranes without utilization of energy from ATP.
Water potential is a potential energy of water. It is designated by the greek later “Psi” – symbol is Ψ
The osmosis can be difined as – “When two solutions of unequal concentrations are seperated by a
semi permiable membrane the solvent (water) diffuses from dilute solution to concentrated solution.”
This process will continue till the concentration of solutions becomes the equal.
When a living plant cell is placed in a hypertonic solution. (a concentrated solution of sugar or salt.)
water moves out of the cell and membrane shrinks away from its cell wall. This phenomenon is known
as plasmolysis. The process of plasmolysis can be reversed if the cell is placed in the hypotonic solution.
The water enters into the cell causing the cytoplasm to develop the pressure against cell wall. This
pressure is called turgor pressure and the swollen condition of a cell is called cell’s turgidity.
The water is absorbed by root hairs moves through cortical cells and reaches xylem by following two
distinct pathways : (1) Apoplast pathway and (2) Symplast pathway.
The movement of water and minerals absorbed by the root system of plants, towards stem and the
leaves is called ascent of sap. Two main theories are proposed (1) Root pressure theory and (2)
Transpiration pull theory. The loss of water from the plant in the form of vapour is known as transpiration
There are three main kinds of transpiration (1) Cuticular (2) Lenticelar and (3) Stomatal. The food is
transported by phloem from source to sink. The hypothesis for the translocation of sugar from source
to sink is known as mass flow or the pressure flow hypothesis.

Read More  Cell structure

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