how transport of food and other substances take place in plants.
Answers
Phloem is the tissue that helps in the transport of food throughout the plant. The different elements of phloem include sieve tubes, companion cells, phloem parenchyma and phloem fibres. Food is transported by a special mechanism caleld as pressure flow hypothesis.
Pressure flow hypothesis is the one which explain the translocation of food molecules by phloem.
The mechanism of translocation involves certain steps.
*As sugar is synthesised in the leaves by the process of photosynthesis, a high concentration of organic substance inside the phloem cells of the leaf creates a diffusion gradient by which more water is sucked into the cells.
*Phloem sap with lot of sugar moves from sugar sources (leaves) to sugar sinks with the help of turgor pressure.Sugar sources are the organs of the plant which synthesise sugars. Sugar sinks are the ones from where the sucrose is removed from the phloem.
*Hydrostatic pressure increases in the phloem sieve tubes, pressure flow beginsand the sap moves through the phloem.
*Osmotic pressure at the sink is reduced. Sucrose from the phloem sap is removed and given to the cells which utilise it by converting it into energy or starch or cellulose.
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