Write an account of the transport of organic substances in the plant.

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Write an account of the transport of organic substances in the plant.

Phloem tissue is made up of four main elements

Sieve tubes are living, tubular cells that disintegrate during development. They are connected end to end, up and down the entire plant. The end cell walls have perforations in them to make sieve plates. The cytoplasm is present but in small amounts and in a layer next to the cell wall. It lacks a nucleus and most organelles so there is more space for solutes to move. The cell walls are made of cellulose so solutes can move laterally a well as vertically.  

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Since the sieve tube element lacks organelles, the companion cell with its nucleus, mitochondria, ribosomes, enzymes etc., controls the movement of solutes and provides ATP for active transport in the sieve tube element. Strands of cytoplasm called plasmodesmata connect the sieve tube element and companion cell. Also, fibres provide support for the sieve tubes.

The final main element is phloem parenchyma, which is a packing tissue, and its main function is to fill the spaces between the other tissues. The cells are roughly spherical in shape, with flattened faces where they press against each other. If the ...

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