Question

Explain different types of elements present in phloem.

Answer 1

Phloem consists of following four elements:
(i) Sieve tubes: These are slender, tube-like structures composed of elongated thin walls placed end to end. Their end walls, sieve plate, are perforated by large number of pores. Sieve tube elements lack nuclei, but they remain alive via adjacent companion cells.
(ii) Companion cells: They are connected with the sieve tubes via plasmodesmata. They are thin-walled cells consisting of dense and active cytoplasm and large, elongated nucleus.
(iii) Phloem parenchyma: As the name suggest, they consist of living parenchyma cells. They are involved in storage and lateral conduction of food.
(iv) Phloem fibres or bast fibres: These are dead cells of phloem possessing a narrow lumen. They are meant for providing mechanical support to the phloem.