-Aqsa, Subject Matter Expert at Edumarz.
Solution: Phloem is a type of complex tissue. It is responsible for the translocation of organic food synthesized by plants. The constituents of the phloem are sieve elements, companion cells, phloem fibers, and phloem parenchyma cells.
Sieve elements – They include sieve-tube members and sieve cells. Sieve tube members are long, slender, tube-like cells. They are joined end to end to form long tubular channels – the sieve tubes. Sieve tube members possess specialized sieve areas on the end walls called sieve plates. Sieve cells are somewhat elongated and narrow with tapering ends. In these cells, sieve areas occur all over the wall and hence cannot be distinguished.
Companion cells – All angiosperms have specialized parenchyma cells, called companion cells. They remain associated with the sieve tube elements. A single companion cell usually extends through the whole length of the sieve tube.
Phloem fibers – These are also known as bast fibers and occur in both the primary and secondary phloem. In the primary phloem, fibers are generally present in the outer part while in the secondary phloem, fibers are distributed in many different ways.
Parenchyma cells– Parenchymatous cells usually remain associated with fibers and sclereids and have lignified walls with secondary thickening are very common in the region of phloem. In monocotyledons, phloem parenchyma remains absent.