Describe the four elements of phloem

CBSE Class 11
1

Describe the four elements of phloem.

2

The phloem is responsible for the transportation of food material from leaves to the other parts of the plant.

The four elements of the phloem are as follows:

1. Sieve tube elements:

  • They are long tube-like structures arranged longitudinally.
  • They are found in association with companion cells.
  • The end walls are perforated in a sieve manner to from sieve plates.
  • Each cell lacks a nucleus. It has a large vacuole and a peripheral cytoplasm.

2. Companion Cells:

  • Companion cells are specialised parenchymatous cells.
  • They help in maintaining the pressure gradient in the sieve tubes.
  • Nuclei of the companion cells control the function the sieve tubes.

3. Phloem Parenchyma:

  • he cells are cylindrical, elongated with tapering ends and dense cytoplasm and nucleus. The cells are connected to each other by plasmodesmatal connections.
  • The cell wall is composed of cellulose.
  • It also stores food and substances such as mucilage, latex and resin.
  • It is absent in monocotyledons.

4. Phloem Fibres:

  • They are also called bast fibres.
  • They are made of sclerenchymatous cells.
  • Phloem fibres are absent in the primary phloem but present in the secondary phloem.
  • Fibres are elongated, unbranded and bear pointed apices.
  • The cells walls are thick.
  • They lose their protoplasm at maturity and become dead.
  • The fibres of jute, hemp and flax are of commercial use.