Question

What is phloem in vascular tissue? Give its components and functions with the help of a diagram.

Answer 1

Phloem:

1. It is a type of living vascular tissue that transports sucrose from source to sink, i.e. from photosynthetic tissues like leaves to other parts of the plant which function as sink such as roots.
2. In phloem organic compound is transported in both directions, i.e. it is bidirectional.

Components of phloem:

Sieve tube elements:

1. It is a long tube-like structure with perforation in the end wall, which form sieve plates.
2. The nucleus is absent in sieve tube elements.
3. Their function is controlled by the nucleus of companion cells at maturity that's why sieve tube elements are connected to companion cells.
4. Gymnosperms lack sieve tubes and companion cells, instead, they have albuminous cells and sieve cells.

Companion cell:

1. It is a parenchymatous cell.
2. Companion cells and sieve tube elements are connected with each other longitudinally by pit fields.
3. The function of companion cells is to maintain a pressure gradient to facilitate the transport of sugar.

Phloem parenchyma:

1. They are cylindrical cells with tapering ends and have dense cytoplasm and nucleus.
2. The function of phloem parenchyma is storage.
3. It stores food, resins, latex, etc.
4. Phloem parenchyma is generally absent in monocotyledons.

Phloem fibers:

1. They are also known as bast fibers.
2. They are sclerenchymatous cells, they lose protoplasm at maturity.
3. Their main function is to provide mechanical strength and support to the conductive cell of the phloem.