Question

Sclerenchyma fibres are absent in
A. Protoxylem
B. Protophloem
C. Metaxylem
D. None of the above

Answer 1

Sclerenchyma is a hard and woody supporting tissue of the plants. On maturity, the sclerenchyma cells usually become dead and non-stretchable. They develop heavily thickened walls made up of lignin. They are found in the non-growing regions of the plants like barks, mature stems, or leaves.

Complete answer:
- Just like the human circulatory system, plants also have a system to transport the water, nutrients, and other substances. This system is known as the vascular system of plants.
- A vascular system is made up of two types of vascular tissues. These tissues are known as xylem and phloem.
- Xylem functions to store and transport water and water-soluble nutrients. Also, it provides mechanical support to the plant.
- Phloem functions to transport sugars, proteins, and other organic substances.
- Based on origin, xylem can be primary xylem and secondary xylem. Primary xylem originates from procambium and it is further divided into Protoxylem and Metaxylem. Protoxylem is first to develop followed by Metaxylem. Sclerenchyma fibres (Xylem fibres) are present in Metaxylem but absent in Protoxylem.
- Based on origin, phloem can be primary phloem and secondary phloem. The primary phloem originates from procambium and it is divided into Protophloem and Metaphloem. Sclerenchyma fibres (Phloem fibres) are present in Metaphloem and usually absent in Protophloem. However, Protophloem can sometimes contain specialized phloem fibres.

Hence, the correct answer is option (A).

Note: Protoxylem is the first xylem to develop. It contains a large amount of living cells and as sclerenchyma fibers are composed of dead cells they do not occur in Protoxylem. Just like Protoxylem, Protophloem is the first phloem to develop. Generally it also lacks sclerenchyma fibers, but it can sometimes have specialized fibres.