Question

Phloem fibers are generally absent in:
A. Protoplasm
B. Metaphloem
C. Primary phloem
D. Secondary phloem

Answer 1

Hint: The vascular tissue which is responsible for transporting the sugar from the source to the sink tissue is called phloem. Phloem also transports mRNAs (messenger RNA) and proteins. The transport process which takes place in phloem is known as translocation.

Complete answer:
Phloem fibers are also known as bast fibres. These are plant fibres that are collected from the past or phloem which surrounds the stem in some dicotyledonous plants. These fibres help in supporting conductive cells of phloem and it provides the strength to stem. The fibres that are present in the monocotyledonous plants are known as leaf fibres, which are stiff and hard. The bast fibres are needle-like, pointed, elongated and unbranched in their structure. The phloem fibres of hemp, flax, and jute are used for commercial purposes.

The phloem fibres are composed of sclerenchymatous tissues. These are mainly absent in the primary phloem and present in the secondary phloem. The first formed phloem is the primary phloem which comprises a narrow sieve tube known as protophloem. Metaphloem is formed in the later stage and it consists of bigger sieve tubes. Therefore, it can be concluded that phloem fibres are generally absent in protophloem.

Hence, the correct answer is option (A).

Note: Bast fibres are used in many industries because they have high tensile strength such as burlap, paper, yarn, ropes, and textiles. The flexibility in bast fibres comes due to the presence of fibre nodes. Nodes are absent in seed hairs of cotton.