Question

The fibers associated with phloem are known as
a. Wood fibers
b. Surface fibers
c. Bast fibers
d. Hard fibers

Answer 1

In plants, the vascular tissues are present in the form of bundles consisting of the xylem and the phloem. The xylem is associated with transport of water and other materials from the roots to the other parts of the plant and the phloem transports sugars and other fluids from the leaves to different parts of the plant. The secondary growth of the xylem and phloem gives rise to a number of cells that represents secondary growth.

Complete answer:
The phloem tissue consists of conducting cells as well as parenchymal cells. The sieve elements are the conducting cells while the parenchyma cells consist of both specialized companion cells and unspecialized cells such as fibres and sclereids.

The phloem fibres are narrow and elongated cells and they are dead at maturity. It is present both in the phloem and the secondary phloem. The phloem fibres form secondary wall thickenings in between the primary cells wall and the plasma membrane and tend to lose their protoplast. The secondary wall is made up of lignin. In the secondary phloem, the phloem fibres give rise to form the bast fibres.

Bast fibres are the long, narrow supportive cells that provide tensile strength but they do not limit the flexibility. They are also found as bast surrounding the stem of certain dicotyledonous cells. It supports the conductive cells of the phloem and function to provide strength to the stem. Bast fibres are economically important fibres and are used in high quality textiles, ropes, yarn, paper, composite materials and burlap.

Hence, the correct answer is option (C).

Additional information:

Wood fibers are extracted from the trees and are cellulose materials and are used to make paper. They are extracted from hardwood trees and the softwood or coniferous trees.
Surface fibres are the fibres that grow from the seeds, leaves or fruits of plants. The important surface fibres are cotton that is obtained from the seeds fibres and coconut coir.
Hard fibres are derived from the leaves and fruits of monocotyledonous plants. These are obtained from the supporting tissues of large leaves from tropical and subtropical plants.

Note: The vascular bundles in the plants are made up of the xylem and the phloem fibres. The phloem fibres are associated with the transport of soluble organic compounds which are produced during the process of photosynthesis. The phloem fibres are known as bast fibres and are commercially very important fibres. They are lignified fibres associated with providing strength to the plant.