Question

Distinguishing feature of closed vascular bundle is
A. Presence of cambium
B. Absence of cambium
C. Ring of vascular bundles
D. No vascular bundles

Answer 1

Hint: Generally the vascular system in plants are of two types; open vascular system and closed vascular system. In an open vascular bundle, an interfascicular cambium is present in between phloem and xylem. Phloem and xylem are not in direct contact with each other. In closed vascular bundles, interfascicular cambium is absent. There is direct contact between phloem and xylem.

Complete step by step answer: The vascular system of plants is described briefly below:
The vascular bundles are composed of xylem and phloem together.
Cambium is present between phloem and xylem in dicotyledonous stems. Due to the presence of cambium they have a feature to form secondary xylem and phloem tissues, and hence are called open vascular bundles.
The vascular bundles lack cambium in the monocotyledons and hence they do not form secondary tissues they are referred to as closed. In roots, there is a radial arrangement where xylem and phloem within a vascular bundle are arranged in an alternate manner along the different radii.
When the xylem and phloem are jointly situated along the same radius of vascular bundles, this arrangement is known as conjoint type of vascular bundles. This type of vascular bundles are common in stems and leaves. In conjoint vascular bundles, the phloem is generally located only on the outer side of xylem.
In closed vascular bundles the cambium is absent and hence it is not capable of forming secondary xylem and phloem tissues. Closed vascular bundles are generally predominant in the monocotyledons.
Distinguishing feature of closed vascular bundle is the absence of cambium. So, the correct answer is option (B).

Note: Monocotyledonous and dicotyledonous plants show marked variation in their internal structures. The increase in the girth (diameter) of the organs is common in most of the dicotyledonous roots and stems and it is by the activity of secondary growth of the vascular cambium and the cork cambium. The wood is actually a secondary xylem.