Question

Vascular bundles in monocotyledons are considered closed because
A. There are no vessels with perforations
B. Xylem is surrounded all around phloem
C. A bundle sheath surrounds each bundle
D. Cambium is absent

Answer 1

Hint:In monocot plants, the vascular bundles are composed of two types of tissues, that is, the xylem and phloem, which helps in the transport of water, minerals as well as organic food substances. The vascular bundles are of two types, namely closed type, and open type.

Complete Answer:
While studying the anatomy of a monocot stem, it can be found that the vascular bundles are not arranged in the form of a circle, but in a scattered pattern throughout the ground tissue. A well-defined pith is absent in monocot stems. The nature of the vascular bundles is determined by the presence or absence of a highly dividing meristematic tissue known as the cambium. Due to the absence of cambium, the vascular bundles in monocots are said to be closed. This absence of cambium in monocots results in no secondary growth and no new cells are formed within the vascular bundles.
Considering the other given options:
In monocot plants, the vessels which are a component of xylem tissue are perforated in nature, therefore the given option is incorrect.
The xylem and phloem are present as scattered throughout the ground tissue, and hence xylem cannot be found surrounding the phloem. Thus this option is also incorrect.
The bundle sheath cells do surround the vascular bundles, but this is for the protective action on the veins on the leaves, and this is not the reason for closed vascular bundles.

Therefore, by considering the given options, the most appropriate reason for the statement is D, closed vascular bundles in monocots is due to the absence of cambium.

Note: Open vascular bundles are a characteristic feature of Dicot plants. The meristematic tissue known as cambium is present in between the xylem and phloem, facilitating secondary growth. The type of cambium present in it is known as Fascicular cambium.