Question

Why are vascular bundles closed in monocots?
A) Xylem and phloem are present
B) Xylem and phloem are in separate bundles
C) Vascular cambium is present between xylem and phloem
D) Vascular cambium is not present

Answer 1

Hint: The vascular bundle is part of the transport system for vascular plants. The transport itself takes place in the stem, which exists in two forms: xylem and phloem. Both of these tissues are present in the vascular bundle, which also includes supporting and protective tissues.

Complete answer:
The vascular system consists of complex tissues, phloem and xylene. The xylem and the phloem together are vascular bundles of dicotyledonous stems, cambium is present between phloem and xylem. Owing to the presence of cambium, such vascular bundles have the ability to form secondary xylem and phloem tissues, and are thus referred to as free vascular bundles.
In monocotyledons, there is no cambium present in the vascular bundles. Therefore, they do not form secondary tissues and are therefore referred to as closed tissues.

Vascular bundles are scattered in the tissues of the ground. They are of different sizes, with the smaller being limited to the periphery. They appear to be embedded in the tissue of the ground. Each vascular bundle is encircled by a bundle sheath made of sclerenchyma. There's no bundle cap in there.

Each vascular bundle is joint, collateral or lepto centric and closed, i.e. there is no cambium. Protoxylem and metaxylem are arranged in the form of capital 'Y.' Phloem is situated between and above the metalaxyl. Usually, a protoxylem lacuna is formed. In them, secondary vascular tissues are not formed as there is no cambium.

The correct answer is option (D) i.e, Vascular cambium is not present.

Note: Vascular bundles typically represent the organisation of two vascular tissues, phloem and xylem. Phloem is a route for dissolved carbohydrates that are transported from tissues that are net producers of photoassimilates to tissues that are net users.

In addition, phloem provides a pathway for translocation of peptides, proteins and mRNAs involved in plant growth and development and in the defence against pathogens. The xylem is the primary transport mechanism for water and mineral nutrients from the root to the evapo-transpiration sites in the shoot system.