Question

Vascular bundles in dicot stem are
a. Open, collateral, endarch
b. Closed, collateral, endarch
c. Open, collateral, exarch
d. Closed, collateral, exarch

Answer 1

The vascular bundle is an isolated unit of longitudinal filaments of conductive tissue, consisting mainly of xylem and phloem, and often enclosed by thick-walled or other scattered cells. through the xylem. In dicot stem, secondary growth occurs which helps in the increase of the girth of the plant.

Complete answer:
Let's study some important terms before answering the question.
Endarch is the arrangement in which the protoxylem is directed towards the center and the metaxylem is directed towards the periphery. In exarch arrangement, the protoxylem faces the periphery and metaxylem faces towards the center. In open vascular bundles, cambium is present between phloem and xylem and therefore the Phloem and xylem are not in direct contact with each other. Whereas in closed vascular bundles, the phloem and xylem are in direct contact with each other since the cambium is absent.

Now looking at the given options;

Option A is correct: In a dicotyledonous stem, the vascular bundles are Open, Collateral and Endarch.
Option B is incorrect: The vascular bundles present in monocotyledonous stem are closed, collateral, and endarch.
Option C is incorrect: Open, collateral exearch type of vascular bundles are not found in any part of the plant.
Option D is incorrect: Closed, collateral, exarch vascular bundles are also not found in any part of the plant.

Hence, the correct answer is option (A).

Note: The vascular bundle originates from the procambium of the apical meristem. At the promeristem stage, all cells are usually isodiametric. During the targeted longitudinal division, some cells become separated as spots or threads. These cells are smaller and elongated and have a dense cytoplasm. This meristematic tissue is called procambium, which is said to produce vascular binding elements.
The Ground tissue between the bundles is a medullary beam that supports the lateral transport of minerals, water and other substances. The vascular bundle also provides mechanical support. The fascicular cambium in bonds forms secondary tissue during secondary growth.