Question

Some vascular bundles are described as open because these
A. Possess conjunctive tissue between xylem and phloem.
B. Are not surrounded by pericycles.
C. Are surrounded by pericycle but no endodermis.
D. Are capable of producing secondary xylem and phloem.

Answer 1

Vascular bundles refer to the conducting tissues of the plant. These are xylem and phloem. They collectively form vascular bundles. The vascular bundles that have cambium are termed open. The cambium is a tissue that undergoes secondary growth. It forms the secondary thickening of woody plants.

Complete answer: The cambium is a cylindrical tissue that forms layers in stems and roots. It is a kind of meristem and is found in woody plants. It forms the parts between the bark and the wood of the stem. The vascular tissues of the plant that are xylem and phloem form the vascular bundles by interconnecting. The vascular bundles that have cambium attached to them are termed open vascular bundles. The cambium results in secondary growth of roots and stems that result in thickness in plants.
The open vascular bundles consist of interfascicular cambium in between phloem and xylem. The cambial cells produce secondary xylem cells toward the central axis of the stem by dividing actively. On the other hand, secondary phloem cells are produced toward the outside dimension. Thus, the open vascular bundles that consist of cambium are capable of producing secondary xylem and phloem.
a) The conjunctive tissue is a type of connective tissue that forms a layer between the phloem and xylem. This is ground tissue.
b) Pericycle cells are supporting cells of vascular plants. They help in protecting and supporting the plant. They surround the xylem and phloem and hold the plants upright. It is majorly present between endodermis that is the outer layer of plants and the phloem.
Hence, the correct answer is option D.

Note: The secondary xylem and secondary phloem have almost similar functions to primary xylem and primary phloem but they differ in their structure widely. The secondary xylem is seen only in dicots. It has short and wide vessels. The secondary xylem forms the pit fields in plants. The secondary phloem on the other hand forms the inner bark of the tree.