Question

In leaves, the vascular bundles are
A. Bicollateral and open
B. Collateral and open
C. Collateral and closed
D. Radial and exarch

Answer 1

The term vascular bundle refers to the xylem and phloem of the plants i.e. xylem and phloem are the components of vascular bundle. Collateral vascular bundles refer to the arrangement in which the xylem and phloem are placed together along the same radius– phloem outside and xylem towards the inner side. The bicollateral vascular bundle refers to the arrangement where phloem is present outside the xylem as well as inside it. Example : cucurbitaceae family.

Complete step by step answer:
Talking of leaves, the xylem and phloem in the vascular bundles are arranged in such a manner that they lie along the same radius. The phloem forms the outer radius while the xylem forms the inner radius. Hence, the vascular bundles in leaves are collateral.
The vascular bundles are considered open and closed on the basis of the presence of cambium. If a layer of cambium is present between the xylem and the phloem, it is considered as an open arrangement of the vascular bundle. In leaves, this layer of cambium is absent between the xylem and phloem. Hene in leaves, the arrangement is of closed type.
Thus we come to the conclusion that in leaves, the vascular bundles are of collateral and closed type. So, the correct answer is option (C).

Note:
The arrangement is the same collateral and closed in both monocot and dicot leaves. The cambium is a representative of secondary growth in plants. Conjoint is the term which explains that the xylem and phloem are placed together in the vascular bundle.