Question

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

Answer 1

Hint: The seeds of various plants have cotyledons for storing the nutrition for the embryo. There can be one or two cotyledons in the embryo. The one cotyledon gives the monocot or monocotyledons. They are usually grass-like plants.

Complete answer:
Xylem and phloem make the vascular bundle. They will transport water and food respectively. They have various other sub vessels which help them to carry out these functions. Monocots have the outside edge of the stem filled with vascular bundles. They have no pith. In the cortex region, they are surrounded by large parenchyma cells.

Option A: Xylem is surrounded all around by phloem: Only in amphicribral arrangement, the phloem surrounds the xylem.

Option B: There are no vessels with perforations: Sieve tubes in the xylem and phloem are perforated vessels making the transportation of food easy.

Option C: A bundle sheath surrounds each bundle: The xylem and phloem are surrounded by bundle sheath. It has sclerenchyma cells tightly arranged around the bundle or veins. But this is not the reason for why the monocot vascular bundle is called closed.

Option D: There is no secondary growth: Due to absence of cambium in monocot's vascular system, they lack secondary growth which is growth in girth means thickness.

So the answer is option D: There is no secondary growth.

Note:
The Aleurone layer is present in the monocotyledonous endospermic seed. It surrounds the endosperm. This layer is one cell thick. The main work of this layer is to nourish the embryo in the seed. It is a protein-rich layer of endospermic cells. Some secretions from this layer help in the germination.