Question

Vascular bundles in monocotyledons are considered closed because

• A. There are no vessels with perforations
• B. Cambium is absent
• C. A bundle sheath surrounds each bundle
• D. Xylem is surrounded all around by phloem

Answer 1

The correct option is B

Cambium is absent

The correct option is B.

Explanation of the correct option:

1. Monocotyledons, also known as monocots, are flowering plants that resemble grass and often have only one cotyledon, or embryonic leaf, in their seeds.
2. A vascular bundle is a part of the transport system of vascular plants.
3. The actual transport takes place in the stem, which comes in the xylem and phloem forms.
4. In plants, the tissue layer known as the cambium provides cells that are only partially differentiated for plant growth.
5. It is located where the xylem and phloem meet.
6. Monocotyledons lack a cambium in their vascular bundles.
7. The vascular bundles in a monocotyledonous stem are often dispersed throughout the ground tissue rather than grouped in a circle.
8. As in many dicotyledonous species, there is no distinct pith in this species.
9. The xylem of the bundles is already pointed in the direction of the middle of the stem, just like in dicots.
10. Contrary to dicots, monocotyledonous plants' vascular bundles do not have a layer of meristematic tissue (cambium).
11. Thus, the vascular bundles of monocots are said to be closed since no new cells can grow inside of them, whereas the vascular bundles of dicot plants can.

Explanation of the incorrect option:

Option A:

1. There are gaps in cells with perforated cell walls.
2. The cell membrane and cell wall of a biological cell contain holes.
3. The perforation plates, an area or areas in which there is no common wall material or membrane, are modified in some angiosperm plants' xylem and phloem cell end walls.
4. A vascular bundle is a part of the transport system of vascular plants.
5. The stem, which is separated into two types: xylem and phloem, is where the transport takes place.
6. Both of these issues can be found in a vascular bundle, which also contains supporting and protecting tissues.

Option C:

1. The bundle sheath in a leaf is a layer of parenchyma that surrounds the vasculature in a tightly packed arrangement and serves as a conduit between the vasculature and the mesophyll cells.
2. Bundle-sheath cells are photosynthetic cells that are closely packed in a sheath around a leaf vein.
3. It forms a protective covering over leaf veins and is made up of one or more cell layers, usually parenchyma.
4. Between the bundle sheath and the leaf surface, mesophyll cells are haphazardly organized.

Option D:

Concentric leptocentric/amphivasal refers to the vascular bundle when the phloem is entirely encircled by the xylem.

Final answer: Vascular bundles in monocotyledons are considered closed because cambium is absent.