Question

Secondary xylem and phloem in dicot stem are produced by

• A. vascular cambium
• B. phellogen
• C. axillary meristems
• D. apical meristems

Answer 1

The correct option is A

vascular cambium

The correct option is A.

Explanations of the correct option:

1. Vascular cambium is known as the secondary meristematic tissue which differentiates to produce cork.
2. The cork is a hardened woody tissue.
3. It is located between the primary xylem and primary phloem in the vascular bundle.
4. It helps in the production of exterior bark cells.
5. Hence, it helps in the production of secondary phloem and secondary xylem.
6. Secondary xylem is formed inside of the ring of cambium (cambial ring) whereas the secondary phloem is formed outside of the cambium.

Explanations of the incorrect options:

Option B:

1. The phellogen produces secondary tissue more on the outer side than the inner side.
2. It is the secondary meristem that helps to replace the epidermis when the secondary growth displaces and ultimately destroys, the epidermis of the primary plant body.
3. It helps in the differentiation of phelloderm (inside layer of the cork cambium) and phellem (protective outer tissue of bark).
4. It does not produces secondary phloem and secondary xylem.

Option C:

1. Axillary meristems are present in the axils of the leaf and help in differentiation.
2. They lead to branching of the plant.
3. Hence, this is an incorrect option.

Option D:

1. Apical meristems are located in the shoot tips and as well as root tips.
2. They differentiate to increase the roots and shoot tips and increase the vertical height of the plant.
3. Thus, this is an incorrect option.

Final answer: Secondary xylem and phloem in the dicot stem are produced by the vascular cambium.