Question

Vascular cambium produces
A. Primary xylem and primary phloem
B. Secondary xylem and secondary phloem
C. Primary xylem and secondary phloem
D. Secondary xylem and primary phloem

Answer 1

Hint: The meristematic layer which is responsible for cutting off the vascular tissue such as xylem and phloem is known as vascular cambium. It is the tissue for the main growth in the stem and roots of many plants mostly in dicot.

Complete answer:
A ring of cambium formed by the joining of intrafascicular and interfascicular cambium and it is known as vascular cambium. In the dicot stem, the cells of the cambium which is present between the primary xylem and the primary phloem are the intrafascicular cambium. The cells of the medullary rays which join the intrafascicular cambium become meristematic and form the interfascicular cambium and as a result, the continuous ring of cambium is formed. The cambial ring becomes active and starts to cut off the new cells in both the inner and outer side. The cutoff towards the pith develops into the secondary xylem while the cut off towards the periphery develops into secondary phloem.
The primary and secondary phloems generally get squeezed due to the continued formation and deposition of secondary xylem. The primary xylem remains more or less intact around the centre. The vascular cambium is mainly responsible for increasing the diameter of stems and roots and for forming the woody tissue.
Hence, the correct answer is ‘B. Secondary xylem and secondary phloem’.

Note: The cambium is more active on the inner side than on the outer and as a result of this, the amount of secondary xylem produced is more than the secondary phloem. The activity of cambium is under the control of many physiological and environmental factors.