Question

Root cambium is derived from
A. Primary meristem
B. Secondary meristem
C. Intercalary meristem
D. Apical meristem

Answer 1

Hint: In plants, growth is of two types. Primary growth and secondary growth. The increase in length of stem and roots are caused by primary growth. Secondary growth is responsible for the increase in girth.

Complete step by step answer:
THe woody plants grow in two ways. Primary or apical growth and secondary or lateral growth. Note that secondary growth is absent in leaves.
There are two tissues that are responsible for the secondary growth in plants. They are vascular cambium and cork cambium. In roots, cambium is derived from secondary meristem.
In dicot roots, xylem and phloem are arranged in separate bundles. The Cambial strip formed when cells just inside the phloem become meristematic. After this, cells of the pericycle just outside the protoxylem also become meristematic to form a cambial strip. Both of these together form a wavy band of cambium in roots.
After formation of the cambial ring, the cell becomes active. Secondary xylem formation happens towards the inside and secondary phloem towards the outside. Because of this, the epidermis rupture takes place due to stretch caused by the newly formed cells.
Pericycle also becomes meristematic to form cork cambium. Note that another name of cork cambium is phellogen. It cuts off cells inwards called the phelloderm or secondary cortex. It cuts off mew cells outwards called phellem or cork.
Phellem, phellogen and phelloderm are together called periderm.

Hence the correct option is B.

Note:
The determination of the age of plants is done by counting the number of annual rings called Dendrochronology. It is seen in dicot stems, especially those belonging to the temperate regions in the world.
They are called growth rings and consist of both spring wood and autumn wood.