Question

Read the different components from (a) to (d) in the list given below and tell the correct order of the components with reference to their arrangement from the outer side in a woody dicot stem.
a.Secondary cortex
b.Wood
c.Secondary phloem
d.Phellem
A.(d), (c), (a), (b)
B.(c), (d), (b), (a)
C.(a), (b), (d), (c)
D.(d), (a), (c), (b)

Answer 1

The stem gives support to the plant and allows facilitation of water and nutrients between different parts of the plant that allows the plant to grow. The vascular bundles of the dicot stem are arranged in a ring.

Complete step by step answer:
Dicot stems just like dicot roots have an external epidermis layer for protection. A layer of ground tissue called the phellem or cork is located beneath the epidermis. Beneath the phellem, lies vascular bundles of cambium which forms a ring unlike monocot stems. Cambium consists of the cells that divide to expand the girth of the stem.
Within the vascular bundles, the phloem is located exterior to the cambium ring along with the sclerenchyma ground tissue. Xylem is located in the interior part of the cambium ring and together these vascular tissues allow transport of water and nutrients in different parts of the plant. Pith is the ground tissue that is located to the interior of the cambium ring.
The stem provides primary and secondary growth to the plant. The non-woody stems, of green and soft plants undergo primary growth and have an annual life cycle. Growth of wider stem and roots is due to the secondary growth which originates from lateral meristem. The woody stems undergo secondary growth. This gives rise to the growth of the secondary vascular bundle tissues like secondary xylem and secondary phloem and secondary cortex.
The secondary cortex is in the interior of cambium and collenchyma and parenchyma in the interior of the secondary cortex. Secondary phloem is in the exterior of vascular cambium and has autumn wood and spring wood to the interior of cambium. Primary xylem is to the interior of wood followed by pith.

Hence, the correct order from the outer to the inner side of the dicot stem is phellem > secondary cortex > secondary phloem > wood and the correct option is (d).

Note:
The dicot woody stem is a result of the secondary growth that originates from the lateral meristem. However, the monocot stem does not undergo secondary growth and has a random thickening of the girth.