Question

Secondary growth is absent in
A. Dicot stem
B. Gymnosperms
C. Monocot stem
D. Dicot root

Answer 1

In dicotyledonous plants and gymnosperms, vascular cambium and cork cambium called lateral meristems, appear later in life. The lateral meristems cause an increase in girth of the organ in which they are active. The increase in girth of plant organs is called secondary growth.

Complete answer:
The increase of stem and thickness of root due to lateral meristems which are not present in herbaceous plants and the growth of the plant body occurring outward is called secondary growth. It is more important for woody plants because they need support in their roots and stems as they are taller than the other plants.
Dicot stem – They have a well defined cuticle with epidermis. It is solid and mainly consists of epidermis, hypodermis, pericycle, pith, etc. The vascular cambium divides into xylem and phloem. Due to the formation of secondary xylem and phloem the thickness of the stem increases. The bark of the plant forms by the help of cork cambium and it contains the suberin (the water-repellent substance) which helps to stand the bark in all environmental conditions.
Gymnosperms – These are seed bearing, non-flowering plants. Secondary growth is present in gymnosperms.
Monocot stem – These are circular-shaped stems with lateral branches. It contains epidermis, hypodermis, ground tissue, etc. They are hollow at the centre and no secondary growth occurs due to absence of vascular cambium.
Dicot roots – Secondary growth takes place in the root system after the cells stop elongated in the maturation zone.

So, the correct answer is option (C) monocot stem.

Note –
Cork is a simple type of tissue because it contains only one type of cell. The cells of cork are rectangular in shape and their protoplast contains tannins and chloroplasts. Cork gives new cells on both the sides forming a phellem on the outer side and the phelloderm on the inner side. It is light in weight and does not catch fire easily.