Question

Quiescent centre is present in
A) Shoot apex
B) Root apex
C) Both A and B
D) Meristematic tissue

Answer 1

Hint:Quiescent centre is also called an organizing centre which consists of slow dividing cells. In most cases, it is composed of 1000 cells.

Complete answer:
A quiescent centre in the root apex is in the shape of a hemisphere and its face is towards the root tip of the plant. Let us analyse the options to find the correct answer.

>Option A: The growing tip of a shoot in a plant is called a shoot apex and it consists of an apical meristem and leaf primordia. It does not have a quiescent centre. Hence, this is an incorrect option.
>Option B: Root apex is the tip of a plant root populated by meristematic cells which on repeated division form root tissues. The division rate of these cells is different at the centre and the periphery. The central cells divide slowly than the surrounding cells forming the quiescent centre of root apical meristem or the root apex. Hence, this is the correct option.
>Option C: Option A is incorrect, therefore, this is an incorrect option.
>Option D: Meristematic tissue in plants have undifferentiated cells which undergo continuous division to form tissues and organs of the plant The content of DNA is very high in them and they divide actively their whole life. They do not have a quiescent centre. Hence, this is an incorrect option.

Additional Information:
-A quiescent centre is used as a reserve meristem by the plants.
-In Arabidopsis, the quiescent centre has only 4 cells.
-It is mostly observed in roots which are actively growing but does not appear in dormant roots or in cases where the root cap is removed.

Thus, the correct answer is option (B) Root apex.

Note:A quiescent centre has fewer cell organelles. The rate of mitotic division is very less contributing to lower synthesis of DNA, RNA and Proteins.Cells of cortex and stele are usually found in this region.