Question

Microtubules are absent in
A. Mitochondria
B. Flagella
C. Spindle fibers
D. Centriole

Answer 1

Microtubules are polymeric structures made up of tubulin which serve many purposes such one being maintaining the structural integrity of cells and organelles. Microtubes are also involved in the formation of cilia and flagella in bacteria and other motile cells.

Complete answer: Microtubules are long polymeric proteins found within the cytoplasm which provides structural support to various organelles and even the entire cell in general. The microtubules along with other microfilaments make up the exoskeleton of the cell. Microtubules are made up of two monomeric proteins alpha and beta-tubulin. Microtubules can be of various lengths. They are also found in cilia/flagella, mitotic spindle, and centrioles.
-The flagella and the cilia are made up of microtubules nucleated from the base of the cell wall In bacteria. Here the microtubules form the precursor for the entire structure. This is also the case for centrioles.
-Centrioles are cylindrical structures that make up the centrosome. It is made from 9 microtubule structures each attached to two partial microtubule structures. Mitotic spindle or spindle fibers are the fibers sent by the centriole during metaphase of mitosis.
-There the fiber polymerizes to reach the center of the chromosome and once the chromosome has split, the fibers depolymerize to pull the chromosome to each side. The polymerization and depolymerization is done by microtubules.
-The mitochondria are double layered plasma-filled membranes which are responsible for the production of energy. No microtubules are involved in mitochondria as it does not serve any structural purpose.
Therefore, the correct option is A.

Note: Microtubules are polymeric substances which are made from alpha and beta-tubulin proteins. They serve mainly as structural components in several cellular processes. Such processes include forming physical structures such as cilia and flagella, cell division by serving centrioles and mitotic spindle formation, and much more.