Chapter 10, Problem 9A

Summary Introduction

To hypothesize:

The reason plant cells might not need centrioles for mitosis or meiosis

Introduction:

During prophase stage, spindle apparatus which consists of spindle fibers, centrioles and aster fibers appear in the animal cells. The spindle apparatus helps in moving and organizing the chromosomes before cell division. In plant cells however, centrioles are absent and only spindle fibers are present.

Answer to Problem 9A

Centrioles are absent in plant cells but they do have spindle fibers and centrosomes which help in organizing the chromosomes during mitosis and meiosis. These function similar to centrioles in animal cells.

Explanation of Solution

Spindle apparatus is very important in animal cells during cell division. It helps in aligning the chromosomes along the equator so that the new cells receive one complete copy of the DNA. The centrioles are a pair of microtubule structures produced in animals and in some protest cells. They migrate to the poles of the cells and produce another set of microtubules called aster fibers which have a star like appearance. The whole structure including the spindle fibers, centrioles and aster fibers is called spindle apparatus.

Centrioles are not part of spindle apparatus in plant cells. They have centrosomes that produce spindle fibers. These spindle fibers help in aligning the chromosomes along the equator by attaching to the sister chromatids on both sides of the centromere and then attaching to the opposite poles of the cell.

Hence centrioles are not necessary in plant cells.