Question

With the help of suitable diagrams, explain mitosis in detail.

Answer 1

Mitosis cell division is completed in two steps.

1. Division of nucleus (karyon (nucleus) + kinesis (division) = Karyokinesis)
2. Division of cytoplasm (cyto (cytoplasm) + kinesis (division) = cytokinesis))

I. Karyokinesis is further divided into four steps:

(i) Prophase: It is the first stage of mitosis that is marked by the initiation of the condensation of chromosomal material. Each chromosome is composed of two chromatids, which are attached by the centromere. At the end of prophase, the mitotic spindle begins to form from the centrioles. The nuclear membrane and the nucleolus disappear completely by the end of this stage.

(ii) Metaphase: It is the second stage of mitosis in which the condensation of the chromosomal material and the spindle formation gets complete. The spindle fibres get attached to the kinetochores of the chromosomes and the chromosomes get aligned along the metaphase plate in the middle of the nucleus.

(iii) Anaphase: It is the stage of mitosis where the centromere of the chromosomes split and the chromatids get separated. The contraction of the spindle fibres moves the sister chromatid apart, towards the two opposite poles.

(iv) Telophase: It is the last stage of mitosis. In this stage, chromosomes finally reach their respective poles. The spindle fibres disappear and the nuclear envelope reappears around the chromosome cluster. Also, the nucleolus, Golgi complex, endoplasmic reticulum, and other cell organelles re-appear.

II. Cytokinesis:

The cytoplasm divides by cytokinesis and two new cells are formed which are called as daughter cells. In this process, a notch is formed at the equatorial plane of the cell which deepens gradually and thereby two new cells are formed. However, in case of plant cells, instead of the notch, a cell plate is formed exactly along midline of the cell and thus cytokinesis is completed.

Cytokinesis