Biology - Cell Division

Introduction

• The process of division of parent cell into two or more daughter cells is known as cell division.

• In early 1880s, Flemming first observed the process of cell division.

• Following are the three types of cell division −

  • Amitosis

  • Mitosis &

  • Meiosis

• Let’s discuss each of them in brief −

Amitosis

• Parent cell gets divided into two parts, and each of them grows as a new complete organism.

• Amitosis can be seen in less developed organisms. E.g. bacteria

• Amitosis is also known as binary fission.

• There is no stage of division, cell directly gets divided into two new organisms.

Mitosis

• The process of division of parent cell into two new identical cells is known as mitosis.

• In both the new cells, the number of chromosomes remain same.

• Mitosis (cell division) occurs only in eukaryotic cells.

• In mitosis, the division of the nucleus is preceded by the S stage (i.e. interphase - during this phase, the DNA is replicated).

• After the interphase, the cytokinesis process begins, which divides the cytoplasm, cell organelles, and cell membrane into two new cells.

• The process of mitosis is divided into the following stages −

  • Prophase

  • Prometaphase

  • Metaphase

  • Anaphase

  • Telophase

• The stages of mitosis are described in the following image −

• Let’s discuss each of them in brief −

Prophase

• During the prophase, cell prepares to get divided.

• The prophase process is also known as chromosome condensation, as chromatin fibers condense into discrete chromosomes.

• Each chromosome has two chromatids and these two chromatids are joined at a place known as centromere.

Prometaphase

• In this phase, the nuclear envelope gets disintegrated into small membrane vesicles.

Metaphase

• In this phase, the two centrosomes start pulling the chromosomes towards opposite ends of the cell and ensure the equitable distribution of chromosomes.

Anaphase

• In this phase two identical daughter chromosomes are formed.

Telophase

• Telo is a Greek word meaning ‘end’.

• In this phase, the nuclear envelop gets broken and a new nuclear envelop forms.

• The new envelope gets formed around each set of separated daughter chromosomes; parallel, the nucleolus reappears.

• Likewise, the mitosis is complete.

Cytokinesis

• Cytokinesis, technically, is not a phase of mitosis, but rather a distinct process, essential for completing the cell division.

• In this phase, cytoplasm begins to divide and completed with the development of two new identical cells.

Meiosis

• Meiosis is a typical type of cell division in which the chromosome number gets reduced by half, creating four haploid cells. Each cell is genetically distinct from the parent cell.

• Meiosis cell division process occurs in all sexually reproducing single-celled and multicellular eukaryotes, including plants, animals, and fungi.

• Meiosis cell division is primarily categorized as Meiosis I and Meiosis II.