Why Do Cells Need to Divide

Organisms, either unicellular or multicellular, are made up of cells. One of the characteristic features of cells is the division. Cells divide for many reasons, including growth, repair and regeneration, and reproduction. The two types of mechanisms of cell division are mitosis and meiosis. During the growth of an organism, new cells are produced by mitosis. The damaged cells in tissues are replaced by mitosis as well. Multicellular organisms produce gametes by meiosis. Unicellular organisms asexually reproduce by mitosis. 

Key Areas Covered

1. What is Cell Division
     – Definition, Types
2. Why Do Cells Need to Divide
     – Importance of Cell Division

Key Terms: Cell Division, Growth, Meiosis, Mitosis, Regeneration, Repair, Reproduction

What is Cell Division

Cell division is the splitting of a parent cell into daughter cells. Depending on the effect on the number of chromosomes in the parent cell during cell division, two types of cell division can be identified. They are mitosis and meiosis. Cell division is shown in figure 1.

Figure 1: Cell Division

Mitosis

Mitosis is a type of cell division, which results in two daughter cells that are identical to the parent cell. This means the number of chromosomes in the nucleus of a particular organism remains unchanged during mitosis. Mitosis occurs in the somatic cells of multicellular organisms. It also occurs in unicellular organisms.

Meiosis

Meiosis is the other type of cell division, which results in four daughter cells. Each daughter cell has half the number of chromosomes of the species. Therefore, meiosis occurs in the germline cells during the production of gametes.

Both mitosis and meiosis occur in four steps known as prophase, metaphase, anaphase, and telophase.

Why Do Cells Need to Divide

According to the cell theory, new cells arise from existing cells. Cell division is the process, responsible for the production of new cells from existing cells. Cells need to divide due to three reasons. They are growth, repair, and reproduction of organisms.

Growth

To grow in size, organisms require new cells. The number of somatic cells in the body can be increased by mitotic divisions. In the early stages of the life of multicellular organisms, cell division by mitosis occurs in accelerated rates to increase the size of the organism. Mitosis does not change the number of chromosomes in the nucleus over generations. Mitosis in tissues is shown in figure 2.

Figure 2: Mitosis in Tissues

Repair and Regeneration

Mitosis is involved in the production of new cells when the tissues of multicellular organisms are injured. It is also responsible for the regeneration of tissues by replacing the dead cells from new cells.

Reproduction

Both mitosis and meiosis are involved in the reproduction of organisms. In multicellular organisms, gametes are produced by meiosis of germ line cells. Gametes are generally haploid, containing half of the chromosome number of the organism. Fusion of gametes produces a new individual. This type of reproduction is called sexual reproduction. Production of gametes is shown in figure 3.

Figure 3: Gamete Formation

In unicellular organisms, reproduction mainly occurs through cell division by mitosis. Bacteria and other unicellular organism reproduce by binary fission in which the main mechanism of cell division is mitosis. This type of reproduction methods is called asexual reproduction.

Conclusion

Cells divide to produce new cells. Cell division is important for three steps of the life cycle of a particular organism. They are the growth, repair, and reproduction. During the growth of a multicellular organism, the number of cells in the body is increased by mitosis. Dead or injured cells are also replaced by mitosis. Finally, multicellular organisms reproduce by the production of gametes by meiosis while unicellular organisms reproduce through mitosis.

Reference:

“Cell Division.” Kazilek, Arizona State Universoty, 3 Feb. 2014, askabiologist.asu.edu/cell-division.

Image Courtesy:

1.”Cell division” by Zappys Technology Solutions by cat.nash (CC BY 2.0) via Flickr 
2.” Mitosis (261 13) Pressed; root meristem of onion (cells in prophase, metaphase, anaphase, telophase)” by Doc. RNDr. Josef Reischig, CSc. – Author’s archive (CC BY-SA 3.0) via Commons Wikimedia 
3. “Production of Gametes” by cat.nash (CC BY 2.0) via Flickr