6.1 - Cell Division

Cell division is a natural process that occurs in all living organisms. In unicellular organisms, cell division is a way of reproduction; in multicellular organisms, cell division is the means of tissue growth and maintenance. New cells need to be produced constantly to replace the dead or old cells. There are two stages of cell division which are karyokinesis and cytokinesis.

• Karyokinesis is the process of nuclear division.
• Cytokinesis is the process of cytoplasm division.

Figure 1 - Cytokinesis occurs in mitosis and meiosis in both animal and plant cells. It is the final steps that results in two new daughter cells. The formation of cleavage furrow is enough to differentiate animal cells from plant cells.

Somatic cells and reproductive cells/gametes are the two types of cells present in living organisms.

• Somatic Cell
  • Definition: All cells in the body except those from the germ line
  • Production: Produced through mitosis
  • Number of chromosomes: Contains diploid number of chromosomes (2n)
  • Examples: Muscle cell, nerve cell, red blood cells etc.
• Gamete
  • Definition: Cells in the sexual organs
  • Production: Produced through meiosis
  • Number of chromosomes: Contains haploid number of chromosomes (n)
  • Examples: Sperms and ova

Diploid cells are cells that have two complete sets of chromosomes, one set from the father ( paternal chromosomes ) and other set from the mother ( maternal chromosomes ). On the other hand, haploid cells have only half the number of chromosomes as diploid – they only have one complete set of chromosomes.

Figure 2 - Haploid (left) refers to only one copy of each of the chromosome. Diploid (right) has two copies of the chromosomes.