Binary Fission – Class 12 | Chapter – 1 | Short Notes Series PDF

Binary Fission: In biology, binary fission is a type of asexual reproduction where a parent cell divides, resulting in two identical cells, each having the potential to grow to the size of the original cell. The word asexual describes a reproduction that occurs without involving sex cells (gametes). Instead, the somatic cells undergo an asexual process that will produce a clone of the parent. The offspring is a clone because its genome will be identical to that of the parent. Binary fission is common among prokaryotes, e.g. archaea, eubacteria, cyanobacteria, and certain protozoans (e.g. amoeba).

Binary Fission

Binary Fission


Binary fission is the process through which asexual reproduction happens in bacteria. During binary fission, a single organism becomes two independent organisms. Binary fission also describes the duplication of organelles in eukaryotes. Mitochondria and other organelles must reproduce via binary fission before mitosis so each cell has ample organelles.

Binary fission is a type of asexual reproduction typically observed in prokaryotes and a few single-celled eukaryotes. In this method of asexual reproduction, there is a separation of the parent cell into two new daughter cells. This process happens with the division and duplication of the parent’s genetic matter into two parts. Here, each daughter cell receives one copy of its parent DNA.

Types of Binary Fission

Binary fission has four forms based on the cytoplasmic division plane.

  • Irregular Binary Fission: Cytoplasm division (cytokinesis) can occur in any plane in this situation. It is most typically perpendicular to the plane of chromosome division (karyokinesis). This type can be found in organisms such as amoebas.

  • Transverse Binary Fission: Cytokinesis occurs along the cell’s transverse axis in transverse binary fission. This division can be seen in Paramecium, a ciliated protozoan. This is where the cytoplasm is separated along the cell’s longitudinal axis.

  • Longitudinal Binary Fission: This is where the cell’s cytoplasm is separated longitudinally. This method of division generally occurs in Flagellates, such as Euglena.

  • Oblique Binary Fission: In this case, the cytoplasm is separated in an oblique manner (i.e. left and right oblique). Ceratium, a dinoflagellate, has this division pattern.

Process of Binary Fission

Binary fission is the way that prokaryotic cells and certain protozoans reproduce. Similar to other modes of asexual reproduction, such as budding and formation of baeocytes (e.g. in cyanobacterium Stanieria), the result is an offspring that has the same genome as the parent. Prokaryotes such as E. coli, Archaea as well as eukaryotes such as euglena reproduce through binary fission.

Binary Fission in Prokaryotes

  • Prokaryotes’ genetic material (chromosomes) is contained as a nucleoid in the cytoplasm.

  • The chromosomes are then replicated starting at the origin of replication. Later, the origin divides, and as the replication continues, the two origins pull the chromosomes with them.

  • After replication, proteins involved in cell division gather at the center of the cell.

  • The FtsZ protein, which forms a ring-like structure in the cell’s core, is vital in this process.

  • This step ensures that the cytoplasm separates without damaging the genetic material.

  • The membrane pinches inwards, generating a septum (new cell wall) down the cell’s center.

  • Finally, the septum splits into two cells, each with its own identity.

  • Crenarchaeota, which lacks a cell wall and the FstZ protein, uses a primitive mechanism called the ESCRT-III system.

Binary Fission in Eukaryotes

  • Some protozoans, such as amoebas, reproduce by binary fission, and some organelles within eukaryotic cells divide similarly to bacteria.

  • The FtsZ protein is involved in binary fission in these cells, as in prokaryotes.

  • The Endosymbiotic theory, which explains how prokaryotes evolved into today’s mitochondria, is based on the binary fission of cell organelles such as mitochondria and chloroplasts.

Binary Fission in Bacteria

Bacteria also reproduce through asexual reproduction and the speed differs between species. The time taken for one bacterial cell to duplicate itself is called doubling time.  Factors such as pH levels, temperature, light, oxygen, osmotic pressure play a factor in bacterial reproduction or bacterial binary fission. The following are the steps involved in the binary fission of bacteria.

The steps involved in the binary fission in bacteria are:

  • Step 1-  Replication of DNA: The bacterium uncoils and replicates its chromosome, essentially doubling its content.
  • Step 2-  Growth of a Cell: After copying the chromosome, the bacterium starts to grow larger in preparation for binary fissions. It is followed by an increase in cytoplasmic content. Another prominent trait of this stage is that the two strands migrate to opposite poles of the cell.
  • Step 3-Segregation of DNA: The cell elongates with a septum forming at the middle. The two chromosomes are also separated in this phase.
  • Step 4- Splitting of Cells: A new cell wall is formed at this phase, and the cell splits at the centre, dividing the parent cell into two new daughter cells. Each of the daughter cells contains a copy of the nuclear materials as necessary organelles.

Examples of Binary Fission

Prokaryotes and eukaryotes also use binary fission as a means of dividing into smaller units. The FtsZ protein is involved in:

  • The chromosomal replication

  • Chromosomal segregation

  • Cell splitting processes

This process leads to the reproduction of most of the bacteria. There are few protozoans in which the process of cell division and cytoplasmic division may differ. Eg. Amoeba, Paramecium, and Euglena. There are below organisms that are reproduced by binary fission:

  • Bacillus subtilis

  • Bacillus cereus

  • Bacillus pumilus

  • Escherichia coli

  • Clostridium perfringens

  • Corynebacterium diphtheriae

  • Amoeba

  • Paramecium

  • Euglena

  • Ceratium

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By Team Learning Mantras