Binary Fission and Mitosis
For unicellular or one-celled organisms cell division is their form of reproduction. In multicellular organisms, mitosis is the way they grow, develop, and repair damaged tissue, but it is not how they reproduce.
Unicellular organisms, cell division is the way they reproduce to make more of their own kind. There are two basic types of unicellular or one-celled life forms on Earth. They are prokaryotes, such as bacteria, and eukaryotes, such as the amoeba. Most of these unicellular organisms do not practice sexual reproduction. Sexual reproduction involves the exchange of special sex cells known as gametes. By now, you may know these gametes or sex cells by the names egg or ova (female) and sperm (male). The resulting offspring has its own identifiable genetic makeup that is a mixture of the two parents.
Unicellular organisms simply divide to produce offspring (daughter cells) genetically identical to the parent or mother cell. Since no sex or exchange of genetic material takes place, this type of reproduction is called asexual reproduction (the prefix 'a-' means 'without or no').
Binary Fission and Mitosis Serve a Similar Function
Binary fission and mitosis are both types of cell division. The results of the two processes are basically the same. A parent cell or mother cell divides to produce two daughter cells that are genetically identical and basically the same size.
Most prokaryotic organisms, such as bacteria, use binary fission as their form of reproduction. "Binary" refers to the number two and "fission" means to split. Binary fission is the reproduction of prokaryotic organisms by cell division that produces two basically similar cells.
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Prokaryotes are very simple, primitive, and tiny. They are so basic that they do not have a nucleus or membrane bound organelles. They also lack spindle fibers. Remember that prokaryotes do have DNA, but they are so simple that they do not need or contain as much of it as eukaryotes do. Many microbiologists describe the DNA of prokaryotes as existing in the form of one circular chromosome, called a plasmid.
Sequential Outline of Binary Fission
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The prokaryotic DNA or chromosome is copied.
This is similar to what happens in the S (synthesis) stage of the eukaryotic cell cycle.
Both of the chromosomes attach to the cell membrane.
Chromosomes are pulled apart and move away from each other as the cell grows.
When the cell grows to approximately twice its original size, cytokinesis takes place.
The cell membrane pinches in to divide the materials into two new cells.
This is similar to the pinching or cleavage furrow in cytokinesis of the mitotic stage of the eukaryotic life cycle.
Bacteria have a cell wall that also forms with the membrane to separate the two daughter cells
It is important to note that a bacterial cell wall is not made of the same cellulose material as that found in plant cells and is not as strong and rigid.
Asexual reproduction can be very advantageous if the organism lives in an environment that is stable and does not change very much. Asexual reproduction produces cells that are genetically identical generation after generation. If their genetics is well-adapted for that environment, and the environment is static, there is no need for genetic variation or change. Sexual reproduction might produce changes in the species that are not beneficial for their survival. In this case, asexual reproduction would be more advantageous than sexual reproduction.
if the environmental conditions change asexual reproduction would be detrimental to the organism's survival. Since asexual reproduction maintains a very consistent genetic makeup, change would be difficult, and the organism might not be able to adapt quickly to the changing environmental conditions. This would be catastrophic to its survival. Sexual reproduction promotes genetic change and would enable the organism to adapt and survive. In this case, sexual reproduction would be more advantageous than asexual reproduction.
The potential to increase numbers is much greater in asexually reproducing organisms for a couple of reasons. First of all, all the individuals of asexually reproducing organisms reproduce individually. They all can divide, and all of their offspring can divide. This creates the potential for expediential growth in numbers.
In sexually reproducing populations, only half, the females, reproduce (this does not mean that the males are not involved, but it is the females that generally deal with the fertilized egg). Additionally, sexual mating habits are very complex. There is competition for mates; there can be issues with the viability of sex organs and sex cells. Fertilization and embryonic development are very complex and lengthy compared to asexual reproduction. But even with all of this, biologists do not consider asexual reproduction more efficient than sexual reproduction. It is simply noted that there are more "costs" to sexual reproduction than asexual reproduction. Sexual reproduction is more involved and therefore has higher related costs. Asexual reproduction would be considered less expensive.