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Binary fission is a type of asexual reproduction in which a parent cell divides to form two identical daughter cells. Each cell further grows until the time they reach maturity. The cells formed during the process of binary fission carries the genetic material or information. The complete process of binary fission in prokaryotes is divided into three stages-DNA replication, Elongation, & Division.
- It is usually observed in prokaryotes like bacteria and eukaryotes such as amoeba.
- Transverse, longitudinal, and irregular fission are some of the types of binary fission.
What is Binary Fission?
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Binary fission is one of the common methods of asexual reproduction in which a parent cell divides into two daughter cells.No spindle formation takes place throughout the process. Thus, DNA replication is initiated with a single DNA molecule which play a significant role in attaching each copy of DNA to the different parts of cell membrane.
- DNA replication of the desired cell marks the beginning of binary fission followed by further elongation and cell division processes.
- In this process, the organism duplicates its own genetic material (DNA) and divides into two parts, each of them carrying one copy of the original genetic material.
- It is the primary method of reproduction in prokaryotes such as E.Coli, Archae, and Euglena.
Binary Fission Diagram
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Conceptually, binary fission is similar to mitotic cell division, observed in higher organisms such as plants and animals but the primary difference arises at the point of their complexity. In higher organisms, the mitotic cell division replenishes the worn-out cells. The binary fission diagram below shows how cell division takes place.
Binary Fission in Ameoba
Types of Binary Fission
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There are different types of binary fission which are categorized depending on the axis of the cell separation namely:
- Irregular
- Transverse
- Oblique
- Longitudinal
Irregular Binary Fission
In the case of irregular binary fission, the parent cell may divide in any plane but the place of division is always perpendicular to the spot where the nuclear division occurred. Binary fission in amoeba is a classical example of irregular type of binary fission.
Transverse Binary Fission
In transverse binary fission, the cytoplasm divides transversely or horizontally between two sets of nuclei forming two unequal daughter cells.
- Paramecium and other species of bacteria divide via this type.
- Regular transverse in some organisms such as Scyphistoma polyps leads to a formation of a chain-like structure called a strobilus.
Oblique Binary Fission
In oblique binary fission, the parent cell divides along an oblique plane creating two unequal daughter cells.
- In simple words, the parent cell divides across its length at an angle.
- Examples of organisms that undergo oblique binary fission are dinoflagellates such as Ceratium.
Longitudinal Binary Fission
In the case of longitudinal binary fission, the cytoplasm splits lengthwise (vertically) forming two similar daughter individuals. Longitudinal binary fission is most commonly found in Euglena.
Similar to binary fission, some metazoan (multicellular) species undergo another type of body division in which a single cell splits into multiple units simultaneously, and this process is known as fragmentation.
Binary Fission in Bacteria
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Binary fission in bacteria is an extremely rapid process. However, the speed differs in different species. And each species requires certain growth conditions.
- For instance, even if all growth-specific environmental factors like pH, temperature, oxygen, light, and moisture are present, the doubling time can be as low as 20 minutes, as observed in Escherichia Coli.
- Doubling time refers to the time an organism takes to divide or double its number.
- On the other hand, the doubling time of Clostridium perfringens, one of the fastest-growing bacteria, is 10 minutes under normal growth conditions.
Steps of Binary Fission in Bacteria
The following are the steps involved in bacteria:
- The double-helical coiled structure unwinds and starts replicating from the start point called ‘origin of replication’
- After the duplication of DNA, the chromosomes segregate into two.
- As the bacterium increases its size before division, the DNA elongates to the opposite poles of the bacterium.
- After replication and cell elongation, the cytoplasm of the cell starts to divide and septum formation begins.
- The septum grows and separates the cytoplasm into two and each cell has equal amounts of replicated DNA.
- The two daughter cells separate from each other completing the process. These cells contain DNA and all the necessary cell organelles.
Binary Fission in Amoeba
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Amoeba is a non-uniform, unicellular eukaryotic organism with a porous cell membrane that encloses the cytoplasm and all other cell organelles. Just like bacteria, amoeba also reproduces through binary fission and its process is quite similar to that of bacteria. Irregular type of binary fission takes place in ameoba.
Steps of Binary Fission in Amoeba
The following steps are observed in the process of binary fission in Amoeba:
- Amoeba starts replicating its organelles and nucleus before the binary fission process.
- The nucleus present in amoeba undergoes mitosis cell division.
- Similar to bacteria, the DNA present in the cell nucleus elongates to the opposite poles of the organism.
- After the complete division of nucleus, the cytoplasm also divides.
- Finally, the cell separates from the center eventually producing two daughter cells.
- These cells contain equal amounts of organelles and genetic material.
Advantages of Binary Fission
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The following are the advantages of binary fission:
- It’s a rapid process, as multiple daughter cells can be produced within a very short time.
- Only one parent is needed for the process.
- Daughter cells are clones of the parent cell.
Disadvantages of Binary Fission
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Though binary fission is very useful for the reproduction of various organisms, it has certain disadvantages which are:
- Unlike meiosis where the exchange of chromosomal segments takes place leading to a high degree of variation, in the case of binary fission no exchange of chromosomal segments takes place. As a result, the degree of variation remains low in the daughter cells.
- Here, the only source of genetic variation is mutation.
- A lack of genetic diversity may lower the survival chances in the ever-changing environment.
Things to Remember
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- Binary fission is an asexual mode of reproduction, observed in prokaryotes and some simple eukaryotes.
- Bacillus subtilis, B.cereus, E.Coli, etc are organisms that undergo fission.
- This is a rapid process where an organism can yield multiple daughter cells in a short time.
- Ftsz is a protein present in most bacteria which is responsible for cell division.
- The degree of genetic variation is very low in binary fission.
Sample Questions
Ques. Differentiate between mitosis and binary fission? (2 marks)
Ans. The table below shows the difference between the two:
| Binary Fission | Mitosis |
|---|---|
| It is most commonly found in prokaryotic organisms. | It is found in eukaryotic organisms, |
| Occurs in unicellular organisms. | Occurs in multicellular organisms. |
| Formation of spindle apparatus does not take place. | Formation of the spindle apparatus takes place. |
| The main function is asexual reproduction. | Growth and development, cell replacement, and asexual reproduction. |
| Rapid Process | Slow Process. |
Ques. What are the similarities between binary fission and mitosis? (2 marks)
Ans. The following are the similarities between the two:
- In both processes, replication of genetic material takes place before the initiation of the cell division process.
- Two identical daughter cells are formed at the end of the cell division stage.
Ques. What are the different types of Binary Fission? (3 marks)
Ans.Depending on the axis of the cell separation binary fission can be of the following types:
- Irregular binary fission
- Transverse binary fission
- Oblique binary fission
- Longitudinal binary fission
Ques. What kind of reproduction is binary fission? In which organisms does it take place? (2 marks)
Ans. Binary fission is an asexual mode of reproduction. It is generally observed in prokaryotes and some simple eukaryotes.
Ques. Write two benefits of Binary Fission. (2 marks)
Ans. Some benefits of binary fission are:
- Only one parent is needed for the process.
- Daughter cells are clones of the parent cell.
Ques. What are some disadvantages of Binary fission? (3 marks)
Ans. Some disadvantages of binary fission are:
- In binary fission no exchange of chromosomal segments takes place. As a result, the degree of variation remains low in the daughter cells.
- Here, the only source of genetic variation is mutation.
- A lack of genetic diversity may lower the survival chances in the ever-changing environment.
Ques. How does binary fission take place in amoeba under favorable and unfavorable conditions? (5 marks)
Ans. Reproduction in amoeba under favorable conditions takes place as:
- Reproduction takes place in the amoeba through binary fission
- It refers to the division that takes place between parent cells.
- When the organism grows, there is a growth in the size of the organism, duplication of its nucleus takes place and division of cytoplasm takes place in the center.
- Two similar daughter organisms arise from a single parent organism.
Reproduction in amoeba under unfavorable conditions takes place as:
- In this case, multiple fission is adopted.
- Amoeba becomes round in shape when conditions are unfavorable.
- It releases a hard covering which forms a protective layer around the organism and is known as a cyst.
- Inside the cyst, the nucleus divides and forms several nuclei.
- This process is followed by cytoplasm division.
Ques. Mention the difference between binary and multiple fission. (5 marks)
Ans. The differences between binary and multiple fission are:
| Binary Fission | Multiple Fission |
|---|---|
| The division of the nucleus takes place into two parts. | The division of the nucleus takes place into multiple parts. |
| Takes place under favorable conditions. | Takes place under unfavorable conditions. |
| Gives rise to two daughter cells. | It gives rise to many cells. |
| Cytoplasm division is followed by every nuclear division. | Cytoplasm division is not followed by every nuclear division. |
| Example: Euglena | Example: Plasmodium |
Ques. Write the steps of binary fission in bacteria. (5 marks)
Ans. The steps of binary fission in bacteria are:
- Highly convoluted DNA uncoils itself.
- The cell initiates replication of its own DNA. As a result, a copy of its own DNA is created.
- After doubling the DNA, the cell starts growing in size. The cytoplasmic content increases significantly and the DNA strands separate and segregate to opposite poles.
- The cell elongates and cross wall or septum formation starts.
- Once the cross formation finishes two daughter cells separate from each other completing the Binary fission process. Two daughter cells contain DNA and all the necessary cell organelles.
Ques. Write steps are observed in the process of binary fission of Amoeba. (3 marks)
Ans. The following steps are observed in the process of binary fission of Amoeba:
- The nucleus containing genetic material(DNA) divides forming two identical daughter nuclei by the process of karyokinesis. The genetic material is equally partitioned.
- Once the karyokinesis is over, division of the cytoplasm takes place which is called cytokinesis.
- As a result, the mother cell divides into two equal-sized daughter cells containing identical genetic material and all necessary organelles.
Ques. What is the ‘lost identity’ in binary fission? (2 marks)
Ans. In Binary Fission, after karyokinesis (nuclear division) and cytokinesis (cell division), nothing is left for the parent cell. Its identity is literally lost. The newborn daughter cells take the position of the parent cell by growing up rapidly.
Ques. Is binary fission is similar to fragmentation? (2 marks)
Ans. No binary fission and fragmentation are not similar to each other:
- In the former process, the parent cell divides into two identical daughter cells.
- While in the later, the parent cell breaks into different parts or fragments which develop into a new organism.
Ques. Can viruses multiply through Binary Fission? (2 marks)
Ans. No, viruses can’t multiply using binary fission.
- This is because, unlike bacteria, viruses don’t have the necessary organelles to reproduce their components.
- It first needs a host cell to multiply.
Ques. Do plants reproduce through binary fission? (2 marks)
Ans. No plants do not specifically reproduce by this method but there are various asexual methods of reproduction through which plants grow.
- For instance, vegetative reproduction is an asexual mode of reproduction where small saplings grow from the ‘buds’ or ‘eyes’ of a potato.
- Similarly, new plants grow from stems and even roots of other plants.
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