Binary Fission: Mechanism, Binary Fission in Amoeba and Paramecium, Types of Binary fission, Binary Fission vs Mitosis, Practice Problems, and FAQs

Let’s do an interesting small activity. Take an apple and cut it in the middle. What do you get?

Yes, you get two pieces of an apple that are almost identical and equal in size. If we take a paper and fold it in the middle and then cut it from the middle. What will we get? Yes, we will get two equal-sized papers.

You all know about asexual reproduction. Do you think that splitting into two is a type of asexual reproduction? Yes, you are correct. The type of reproduction in which one parent organism is split into two is known as binary fission. It is an asexual mode of reproduction, which means it involves only one parent (uniparental). The offspring produced are identical and are of equal size in this case.

                                                 Fig: Binary fission

Now you would like to know more about this type of reproduction. Do you know in how many ways this mode of reproduction occurs and in which all organisms the binary fission takes place? You will get the answers for all the above questions in this article. So, let’s take a dive deep into the details of binary fission.

Table of contents

• Binary fission
• Mechanism of binary fission
• Binary fission in bacteria
• Binary fission in Amoeba
• Binary fission in Paramecium
• Types of binary fission
• Binary fission vs mitosis
• Practice Problems
• FAQs

Binary fission

Binary fission is a type of asexual mode of reproduction that is commonly observed in prokaryotes and some eukaryotes. In this type of asexual reproduction, the parent cell divides into two new daughter cells. During this process, the genetic material of the parent divides and duplicates into two parts. Now each daughter cell receives one copy of its parent genetic material. In prokaryotic organisms, reproduction primarily takes place through binary fission. Binary fission does not include the formation of spindle apparatus. 

Mechanism of binary fission

Binary fission is less complex than mitosis because it does not involve replicating organelles or complex chromosomes. The process begins with the replication of DNA within the cell. The mitochondria have DNA and it also replicates prior to binary fission. After replication, two sets of DNA are formed in a single cell. The plasma membrane allows the cell to split into two. Each daughter cell gets fully functional DNA and therefore, the cell can perform all the activities of life. 

                       GIF: Binary fission doubles the population

Binary fission in bacteria

The process of binary fission is a rapid process and the speed of the process varies from species to species. The term ‘doubling time’ refers to the period of time needed by bacteria to double their cell count. Moreover, every species grows under its own specific conditions, such as optimum pH levels, optimum temperature, oxygen, light, moisture, and osmotic pressure.

Types types of bacteria based on growth requirements 

There are two types of bacteria with different growth requirements as follows:

• Mesophiles
• Extremophiles

Mesophiles

Mesophiles are commonly found in the temperature range of 20 °C to 45 °C. The ambient temperature of a human body is 37 °C and this means that most of the disease-causing bacteria are mesophiles. For example, Mycobacterium tuberculosis causes tuberculosis in humans. It divides every 15 to 20 hours which is very slow as compared to other bacteria, like Escherichia coli. It can divide every 20 minutes and as a result, the population increases in a short time.

Extremophiles

Extremophiles are the type of bacteria that can exist in extremely harsh conditions, such as high temperature, high salinity, and high acidic environments. For example, Deinococcus radiodurans is an extremophilic bacteria and it can survive in thousand times more radiation than a human can. It has the capacity to divide every 48 hours under normal conditions. It can, however, slow down its rate of growth when subjected to unfavourable conditions, such as drought.

Steps involved in binary fission in bacteria

There are four steps involved in the binary fission of bacteria which is a simple amitosis. The various steps are listed below:

• DNA replication
• Cell development
• DNA segregation
• Cell wall formation

DNA replication

During this step, the bacterium uncoils and replicates its chromosomes while attached to the mesosome. As a result, the genetic material gets doubled. A new mesosome develops and gets attached to the daughter chromosome. 

Cell development

The bacterium begins to enlarge after copying the chromosome in order to prepare for binary fission. After that, the cytoplasmic content is increased. A membrane grows between the two mesosomes to push the daughter nucleoids or chromosomes to the opposite sides.

DNA segregation

In the middle of the cell now the cytoplasm undergoes a centripetal constriction to form two daughter protoplasts, each with a nuclear body. The plasma membrane inavginates and continues to grow until the cells are separated. 

Cell wall formation

 A double wall is deposited in the furrow between the daughter protoplasts. In this way during this phase, a new cell wall is formed. As a result, the parent cell splits into two daughter cells in the middle. Each daughter cell receives a copy of genetic material. The newly formed daughter cells are identical and generally half the size of the parent cell. Generally the newly formed cells are separated. Sometimes they do not separate and that gives rise to chains of bacteria. In binary fission the bacterial cell divides before becoming old and two new daughter cells are formed. Hence the bacteria are called immortal. 

                                  GIF: Binary fission in bacteria

Significance of binary fission in bacteria

Binary fission is important for the bacteria because of the following reasons:

• It is a method of asexual reproduction.
• It gives survival advantage to the organisms. 
• This type of bacterial growth is referred to as ‘explosive growth’. This leads to spoilage of foodstuff, curdling of milk and spread of infections.

Binary fission in Amoeba

Amoeba is a single-celled organism that reproduces asexually similar to bacteria by binary fission. The genetic material replicates first. Followed by this the parent cell divides into two daughter cells and these daughter cells are equal-sized. During this method, two identical organisms are produced from a single parent. 

During this procedure, the Amoeba that undergoes binary fission grows larger. The nucleus extends and eventually, it divides into two daughter cells. In this case, the division of the nucleus (karyokinesis) is followed by the division of the cytoplasm (cytokinesis). As a result, two Amoebae are produced from a single parent and the parent identity is lost.

                                                   Fig: Binary fission in Amoeba

Binary fission in Paramecium

Paramecium is described as a genus of unicellular ciliated Protozoa. The presence of thousands of cilia that covers the whole body is a characteristic feature of Paramecium. They are commonly found in freshwater, marine water, and brackish water. 

In paramecium, reproduction takes place through sexual as well as asexual mode. The main mode of reproduction is asexual, whereas the sexual mode of reproduction occurs when there is a scarcity of food or other adverse conditions present.

The asexual mode of reproduction occurs through binary fission. The mature cell splits into two cells, each of which grows quickly and creates a new organism. During favourable conditions, the Paramecium multiplies rapidly and that is up to three times a day. A cell undergoes transverse binary fission, which is followed by mitotic division in the micronucleus. In the macronucleus, amitosis occurs.

               Fig: Binary fission in Paramecium

Types of binary fission

The process of binary fission is of four types on the basis of the plane of the cytoplasmic division as follows:

• Irregular binary fission
• Transverse binary fission
• Longitudinal binary fission
• Oblique binary fission

Irregular binary fission

In this type of binary fission, the cytoplasmic division or cytokinesis occurs in any plane (the cell will be able to divide in any plane). Typically, it occurs perpendicular to the plane of the chromosome division or karyokinesis. This type of fission is found in Amoeba.

                                                      Fig: Irregular binary fission

Transverse binary fission

In this type of binary fission, the cytoplasmic division occurs along with the transverse axis of a cell. This type of division is found in Paramecium which is a ciliated protozoan. Here the cytoplasm is divided along the transverse axis of the cell.

                   GIF: Transverse binary fission

Longitudinal binary fission

In this type of fission, the cytoplasm divides into two along the longitudinal axis of a cell. This method is commonly seen in flagellates, such as Euglena. In Euglena the binary fission starts from the anterior end and the flagellum divides before the cell division normally. 

                     Fig: Longitudinal binary fission in Euglena

Oblique binary fission

In this type of binary fission, the cytoplasm gets separated in an oblique manner Resulting in two unequal cells. This type of cell division is found in Ceratium which is a dinoflagellate.

                   Fig: Oblique binary fission in Ceratium

Binary fission vs mitosis

Practice Problems

Q 1. Identify the organism that reproduces through binary fission.

a. Amoeba
b. Spongilla
c. Yeast
d. Hydra

Answer: Binary fission is one of the types of asexual mode of reproduction. There are many single-celled organisms that reproduce through this method. During this type of division, the parent cell divides and produces two daughter cells. They are identical and of equal size normally. They rapidly grow to an adult organism. Examples of organisms that reproduce through binary fission include Amoeba, bacteria and Paramecium. Hence, the correct option is a.

Q 2. Which of the following is an immortal organism?

a. Planaria
b. Penicillium
c. Amoeba
d. Both b and c

Answer: Amoeba is a unicellular organism and is considered as an immortal organism. This is because they undergo binary fission before becoming old in which their body divides into daughter cells and each daughter cell develops into a new organism. This process continues. Therefore, it is said that they do not die and become immortal. Hence, the correct option is c.

Q 3. Determine the first step involved in the binary fission of bacteria.

a. Cell growth and development
b. Segregation of DNA
c. Replication of DNA
d. DNA splitting

Answer: Binary fission is one of the types of asexual mode of reproduction. During this type of division, the parent cell divides and produces two daughter cells.The first step involved in the process of binary fission of bacteria is the replication of DNA. During this step, the bacterium uncoils and replicates its chromosomes. As a result, the genetic material gets doubled. Hence, the correct option is c.

Q 4. Which group of organisms commonly reproduce through binary fission?

Answer: Many prokaryotic species, including bacteria, reproduce via binary fission. Prokaryotic organisms primarily reproduce through binary fission. 

FAQs

Q 1. In binary fission, ___________ divides first followed by the division of cytoplasm.
Answer: During the process of binary fission, the nucleus divides first (karyokinesis) which is then followed by the division of the cytoplasm (cytokinesis).

Q 2. Name the process through which Planaria reproduce?
Answer: Planaria reproduce through a process called binary fission in which the body is divided into two pieces. The resulting head and tail regenerate followed by binary fission and this forms two new organisms. Planaria also shows true regeneration. 

Q 3. What is the main difference between fragmentation and fission?
Answer: The main difference between fragmentation and fission is as follows:

In fission, a unicellular organism like bacteria breaks up to form two daughter cells and each cell develops into a new organism. In fragmentation, a multicellular organism normally breaks up into various fragments and each fragment develops into a new organism.

Q 4. Why is binary fission considered an immortal process?
Answer: In binary fission the entire parent cell (organism) divides into two daughter cells before they become old. The newly formed daughter cells subsequently mature into adult cells. This process is repeated which makes the cell (organism) immortal.

Q 5. How does multiple fission differ from binary fission?
Answer: Multiple fission is a type of asexual reproductive process in which a parent cell divides into multiple daughter organisms, whereas in binary fission, a cell divides into two daughter cells.

YOUTUBE LINK: https://www.youtube.com/watch?v=A2z2yLYbam0 

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