What is Binary Fission? – Complete NCERT Notes

Introduction

Binary fission is a type of asexual reproduction in which a single parent organism divides into two identical daughter organisms. It is one of the simplest and fastest methods of reproduction and is commonly seen in unicellular organisms.

Binary fission occurs in organisms such as Amoeba, Paramecium, and bacteria.

Definition of Binary Fission

Binary fission is the process in which a single parent cell divides into two genetically identical daughter cells under favorable conditions.

Key Points

It is an asexual mode of reproduction.
Only one parent is involved.
No gametes are formed.
The offspring are genetically identical to the parent.
Common in unicellular organisms.

How Does Binary Fission Occur?

Binary fission takes place in the following steps:

Step	Process
1	The parent cell grows in size.
2	The nucleus divides into two nuclei.
3	Cytoplasm divides.
4	The parent cell splits into two daughter cells.
5	Each daughter cell grows into a complete organism.

Simple Sequence

Parent Cell → Nucleus Divides → Cytoplasm Divides → Two Daughter Cells

Binary Fission in Amoeba

In Amoeba, the nucleus first divides by mitosis.

After nuclear division:

A constriction appears in the middle.
Cytoplasm divides into two parts.
Two daughter Amoebae are formed.

Characteristics

Produces two identical Amoebae.
Occurs under favorable environmental conditions.
Rapid method of reproduction.

Binary Fission in Paramecium

In Paramecium, binary fission occurs across the width of the body.

Process

Nucleus divides.
Cell elongates.
Cytoplasm divides transversely.
Two new Paramecia are produced.

Features

Fast reproduction.
Daughter cells resemble the parent.
Common in freshwater habitats.

Types of Binary Fission

1. Simple Binary Fission

The cell divides into two equal parts.

Example: Amoeba

2. Transverse Binary Fission

Division occurs across the width of the body.

Example: Paramecium

3. Longitudinal Binary Fission

Division occurs along the length of the body.

Example: Euglena

Type	Example
Simple	Amoeba
Transverse	Paramecium
Longitudinal	Euglena

Advantages of Binary Fission

Simple process.
Requires only one parent.
Fast reproduction.
Produces many individuals quickly.
No need for mating.

Disadvantages of Binary Fission

Lack of genetic variation.
All offspring have similar characteristics.
Less adaptability to changing environments.
Diseases can affect all offspring similarly.

Binary Fission vs Multiple Fission

Feature	Binary Fission	Multiple Fission
Number of offspring	Two	Many
Parent division	Once	Repeated nuclear divisions
Example	Amoeba	Plasmodium
Speed	Fast	Produces many offspring at once

NCERT Important Points

Binary fission is an asexual reproductive method.
It occurs mainly in unicellular organisms.
The nucleus divides before the cytoplasm.
Offspring are genetically identical to the parent.
Amoeba reproduces through binary fission under favorable conditions.

Quick Revision Notes

✔ Binary fission is asexual reproduction.

✔ One parent produces two offspring.

✔ Offspring are genetically identical.

✔ Common in Amoeba, Paramecium, Euglena, and bacteria.

✔ Nucleus divides first, then cytoplasm.

✔ Fast and simple method of reproduction.

Practice Questions

Very Short Answer Questions

1. What is binary fission?

Answer: Binary fission is an asexual reproduction process in which one parent organism divides into two identical daughter organisms.

2. Name one organism that reproduces by binary fission.

Answer: Amoeba.

3. How many offspring are produced in binary fission?

Answer: Two offspring.

4. Is binary fission sexual or asexual?

Answer: Asexual.

5. Which divides first during binary fission?

Answer: The nucleus.

Short Answer Questions

1. Explain binary fission in Amoeba.

Answer: In Amoeba, the nucleus divides first into two nuclei. The cytoplasm then divides, resulting in the formation of two identical daughter Amoebae.

2. Write two advantages of binary fission.

Answer:

Rapid reproduction.
Requires only one parent.

3. Why are offspring identical in binary fission?

Answer: Because they are produced from a single parent without genetic mixing.

Fill in the Blanks

Binary fission is a form of asexual reproduction.
Amoeba reproduces by binary fission.
The nucleus divides before the cytoplasm.
Binary fission produces two daughter cells.
Euglena shows longitudinal binary fission.
Paramecium reproduces by transverse binary fission.
Binary fission occurs mainly in unicellular organisms.
The offspring are genetically identical.
Binary fission is a simple method of reproduction.
Bacteria commonly reproduce through binary fission.

Multiple Choice Questions (MCQs)

1. Binary fission is a type of:

A) Sexual reproduction
B) Asexual reproduction
C) Vegetative propagation
D) Pollination

Answer: B

2. Which organism reproduces by binary fission?

A) Human
B) Amoeba
C) Mango
D) Rose

Answer: B

3. How many daughter cells are produced?

A) One
B) Two
C) Three
D) Four

Answer: B

4. What divides first in binary fission?

A) Cytoplasm
B) Cell wall
C) Nucleus
D) Membrane

Answer: C

5. Binary fission commonly occurs in:

A) Unicellular organisms
B) Birds
C) Mammals
D) Reptiles

Answer: A

6. Which type of reproduction is binary fission?

A) Sexual
B) Asexual
C) Vegetative
D) Fragmentation

Answer: B

7. Paramecium shows:

A) Budding
B) Multiple fission
C) Transverse binary fission
D) Regeneration

Answer: C

8. Euglena reproduces by:

A) Budding
B) Longitudinal binary fission
C) Regeneration
D) Spore formation

Answer: B

9. Binary fission produces offspring that are:

A) Different from parent
B) Genetically identical
C) Sterile
D) Mutated

Answer: B

10. Which statement is correct?

A) Two parents are needed.
B) Gametes are formed.
C) One parent produces two offspring.
D) Fertilization occurs.

Answer: C

Conclusion

Binary fission is a simple and efficient form of asexual reproduction in which a single parent cell divides into two genetically identical daughter cells. It is commonly observed in organisms such as Amoeba, Paramecium, Euglena, and bacteria. Understanding binary fission helps students learn the basic mechanisms of reproduction in unicellular organisms as described in NCERT Biology.