Question

Difference between unicellular and multicellular organisms?

Answer 1

Hint: A unicellular organism is an organism that contains only one single cell. Prokaryotic organisms are unicellular organisms but incase of eukaryotic organisms some are unicellular organisms whereas many eukaryotic organisms are multicellular organisms.
Multicellular organisms are those organisms that contain more than one cell. Many eukaryotic organisms are multicellular organisms. For example plants, fungi, animals, tissues, and organs are made up of many cells.

Complete answer:
The main difference between unicellular and multicellular organisms is that unicellular organisms are made up of a single cell whereas multicellular organisms are made up of more than one cell or we can say they are made up of many cells. But still, there are many other differences between unicellular and multicellular organisms. They are described in the below table:

Unicellular organisms	Multicellular organisms
Unicellular organisms consist of single cells only.	Multicellular organisms consist of more than one cell.
All the necessary processes of life are carried out by a single cell only.	Different functions are performed by multiple cells.
They have an irregular shape.	They have a definite shape.
Body organization is simple.	Body organization is complex.
Cell differentiation is absent.	Cell differentiation is present.
The mode of reproduction is asexual reproduction.	The mode of reproduction is both asexual and sexual reproduction.
Asexual reproduction is by binary fission.	Asexually reproduced by mitosis.
Includes both prokaryotes and eukaryotes	Includes both prokaryotes and eukaryotesIncludes eukaryotes only.
Any injury to the cell causes the death of the organism.	Any injury to the cell does not cause the death of multicellular organisms.
These can be autotrophs or heterotrophs.	These include both autotrophs and heterotrophs.
Visible only under a microscope.	Most are visible by the naked eye
Transport occurs by simple diffusion.	Transport occurs by simple diffusion, active, and passive transport.
Lifespan is short as compared to multicellular organisms.	Lifespan is long compared to unicellular organisms.
Examples: Amoeba, Bacteria, Paramecium, and yeast.	Examples: Humans, animals, plants, birds, and insects.

Additional information:
- In unicellular organisms, only one cell performs all the functions to survive. They live in colonies and depend upon each other for their needs.
- Bacteria are the world's oldest form of life. For eg cyanobacteria.
- Examples of archaean are thermophiles, psychrophiles, acidophiles, etc.
- Unicellular fungi are the yeasts.
- Acetabularia is the macroscopic unicellular organism.
- In multicellular organisms, different cells perform distinct functions.
- Multicellular organisms have a long lifespan because they continue to live even if the individual cell dies.

Note: Unicellular organisms have single-cell also known as single- celled organisms. These organisms are very tiny and minute and are visible only under a microscope. Unicellular organisms reproduce by asexual reproduction by the means of binary fission.
Multicellular organisms have more than one cell so performing different cells performs a different variety of functions. These are larger in size so can be observed by the naked eye. Multicellular organisms reproduces by both asexual and sexual reproduction. Asexual reproduction is by mitosis.