Difference between Unicellular and Multicellular Organisms

The difference between unicellular and multicellular organisms is quite apparent – the number of cells. In other words, each and every living species are composed of the cell. Based on the number of cells these organisms possess, they can be classifed into:

  • Unicellular Organisms
  • Multicellular Organisms

Unicellular Organisms

As the name implies, unicellular organisms are made up of a single cell. They are the oldest form of life, with fossil records dating back to about 3.8 million years ago. Bacteria, amoeba, Paramecium, archaea, protozoa, unicellular algae, and unicellular fungi are examples of unicellular organisms. These unicellular organisms are mostly invisible to the naked eye, hence, they are also referred to as microscopic organisms. Most of the unicellular organisms are also prokaryotes.

Also read:  Microbes

Examples of Unicellular Organisms

Some of the examples of unicellular organisms are:

  • Amoeba
  • Euglena
  • Paramecium
  • Plasmodium
  • Nostoc, Salmonella ( Prokaryotic unicellular organisms)
  • Protozoans, Fungi, Algae ( Eukaryotic unicellular organisms)

Multicellular Organisms

Organisms that are composed of more than one cell are called multicellular organisms. Multicellular organisms are almost always eukaryotes. However, bacteria can form large interlinked strcutures such as colonies or biofilms but these can’t be classified as multicellular organisms.

Multicellular Organisms Examples

Some of the examples of multicellular organisms are listed below:

  • All vertebrates and invertebrates
  • All angiosperms, gymnosperms and higher land plants

Difference Between Unicellular And Multicellular Organisms

As stated initially, one major difference between unicellular and multicellular organisms is the cellularity or the number of cells. Read on the explore more differences between the two:

Unicellular Organisms Multicellular Organisms
Unicellular organisms are composed of a single cell Multicellular organisms are composed of more than one cell
Irregular in shape Have a definite shape
Simple body organization Complex body organization
A single cell carries out all necessary life processes Multiple cells perform different functions
The total cell body is exposed to the environment Only the outer cells are exposed to the environment
Division of labour is at the organelle level Division of labour is at cellular, tissue, organs and organ system level
Includes both eukaryotes and prokaryotes Includes only eukaryotes
A lifespan of a unicellular organism is usually short Multicellular organisms have a comparitively longer lifespan
Injury to the cell leads to the death of the organism Injury to a cell does not cause death of the multicellular organism
Reproduce by asexual reproduction Reproduction happens sexually as well as asexually
Cell differentiation is absent Cell differentiation is obvious
They can be autotrophs or heterotrophs They include both autotrophs and heterotrophs
They are microscopic in nature They are macroscopic in nature
Bacteria, amoeba, paramecium, and yeast are examples of unicellular organisms Humans, animals, plants, birds and insects, are examples of multicellular organisms

Also refer: Difference between Prokaryotic and Eukaryotic Cells

For more information on the difference between unicellular and multicellular organisms, their examples, or other related topics, keep visiting BYJU’S website or @ BYJU’S Biology.

Frequently Asked Questions

How do unicellular entities move?

Movement in unicellular entities is brought about through cilia, pseudopodia, flagella, etc. They can locomote to find food and respond to threats by moving away.

How do unicellular organisms eat and reproduce?

Unicellular entities fulfil their nutritional requirements through a process known as phagocytosis. In this process, the single-celled organisms engulfs  food particles using its plasma membrane. This gives rise to an internal structure called the phagosome, where it is eventually digested.

Most unicellular organisms reproduce asexually through binary fission. The process of cell replication and reproduction in unicellular entities is the same in contrast to multicellular organisms.

State one similarity between unicellular and multicellular organisms.

Multicellular and unicellular organisms are similar in a way that they show almost all the life functions and processes such as reproduction and metabolism. They possess RNA and DNA which can display a range of lifestyles that are essential to most of the ecosystem that we currently exist in.

What is cytoplasm?

The cytoplasm is a substance that is present between the nucleus and the cell membrane. It contains the organelles, the cytosol, the cytoskeleton, and other suspended particles.

What is an organelle?

An organelle is a cell structure with specified functions that are suspended in the cytoplasm of eukaryotic cells. In a plant cell, the most prominent organelle is the vacuole, followed by the nucleus.

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