Difference Between Multicellular and Unicellular

The key difference between multicellular and unicellular is that multicellular organisms possess more than one cell while unicellular organisms possess only a single cell.

Based on the cell number, there are two categories of organisms. Namely, they are unicellular and multicellular organisms. The behaviour, anatomy, and the functionalities of unicellular and multicellular organisms vary among each other. Multicellular organisms are the organisms that comprised of more than one cell. They are complex organisms which have varied functionalities. On the other hand, unicellular organisms also called single-celled organisms composed of only one cell. Thus, they have simple biological processes.

CONTENTS

1. Overview and Key Difference
2. What is Multicellular
3. What is Unicellular
4. Similarities Between Multicellular and Unicellular
5. Side by Side Comparison – Multicellular vs Unicellular in Tabular Form
6. Summary

What is Multicellular?

Multicellular, as the name suggests refers to a lot of numbers of cells. Thus, multicellular organisms comprised of more than one cell. Their cell number can vary from two to a few millions of cells. Thus, the cellular differentiation, maturation and growth take place in a more complex manner. The cells that have similar functions get together to form tissues and thereby form organs. Therefore, multicellular organisms show advanced organization patterns. All the multicellular organisms are eukaryotic. Therefore, they have an organized nucleus structure and membrane-bound organelles in their cells. The classic examples of multicellular organisms include members of the kingdom Plantae, Kingdom Animalia and most of the members of the Kingdom Fungi.

Furthermore, multicellular organisms show complex metabolic processes that occur in organ systems. The digestive system, respiratory system, and the reproductive system compose different organs, and these are some examples to show the complexity of multicellular organisms. The size and the shape vary across a wide range in multicellular organisms. The cell size of a multicellular organism is about 10-100 micrometres. The cell shape also differs according to the type of the cell upon differentiation. Moreover, cells perform diverse functions within the body.

The genetic material of multicellular organisms is linear in structure. The genetic material locates inside the nucleus, and the protein expression takes place in a more complicated manner in multicellular organisms. Furthermore, the nutrition requirement is higher for a multicellular organism. Their survival and nutritional patterns vary and are more precise.

What is Unicellular?

Unicellular organisms are the first type of organisms to evolve in nature. They also refer as single-celled organisms. Unicellular organisms compose only one cell. Therefore, complex processes such as cell differentiation do not take place in unicellular organisms. Unicellular organisms do not have complex organizational hierarchy levels since they do not form tissues or organs.

Mostly, unicellular organisms are prokaryotic except for unicellular fungi such as yeast, and unicellular protozoa such as amoeba, paramecium, etc. Therefore, they do not have an organized nucleus and membrane-bound organelles. The members of the Kingdom Monera (Bacteria and Archea) and Kingdom Protista belong to the group of unicellular organisms. Furthermore, unicellular organisms live in all types of environments, but some; Archea is able to tolerate extreme environmental conditions and survive until the conditions become favourable again.

The size of the cell is very small. It ranges between 1-10 micrometres. The shape of the cell may vary, but most single-celled organisms have a protective cell wall covering them. The genetic material occurs as a circular DNA, and the protein expression in unicellular organisms is more similar. Even though they are of primitive nature, most of the unicellular organisms are very important in industrial and biotechnological purposes.

What are the Similarities Between Multicellular and Unicellular?

• Multicellular and Unicellular are two categories of living organisms.
• Both have a plasma membrane structure in their cell.
• Some multicellular and unicellular organisms are parasites.
• Also, both contain DNA and RNA as the genetic material

What is the Difference Between Multicellular and Unicellular?

Multicellular organisms have more than one cell. On the other hand, unicellular organisms have only a single cell. Therefore, this is the key difference between multicellular and unicellular. A further difference between multicellular and unicellular organisms is that the multicellular organisms perform complex functions, and they have tissues, organs, etc. that are composed of many cells. On the other hand, unicellular organisms do not have complex metabolic functions, and they don’t possess tissues, organs, organ systems, etc.

There are more differences between multicellular and unicellular organisms and which are shown in the below infographic on difference between multicellular and unicellular.

Summary – Multicellular vs Unicellular

Organisms may be unicellular and multicellular based on the number of cells they possessed. The organisms that composed of a single cell are unicellular organisms. In contrast, the organisms that composed of more than one cell are multicellular organisms. The complexity of the organism increased in multicellular organisms compared to that of the single-celled organisms. The single-celled organisms perform the basic functions in a cell. In contrast, the cells of the multicellular organism are highly differentiated to perform special functions in the multicellular organism. Thus, this summarizes the difference between multicellular and unicellular.

Reference:

1.“Unicellular and Multicellular Organisms.” Life Science Edited by The University of Tokyo Editorial Committee for Life Science , The University of Tokyo. Available here 

Image Courtesy:

1.”Multicellular Organisms (A Textbook of Animal Physiology, 1899)”By Hooper 14 – Own work, (CC BY-SA 4.0) via Commons Wikimedia  
2.”Paramecium diagram”By Deuterostome – Own work, (CC BY-SA 4.0) via Commons Wikimedia