Organisms can be of various types and complexities. An organism is made up of tiny divisions called cells. One cell can make up the whole organism, or many cells can arrange to form complex organisms.
The more cells, the more complex the organism is. Less the cells of organisms, more the functions of the cells.
Key Takeaways
- Unicellular organisms consist of a single cell, whereas multicellular organisms comprise many cells working together.
- Multicellular organisms show a higher level of specialization and complexity than unicellular organisms.
- Unicellular organisms reproduce through binary fission or budding, while multicellular organisms use sexual or asexual reproduction methods.
Unicellular vs Multicellular Organism
The difference between unicellular and multicellular organisms is that one is made up of one cell, while the other is made up of multiple cells. Unicellular organisms are composed of single cells, while multicellular organisms are composed of more than one or multiple cells, each with a specific function.
The term unicellular means “uni- one” and “cellular-cells”. Thus unicellular organism is an organism made up of only one cell.
One cell makes up the whole organism, and this cell in itself performs all the bodily functions of the cell. There is no division of labour between cells.
The term multicellular means “multi- many” and “cellular-cells”. This multicellular organism is an organism with more than one cell. The number can be a few to over millions.
These cells interact with each other to form the entire organism. Thus in these organisms, division of labour between cells is present.
Comparison Table
| Parameters of Comparison | Unicellular Organism | Multicellular Organism |
|---|---|---|
| No of Cells | Only one cell makes up the whole organism in unicellular organisms. | Few to many cells make up the whole organism in multicellular organisms. |
| Functions | One cell performs all the bodily functions in unicellular organisms. | Different cells are specialized to perform specific functions in multicellular organisms. |
| Tissue formation | There is no tissue formation in unicellular organisms. | Tissue formation takes place in multicellular organisms. |
| Differentiation | Cells do not differentiate in unicellular organisms. | In multicellular organisms, cell differentiation takes place. |
| Labour Division | There is no possibility of division of labour in unicellular organisms. | Division of labour is present in between the different cells of the whole organism. |
| Reproduction | Unicellular organisms reproduce in a simple manner. | Multicellular organisms have complex reproduction. |
What is Unicellular Organism?
An organism made up of only one cell is called a unicellular organism. These are very simple organisms in which one cell carries out all the required functions of the entire organism.
Hence as the name already suggests, these organisms are extremely small, almost microscopic, as they are merely one cell big.
This cell making up the entire body, is not arranged into tissues as it cannot.
The cell is not differentiated into specialized cells for individual functions; however, each cell possesses all the required cell organelles in the cytoplasm required to perform all the bodily functions for the survival of the cell or the entire organism.
As there is no tissue formation or specialization, the entire body of the organism looks the same, and the body organization is simple compared to complex multicellular organisms. There is a division of labour at the organelle level in unicellular organisms.
These organisms include short-lived prokaryotes mainly and some eukaryotes as well, like yeast, bacteria, protistans, some protozoans and so on.
Reproduction is mostly asexual, but conjugation may exist in some. In short, simple organisms with one cell and simple reproduction are called unicellular organisms.
What is Multicellular Organism?
An organism made up of multiple cells is called a multicellular organism. These are organisms that can be simple (made of few cells) or complex (made up of millions of cells).
These cells of the organism rearrange themselves to form associations called tissues, which in turn associate to form organs, organs form organ systems, and organ systems make up the whole organism.
Each cell is specialized to perform a specific function. During the developmental stages of the organism, the cells undergo differentiation and specialization.
The complex interaction between the cells exists through cell junctions and gaps. Thus a highly interactive organism with specialized cells makes up the organism.
Thus specific cells like muscle cells, nerve cells, bone cells etc., are present, which are different from each other both in structure and function.
Usually, these cells are also short-lived, but the organism altogether is long-lived. Thus multicellular organisms have a long life span.
Multicellular organisms include eukaryotes only, like man, dogs, corals, plants and so on. Each of these organisms is complex and interacts with the environment with its outermost cell layer.
Division of labour in these organisms exists at cellular, organ and organ system levels.
Main Differences Between Unicellular and Multicellular Organism
- Unicellular organisms include organisms with only one cell. Whole multicellular organisms include organisms with multiple cells.
- Unicellular organisms are short-lived, while multicellular organisms are long-lived organisms.
- Unicellular organisms have no tissue organization, while multicellular organisms have tissue organization.
- Injury to a cell causes death in a unicellular organism, while in multicellular organisms, repair and regrowth are initiated in case of injury. The individual cell may die, but the organism lives.
- Cell differentiation and specialization are absent in unicellular organisms, whereas the following is present in all multicellular organisms in varying degree.
- Unicellular organisms die easily, whereas multicellular organisms are harder.
- https://www.sciencedirect.com/science/article/pii/0022519374902094
- https://link.springer.com/article/10.1007/s004420000492
Last Updated : 23 August, 2023
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Piyush Yadav has spent the past 25 years working as a physicist in the local community. He is a physicist passionate about making science more accessible to our readers. He holds a BSc in Natural Sciences and Post Graduate Diploma in Environmental Science. You can read more about him on his bio page.
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