Unicellular vs multicellular differences and similarities

Organisms exist on earth as either unicellular or multicellular organisms. The difference between unicellular vs multicellular organisms is based on the number of cells and how they carry out their cellular activities. Technically, unicellular and multicellular organisms are the two kinds of organisms found on earth.

Unicellular organisms are usually prokaryotes, which have a simple organization and are smaller in size. Hence, they are not usually seen with naked eyes. Multicellular organisms, on the other hand, are typical eukaryotes that contain differentiated cell types in the body in order to perform various functions separately.

It took one billion years after the formation of the earth for a unicellular organism to appear on earth. For approximately 2 billion years, unicellular organisms existed alone on earth before the multicellular organisms manifested. The first multicellular organisms probably arose about 600 million years ago. According to evolution, the development of multicellular organisms probably began with the formation of groups of cells formed in several ways.

Hence, the major difference between unicellular and multicellular organisms is their cellular structure. Unicellular organisms, also known as single-celled organisms comprise just a single cell whereas multicellular organisms are made up of multiple cells. This article discusses the similarities and differences between unicellular vs multicellular organisms.

What are unicellular organisms?

Unicellular organisms are organisms that are made up of just a single cell and carry out all their life processes in a single cell. These organisms are also known as single-celled organisms. Unicellular organisms consisting of only a single cell are still capable of performing different life processes or cellular activities.

Therefore, a unicellular organism is able to survive because reproduction, feeding, excretion, and digestion all occur in this one single cell. These organisms consist mainly of prokaryotic organisms such as bacteria and archaea, as well as a few eukaryotic organisms like protozoa, unicellular algae, and unicellular fungi. These organisms are microscopic and can only be seen under a microscope. Nevertheless, there are some organisms that are partially unicellular, e.g Dictyostelium discoideum. Moreso, unicellular organisms can be multinucleate, such as Plasmodium, Caulerpa, and Myxogastria.

Furthermore, the majority of multicellular organisms have a unicellular life-cycle stage. For instance, gametes are reproductive unicells for multicellular organisms. Moreso, multicellularity seems to have evolved independently many times in the history of life. It is said that single-celled organisms are the oldest form of life with protocells possibly emerging 3.8 to 4 billion years ago. The first unicellular organism is called LUCA (Last Universal Common Ancestor) which probably existed around 3.5 billion years ago. Scientists believe that this one cell gave rise to all the subsequent life on earth. LUCA was one of the earliest prokaryotic cells in unicellular organism evolution.

Characteristics of unicellular organisms

  1. These organisms are microscopic, thus, they cannot be easily observed through the naked eye.
  2. The majority of unicellular organisms commonly reproduce via asexual reproduction methods like fragmentation, budding, and binary fission.
  3. Very few single-celled organisms can reproduce sexually via conjugation.
  4. Being single-celled, the arrangement of the cell is quite simple.
  5. These organisms can develop and strive well in extreme salinity, heat, acidity, etc.

What are multicellular organisms?

Multicellular organisms are organisms that are made up of more than one cell (multiple cells) which are to varying degrees integrated and independent. These organisms arise in various ways including cell division or by aggregation of many single cells.

The term “multi” refers to something that is more than one. Therefore, multicellular organisms are made up of many cells. These organisms have distinct cell organelles and are capable of carrying out different life processes or separate cellular activities inside the organism’s body. Multicellular organisms consist of only eukaryotic organisms such as insects, plants, animals, humans, birds, most fungi, and many algae.

These organisms are developed by cellular specialization and division of labor. Cell specialization in multicellular organisms allows cells to work in coordination for the proper functioning of an organism. The cells of multicellular organisms are therefore efficient in a single process and then carry out various processes by depending on other cells. Nevertheless, there are organisms that are partially unicellular and partially multicellular such as the slime molds and the genus Dictyostelium.

Characteristics of multicellular organisms

  1. These organisms are macroscopic and are easily seen with the naked eye.
  2. The majority of multicellular organisms usually reproduce through sexual methods (by the formation of a zygote).
  3. Very few multicellular organisms reproduce asexually through means like budding, spore formation, etc.
  4. Due to the multiple cell composition of these organisms, their cell arrangement is quite complex.
  5. The size of a multicellular organism will increase as the number of cells increases.

Unicellular vs multicellular examples

Unicellular organisms
Multicellular organisms
Euglena
Amoeba
Unicellular algae
Protozoa
Yeast
Bacteria
Sporozoans
Paramecium
Humans
Animals
Birds
Insects
Fishes
Fungi
Plants
Multicellular algae
Unicellular vs multicellular examples

What is the difference between unicellular and multicellular organisms?

The difference between unicellular vs multicellular organisms is majorly due to the difference in the number and arrangement of the cells as well as how the cell functions. One difference between unicellular and multicellular organisms is that unicellular organisms are made up of just a single cell whereas, multicellular organisms are made up of multiple cells. Therefore, the major factor used to compare and contrast unicellular and multicellular organisms is the number of cells that make up the organism

Another difference between unicellular and multicellular organisms is the way they carry out their cellular activities and life processes. In unicellular organisms, all their cellular activities are performed by a single cell, while the cells in multicellular organisms carry out specific cell activities by working together in groups. The arrangement of cells in a unicellular organism is much simpler whereas cell arrangement in multicellular organisms is found to be complex.

Criteria for comparison
Unicellular organisms
Multicellular organisms
Cell
A unicellular organism is made up of just a single cell.
A multicellular organism is made up of multiple cells.
Shape
They are irregular in shape
The shape of these organisms is well-defined
Size
These organisms are smaller in size
These organisms are comparatively larger in size
Nature
They are microscopic in nature
They are macroscopic in nature
Cell type
This group of organisms comprises organisms with both prokaryotic and eukaryotic cell types
This group of organisms comprises organisms with only eukaryotic cell types
Cell organization
The cell organization of a unicellular organism is simple
The cell organization of a multicellular organism is complex
Cell differentiation
There is no cell differentiation in unicellular organisms. However, yeast, a unicellular organism may undergo differentiation
Specialized cell differentiation occurs in these organisms
Life span
These organisms have a short life span
The life span of multicellular organisms is longer
Evolution
The oldest life forms evolved 3.8-4 billion years ago
They evolved from the prokaryotes
Mode of nutrition
These organisms can be autotrophs or heterotrophs
Multicellular organisms include both autotrophs and heterotrophs
Operational efficiency
The operational efficiency of unicellular organisms is low.
The operational efficiency of multicellular organisms is high
Reproduction
Reproduction occurs through budding and binary fission
Reproduction occurs through gamete fusion
Injury effect
Injury to the cell leads to the death of the unicellular organism
Injury to a cell does not cause the death of the multicellular organism
Transport mechanism
In single-celled organisms, simple diffusion is used as the transport mechanism
In multicellular organisms, simple diffusion, active transport, and passive transport are the used transport mechanisms
Regeneration ability
These organisms show a greater tendency to regenerate.
These organisms show low regeneration ability.
Examples
Bacteria, Protozoans, amoeba, paramecium, yeast, etc are examples of unicellular organisms
Insects, Humans, Animals, Plants, birds, etc are examples of multicellular organisms
A table showing the differences between unicellular vs multicellular organisms

Unicellular vs multicellular similarities

  1. They are both made by a functional unit of life known as a cell.
  2. Both the cells of unicellular and multicellular organisms have cytoplasm and a plasma membrane.
  3. They both contain DNA and ribosomes for gene expression.
  4. In both organisms, cell division usually occur through mitosis or meiosis.
  5. Unicellular and multicellular organisms both need cellular energy to function.

Despite the differences between multicellular vs unicellular organisms, these organisms still share something in common. Listed above are the similarities between unicellular and multicellular organisms.

Unicellular vs multicellular advantages

  1. One advantage of multicellular organisms over unicellular organisms is that their cells can take care of each other.
  2. Multicellular organisms have a competitive advantage of a bigger size, compared to unicellular organisms.
  3. The longer lifespan of multicellular organisms is of an advantage over unicellular organisms
  4. Unicellular organisms require less energy because they are made up of one cell compared to multicellular organisms that require more energy to feed their multiple cells.
  5. Multicellular organisms are at risk of infection from unicellular organisms.
  6. Being multicellular involves a complex cellular make-up, hence, it takes longer for the complex parts of the organism to develop to maturity compared to single-celled organisms.
  7. Unicellular organisms show a greater tendency to regenerate compared to multicellular organisms that show low regeneration ability.

Conclusion

An overview of unicellular vs multicellular organisms with differences and similarities
An overview of unicellular vs multicellular organisms

The difference between unicellular vs multicellular organisms is majorly due to the difference in the number and arrangement of the cells as well as how the cell functions. Unicellular organisms are made up of just a single cell whereas multicellular organisms are made up of multiple cells. However, these organisms are similar in the sense that they are both made by a functional unit of life known as a cell. Moreso, they both contain DNA and ribosomes in the cell for gene expression.

Leave a Comment