Acellular Organisms - Meaning, Types and Function

Edited By Irshad Anwar | Updated on Jun 06, 2025 06:04 PM IST

All the basic things that take place in a living body are performed in the fundamental unit of the living system known as the ‘Cell’. The cell was first discovered by Robert Hooke. There is a life which exists on the Earth which is supported by various living and non-living things. When we talk about which things these living and non-living things are made up of. So the answer is that non-living things are made up of the fundamental unit of matter, which is the “atom”. Acellular also refers to substances which are not considered completely living or cells as viruses and various vaccines. Acellular Organisms are one of the most important topics in biology.

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Acellular – Meaning
Viruses
Viroids
Prions
Difference between Cellular and Acellular

Acellular Organisms - Meaning, Types and Function

Some fundamentals of the cell are discussed below:

The cell is the place where all the metabolic and chemical reactions take place.
The cell has organelles which have specific functions. Like plasma membrane allows the entry and exit of food and waste.
The cell membrane acts as a barrier which protects the internal components of the cell.
Cells also help in regulating the movement of substances both in and out through processes like diffusion, osmosis and active transport.
Division of cells takes place through mitosis, where growth and repair of the cell occur, while, in sexual reproduction, meiosis takes place.

Acellular – Meaning

In biology, the term "acellular" defines anything that is not made of or divided into cells. It describes entities like viruses, viroids, and prions, which lack a cellular structure and do not perform independent life processes. These acellular forms rely on host organisms for survival and reproduction.

What are Acellular Organisms?

Acellular organisms lack a cellular structure, in contrast to typical living organisms that comprise one or more cells. Examples of such organisms are viruses, viroids, and prions. These do not have their own cellular machinery, like organelles or enzymes, to maintain independent life, and hence they rely on host cells for reproduction and metabolic activities.

Acytota and Cytota

Acytota and Cytota are the two fundamental biological categories. Acytota is made up of acellular entities, such as viruses, viroids, and prions, that have no cellular structure and must use a host organism for their survival. Cytota includes all forms of cellular life, ranging from prokaryotes to eukaryotes, having distinct cellular structures and thus having independent metabolic functions. This allows us to distinguish cellular life from acellular life.

Viruses

Below are few characteristics of viruses:

Viruses are non-cellular infectious agents made of genetic material (DNA or RNA) enclosed in a protein coat called a capsid.
They are inactive outside living cells but become active and multiply only inside host cells (obligate parasites).
They infect plants, animals, bacteria, and even fungi.
Example: HIV, Influenza virus, Tobacco Mosaic Virus (TMV).
The structure may be helical, polyhedral, or complex, depending on the type of virus.
Viruses can cause diseases like AIDS, flu, smallpox, and measles.

Viroids

Following are some characteristics of viroids:

Viroids are smaller than viruses and consist of only a short strand of circular RNA, with no protein coat.
They infect plants, causing diseases that can affect crop production.
Viroids are replicated inside host cells using the host's enzymes.
First discovered by Theodor Diener in 1971.
Example: Potato spindle tuber viroid (PSTVd).
They do not code for proteins, but can still disrupt normal cell function.

Prions

The characteristic features of certain Prions are given below:

Prions are infectious protein particles that contain no genetic material (no DNA or RNA).
They cause diseases by changing the shape of normal proteins in the brain.
Prions are highly resistant to heat and disinfectants.
Example: Mad Cow Disease (BSE), Creutzfeldt–Jakob disease (CJD) in humans.
Discovered by Stanley Prusiner, who won the Nobel Prize.
Prion diseases affect the nervous system, leading to brain damage and death.

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Difference between Cellular and Acellular

The basic difference between cellular and acellular is discussed below in the table:

Cellular Organisms	Acellular Organisms
Living organisms are made up of one or more cells.	Organisms that are not made up of cells.
It has a cell structure and contains organelles like cell membranes, cytoplasm, mitochondria, etc.	Do not have any type of cell organelles. only contain protein and genetic material for viruses.
Consider into living organisms category	Generally not considered into the category of fully living creatures.
Perform metabolic processes independently	Cannot perform independent metabolic processes.
Can reproduce on their own.	Required for a host for replication example virus.
Can easily survive independently in different environments and conditions.	Organic compounds like lactic acid are produced by acellular cells.
Cells have compounds like proteins and enzymes.	No cells are present, and compounds are also absent.
Can easily perform simple to highly complex processes.	Generally simple in structure then compared to cellular organisms.

Also Read

Structures in Bacteria	Bacterial viruses
Archaebacteria	Ascomycetes
Virology	Basidiomycetes

Frequently Asked Questions (FAQs)

1. What are viruses? Why are they known as acellular?

Viruses are the pathogens which are made up of a protein coat and genetic material which may be DNA or RNA. The viruses are not viable in the environment they become when they enter the host. They are made up of only protein and DNA/RNA and they replicate inside the host by using the energy from the host. Hence, viruses are known as acellular.

2. Why are protozoans known as acellular?

Protozoans are the eukaryotic microorganisms which exist mainly as unicellular. The maximum protozoans are pathogenic in nature and have the protoplasmic level of organization and in case of Amoeba the body is not limited to the cytoplasmic boundaries so it is regarded as the acellular.

3. What is a cell?

Cell is a basic fundamental living unit present in a living body. Cell was discovered by Robert Hook when he observed a honeycomb structure in a microscope invented by him.

4. What are acellular organisms?

These are the organisms which cannot be divided into discrete cells or it may be a something like an organic material but not consists of individual cells.

5. How are acellular organisms different from the unicellular organisms?

Unicellular organisms consist of single cell microorganisms which can have single cells like amoeba. Acellular means the non living thing which does not contain any type of cell or it may not be divided into cells hyphae produced by fungi.