A living thing pertains to any organism or a life form that possesses or shows the characteristics of life or being alive.
But the viruses are not perfectly fitting in that definition. For a long time, scientists are trying to understand the real nature of viruses and the quest is still going on.
Understand Whether Viruses are Living/Non-Living
1. Organized Structure
Every living thing is consists of a single cell-like bacteria or multicellular like humans and plants.
According to science, a cell is a fundamental unit of every living thing. Also, most of those cells carried out several organized functions.
Mitochondria and ribosomes are very essential cell organelles present in every cell but it’s not present in the case of viruses.
The virus doesn’t have anything as normal living things have. The virus has a protein or lipid coat that protects its DNA or RNA from the outer environment.
On the other hand, all living things have a cell wall or cell membrane around it. Viruses don’t have an organized structure as all living organisms have.
2. Capability of Reproduction
One of the basic urges in nature is for a species to pass on its genetic information from one generation to another.
Viruses definitely reproduce but not as all other living things. All viruses need a host to reproduce.
In the absence of a host, the virus behaves as a non-living thing and it can not reproduce.
The virus can only reproduce in the host’s body using the host’s cell machinery.
The virus injects its genetic material into the host’s body where copies of viruses are made. The virus can’t reproduce independently.
Recently, new studies on mimivirus showed that these viruses have the tools for making copies of their DNA.
This suggests that certain types of viruses may actually be living.
3. Response to External Stimuli
Every living thing responds to external stimuli and adapts to the external environment.
Responses to stimuli mean an immediate reaction to changes but it’s not happening in the case of viruses.
They don’t respond to touch, sound, or light the way other living things respond.
In the case of all living things, cells bind to other cells.
Organism passes their genetic information and evolves with time but this action is much more active and complex than any viruses.
Viruses interact with the external environment but it simply occurs based on the virus’s chemical makeup and the environment in which it ends up.
There has not been enough research done to definitely say that viruses don’t react to external stimuli.
Every single living organism grows in terms of size as well as complexity. Living organisms use nutrients to grow larger in size.
This is certainly not true about viruses, the viruses hijack the host’s cell machinery and make its viral components which leads to the formation of new viruses.
Virus neither increases in size nor in complexity throughout the life cycle. Viruses do not grow.
5. Energy Requirement
Outside of the host, the virus becomes completely inactive until it again comes in contact with the host.
They do not use their own energy hence some scientists consider them as not alive. The virus only uses the host’s energy and machinery to make its copies.
This criterion is somewhat tricky. Some bacteria also use the energy of the host for its survival yet they are considered as living organisms.
Metabolism includes all chemical reactions involved in maintaining the living state of a living cell or organism.
It can be subdivided into 2 categories i.e. Anabolism and Catabolism.
Anabolism involves the synthesis of a complex molecule from simpler ones during which energy is absorbed.
Catabolism involves the breaking of complex molecules to form simpler ones that release energy.
Examples of the essential metabolic process involved in cell growth, respiration, reproduction, response to stimuli, sustenance, bio-molecular syntheses, waste elimination, and other homeostatic processes.
Most of the above processes are not happening in the viruses.
Scientists applied the above criteria to know whether viruses are alive or not. The answer is unclear.
As new research is carrying out, we hope that one day we would get a clear answer.
Till then happy reading and happy questioning.
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