Thread: Virus a living organism?

Originally Posted by wikipedia

Argument continues over whether viruses are truly alive. According to the United States Code, they are considered microorganisms in the sense of biological weaponry and malicious use. Scientists, however, are divided. They have no trouble classifying a horse as living, but things become complicated as they look at simple viruses, viroids and prions. Viruses resemble other organisms in that they possess nucleic acid, and can respond - in infected cells - to their environment in a limited fashion. They can also reproduce by creating multiple copies of themselves through simple self-assembly.

Viruses do not have a cell structure, regarded as the basic unit of life. They are also absent from the fossil record, making phylogenic relationships difficult to determine. Additionally, although they reproduce, they do not metabolise on their own and therefore require a host cell to replicate and synthesise new products. However, bacterial species such as Rickettsia and Chlamydia, while living organisms, are also unable to reproduce outside of a host cell. An argument can be made that all accepted forms of life use cell division to reproduce, whereas all viruses spontaneously assemble within cells. The comparison is drawn between viral self-assembly and the autonomous growth of non-living crystals. Virus self-assembly within host cells also has implications for the study of the origin of life, as it lends credence to the hypothesis that life could have started as self-assembling organic molecules.

If viruses are considered alive, then the criteria specifying life will have been permanently changed, leading scientists to question what the basic prerequisite of life is. If they are considered living then the prospect of creating artificial life is enhanced, or at least the standards required to call something artificially alive are reduced. If viruses were said to be alive, the question could follow of whether other even smaller infectious particles, such as viroids and prions, would next be considered forms of life

I know a virus isn't technically a living organism, but what do you guys think? Do you think it should be that one exception to the rule of what is a living organism and what isn't?

Its always being debated but there's never an agreed decision; must be more fun to argue about it than to decide upon an answer!

Originally Posted by Robbie

Its always being debated but there's never an agreed decision; must be more fun to argue about it than to decide upon an answer!

Isn't that always the case?

Maybe we could define life as anything made up of a cell or cells, or can reproduce? But, of course, this is on the side of labeling the virus as alive. Which I am not sure of either.

Originally Posted by Nanobrain

Maybe we could define life as anything made up of a cell or cells, or can reproduce? But, of course, this is on the side of labeling the virus as alive. Which I am not sure of either.

Nanobrain is on the right track:

As with anything in science a term must be defined:

what is life?

what is alive?

These definitions are neither correct or incorrect but necessary for any litmus to be established before criteria compared.

Is billiards a 'sport'. We can argue until the cows come home until one particular definition of 'sport' is provided.

Well, that's the thing. Scientists have defined life; and have given seven criteria for something to be considered a living organism: feeding, movement, reproduction, breathing/respiration, excretion, growth/development, and sensitivity (reaction to stimuli). Of course, while it is not one of the seven characteristics listed, living things also eventually die and have the cell as their basic building blocks. Now viruses (as far as I know) violate 3 of these <9> characteristics. They don't reproduce (except with the help of host cells), they don't need to feed (they just kind of go into 'lock down' when they aren't in host cells), and finally, they don't <really> have a cell as their basic building block.

But we have to admit that they closely resemble living things, and act much like them.

Maybe life should be defined as anything that uses it's internal DNA or RNA strand(s)' encoded information to function? Next to the cell, it seems as if DNA/RNA are next in line in the world of life in biological beings.

trees are living but they don't meet all that criteria. They don't have excretions or move.

Originally Posted by shawngoldw

trees are living but they don't meet all that criteria. They don't have excretions or move.

Actually trees do move, I think. They move (not necessarily grow) towards light, or so I believe.

But I'm sure they excrete, though. It's important to note that by excretion I mean 'give off waste'.

In any case, you may be right about the movement bit; there are many organisms (can't name 'em off the top of my head) that don't meet the seven criteria for being living; but because they fit into a certain area in the taxonomy of living things, they're still considered living. This contributes to the controversy over the viruses' current standing.

I think even with a layman's understanding of a living organism you would most likely tend to include viruses in the group of living microorganism rather than regarding them dead matter. The definition of life by magical seven criteria like respiration and metabolism seems antiquated and very much based on multicellular organisms (humans have that tendency to consider themselves the center of all things). Doesn't the the world of science at least agree on viruses deserving the name "organism" which clearly sets them apart from things like stones? In fact, I'd like to see a dictionary description of the word "organism" that does not make use of the word "living". Even though this is entirely up to definition and somewhat arbitrary, a meaningful definition better make sense. I like Nanobrains suggestion to make the possession or use of DNA/RNA a necessary and sufficient condition for life (at least until we encounter extraterrestrial alternatives :wink: ).

Originally Posted by scientstphilosophertheist

Well, that's the thing. Scientists have defined life; and have given seven criteria for something to be considered a living organism: feeding, movement, reproduction, breathing/respiration, excretion, growth/development, and sensitivity (reaction to stimuli). Of course, while it is not one of the seven characteristics listed, living things also eventually die and have the cell as their basic building blocks. Now viruses (as far as I know) violate 3 of these <9> characteristics. They don't reproduce (except with the help of host cells), they don't need to feed (they just kind of go into 'lock down' when they aren't in host cells), and finally, they don't <really> have a cell as their basic building block.

But we have to admit that they closely resemble living things, and act much like them.

I've been in science for over 30 years and there is no one group of scientists who 'define life' with any authority over any other definition. It's 'their' definition and does a virus meet 'their' definition. There are dozens of definitions of life and no one definition with 5 , 7 or 700 criteria is definative. Put a thousand biology-related scientists in a room and you'll end up with a dastardly deeds before they'd agreed to any definition.

Originally Posted by scientstphilosophertheist

Originally Posted by shawngoldw

trees are living but they don't meet all that criteria. They don't have excretions or move.

Actually trees do move, I think. They move (not necessarily grow) towards light, or so I believe.

But I'm sure they excrete, though. It's important to note that by excretion I mean 'give off waste'.

In any case, you may be right about the movement bit; there are many organisms (can't name 'em off the top of my head) that don't meet the seven criteria for being living; but because they fit into a certain area in the taxonomy of living things, they're still considered living. This contributes to the controversy over the viruses' current standing.

I would think that the waste given off by trees is oxygen... Plants' movement toward light (called phototropism) isn't really movement, it is growth. The plant senses light on one side of it, and due to some chemical (i'll say auxins, but don't quote me on that), the cells on the non-light side of the plant elongate, effectively bending the plant toward the light source.

Originally Posted by Jellyologist

Originally Posted by scientstphilosophertheist

Well, that's the thing. Scientists have defined life; and have given seven criteria for something to be considered a living organism: feeding, movement, reproduction, breathing/respiration, excretion, growth/development, and sensitivity (reaction to stimuli). Of course, while it is not one of the seven characteristics listed, living things also eventually die and have the cell as their basic building blocks. Now viruses (as far as I know) violate 3 of these <9> characteristics. They don't reproduce (except with the help of host cells), they don't need to feed (they just kind of go into 'lock down' when they aren't in host cells), and finally, they don't <really> have a cell as their basic building block.

But we have to admit that they closely resemble living things, and act much like them.

I've been in science for over 30 years and there is no one group of scientists who 'define life' with any authority over any other definition. It's 'their' definition and does a virus meet 'their' definition. There are dozens of definitions of life and no one definition with 5 , 7 or 700 criteria is definative. Put a thousand biology-related scientists in a room and you'll end up with a dastardly deeds before they'd agreed to any definition.

Well I can't argue with you if you've been in science for 30 years. I'm just going off of my knowledge (I'm still a senior in high school), which is very limited compared to yours. In any case, every book/website/teacher that I've come across have stated that those are the criteria that scientists use to determine whether something is living or not.

Originally Posted by scientstphilosophertheist

Originally Posted by Jellyologist

Originally Posted by scientstphilosophertheist

Well, that's the thing. Scientists have defined life; and have given seven criteria for something to be considered a living organism: feeding, movement, reproduction, breathing/respiration, excretion, growth/development, and sensitivity (reaction to stimuli). Of course, while it is not one of the seven characteristics listed, living things also eventually die and have the cell as their basic building blocks. Now viruses (as far as I know) violate 3 of these <9> characteristics. They don't reproduce (except with the help of host cells), they don't need to feed (they just kind of go into 'lock down' when they aren't in host cells), and finally, they don't <really> have a cell as their basic building block.

But we have to admit that they closely resemble living things, and act much like them.

I've been in science for over 30 years and there is no one group of scientists who 'define life' with any authority over any other definition. It's 'their' definition and does a virus meet 'their' definition. There are dozens of definitions of life and no one definition with 5 , 7 or 700 criteria is definative. Put a thousand biology-related scientists in a room and you'll end up with a dastardly deeds before they'd agreed to any definition.

Well I can't argue with you if you've been in science for 30 years. I'm just going off of my knowledge (I'm still a senior in high school), which is very limited compared to yours. In any case, every book/website/teacher that I've come across have stated that those are the criteria that scientists use to determine whether something is living or not.

It's a positive that young folks your age are on a science forum and participating.

Fortunately you are about to enter a stage in life in which you start to question what you've been taught in school. Learn not to accept ideas because teachers or others propose them but because you've developed confidence in your own judgement through scientific methodology.

If you are off to college be sure to define terms in your first paper in your first year. Some prof is just itching to put big red circles around some statement like 'my teachers said' to get you to think for yourself. He doesn't give a crap what Mrs Smith back in Jefferson High said. Experience profs have as their primary task to tatoo critical thinking across the psyche of new students. Almost traumatize them into thinking for themselves.

I think that all organisms that are classified as living do meet all seven characteristics of living organisms that have been defined by scientists in one way or another, even if it is not blatant. Plants definitely do move towards light by phototropism and also show sensitvity/irritability, by response to light and to factors affecting photosynthesis. but since viruses don't meet all the seven charcteristics, In fact they meet none of them, and are only able to reproduce when inside a living cell, it seems logical to suggest that they are not living. From another perspective, something that is alive, is something that would die, but can viruses die? They can be deactivated, but can they die? I doubt it. The only way that viruses can be considered alive is by altering the definition of life itself, but personally, I agree with the current existent one , and I think that viruses are not living things.

We could just label a virus as a simple nonliving function.