[Seany (OP)]

I understand that bacteria has a nucleus, whilst a virus doesn't.. But viruses still multiply themselves and seems to have a want to live. Surely that makes  them a living thing?

[Chemistry4me]

We were taught that all living things could do MRS.(C).GREN which stands for movement, respiration, sense, circulation (although that one is a bit dodgy), growth, reproduce, excrete, and nutrition (or something along those lines). I'm fairly sure that viruses can only carry out two of those functions, if my memory is correct. []

[Seany (OP)]

I do see your point.
Viruses

Move -- yes

Respire? -- (No. Viruses do not have the ability to respire on their own. They need to use the mitochondria of their host cells in order to use the process of respiration of the cell they have invaded. So, in other words,you could say that viruses "borrow" the respiratory ability of a cell, and that can be aerobic or anerobic, with or without oxygen.)

Sense -- no

Circulation -- no

Growth -- yes

Reproduce -- yes? multiplying in a way..

Excrete -- No idea..

Nutrition -- Surely they eat on something??

I'm still not sure whether MRS GREN has to agree for it to be living..! It's very vague!

[LaurenaS]

Bacteria are considered a living organism since it contains a cell (single) to survive on its own body and reproduce. A virus on the other hand is dependent on a host cell to survive and reproduce.

[alancalverd]

Just like liver fluke or a whole raft of complex living organisms.

[Bored chemist]

It's an interesting definition- life is notoriously complex so it's no shock that it's hard to define.

The given definition excludes humans (among many others).
A human can't reproduce.
(It takes two- as the song goes).

Viruses

Move -- yes

No, not really.
They get moved by other things, but they can not move themselves- except in a very limited way. Some actively move their genetic material into the cell they infect.

[Hayseed]

In recent years, we have found DOUBLE(probably more) the amount of life on this planet.  These are the lifeforms that predator bacteria and viruses.   They are classified as life.

We are just beginning to crack this new discovery.   There is probably much more biomass in the planet, than on the planet.

And some now suspect many more lifeforms on a super small scale.  It's quite puzzling.

[evan_au]

A virus on the other hand is dependent on a host cell to survive and reproduce.

This definition also excludes humans, since we depend on a biosphere (or a spacecraft/submarine) to metabolize, grow and reproduce.
- In reality, all life is interdependent, they just differ in degree

Some other definitions of life emphasize the copying of genetic information into new individuals
- which viruses do, in the right environment (like a cell)
- which humans also do, in the right environment (like a hotel)

[Petrochemicals]

In recent years, we have found DOUBLE(probably more) the amount of life on this planet.  These are the lifeforms that predator bacteria and viruses.   They are classified as life.

We are just beginning to crack this new discovery.   There is probably much more biomass in the planet, than on the planet.

And some now suspect many more lifeforms on a super small scale.  It's quite puzzling.

https://oceanexplorer.noaa.gov/facts/marinemicrobes.html

[Hayseed]

It's been awhile since I checked, but if I recall, this was found by environmental DNA assays. And some of the critters can not survive a lab environment.....or even be found yet.  They assayed everything.  Air, water, ice, soil, rock, oceans.

The last I heard, they were trying to establish the entity between the living and the non-living.   With not too much luck.

[axscientist]

Bacteria are cells. Some are pathogens (harmful) while some actually help us (such as the ones in our stomach that help us digest food). Viruses are capable of attacking our body cells and bacteria. They are both living things. Nonliving things do not reproduce, do not feed themselves in order to grow or thrive, and does not use energy (e.g. rocks, dead leaves, etc.)

Viruses and bacteria are alive.

[alancalverd]

All the things we classify as living, transpire water in some way. Viruses don't.

[Bored chemist]

Nonliving things do not reproduce, do not feed themselves in order to grow or thrive, and does not use energy

This guy
https://en.wikipedia.org/wiki/Wendell_Meredith_Stanley
was the first person to produce a crystal of a virus (the tobacco mosaic virus).
You can't crystallise something which is reproducing, feeding or using energy.
So it's clear that viruses don't do those things.
So they are not alive

[alancalverd]

Yes but....people have grown wheat from 5000-year-old seeds found in the pyramids. Not much to choose between crystalline TMV which reproduces when introduced to its favored host, and wheat that does nothing for centuries and germinates as soon as it is wet. Indeed there is a vault of seeds being preserved in "crystalline" conditions just in case anyone survives the next nuclear war and can remember the code to the door in Svalbard. Is a wheat seed dead or live? 

[set fair]

Viruses possess some characteristics of life, it makes sense to call them alive in some cotexts eg they don't want to kill their host before the host can transmit them to a new host. Perhaps it was after the discovery of prions that scientists decided that theyhad to draw a line somewhere.

Sense, you could make a case for viruses being able to sense things.

[Colin2B]

Perhaps it was after the discovery of prions that scientists decided that theyhad to draw a line somewhere.

It goes back a lot further than that. Trouble is the line can be difficult to define.
For example, would you say a virus senses its target cell and moves in, or does it randomly bump into things until it’s coating sticks?

[syhprum]

My priest tells me one human and the holy ghost is sufficient

[Tomassci]

This topic gets complicated fast. Now, we might say that viruses are just chemical packets, but packets of chemicals don't encode for themselves... On the other side, they need life to do the trick. (Which makes me think about one thing - could a virus theoretically be replicated without using a cell?)
But wait, it gets more confusing. We have viruses that have a DNA count and some genes that are close to what we consider "life" and on the other side we have bacteria that hide in cells and replicate in them.

[sceptic-eng]

If a virus has a DNA double spiral then surely it is alive and can mutate.  If we freeze it can survive.

[Bored chemist]

If a virus has a DNA double spiral then surely it is alive

No.