cell theory and why it is not a theory

[dragonstar57]

cell theory (Cell theory refers to the idea that cells are the basic unit of structure in every living thing)

and that all living things have certain characteristics but those characteristics are part of the definition

so any "life" that violated this theory would not actually BE life

its like theorizing that all dogs bark and then redefine the word dog to mean (a 4 legged animal that barks)

if there was a dog that was injured and could no longer bark it would cease to be a dog by this (redefined) definition.

Edited January 14, 2011 by dragonstar57

[Ringer]

I don't really know what you mean by this. A cell is the most basic object the meets all criteria for life. Something is living if it reproduces, develops, self-regulates, and some others that I can't think of for some reason. If something was discovered that met the criteria for life and was not made up of cells as we know them cell theory would be falsified. How, then, is it not a theory?

[ajb]

Cell theory refers to the idea that cells are the basic unit of structure in every living thing...

 

known on Earth to date*.

 

I understand the reservation here. If something without a cell structure is then defined to be alive, which may not be as easy as it first sounds, then the theory will be falsified. I don't think that any robust definition of life would require cells to be stipulated in the definition.

 

Of course, it maybe the case that "life without a cell" will be very hard to spot, even if our planet is full of such "organisms".

 

Furthermore, it is conceivable that the definition of life will require some revision yet as we explore extremophiles and the possibility of life in the universe.

 

----------------------------------------

 

* There is the question about viruses, these don't have a cell structure. It will depend on who you ask if they are alive or not. I know that some biologists prefer to think of them as "remnants of a past microscopic world" rather than being alive. Largely this is a moot question as it does not matter to virus research if they are classified alive or not. However, it is known that viruses evolved after cells and thus finding a virus in space (known not to be of Earthly origin) would suggest cells also exists in space.

[CharonY]

I know that some biologists prefer to think of them as "remnants of a past microscopic world" rather than being alive.

 

Well, I would not know why they would be called remnants.Also, they are generally considered to be mobile genetic elements (or selfish agents, if you want) that may have arisen very early in history.

[dragonstar57]

the definition of life i was taught was that it has the "GRIMM" characteristics

Grows

Reproduces

Irritability

Moves

Metabolizes

then these same ideas were presented as a theory as if there might be some "life" on another planet

but what i was saying that you can't really theorize that something has its defining characteristics because if it did not have them it would simply be something else.

[Ringer]

the definition of life i was taught was that it has the "GRIMM" characteristics

Grows

Reproduces

Irritability

Moves

Metabolizes

then these same ideas were presented as a theory as if there might be some "life" on another planet

but what i was saying that you can't really theorize that something has its defining characteristics because if it did not have them it would simply be something else.

 

That's tautological and isn't really saying anything. I think the problem you are having is assuming that without cells something wouldn't be alive, but if it did all these things without cells than why would it not be alive? If it did grow, reproduce, etc without the use of cells it would still be considered alive; it just would not have any sort of cellular structure. Hard to really imagine what that would be like, but so was DNA before its structure was discovered.

[dragonstar57]

That's tautological and isn't really saying anything. I think the problem you are having is assuming that without cells something wouldn't be alive, but if it did all these things without cells than why would it not be alive? If it did grow, reproduce, etc without the use of cells it would still be considered alive; it just would not have any sort of cellular structure. Hard to really imagine what that would be like, but so was DNA before its structure was discovered.

based on what I was taught was the official definition of life it would not be alive.

[Ringer]

And why, exactly, would it not be considered alive?

[Ophiolite]

based on what I was taught was the official definition of life it would not be alive.

There is no official definition of life. At an exobiology conference six or seven years ago delegates were asked for defintions of life. AS I recall over one hundred distinct definitions were offered.

 

There are other more useful aspects of cell theory than the one which limits life to cellular forms. A simple modification of the theory to apply to terrestrial life as currently known avoids the problems you seem to feel exist.

[dragonstar57]

my biology teacher said it as if this was some kind of standard for life (i think they said something about NASA needing a way to tell if something was alive)

and then said that even though that was the points that needed to be present for it to be alive.

then said that cell theory was the theory that life had those things.

what i did not understand was that it was presented as both a theory and a fact.

Edited January 15, 2011 by dragonstar57

[Ophiolite]

my biology teacher said it as if this was some kind of standard for life .

Most of the definitions have a great deal in common, but there is no generally agreed definition. In the early stages of studying any subject it is important to simplify, so the teacher will be following one of the more common definitions and presenting it as standard. that's reasonable, but you are no aware that it is a simplification.

 

Without knowing exactly what (s)he said I can't really comment on the issue of it beiing presented as fact and theory.