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We say cell wall is dead but nobody says cell membrane is dead.

Is cell membrane living or dead ? If it is not dead then why is it not included in protoplasm :

Protoplasm is the living contents of a cell that is surrounded by a plasma membrane.

(Source : Wikipedia)

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neither the cell wall is living nor is the membrane. It is not dead either. Being a vital part of the cell it is essential for life but the concept of life doesn't apply to it. –  WYSIWYG Oct 24 '13 at 10:41
    
In addition to the comment from @WYSIWYG, you must also define what aspects of the cell membrane you are talking about - only the lipid bilayer or also the embedded proteins? The latter are most definately "alive". –  fileunderwater Oct 24 '13 at 12:13
    
Also, you question seems to imply that plasma membrane is something distinct from cell membrane, when they are actually alternative names for the same thing. –  fileunderwater Oct 24 '13 at 12:20
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Woah, @fileunderwater how are proteins living? –  terdon Oct 24 '13 at 16:45
    
@terdon Which is why I wrote "alive" and not living... What I was getting at was that membrane proteins are essential for cell function and are dynamically synthesized, while the lipid molecules are more of a passive component. But I agree the comment was probably confusing. –  fileunderwater Oct 24 '13 at 17:18
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1 Answer 1

It is neither living nor dead. It is simply not alive the way that any other collection of chemicals is not alive. Is salt alive or dead?

A cell's membrane consists of a collection of chemicals (mainly lipids and proteins). Individual chemicals can never be considered living or dead, any more than rocks or water can be living or dead. While the actual definition of life is tricky, everyone agrees that in order to be alive you need to (at the very least)

  1. Somehow interact with your environment
  2. Be able to make more copies of yourself

Therefore, the cells themselves are alive but the individual parts of the cells are not since they cannot make copies of themselves (this gets complicated when considering some organelles but never mind that here). Similarly, you are alive but your teeth are not. While you can make more of you (you can have children) your teeth cannot make more teeth.

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While I agree with the basic message in your answer, I also feel that this is a bit restrictive, especially when comparing to natural language. Earlier I was also considering e.g. teeth, and wouldn't you agree that the pulp can be labeled "living tissue" while the enamel is "dead"? Along the same lines, in plants (which can reproduce clonally, so living cannot be defined at the level of the whole organism), some cells are dead (but their cell walls might still provide a function), while others are living.... –  fileunderwater Oct 24 '13 at 18:25
    
[cnd:] What about the cell walls around the living cells - are those living or dead, if they have exactly the same structure as the cell walls surrounding dead cells? I realize that this is bordering on questions concerning language and philosophy, but I feel that the possibility to talk about components of organsisms as living or dead is useful. Or do you have any other terms as suggestions? –  fileunderwater Oct 24 '13 at 18:30
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@fileunderwater I can appreciate what you are saying but I think using the term 'alive' and 'dead' is confusing since we are talking about life. I think what you are mentioning is more related to whether or not something is capable of changing or being replenished. I would suggest the terms 'static' and 'dynamic' –  von Mises Oct 24 '13 at 20:36
    
@vonMises I honestly think that these terms are even more confusing. Good luck trying to convince people that enamel and hair is 'static' while pulp and hair sacks are 'dynamic' - I don't see how this would improve communication, especially with laymen. –  fileunderwater Oct 25 '13 at 8:12
    
@fileunderwater it comes down to semantics. Living is not the same as alive and the opposite of living tissue is not dead tissue. Teeth are not dead and neither are rocks, they are simply not living. The point is that life needs metabolism and reproduction, things that cannot do both are not alive. The cell's membrane is not alive, the cell itself is. Your hand is not alive, despite being made of "living tissue", you are. "Living" tissue consists of cells, each of which is indeed alive, the tissue itself is not. –  terdon Oct 25 '13 at 16:42
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