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As the title says, are all cells organisms? Why or why not?

As I understand, not every cell is an organism because some of them -those which aren't organism- require the rest of the organism to live. But arguing with someone about that, he says that, for that matter, every cell needs of others to live in some way or another, or that they can be kept alive and sometimes reproduce in a petri dish, without the need of the organism. So every cell, he says, even those which constitute larger organisms are organisms in themselves. I tell him that saying every cell is an organism is awkward, that would imply that every multi-cellular organism is really a colony, rather than an organism.

Is this only a philosophical question or can we say for sure, for example, that an epidermal stem cell or a lymphocyte are not organisms?

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    $\begingroup$ I would say that some cells are considered organisms (e.g. bacteria) but others not. For example, a skin cell wouldn't be considered an organism because it can live by itself, it needs to be part of something bigger. $\endgroup$ – Mud Warrior Sep 16 '16 at 17:56
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    $\begingroup$ it is very true the cell is living, but we cant always call it an organism. "Life" and "individual organisms" are 2 different concepts. $\endgroup$ – Always Confused Sep 16 '16 at 18:37
  • $\begingroup$ MattDMo's argument is that a single cell from within a human, if extracted from the body is not perfectly self sustaining. Would it not apply then to a human extracted from our own environment? The middle of space? We could not survive there. So are we not organisms? I myself couldn't find food or water in space that's for sure. Put me in an all you can eat buffet restaurant however, and I assure you I will not starve. Like I said, not much of an answer, but certainly food for thought. $\endgroup$ – R.Hull Sep 16 '16 at 20:18
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    $\begingroup$ What is the point of this semantic debate? $\endgroup$ – Superbest Sep 17 '16 at 10:55
  • $\begingroup$ Related: biology.stackexchange.com/questions/7053/… $\endgroup$ – MattDMo Sep 17 '16 at 17:06
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Your friend is incorrect. From Wikipedia:

The word organism may broadly be defined as an assembly of molecules functioning as a more or less stable whole that exhibits the properties of life.

(Viruses are specifically excluded, as they depend on a host cell to fulfill all the functions of life.)

While cells extracted from a multicellular organism like a plant or a person may be able to be cultured in vitro for a time, they cannot survive independently - they require the intervention of humans (or very well-trained monkeys) to obtain nutrients and oxygen, and process/remove waste. A unicellular organism like a bacterium, for example, can handle these functions on its own - it can either synthesize or find a source for its own nutrients, and can reproduce on its own to create more organisms.

The key difference is being self-sustaining. An organism needs to be able to feed itself, take care of its waste, reproduce a full version of itself, respond to stimuli, etc. (see the "properties of life" link above). A single cell from a multicellular organism cannot do all that without assistance (kind of like a virus, actually), while a true unicellular organism can.

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  • $\begingroup$ MattDMo's argument is that a single cell from within a human, if extracted from the body is not perfectly self sustaining. Would it not apply then to a human extracted from our own environment? The middle of space? We could not survive there. So are we not organisms? I myself couldn't find food or water in space that's for sure. Put me in an all you can eat buffet restaurant however, and I assure you I will not starve. Like I said, not much of an answer, but certainly food for thought. $\endgroup$ – R.Hull Sep 16 '16 at 20:18
  • $\begingroup$ What do you make of this answer. If it is correct and your answer is correct, it would seem to mean that cells are alive, but they aren't organisms. But then that would contradict your premise for organism-ness (IE organisms have to be alive). So this sole-upvoted answer would have to be wrong, or your is wrong? One thing to note: a human is no more self-sustaining outside it's environment than a cell is. So maybe this answer does not stand up to scrutiny, even though at first I agreed with it! $\endgroup$ – GreenAsJade Sep 17 '16 at 0:49
  • $\begingroup$ @GreenAsJade This answer is saying that certain cells are alive and not organisms. The criteria specified in this answer are "stable" and "alive"; those cells meet the second criteria but not the first. Based on your comment, you appear to be assuming all cells have the same capabilities - but they do not. $\endgroup$ – Izkata Sep 17 '16 at 4:33
  • $\begingroup$ @R.Hull this entire thing is really a semantic argument in the truest sense of the phrase, as we are arguing about the meaning of a term that ultimately matters very little to the organisms/cells involved. Yes, your space-extraction argument is true to an extent, but I am assuming that the extracted cells are put into a hospitable environment where they can find food, etc. A sulfur-dependent chemosynthetic bacterium from a deep ocean vent won't survive if you just put it in plain tap water, just like a plant won't survive in complete darkness. $\endgroup$ – MattDMo Sep 17 '16 at 16:57
  • $\begingroup$ @GreenAsJade Izkata pretty much got it right. Just because something is alive doesn't mean it's an organism, and one could argue that terminally-differentiated keratinocytes (corneocytes) in the skin are not truly "alive" because they can no longer reproduce. Even many types of lymphocytes, to take the OP's example, cannot reproduce at all, or cannot reproduce alone, in the absence of signals sent from other cells (for example, follicular B cells in the spleen require antigen, Tfh cells, and follicular dendritic cells to send the signals to divide and differentiate into plasma cells). $\endgroup$ – MattDMo Sep 17 '16 at 17:05
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Many large organisms cannot survive without the help of other non-species organisms. For example ~ the ant species "Formica subintegra" cannot survive because they are physiologically unable to forage for and nurse their colony. They must raid other ant colonies to take slave care-givers.

While reading everyone's thoughts & deliberating, I've decided to reject the idea of "life" entirely.

At one stage, life needed to be created from non-life and this process would require the original arrangement of "non living" molecules to have the "properties of life" in order to create life to begin with.

Ex: chemical evolution in lipids.

Let us evaluate a lipid molecule's "properties of life"

(drawing definitions from wikipedia)

Homestasis: Lipids must maintain a molecular balance to be categorized as a lipid, their current state. Like us, this process of seeking balance is largely beyond their "free will" (or conscious awareness). Should either we or they become overcharged with electrons our current state would burn to ash and all functionality as a whole is lost.

Organization: "being structurally composed of one or more cells – the basic units of life"

How is it possible, that cells are established as life and then used to define what life is? I reject this circular thought.

Metabolism: "transformation of energy by converting chemicals and energy into cellular components (anabolism) and decomposing organic matter (catabolism). Living things require energy to maintain internal organization (homeostasis) and to produce the other phenomena associated with life."

Living things require a balance of energy, to be specific. Lipids may not transform energy but they have clear agency that effects 'other' molecules (being polarized) which does include asserting their agency upon the energy within those molecules, we also know they form structures and can create isolated environments for further chemical evolution. Indeed this is a tricky question, but life is a poorly defined concept, queue this forum. <3

Growth, response to stimuli, adaptation, I feel, are answered above. That or I am getting lazy, this took longer than I thought to articulate. I'll stop here and await new thoughts. Thank you for the platform, you're my kind of people, merely by asking this question, regardless of the answer.

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