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What is life

  1. Mar 15, 2006 #1

    wolram

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    I think if a human had no senses then life would be a mute point, the same for single celled organisms, they fit with our definition of life, but surly if an
    organism can not sense its world is it alive ?
     
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  3. Mar 15, 2006 #2

    Ouabache

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    Do you know of an organism that cannot sense its world?
    If not, this sounds like a philosophical question.:rolleyes:
     
    Last edited: Mar 16, 2006
  4. Mar 15, 2006 #3

    wolram

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    As in my first post a human could be comatos and still be alive, ie have no
    sense of its suroundings, philosophy does not enter the question.
     
    Last edited: Mar 15, 2006
  5. Mar 16, 2006 #4
    Well, it depends on what is meant by "sensing the outside world". Even a single cell continuously exchanges stuff with the external world, be it big macromolecules or small molecules. And a whole series of internal or external mechanisms arise due to this exchange. Isn't this kind of sensing? For a man in coma, the exchange still goes on, and the body reacts in some way. The problem for men is consciousness, not life itself.

    J
     
  6. Mar 16, 2006 #5

    DocToxyn

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    Wolram, I think you are dancing around the issues of biological basis of life, which we have discussed here before, and quality (or perhaps sensation) of life. These are arguably separate issues. Since you use the topic of senses lets look at it this way, is a blind person slightly less alive than a person with all their senses? How about someone who is blind and deaf...even less alive? What about someone that has intact senses, but lacks the ability to respond to them, i.e. quadriplegics? I'm not trying to invalidate your questions, just trying to put a different perspective to them.
     
  7. Mar 16, 2006 #6

    wolram

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    Hi Doc, i am just trying to understand what life is.

    is a prion alive, is a virus alive, is a computer virus alive, they all have some of the definitions for life.
    us humans are just water and a few chemicals, what is the magic ingredient that makes us alive ?
     
  8. Mar 16, 2006 #7

    selfAdjoint

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    Prion, no.
    Virus no.
    Computer virus, no.


    Us, and bacteria, and cellular life in general, yes.

    The reasons, as Doc Toxyn says, have been discussed before. Look 'em up.
     
  9. Mar 16, 2006 #8

    DocToxyn

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    Key word...some. One must have all the requirements in order to satisfy the definition, you can't be mostly alive (or dead, although Billy Crystal's character in the Pricess Bride might argue with that!). Also there is no magic ingredient that makes life, it is the sum or result of the processes that those ingredients are involved in that ultimately add up to life.
     
  10. Mar 16, 2006 #9

    wolram

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    Where are the relevant pages please i have looked.
     
  11. Mar 16, 2006 #10
    The common features that are generally agreed upon:

    1. catalyze reactions faster than they'd occur inorganically
    2. bound yourself from your environment
    3. Reproduce yourself.
    4. Be autonomous

    there are grey areas.

    The definition is not particularly useful. If I'm comatose my quality of life is nil though my cells meet the criteria for life. Many entities meet some of the requirements but not all. Many things are inarguably live but can't (for example) reproduce (sterile) or some such. Some things like obligate parasitic bacteria are not much more than a virus - but classified as alive even though they can't live outside a host cell.

    It's not a clean topic. Bush's 'culture of life' makes less sense still.

    Why do you ask? that might be a more fruitful way to get at a useful answer.
     
  12. Mar 16, 2006 #11

    wolram

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    Patylou, i ask the question so that life can be recongnizied in any envirioment, (is) our definition of life fool proof?
     
  13. Mar 17, 2006 #12

    DocToxyn

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    Last edited by a moderator: Apr 22, 2017
  14. Mar 19, 2006 #13

    Ouabache

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    I believe you have answered your own question. A human may be comatose and still is alive. A few others have given good explanations with regard to your initial query.

    Let me also expand here. I differ with your description, that the comatose human does not sense its surroundings. If a comatose person is too warm it perspires, if too cold it shivers, if it needs oxygen it breathes. The first two are the result of directly sensing of its surroundings. The third is a biological requirement. If oxygen is deficient in the surroundings (e.g. underwater, atop high mountains, outerspace), humans react by gasping for air, as a result of sensing their surroundings.
     
    Last edited: Mar 20, 2006
  15. Mar 19, 2006 #14
    There are times when I am convinced that a single-celled organism is more alive than most humans.

    However, this would be wrong because humans are nothing more that a collection of single celled organisms.:eek:
     
  16. Mar 20, 2006 #15

    selfAdjoint

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    Au contraire, a human, or any metazoan is a multicellular system. Those single cells are not free living organisms but are specialized and integrated by intracellular processes.
     
    Last edited: Mar 20, 2006
  17. Mar 22, 2006 #16
    I view the "biological virus" to be alive as compared to the "computer virus" which is not alive. It is of course a matter of definition, I define "life" as "self generated action mediated by DNA". All forms of life meet this definition, thus the biological virus is alive, the computer virus not. The more common list of life characteristics we find in biology textbooks occur within the host cell of the virus, very common in any parasitic mode of life. Prions, being only composed of protein, also do not meet my definition of being alive. Of course my view is open to attack.
     
  18. Apr 3, 2006 #17
    Would your interpretation of the differenciation of cells translate to a "system" of autoworkers doing specifically designated and differenciated tasks? Do we not consider them each an individual organism?

    And what category would a Macrophage belong to? Or a Stem Cell? And even more interestingly the Mitochodria (so-called organelle) has its own DNA. It is its own closed system... it can convert enough ADP to ATP to feed an entire cell... as well as itself.

    I'll give you the obvious point in that unicelled organisms have evolved, adapted and developed (over many billions of years) to the point where they have found a better survival route through cooperative living... thus, we view this unwitting "accomplishment" as an individual"organism" or "compilation of differenciated cells".
     
  19. Apr 3, 2006 #18
    This could theortically possible some day.Some day there might bugs formend on by humans and they somehow mutate and they enventrally start reproducing with other peoples computers.
     
  20. Apr 4, 2006 #19

    DaveC426913

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    Your definition of life has the DNA molecule as a requirement?
     
  21. Apr 5, 2006 #20
    Yes. If you disagree [which I see is the argument of Taoist]please provide a single example of a form of life on earth that does not contain DNA. To be alive, one must "survive" and "reproduce". Highly complex proteins perhaps can do the first, but not the second. The virus contains DNA, it can survive and reproduce (does not matter where in space and time), it is alive.
     
  22. Apr 7, 2006 #21
    A virus contains either V(viral)DNA or VRNA. This is a much less evolved form of RNA or DNA. The structure of this molecule is simple and always single stranded... which does not really class it as the DNA we know.

    It cannot reproduce without a host cell that it can utilize as a "factory" to produce more copies of it self. Any mutation (ie:evolution) that takes place in a virus must take place when it has found a host cell. It has been speculated that a virus can withstand the rigors of outerspace but it wil not be reproducing there unless it gets under the suit of someone doing an EVA, and into one of their cells.

    Here's one explaination:

    http://www.epidemic.org/theFacts/viruses/anatomyOfTheVirus.html [Broken]
     
    Last edited by a moderator: May 2, 2017
  23. Apr 8, 2006 #22
    Yes, thank you...but of course DNA and RNA in whatever form are always polymers of nucleotides, with DNA having sugar deoxyribose and RNA sugar ribose. Thus, to be more specific, you are correct, I must modify my definition of life to: life = self generated action mediated by nucleic acid (either DNA or RNA). I care not what form of nucleic acid (primitive or advanced)--nor where in space-time the reproduction occurs (in a host cell or not). The facts are (1) virus have self generated action (2) virus have nucleic acids (3) virus survive over time (4) virus reproduce in a very specific manner (5) virus evolve---virus are alive.
     
  24. Oct 3, 2007 #23
    Viruses are not living.

    To be living, something must gather energy (metabolism) and react dynamically to its environment (homeostasis). Viruses are essentially lazy floating pieces of genetic material with a protein shell, sort of like a CD-R in a leather case. If, for some reason, that piece of genetic material happens to be able to enter an organism and make the organism "print" more copies, it's still not gathering energy or responding to it's situation.

    On the macro scale, this is less clear. Viruses as populations can react to their environment through microevolution in the same way that those .01% of bacteria that Lysol can't kill will eventually become the new generation of successful bacteria. But this isn't happening on the level of individual organisms.

    What is confusing to me is the line between collecting energy and stealing it from your host cell. Viruses use the energy collected by cells to replicate and build protein shells for their viral offspring, but again, this energy isn't being processed by the individual virus.
     
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