1. SubscriberAThousandYoung
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    22 Dec '08 14:571 edit
    I was at a party last night and my wisdom was sought. I was asked three questions that I had a hard time with when I got put on the spot.

    #1: What is the definition of "life"? How come viruses aren't alive? If you say it has to "live on it's own" then what about parasites, and the fact that most life needs to feed on other life?

    #2: What's the difference between a fungus and an animal?

    #3: What's a retrovirus?

    These are not new questions for me, but I had a hard time giving answers. What are the right answers?
  2. Standard memberPBE6
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    22 Dec '08 15:551 edit
    Originally posted by AThousandYoung
    I was at a party last night and my wisdom was sought. I was asked three questions that I had a hard time with when I got put on the spot.

    #1: What is the definition of "life"? How come viruses aren't alive? If you say it has to "live on it's own" then what about parasites, and the fact that most life needs to feed on other life?

    #2: What's the new questions for me, but I had a hard time giving answers. What are the right answers?
    I don't think you have to be embarrassed if you don't know the answers to these, unless you're a biology professor. I'm not, I didn't, and I'm not. 🙂

    #1: What is the definition of "life"? How come viruses aren't alive? If you say it has to "live on it's own" then what about parasites, and the fact that most life needs to feed on other life?

    There's no clear definition of life at present. One of the commonly used criteria used to identify living things is that they need to be able to produce most if not all of the chemicals they need for their own metabolism. As I understand it, viruses don't have a metabolism per se, they just replicate using a host cell as a virus factory, so if you used the proposed criterion you would identify viruses as non-living. However, I don't think this criterion is definitive in any sense (otherwise there'd be no debate about whether viruses are alive or not!).

    #2: What's the difference between a fungus and an animal?

    I originally would have said "a fungus is like a plant", but apparently it's more like an animal:

    http://upload.wikimedia.org/wikipedia/commons/0/09/Tree_of_life.svg

    However, fungi do have cell walls whereas animals do not. There are lots more differences, but that seems to be a pretty fundamental one.

    #3: What's a retrovirus?

    According to Wikipedia:

    "A retrovirus is any virus belonging to the viral family Retroviridae. They are enveloped viruses possessing an RNA genome, and replicate via a DNA intermediate."

    http://en.wikipedia.org/wiki/Retroviruses

    HIV falls into this category.
  3. Joined
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    22 Dec '08 15:592 edits
    Originally posted by AThousandYoung
    I was at a party last night and my wisdom was sought. I was asked three questions that I had a hard time with when I got put on the spot.

    #1: What is the definition of "life"? How come viruses aren't alive? If you say it has to "live on it's own" then what about parasites, and the fact that most life needs to feed on other life?

    #2: What's the new questions for me, but I had a hard time giving answers. What are the right answers?
    I will give my own half-answer to question 1;

    I know that it is part of conventional thinking that viruses are not defined as “alive” and I don’t really understand why that is but, because there is not such thing as “the correct” meaning of a word (such as the word “alive&rdquo😉 because all meanings we assign to words are alternately arbitrary and we can define words which ever way we like and, because I see no good reason why we shouldn’t think of viruses as “alive”, I would say that viruses are “alive” and I don’t believe it is either “correct” or “incorrect” for me to say that.

    However, I would like to know why it is part of conventional thinking that viruses are not defined as “alive” for I have no idea why this is so.
    It may have something to do with viruses not having any respiration but, if so, I think that is a very weak reasoning.
  4. SubscriberAThousandYoung
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    23 Dec '08 15:42
    Originally posted by PBE6
    I don't think you have to be embarrassed if you don't know the answers to these, unless you're a biology professor. I'm not, I didn't, and I'm not. 🙂

    [b]#1: What is the definition of "life"? How come viruses aren't alive? If you say it has to "live on it's own" then what about parasites, and the fact that most life needs to feed on other life?


    There ...[text shortened]... ttp://en.wikipedia.org/wiki/Retroviruses

    HIV falls into this category.[/b]
    I'm a science teacher with a BS in Chemical Biology, so I should know these things.
  5. Joined
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    23 Dec '08 16:552 edits
    Originally posted by Andrew Hamilton
    I will give my own half-answer to question 1;

    I know that it is part of conventional thinking that viruses are not defined as “alive” and I don’t really understand why that is but, because there is not such thing as “the correct” meaning of a word (such as the word “alive&rdquo😉 because all meanings we assign to words are alternately arbitrary and we ...[text shortened]... to do with viruses not having any respiration but, if so, I think that is a very weak reasoning.
    The reason why a virus is not considered alive, is because it's not. It
    actually doesn't do anything on its own, and it requires nothing (or
    extremely little) to stay intact for extended periods of time.

    There's a reason why computer viruses are called... well, viruses. And a
    computer virus makes an excellent example when trying to understand
    exactly how a normal virus works. Just like a real virus, a computer virus
    can't do anything at all on its own. The computer virus is not a program
    in itself (or it would be called malware). Only when loaded by a
    compatible program will the virus be able to do anything, or rather, it will
    by its very structure cause the host program to behave contrary to its
    intended purpose. A real virus is exactly like that in principle. When a
    compatible host cell picks up the virus, the RNA/DNA-encoding that the
    virus is, will cause the cell to alter its own behaviour and function. It can
    duplicate the virus. It can disrupt processes internal to the host
    organism and so on. What the cell does when attached to a virus, is
    what defines the virus itself.

    So, a virus is not a living thing at all, but an encoded structure that when
    it comes in contact with a compatible cell (program) can cause it to wreak
    havoc with the host organism (the system).

    Or so I've been told. 🙂
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    23 Dec '08 17:32
    Originally posted by AThousandYoung
    #3: What's a retrovirus?
    It's a virus very much like the seventies.
  7. Standard memberPBE6
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    23 Dec '08 22:13
    Originally posted by Jigtie
    The reason why a virus is not considered alive, is because it's not. It
    actually doesn't do anything on its own, and it requires nothing (or
    extremely little) to stay intact for extended periods of time.

    There's a reason why computer viruses are called... well, viruses. And a
    computer virus makes an excellent example when trying to understand
    exact ...[text shortened]... cause it to wreak
    havoc with the host organism (the system).

    Or so I've been told. 🙂
    The reason why a virus is not considered alive, is because it's not.

    You have been misinformed. There is currently a debate in the scientific community about whether viruses are living or non-living.

    There's a reason why computer viruses are called... well, viruses.

    Yes, there is. It's because they model viral behaviour, not simply because they are considered non-living or the fact that they manipulate the host organism into virally beneficial behaviour. Most parasites behave in a similar manner, a striking example being the nematomorpha parasite that persuades grasshoppers to commit suicide in order for it to procreate:

    http://en.wikipedia.org/wiki/Hairworm
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    23 Dec '08 22:216 edits
    Originally posted by Jigtie
    The reason why a virus is not considered alive, is because it's not. It
    actually doesn't do anything on its own, and it requires nothing (or
    extremely little) to stay intact for extended periods of time.

    There's a reason why computer viruses are called... well, viruses. And a
    computer virus makes an excellent example when trying to understand
    exact cause it to wreak
    havoc with the host organism (the system).

    Or so I've been told. 🙂
    …It actually doesn't do anything on its own, and it requires nothing (or
    extremely little) to stay intact for extended periods of time. .…


    That is also true for certain disease-causing bacteria and also certain parasitic worms -outside the body they are in the form of dormant spores (or dormant eggs in the case of the worms) that, just like viruses, “requires nothing (or extremely little) to stay intact for extended periods of time” while they are not inside a living host.
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    23 Dec '08 22:26
    One possible definition of life is 'the ability to self assemble, (see Jacob and Monod, Chance and Necessity). In this repect, viruses are alive. But, so are crystals!
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    23 Dec '08 23:19
    Sounds like a great party
  11. Standard memberblack beetle
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    24 Dec '08 05:36
    Originally posted by Silent Pawn
    Sounds like a great party
    😀😀
  12. Devonshire
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    24 Dec '08 18:23
    Originally posted by Silent Pawn
    Sounds like a great party
    LOL...merry christmas!
  13. Devonshire
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    24 Dec '08 18:25
    Originally posted by PBE6
    I don't think you have to be embarrassed if you don't know the answers to these, unless you're a biology professor. I'm not, I didn't, and I'm not. 🙂

    [b]#1: What is the definition of "life"? How come viruses aren't alive? If you say it has to "live on it's own" then what about parasites, and the fact that most life needs to feed on other life?


    There ...[text shortened]... ttp://en.wikipedia.org/wiki/Retroviruses

    HIV falls into this category.[/b]
    "Animals don't have cell walls" You sure about that?
  14. SubscriberAThousandYoung
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    25 Dec '08 12:38
    Originally posted by Silent Pawn
    Sounds like a great party
    I'm a wild man.
  15. Standard memberPBE6
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    26 Dec '08 03:00
    Originally posted by divegeester
    "Animals don't have cell walls" You sure about that?
    Yep. They definitely have cell membranes, but not cell walls:

    http://en.wikipedia.org/wiki/Cell_wall
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