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Multicelular Organisms and Cell Colonies

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Multicelular Organisms and Cell Colonies

Postby thorwaldsenb » Tue Mar 22, 2005 12:38 am

Hi, I'm studying biology in the university and I'm looking for help on a question I need to answer... How can we or how do biologists define the difference between a multicellular organism like a protist algae and a colony of single-celled creatures like bacteria? Thanks for any answers and/or links to papers on the subject!

p.s. I'm new here so if I'm going about this forum thing the wrong way, I mean no offense! :wink:
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Postby Poison » Thu Mar 24, 2005 4:09 pm

As much as I know colonies (like volvox) have specialized cells for certain activities like reproducion. But colonies cannot form tissues while multicellular organisms can.
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Postby 2810712 » Fri Mar 25, 2005 10:14 am

The division of labour is done to a lesser degree in colonies of microbes , sometimes it is even absent . But, the same is seen in multicellulars to a higher degree. Thus, the cells in a colony are less differentiated , than the cells in a tissue. Thus , the members of a colony depend on each others to a lesser extent than those in multicellulars, tha's why we don't group them to a single organism.

hope this helps.

thanks,

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Postby MrMistery » Fri Mar 25, 2005 8:58 pm

If you cut a colony in half the members will probably survive but what were to happen if someone were to cut you or me in half???
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Postby thank.darwin » Sat Mar 26, 2005 4:14 pm

In our body cells are specialized to carry out certain tasks... If for any reason we were to be cut in half our body would be separated from organs that carry out specific tasks... the heart would not get blood to the whole body... I could list a hundred things that would go wrong... :lol: - Don't make me :lol:
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Postby mith » Sat Mar 26, 2005 6:14 pm

@MrMystery

Worms can survive when cut in half even though it's a multicellular. Also note that cells such skin cells can survive in culture even when separated from the organism itself.
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Postby MrMistery » Sat Mar 26, 2005 6:51 pm

I said you or me mithrill. Do you consider yourself a worm? :D :D
Skin cells can survive in culture but only in culture. Without an external food source they die
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Postby thorwaldsenb » Sat Mar 26, 2005 7:59 pm

OK, first of all, thanks a lot for the explanations, I've almost got this straight. Let me try to summarize what I've learned so far:

Unicellular organisms are made of one cell that can survive alone, although it can interact with other organisms.

Colonies are groups of unicellular organisms that could survive alone if separated (because of the above definition), but they benefit greatly from their interaction, sometimes reaching such a degree of organization that they divide the tasks to be done (like ants for example).

Multicellular organisms are groups of cells that have evolved to cooperate with each other to a degree that they could not live alone since they are specialized to do only some specific tasks, and need the other cells to complement them.

Of course, nothing is black and white, so there is a grey zone, like for example in the Volvox colonies, where they might be able to survive alone, although they are highly specialized (having specific sexual cells for example).

There are some questions left. What about simbiotic organisms? Those might be as simple as two cells living together (take the case of lichen, made of an algae with a fungus), but one could argue that they cannot live without each other, since each one is specialized to do something diferent, and they must complement each other. Does that make them a colony? a pluricellular organism?
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Postby biostudent84 » Sun Mar 27, 2005 5:04 am

I had trouble with this question a long time ago. Then I learned what I believe to be the most prominent difference.

A multi-cellular organism, like you or me, has identical DNA in all our cells.
A colony, like streptococcus, is a network of different organisms, so two samples of DNA from differing cells would not be identical.
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Postby James » Sun Mar 27, 2005 3:30 pm

biostudent84 wrote:A multi-cellular organism, like you or me, has identical DNA in all our cells.A colony, like streptococcus, is a network of different organisms, so two samples of DNA from differing cells would not be identical.


Even between cells doing the same job?
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Postby mith » Sun Mar 27, 2005 5:18 pm

@MrMistery
Shhh, you're not supposed to know

@thorwaldsenb
In symbiotic relationships, it depends on how attached the two organisms are. You could argue that eukaryotic cells are symbiotic since theres organelles within the cell. And of course if one dies out, the other dies too.

Concerning lichens, if lichens are placed in a dark place, the fungus will soon devour its algal partner, while the reverse happens if the lichen...well I forget but if the environment doesn't accomodate the fungus, the algae lives by itself since the fungus dies.

If you have time read "acquiring genomes." Quite informational book about symbiots and evolution of species. And then again you should also read spiderman comics :D.
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Postby MrMistery » Sun Mar 27, 2005 7:14 pm

Lichens are considered dual organisms. Butin a forest, besides lichens you will also find algae and fungus living by themselves: since it is much easy to live together there will be a lot more lichens though...
No matter what the example, symbiotic organisms are not considered as being a colony, nor a single organism. They are simply simbiotic organisms :D :D
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