Why are anaerobic organisms simple and aerobic organisms complex?

Michael Kolotila x3887 mkolotila at NECCADM1.NECC.MASS.EDU
Tue Nov 28 09:26:07 EST 1995


Hi Jonathan;
You have a good point.  The point that I was trying to make was that 
aerobic organism, such as bacteria, are as "simple" as anaerobic 
bacteria.  However, when you become multicellular over a certain size gas 
exchange for metabolism becomes a problem along with waste, nutrient, and 
heat transfer.  Also, since anaerobic bacteria do not use oxygen as their 
terminal electron acceptor, the can use other substances and if my 
understanding is correct generate as much energy as aerobe.  One 
Clostridium, an anaerobe, has a generation time under ideal conditions of 
8 minutes.  I find it hard to believe that it can derive enough energy 
from glycolysis or fermentation to support that type of growth rate.  
Rather they use inorganic substances such as sulfur or organic substances 
such as carbon for their terminal electron acceptor.  Hope that this 
addresses your questions.  I suppose I thought that I was answering the 
question I thought she was asking, since the most complex aerobic 
organisms are multicellular.
Michael

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 Michael P. Kolotila, Ph.D.        * e-mail: mkolotila at neccadm1.necc.mass.edu   
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On 27 Nov 1995, Jonathan Ewbank wrote:

> in answer to the question in the subject line,
> 
> mkolotila at NECCADM1.NECC.MASS.EDU (Michael Kolotila x3887) wrote:
> 
> >Hi Joy;
> >It is a matter of being multicellular.  Aerobic bacteria have a level of 
> >complexity on par with anaerobic bacteria.  However, when you are 
> >multicellular gas exchange through diffusion becomes a problem.  
> >Diffusion is effective over short distances.  Open a bottle of perfume in 
> >a room and see how it takes to reach the other side.  So with 
> >multicellular organisms it becomes neccessary to specialize cells into 
> >structures that will transport oxygen to all of the cells.  Then you can 
> >expand the problem to nutrients and waste removals.  The upshot is that 
> >you engineer a complex organism.
> >Hope that this helps.
> 
> perhaps i am failing to understand your answer correctly, but it doesn't 
> seem to address the question asked. it's a reasonable explanation for why 
> aerobic multicellular organsims need specialized structures, but if an 
> organism is anaerobic, by definition it would not be limited by diffusion 
> of oxygen. i suspect the answer is that complexity requires energy, and 
> the amount of energy available through aerobic respiration significantly 
> exceeds that available through anaerobic metabolism.
> 
> j.
> 
> 
> ewbank at monod.biol.mcgill.ca
> 
> 



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