Why are anaerobic organisms simple and aerobic organisms complex?

Jonathan Ewbank ewbank at monod.biol.mcgill.ca
Mon Nov 27 13:43:56 EST 1995

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.


ewbank at monod.biol.mcgill.ca

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