World Builders™                                                                   Session Four --  Microbiology             

         The Three Domains   

Scientists have divided all life forms on earth into three domains.

     Scientists are looking for the roots of life, looking for the first organisms that appeared on earth.  Was there one cell from which all other life forms are descended?  So far the answer seems to be no.  LIfe may have come out of a community of tiny organisms struggling to be alive.

     One way of studying this is to compare the DNA of different species of micro-organisms and also of more complex life forms.  So far the scientists have not found one cell that is the beginning of everything alive here.  Rather they have found hints of our beginnings which are intriguing. 

     Based on what they know today, scientists have divided living creatures into three domains.  

     Each domain consists of groups of life forms that are related to each other and have characteristics in common.  We are looking at these domains now because they are the most fundamental divisions of life forms.  These domains describe the characteristics of every living creature that we know about.  Learning about them is an important part of this unit.

Choose the domain that you would like to read about next.

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