Ask A Scientist© Molecular Biology Archive

name       michelle
status     student
age        15

Question - What is the scientific name of the smallest organism??

Dear Michelle,
Your question hits one of the fundamental questions of
life: what is an organism? What do you define as
necessary for life, what are the requirments to be an
organism? Let's define an organism as a living thing
that is able to live independent of other organisms,
that has a metabolism, and that reproduces with
offspring identical to the parent. I guess the
smallest organisms would be bacteria. Bacteria differ
in size but the lower limit of the length of the
bacterial body would roughly be 1 micrometer (a
thousand's of a milimeter).
However, when you include organisms that live as
parasites on, or in, others, then viruses are
included, and these are much smaller than bacteria. It
would be acceptable to include parasites, because
parasitic life forms are also found with bigger
organisms (bacteria, worms, etc). There is no
fundamental reason to exclude parasites as living
organisms. Therefore, viruses can be included as
organisms, thus, they are the smallest living
organisms. They have a metabolism, they have DNA or
RNA for reproduction (although they use the machinery
of their involuntary host cells to do so), their
offspring is identical to the parents. Does that
satisfy your interpretation of a living organism?

Viruses are built of RNA (or DNA) wrapped in proteins.
They have different shapes and sizes.

Your question exemplifies how scientific answers
depend on precise definitions. You can train yourself
to be specific in the question you want to ask. Then
you design a hypothesis that can be tested.

This is not to say that science is narrow-minded. Once
you have set your definitions and designed your
hypothesis, you try to find the flaws. In the example
above, I started with a definition (which included
that organisms must live independently) and I tested
if all organisms were included in that definition.
Then I decided that parasites were incorrectly
excluded, and I had to alter my definition. A
scientist always tries to find the one observation
that does not fit the hypothesis, and then examines if
the observation is true, and thus if the hypothesis
is not correct and in need of refinement.

You can question basically every hypothesis. When you
do that, you enter the field of phylosophy. How do you
define life, what is your definition of an organism?
Can you come up with a hypothesis to test if your
definition is correct? These are great things to think
about, and excellent training for every scientist and
scientist-to-be.

Have fun!
Trudy
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