|Is there a living thing that does not move? |
That´s an interesting question. There are lots
of organisms that are sessile--- meaning that they
don´t move-at least after they´ve reached a
certain point in their life. For example, lots of
plants release seeds that move by wind, water, or
by catching a ride with animals (for example the
fluffy seeds of dandelions or the bristly seeds of
thistle), but once they land in a spot where they
can grow, they put out roots and don´t move for
the rest of their lives (they too might release
seeds that can move away from the parent plant
though). Similarly, many marine organisms, like
oysters and sponges (to name a few) move through
the water by drifting early in their life (this is
called a `pelagic stage´) but once they settle in
an area, like a rocky sea surface, they will
attach for life. That´s how features like oyster
beds and coral reefs form!
There are some living organisms that don't
move. Two examples are adult barnacles and coral!
In the field of biology, we have defined a set
of requirements that characterize what a living
thing is. One of the requirements is that living
things respond to stimuli, and usually this means
motion. Essentially all living things move, even
if they move very slowly (like plants growing
toward the sun), or rarely (like coral, which only
moves when its survival is threatened by danger or
lack of food), or only during one phase of their
lifetime (like female scale insects, which crawl
as juveniles, but become immobile as adults).
There may be exceptions out there because Earth is
a wild place and organisms exist that defy our
efforts to categorize and organize them, but it's
safe to say that most all living things move.
Good question! For an organism to move, it
must have specialized parts designed to give it
motion. For example, in small bacteria, there
might be flagella (microscopic tails) or hairs
that can be triggered to flex or rotate in order
to produce motion. In larger animals like humans,
specialized tissue called muscle can contract and
expand, permitting rotation and movement at a
macroscopic level. So by these definitions, there
could be many things that do not move. A great
majority of plants, for instance, lack specialized
tissue to move. But plants are okay with that,
because while most organisms need to move to find
and collect food, a plant’s big “food” source is
the Sun, and it’s always in the sky so plants
don’t need to move!
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