WASHINGTON — Like kids taking apart a fine Swiss watch,
scientists are laboring to understand what makes the biological
clock that's inside every living creature tick. Researchers have
long known that bacteria, flies, worms, flowers, oak trees and
human beings all have tiny internal timepieces that keep them on
a roughly 24-hour cycle, the time it takes the Earth to spin
once on its axis. ``Living cells can actually tell the time and
use this information to control their behavior,'' said Hugh
Nimmo, a plant biologist at the University of Glasgow, Scotland,
Many questions remain to be answered, however, such as how the
clocks work at the level of individual molecules. To find out,
some scientists are building simple biological clocks in a test
tube. ``If you can build it, you really understand it,'' said
Jonathan Arnold, a geneticist at the University of Georgia in
Athens. ``It's very important that we know how the clock works
at the molecular level.'' `` Biological timekeeping is a core
property of life on a