A Biological Clock
Every living thing has what scientists call a biological clock that
controls behavior. The biological clock tells (51) when to
form flowers and when the flowers should open. It tells (52)
when to leave the protective cocoons and fly away, and it tells animals and
human beings when to eat, sleep and wake. Events outside the
plant and animal (53) the actions of some biological clocks.
Scientists recently found, for example, that a tiny animal changes the color of
its fur (54) the number of hours of daylight. In the short
(55) of winter, its fur becomes white. The fur becomes gray
brown in color in the longer hours of daylight in summer. Inner
signals control other biological clocks. German scientists found that some kind
of internal clock seems to order birds to begin their long migration
(56) twice each year. Birds (57) flying
become restless when it is time for the trip, (58) they
become calm again when the time of the flight has ended.
Scientists say they are beginning to learn which (59)
of the brain contain biological clocks. An American researcher, Martin Moorhead,
said a small group of cells near the front of the brain (60)
to control the timing of some of our actions. These (61)
tell a person when to (62) , when to sleep and when to seek
food. Scientists say there probably are other biological clock cells that
control other body activities. Dr. Moorhead is studying
(63) our biological clocks affect the way we do our work.
For example, most of us have great difficulty if we must often change to
different work hours. (64) can take many
days for a human body to accept the major change in work hours. Dr. Moorhead
said industrial officials should have a better understanding of biological
clocks and how they affect workers. He said (65)
understanding could cut sickness and accidents at work and would help increase a
factory’s production.
