A chicken lays an egg.You feel sleepy.And a tree loses its leaves.All of these things,and many more,happen in a certain way,at a certain time each day or each year.They take place because of something called an internal clock.The word internal means "inside of",and the internal clock is inside a certain part of every plant and animal.For example,there is an internal clock in the head of a chicken.
The internal clock receives a signal or message from the world around it.Some of these signals include light,heat,darkness and cold.When the internal clock gets the signal,the body of the plant or animal produces a chemical that causes the living thing to do different actions.For example,daylight signals the chicken's internal clock to make a chemical.Then this chemical causes the chicken to lay eggs.
People are learning a lot about internal clocks.Farmers have even learned how to fool a chicken's internal clock so that the chicken lays more eggs!
( )1.A signal is ______________.
A.a chemical B.a message C.internal D.inside
( )2.The clock described in the story is called internal because it ___________.
A.means "inside of" B.is inside every plant or animal
C.never stops running D.produces a signal
( )3.Which of the following can be the signal to a tree?
A.The sky is clear. B.Farmers have their harvest.
C.Leaves fall down the tree. D.the day gets cooler and cooler
( )4.In the chain of events below,what is missing? Daylight acts as a signal.A chicken's
internal clock receives the signal.—?—The chicken lays an egg.
A.The chicken moves its body. B.The chicken is fooled by the farmer.
C.The chicken makes a chemical D.The chicken sees the daylight.
( )5.What do you think farmers do to make chickens lay more eggs? They_________.
A.make the chickens do different actions
B.keep the chickens in a cooler place
C.feed the chickens a special chemical
D.turn on lights in the chicken house at night
1B 2B 3C 4C 5D
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