Read the text below in order to answer questions 24 to 28.

¹ When the sun rises on a warm and sunny day you can see the trumpet-

shaped flowers of the morning glory open up. When they close late in the

³ afternoon primrose flowers open and before daylight arrives the next morning

they close again.

⁵ Biological rhythms, like the opening and closing of flowers happen all over

nature. But not all of them are daily rhythms. Some, like the beating of your

⁷ heart, occur every second. Other rhythms are based on months, seasons or

years.

⁹ Scientists use the term biological clock to describe the timing that controls

biological rhythms. But what is this clock and where can you find it? In animals it

¹¹ is probably controlled by the brain, but in plants and other living things that

have no brain it must be something else.

¹³ The biological rhythms of seashore organisms are connected to the rise and fall of the water. When the tide comes in they open their shells and get food,

¹⁵ when the water goes back the shells close to protect the animals from the dry

air.

¹⁷ The migration of animals is also an event that happens when a signal is sent

out. When days become shorter birds leave the northern parts of the world and

¹⁹ fly south where it is warm and they have enough food. In the summer they fly

back to have babies.

²¹ Humans also have biological clocks that control their daily rhythms. Body

temperature, blood pressure sleeping and waking up have a 24-hour rhythm.

²³ Many illnesses have a yearly rhythm. Colds and flus often happen in winter.

Measles occur mostly during the spring and summer.

²⁵ When people travel by plane from one continent to another they often cross

many time zones. Their internal clocks don’t seem to work correctly. We call this

²⁷ jet lag. It makes you feel tired and it takes many days for your

body’s biological clock to get used to the new place.

²⁹ People who work night shifts also have problems with their biological

clocks. In general, they may not be as alert or active as people who work during

³¹ the daytime. They also have more accidents during work. Sometimes they

ave more health and sleeping problems than other people.

³³ By using the right medicine you can fight off problems that are connected with

different times of day. Heart attacks and strokes often ³⁵ happen in the morning hours—

between the time you get up and noon. Asthma often occurs between midnight and the morning hours. So when people ³⁷ with weak hearts take their medicine right after

waking up it might prevent a heart attack.

³⁹ Biological clocks control many rhythms of life. We are learning more and more

about these rhythms. Doctors are looking for new ways to make travelling more

⁴¹ comfortable and medical treatment more effective.

(http://www.english-online.at/biology/biological-clock/biological-rhythms-in-nature.htm. Acesso em: 10 fev.2104)