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As bananas ripen, the green skin turns yellow gradually.Chemical changes occur in the flesh of the fruit as well: starch (淀粉) changes to sugar; pectin(果胶)breaks down, losing its stiffness; and the flesh softens.

       Is ripening fruit a self-contained system, or is the rate of these changes affected by the environment? We designed the experiment below to see if different atmospheres, produced by different packaging, affected the rate of ripening.You will vary the atmosphere surrounding unripe bananas and observe the effect on the ripening process.

       Now set up the bananas in their environments as follows:

       1.Put two green bananas in a paper bag and fold the top over to seal out the air.

       2.Put one green banana and the very ripe banana in the other paper bag and fold over the top.

       3.Put two green bananas in a plastic bag and seal it.

       4.Wrap (包) one green banana tightly in a plastic bag.

       5.Leave one green banana exposed to the air.

       Leave the fruit alone for four or five days to ripen.Ripening fruit "breathes".This means that it takes up oxygen and gives off CO2.Oxygen is extremely important and necessary for the chemical reactions involved in ripening.In addition, ripening fruit gives off another gas, called ethylene (乙烯).Not only is ethylene a product of ripening fruit, it also promotes the further ripening of the fruit.

    Paper bags tend to keep the ethylene in, but they allow oxygen and ethylene to pass through slowly.Plastic bags do not allow the free flow of oxygen or ethylene.In this experiment, the green banana in paper bag with the ripe banana should ripen most quickly.The green bananas in the paper bag should ripen faster than the bananas in the plastic bag.The banana left exposed to air has an unlimited supply of oxygen, so it will turn brown most quickly.You will notice that the side of this banana that rests on the counter will ripen more quickly than the other sides, because it has the closest contact (接触) with its own ethylene.The banana that is tightly wrapped in plastic has no oxygen supply and should ripen most slowly.Now can you see why bananas are sealed in plastic in many supermarkets?

1.What makes the green banana in Bag 2 ripen more quickly than the ones in Bag 1?

       A.Ethylene from the very ripe banana.  B.The free flow of oxygen or ethylene.

       C.CO2 from the very ripe banana.      D.The limitation of oxygen supply.

2.How can we slow down the ripening of bananas exposed to the air?

       A.To rest them on the counter.            B.To keep them in the basket.

       C.To put them on the ground.              D.To hang them up from the ceiling.

3.It can be concluded from the passage that ____.

       A.the ripening banana is a self-contained system

       B.the rate of ripening bananas is affected by the environment

       C.wrapped bananas experience no chemical changes to ripen

       D.ripening bananas give off oxygen, CO2 and ethylene

4.Why are bananas sealed in plastic in many supermarkets?

       A.To make them ripen more quickly.      B.To make them ripen more slowly.

       C.To make banana flesh soften.            D.To turn green bananas yellow.

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    Although the cat doesn’t realize this, its body is getting ready for action.

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    Something like this also happens to people. When we are excited, angry, scared, or aroused by other emotions, our bodies go through many physical changes. Our hearts beat faster, and our muscles get tense. All of these changes make us more alert and ready to react. We, too, get ready to defend ourselves or run.

    Human beings, however, have a problem that animals never face. If we give way to our feelings and let them take over, we can get into trouble. Have you ever said something in anger—or hit somebody—and regretted it later? Have you ever shouted at a teacher, told somebody you were lonely or said you were in love, and then wished later you had kept your mouth shut? It isn’t always wise to express your feelings freely.

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    Feelings that you keep all bottled up inside don’t just go away. It’s as if you bought some bananas and stuck them in a cupboard. You might not be able to see them, but before long you’d smell them. And if you opened the cupboard, chances are that you’d see little fruit flies hovering all over them. They’d be rotten.

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72. It’s mentioned in the passage that human beings get into trouble because ______.

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    As bananas ripen, the green skin turns ye11ow gradually. Chemical changes occur in the f1esh of the fruit as well:starch(淀粉)changes to sugar;pectin(果胶)breaks down,losing its stiffness; and the f1esh softens.
Is ripening fruit a self-contained system, or is the rate of these changes affected by the environment? We designed the experiment below to see if different atmospheres, produced by different packaging, affected the rate of ripening. You will vary the atmosphere surrounding unripe bananas and observe the effect on the ripening process。
Now set up the bananas in their environments as follows:
1. Put two green bananas in a paper bag and fo1d the top over to seal out the air.
2.Put one green banana and the very ripe banana in the other paper bag and fold over the top.
3. Put two green bananas in a plastic bag and seal it.
4. Wrap(包)one green banana tightly in a plastic bag.
5. Leave one green banana exposed to the air.
Leave the fruit a1one or five days to ripen. Ripening fruit“breathes”. This means that it takes up oxygen and gives off C02. Oxygen is extremely important and necessary for the chemical reactions involved in ripening. In addition, ripening fruit gives off another gas, called ethylene(乙烯). Not only is ethylene a product of ripening fruit, it also promotes the further ripening of the fruit.
Paper bags tend to keep the ethylene in, but they allow oxygen and ethylene to pass through slowly. Plastic bags do not allow the free flow of oxygen or ethylene. In this experiment, the green banana in paper bag with the ripe banana should ripen most quickly. The green bananas in the paper bag should ripen faster than the bananas in the plastic bag. The banana left exposed to air has an unlimited supply of oxygen, so it will turn brown most quickly. You will notice that the side of this banana that rests on the counter will ripen more quickly than the other sides, because it has the
closest contact(接触)with its own ethylene. The banana that is tightly wrapped in plastic has no oxygen supply and should ripen most slowly. Now can you see why bananas are sealed in plastic in many supermarkets?
72. What makes the green banana in Bag 2 ripen more quickly than the ones in Bag 1?
A. Ethylene from the very ripe banana.            B. The free flow of oxygen or ethylene
C. C02 from the very ripe banana.                     D. The limitation of oxygen supply.
73. How can we slow down the ripening of bananas exposed to the air?
A. To rest them on the counter.                                   B. To keep them in the basket.
C. To put them on the ground.                                     D. To hang them up from the ceiling
74. It can be concluded from the passage that          .
A. the ripening banana is a self-contained system
B. the rate of ripening bananas is affected by the environment
C. wrapped bananas experience no chemical changes to ripen
D. ripening bananas give off oxygen, C0, and ethylene
75. Why are bananas sealed in plastic in many supermarkets?
A. To make them ripen more quickly.                B. To make them ripen more slowly.
C. To make banana flesh soften.                        D. To turn green bananas yellow.

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Is ripening fruit a self-contained system, or is the rate of these changes affected by the environment? We designed the experiment below to see if different atmospheres, produced by different packaging, affected the rate of ripening. You will vary the atmosphere surrounding unripe bananas and observe the effect on the ripening process。

Now set up the bananas in their environments as follows:

1. Put two green bananas in a paper bag and fo1d the top over to seal out the air.

2.Put one green banana and the very ripe banana in the other paper bag and fold over the top.

3. Put two green bananas in a plastic bag and seal it.

4. Wrap(包)one green banana tightly in a plastic bag.

5. Leave one green banana exposed to the air.

Leave the fruit a1one or five days to ripen. Ripening fruit“breathes”. This means that it takes up oxygen and gives off C02. Oxygen is extremely important and necessary for the chemical reactions involved in ripening. In addition, ripening fruit gives off another gas, called ethylene(乙烯). Not only is ethylene a product of ripening fruit, it also promotes the further ripening of the fruit.

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closest contact(接触)with its own ethylene. The banana that is tightly wrapped in plastic has no oxygen supply and should ripen most slowly. Now can you see why bananas are sealed in plastic in many supermarkets?

72. What makes the green banana in Bag 2 ripen more quickly than the ones in Bag 1?

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C. C02 from the very ripe banana.                     D. The limitation of oxygen supply.

73. How can we slow down the ripening of bananas exposed to the air?

A. To rest them on the counter.                                   B. To keep them in the basket.

C. To put them on the ground.                                     D. To hang them up from the ceiling

74. It can be concluded from the passage that          .

A. the ripening banana is a self-contained system

B. the rate of ripening bananas is affected by the environment

C. wrapped bananas experience no chemical changes to ripen

D. ripening bananas give off oxygen, C0, and ethylene

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A. To make them ripen more quickly.                B. To make them ripen more slowly.

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    Now set up the bananas in their environments as follows:

1. Put two green bananas in a paper bag and fo1d the top over to seal out the air.

    2.Put one green banana and the very ripe banana in the other paper bag and fold over the top.

    3. Put two green bananas in a plastic bag and seal it.

    4. Wrap(包)one green banana tightly in a plastic bag.

    5. Leave one green banana exposed to the air.

    Leave the fruit a1one or five days to ripen. Ripening fruit“breathes”. This means that it takes up oxygen and gives off C02. Oxygen is extremely important and necessary for the chemical reactions involved in ripening. In addition, ripening fruit gives off another gas, called ethylene(乙烯). Not only is ethylene a product of ripening fruit, it also promotes the further ripening of the fruit.

Paper bags tend to keep the ethylene in, but they allow oxygen and ethylene to pass through slowly. Plastic bags do not allow the free flow of oxygen or ethylene. In this experiment, the green banana in paper bag with the ripe banana should ripen most quickly. The green bananas in the paper bag should ripen faster than the bananas in the plastic bag. The banana left exposed to air has an unlimited supply of oxygen, so it will turn brown most quickly. You will notice that the side of this banana that rests on the counter will ripen more quickly than the other sides, because it has the

closest contact(接触) with its own ethylene. The banana that is tightly wrapped in plastic has no oxygen supply and should ripen most slowly. Now can you see why bananas are sealed in plastic in many supermarkets?

72. What makes the green banana in Bag 2 ripen more quickly than the ones in Bag 1?

A. Ethylene from the very ripe banana.            B. The free flow of oxygen or ethylene

C. C02 from the very ripe banana.                     D. The limitation of oxygen supply.

73. How can we slow down the ripening of bananas exposed to the air?

A. To rest them on the counter.                                   B. To keep them in the basket.

C. To put them on the ground.                                     D. To hang them up from the ceiling

74. It can be concluded from the passage that          .

A. the ripening banana is a self-contained system

B. the rate of ripening bananas is affected by the environment

C. wrapped bananas experience no chemical changes to ripen

D. ripening bananas give off oxygen, C0, and ethylene

75. Why are bananas sealed in plastic in many supermarkets?

A. To make them ripen more quickly.                B. To make them ripen more slowly.

C. To make banana flesh soften.                        D. To turn green bananas yellow.

查看答案和解析>>

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As bananas ripen,the green skin turns ye11ow gradually.Chemical changes occur in the flesh of the fruit as well:starch(淀粉)changes to sugar;pectin(果胶)breaks down,losing its stiffness;and the flesh softens.

    Is ripening fruit a self-contained system,or is the rate of these changes affected by the environment?We designed the experiment below to see if different atmospheres,produced by different packaging,affected the rate of ripening.You will vary the atmosphere surrounding unripe bananas and observe the effect on the ripening process.

    Now set up the bananas in their environments as follows:

1.Put two green bananas in a paper bag and fo1d the top over to seal out the air.

    2.Put one green banana and the very ripe banana in the other paper bag and fold over the top.

    3.Put two green bananas in a plastic bag and seal it.

    4.Wrap(包)one green banana tightly in a plastic bag.

    5.Leave one green banana exposed to the air.

    Leave the fruit a1one for five days to ripen.Ripening fruit “breathes”.This means that it takes up oxygen and gives off C02.Oxygen is extremely important and necessary for the chemical reactions involved in ripening.In addition, ripening fruit gives off another gas, called ethylene(乙烯).Not only is ethylene a product of ripening fruit, it also promotes the further ripening of the fruit.

Paper bags tend to keep the ethylene in, but they allow oxygen and ethylene to pass through slowly.Plastic bags do not allow the free flow of oxygen or ethylene.In this experiment, the green banana in paper bag with the ripe banana should ripen most quickly.The green bananas in the paper bag should ripen faster than the bananas in the plastic bag.The banana left exposed to air has an unlimited supply of oxygen, so it will turn brown most quickly.You will notice that the side of this banana that rests on the counter will ripen more quickly than the other sides, because it has the closest contact(接触) with its own ethylene.The banana that is tightly wrapped in plastic has no oxygen supply and should ripen most slowly.Now can you see why bananas are sealed in plastic in many supermarkets?

1.What makes the green banana in Bag 2 ripen more quickly than the ones in Bag 1?

A.Ethylene from the very ripe banana.       B.The free flow of oxygen or ethylene

C.CO2 from the very ripe banana.             D.The limitation of oxygen supply.

2.How can we slow down the ripening of bananas exposed to the air?

A.To rest them on the counter.                 B.To keep them in the basket.

C.To put them on the ground.                  D.To hang them up from the ceiling

3.It can be concluded from the passage that          .

A.the ripening banana is a self-contained system

B.the rate of ripening bananas is affected by the environment

C.wrapped bananas experience no chemical changes to ripen

D.ripening bananas give off oxygen, C0, and ethylene

4.Why are bananas sealed in plastic in many supermarkets?

A.To make them ripen more quickly.         B.To make them ripen more slowly.

C.To make banana flesh soften.                D.To turn green bananas yellow.

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