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.

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