Yes, We Have
Ripe Bananas

Starring

You and Your Students!

Directed By

Vicki Cobb, Education World Science Editor

Synopsis

How can you speed up (and slow down) the way bananas ripen?

Genre

• Life Sciences

Required Props

• 7 very green bananas
• 1 very ripe banana
• 2 small brown paper bags (lunch-size bags work best)
• a resealable plastic bag
• plastic wrap
• a marker
  
  

  Setting the Scene

  A banana is a living system that changes or ripens over time. The ripening process is accompanied by changes in color, texture, odor, and, of course, taste. Whenever easily observable changes occur, you can be sure you have a good subject for scientific investigation.

  Begin the activity by asking your students how they can tell an unripe banana from a ripe one.

  Then ask:

• Is ripening fruit a self-contained system (is it built into the banana itself), or is the rate of the change affected by the environment?
• Do different atmospheres, produced by different packaging, affect the rate of ripening?

  Those are the questions this activity will set out to answer.

  Stage Direction

  Set up this activity as a class project; or students might work in small groups to carry it out.

  Show-Biz Science is scripted by popular children's book writer Vicki Cobb. Click to learn more about Vicki or to read a brief synopsis of her philosophy of teaching science. Visit our archive of archive of Show-Biz Science Activities. Watch for a new activity each week. Then chat with Vicki -- share your feedback and ask your questions about teaching science -- on our special Showbiz-Science message board. Be sure to visit Vicki's Kids' Science Page for more great science fun, a complete list of her books, and information about how you can invite Vicki to come to your school. And don't miss her library of science videos too. Or visit Vicki and other great authors of nonfiction for children at the INK Think Tank.

  Plot

  Act I
  Set up the bananas in their environments as follows:

  1. Put two green bananas in a paper bag. Fold over the top of the bag several times to seal out the air. Mark the contents on the bag.
  2. Put one green banana and the very ripe banana in the other paper bag. Fold over the top of the bag in the same way. Mark its contents on the bag.
  3. Put two green bananas in a zippered plastic bag. Seal the bag closed.
  4. Wrap one green banana in several layers of plastic wrap. Be certain it is sealed tightly at each end.
  5. Leave one green banana exposed to the air.

  Act II
  Leave the fruit alone for four or five days to ripen. Do not open any of the bags during that period. On the fifth or sixth day, examine all the fruit.

• Which fruit is still green?
• Which is most yellow?
• Which is most brown?
  
  You can eat the ripe bananas or put them back and allow the experiment to continue for another day or two.
  
  

  Behind the Scenes

  Ripening fruit "breathes," or respires. That means that it takes up oxygen and gives off carbon dioxide. Oxygen is essential for the chemical reactions involved in ripening.

  In addition, ripening fruit gives off another gas -- called ethylene. Not only is ethylene a product of ripening fruit, in some mysterious way it also stimulates the further ripening of the fruit. For that reason it has been called the "ripening hormone." (Hormones are chemicals produced by living things that stimulate cellular changes.)

  Paper bags tend to keep in ethylene, but they are porous enough to allow oxygen (and ethylene) to pass through. As a result,

• the green banana in the paper bag with the ripe banana should ripen most quickly. It has both oxygen and extra ethylene from the ripe banana.
• the green bananas in the paper bag should ripen faster than the bananas in the plastic bag because they have more oxygen.
• the banana exposed to the 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 most intimate contact with its own ethylene.
• the banana that is tightly wrapped in plastic has no oxygen supply and should ripen most slowly. However, if all the air is not sealed out of the package, this banana will ripen first. It will have oxygen and will be in contact with its own ethylene.

  Now you can see why supermarkets sometimes sell bananas sealed in plastic.

  The End

  How does this experiment explain how one rotten apple spoils the barrel?

  Article By Vicki Cobb
  Education World®
  Copyright © 2007 Education World

  03/08/2007