LESSON 14: Brown Bananas
ESTIMATED TIME Setup: 5 minutes | Procedure: The effects can be observed over 4–5 days.
• DESCRIPTION
• MATERIALS
Place bananas in different types of packages to
affect the rate of ripening.
• OBJECTIVE
This lesson demonstrates the effects of the
environment on the ripening process of fruits.
Students place bananas in different packages to
explore what material slows the ripening process
the most. The lesson can be extended to address
enzymes in more detail.
• CONTENT TOPICS
Scientific inquiry; chemical reactions; food chemistry
Green bananas
Small brown paper bags (lunch bag)
o Plastic bags with twist ties
o Plastic wrap
o
o
Always remember to use the appropriate safety
equipment when conducting your experiment.
Refer to the Safety First section in the Resource Guide
on pages 391–393 for more detailed information about
safety in the classroom.
Jump ahead to page 182 to view the
Experimental Procedure.
NATIONAL SCIENCE EDUCATION STANDARDS SUBJECT MATTER
This lesson applies both Dimension 1: Scientific and Engineering Practices and Dimension 2: Crosscutting Concepts
from “A Framework for K–12 Science Education,” established as a guide for the updated National Science Education
Standards. In addition, this lesson covers the following Disciplinary Core Ideas from that framework:
• PS1.A: Structure and Properties of Matter
• PS1.B: Chemical Reactions
• ETS2.B: Influence of Engineering, Technology, and Science on Society and the Natural World
(see Analysis & Conclusion)
OBSERVATION & RESEARCH
BACKGROUND
Matter often changes, and these changes can be physical
or chemical. A physical change is any change in a
substance’s form that does not change its chemical
makeup. The chemical formula of the substance stays the
same before and after the change. A chemical change or
chemical reaction is a change that takes place when
atoms of a substance are rearranged, and the bonds
between the atoms are broken or formed. During a
chemical reaction, the structure or composition of the
materials changes.
Chemical reactions occur around us all the time. They
even take place inside of our bodies. When we breathe,
we take in oxygen from the air, which combines with
glucose (a simple sugar) in our bodies. These substances
react to produce carbon dioxide and water vapor, which
we exhale. In addition, the glucose in our bodies is
broken down by our cells to give us energy. That glucose
comes from the foods we eat, such as corn, bread, fruits
(like bananas!), and so on.
Before fruit is eaten, it has to ripen. The ripening process
causes the fruit to become more appealing to humans
(and many other animals). Its flavor generally becomes
sweeter, and its color changes (usually from green to red,
yellow, or blue). The ripening process is triggered by the
hormone ethylene, produced by growing plant tissues.
Ethylene is an odorless gas. In addition, plants produce
ethylene in response to environmental stress, such as
heat or damaged plant tissue. Even simply picking the
fruit causes the production of ethylene and initiates the
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LESSON 14: Brown Bananas
ripening process. As the fruit ripens, it releases more
ethylene gas. Because the gas diffuses easily, it can
travel throughout the plant and into the air to nearby
fruits or plants. Diffusion is the movement of fluid
particles from an area of high concentration to an area
of low concentration.
Ethylene causes many chemical reactions in the plant to
occur faster. For example, the starch in the fruits breaks
down quicker into glucose, making the fruit sweeter.
The cell walls are broken down quicker, making the fruit
softer, and chlorophyll, the chemical substance that gives
plants their green color, breaks down faster, causing the
fruit to change color.
Bananas are generally picked before they are ripe so they
can be transported long distances. Bananas will ripen
more quickly if placed in closed paper bags because
paper bags keep ethylene inside but are porous enough to
allow oxygen to pass through. Plants use oxygen to
produce ethylene. Therefore, plastic bags, which do not
allow additional oxygen to pass into the bag, ripen more
slowly. Bananas that are tightly wrapped in plastic have
no oxygen supply and should ripen at the slowest rate,
which may not even be noticeable. However, if all the air
is not sealed out of a package, the bananas in that
package may ripen first because they have oxygen and
will be in close contact with their own ethylene.
CONNECT TO THE YOU BE THE
CHEMIST CHALLENGE
For additional background information, please
review CEF’s Challenge study materials online at
http://www.chemed.org/ybtc/challenge/study.aspx.
• Additional information on physical and chemical
changes and diffusion can be found in the
Classification of Matter section of CEF’s Passport
to Science Exploration: The Core of Chemistry.
HYPOTHESIS
uBananas will ripen the fastest if placed
in a closed paper bag because oxygen gas
can pass easily through the paper bag, but not
through plastic bags or plastic wrap, which will
allow the ripening process to occur.
Fun Fact
Most fruits are picked before
they are ripe, so they can
FORMULAS & EQUATIONS
Plants send signals using hormones, but most hormones
travel through the plant. The hormone that signals ripening,
ethylene, can travel through the air.
survive travel to different parts
of the world.
Ethylene is a hydrocarbon gas with the chemical
formula C2H4.
Oxygen gas is needed to produce ethylene gas.
The gaseous form of oxygen has the chemical
formula O2.
Glucose is a simple sugar produced by plants.
Its chemical formula is C6H12O6.
Fun Fact
A rotten apple can spoil
the whole bunch because
of ethylene!
You Be The Chemist® Activity Guide | page 180
LESSON 14: Brown Bananas
DIFFERENTIATION IN THE CLASSROOM
LOWER GRADE LEVELS/BEGINNERS
Perform the experiment as described on page 182, but
spend more time on physical and chemical changes.
Take one banana and cut it in half. Ask the students what
type of change occurred—a physical change! Then, show
the students two bananas, one green and one yellow.
Ask the students what type of change causes a banana to
change from green to yellow—a chemical change!
Another option is to focus on the difference between fresh
and spoiled food and discuss ways to keep foods fresh.
HIGHER GRADE LEVELS/ADVANCED STUDENTS
DESCRIPTION
Place bananas in different types of packages to affect the
rate of ripening.
OBJECTIVE
This lesson demonstrates the effects of the environment
and the role of gases, chemical reactions, and enzymes on
the ripening process of fruits. Students place bananas in
different packages to explore what material slows the
ripening process the most.
OBSERVATION & RESEARCH
Matter often changes, and these changes can be physical
or chemical. A physical change is any change in a
substance’s form that does not change its chemical
makeup. The chemical formula of the substance stays the
same before and after the change. A chemical change or
chemical reaction is a change that takes place when atoms
of a substance are rearranged, and the bonds between the
atoms are broken or formed. During a chemical reaction,
the structure or composition of the materials changes.
Chemical reactions occur around us all the time. They
happen in our bodies, in our cars, and in our kitchens!
People eat different foods that the body uses for energy.
Before fruit is eaten, it has to ripen. The ripening process
causes the fruit to become more appealing to humans
(and many other animals). Its flavor generally becomes
sweeter, and its color changes (generally from green to
red, yellow, or blue).
The ripening process is triggered by the hormone
ethylene, produced by growing plant tissues. Ethylene is
an odorless gas. In addition, plants produce ethylene in
response to environmental stress, such as heat or damaged
plant tissue. Even simply picking the fruit causes the
production of ethylene and initiates the ripening process.
As the fruit ripens, it releases more ethylene gas. Because
the gas diffuses easily, it can travel throughout the plant
and into the air to nearby fruits or plants. Diffusion is the
movement of fluid particles from an area of high
concentration to an area of low concentration.
Ethylene triggers the production of different enzymes that
speed up various chemical reactions in the plant. Enzymes
are proteins with a special structure that serve as catalysts
for specific chemical reactions. A catalyst is a substance
that helps to change the rate of a reaction and is not
changed or consumed in the process. For example, certain
enzymes help to break down the fruit’s starch into glucose,
break down the cell walls, or break down chlorophyll,
making the fruit, sweeter, softer, and a different color.
Bananas are generally picked before they are ripe, so they
can be transported long distances. Bananas will ripen
more quickly if placed in closed paper bags because paper
bags keep ethylene inside but are porous enough to allow
oxygen to diffuse into the bag. Plants use oxygen to
produce ethylene. Therefore, plastic bags, which do not
allow additional oxygen to pass into the bag, cause the
bananas to ripen more slowly. Bananas that are tightly
wrapped in plastic have no oxygen supply and should
ripen at the slowest rate, which may not even be
noticeable. However, if all the air is not sealed out of a
certain package, the bananas in that package may ripen
quickly because they have oxygen and will be in close
contact with their own ethylene.
CONNECT TO THE YOU BE THE
CHEMIST CHALLENGE
For additional background information, please
review CEF’s Challenge study materials online at
http://www.chemed.org/ybtc/challenge/study.aspx.
• Additional information on physical and chemical
changes and diffusion can be found in the
Classification of Matter section of CEF’s Passport to
Science Exploration: The Core of Chemistry.
• Additional information on chemical reactions and
catalysts can be found in the Chemical Reactions
section of CEF’s Passport to Science Exploration:
Chemistry Connections.
You Be The Chemist® Activity Guide | page 181
LESSON 14: Brown Bananas
EXPERIMENTATION
As the students perform the experiment, challenge them
to identify the independent, dependent, and controlled
variables, as well as whether there is a control setup for
the experiment. (Hint: If the type of package is changed,
does the rate of ripening change?) Review the
information in the Scientific Inquiry section on pages
14–16 to discuss variables.
NOTES
EXPERIMENTAL PROCEDURE
1. Put one green banana in a paper bag, and fold
the top over several times to close the bag.
2. Put one green banana in a plastic bag, twist the
top, and fasten with a twist tie. (Leave air inside.)
3. Wrap one green banana in a few layers of plastic
wrap. Seal it tightly at each end.
4. Leave the bananas for 4–5 days. (Do not open
the bags or wrapping!) After 4–5 days, open the
bags to observe the results.
DATA COLLECTION
Have students record data in their science notebooks or on
the following activity sheet. What do the bananas look like
at the beginning of the experiment? What does each
banana look like after 4–5 days? You can use the table on
the activity sheet (or a similar one of your own) for
students to record their data.
Fun Fact
Technically, tomatoes are fruits,
but they are often considered
vegetables because they do not
have a sweet taste, which is
associated with fruits.
You Be The Chemist® Activity Guide | page 182
LESSON 14: Brown Bananas
ANALYSIS & CONCLUSION
Use the questions from the activity sheet or your own
questions to discuss the experimental data. Ask students
to determine whether they should accept or reject their
hypotheses. Review the information in the Scientific
Inquiry section on pages 14–16 to discuss valid and
invalid hypotheses.
• Temperature affects the ripening process too. If the
temperature is hot, the fruits will ripen more quickly.
When fruits are refrigerated, the ripening process is
slowed. Although a banana peel will turn brown in the
refrigerator, the banana itself will still be good to eat
for a while, because the ripening of the actual fruit is
slower.
ASSESSMENT/GOALS
Upon completion of this lesson, students should be able
to …
• Apply a scientific inquiry process and perform an
experiment.
• Differentiate between physical and chemical changes
and give examples of each.
• Explain the process of diffusion.
• Understand that the ripening of fruit is a result of a
chemical reaction.
• Describe two major gases involved in the ripening
process.
• Explain ways to slow down the ripening process.
• Define enzymes and catalysts and explain their
role in chemical reactions (see Differentiation in
the Classroom).
MODIFICATIONS/EXTENSIONS
Modifications and extensions provide alternate methods
for performing the lesson or similar lessons. They also
introduce ways to expand on the content topics presented
and think beyond those topics. Use the following
examples or have a discussion to generate other ideas
as a class.
• Before the lesson, ask the students if they have ever
eaten a green, unripe banana. Ask the students how
unripe bananas taste—flavorless/bitter. Ask them if
they know why the bananas are green and not yellow.
• Fruit produces ethylene in response to bruising or
wounding. Try bruising two bananas and putting
them in a paper or plastic bag. Do they ripen faster
than undamaged bananas?
• Test out other setups. If you have more bananas, you
will have more ethylene. Does putting more than one
banana in the package cause the fruit to ripen faster?
Likewise, set up a control. Leave a banana or
bananas outside of a bag. What do you notice?
REAL-WORLD APPLICATIONS
• The ripening bananas produce enough ethylene that
you can use them to ripen other fruits faster. If you
have some hard, unripe pears that you want to eat soon,
put them in a paper bag with a banana. The ethylene
produced by the banana and trapped by the paper bag
will cause the pears to ripen faster.
• Today, fruits are generally stored in cool warehouses
with filter systems that absorb ethylene. This allows
us to enjoy different fruits, like apples, throughout
the year.
• Many people automatically put fruits in their
refrigerator when they get home from grocery
shopping. However, doing so slows down the
ripening process, preventing the fruits from ripening
properly. While putting them in the refrigerator does
make them last longer, they will most likely taste
better when allowed to ripen naturally.
• Glucose is a simple sugar that provides energy to all
of the cells in your body. The cells take in glucose
from the blood and break it down for energy.
The glucose in the blood comes from the food that
you eat. When you eat food, glucose gets absorbed
from your intestines and distributed by the
bloodstream to all of the cells in your body. Your
body tries to keep a constant supply of glucose for
your cells by maintaining a constant glucose
concentration in your blood. The glucose is used to
produce energy so we can walk to class, ride a bike,
and so on. Extra glucose is stored in the liver and
muscles as glycogen. When needed, your body
breaks the glycogen back down into glucose to use.
People with diabetes have abnormal levels of glucose
in their blood.
COMMUNICATION
Discuss the results as a class and review the activity sheet.
Review the information in the Scientific Inquiry section on
pages 14–16 to discuss the importance of communication
to scientific progress.
You Be The Chemist® Activity Guide | page 183
LESSON 14 ACTIVITY SHEET: Brown Bananas
OBSERVE & RESEARCH
1. Write down the materials you see. ____________________________________________________________________
______________________________________________________________________________________________________
______________________________________________________________________________________________________
2. How might these materials be used? __________________________________________________________________
______________________________________________________________________________________________________
______________________________________________________________________________________________________
3. Define the following key terms. Then, provide an example of each by writing the example or drawing/pasting an
image of the example.
Term
Definition
Example (write or add image)
Physical change
Chemical reaction
Diffusion
4. Consider whether a banana will ripen fastest in a paper bag, plastic bag, or plastic wrap and why.
uWrite your hypothesis. ______________________________________________________________
______________________________________________________________________________________
______________________________________________________________________________________
You Be The Chemist® Activity Guide | page 184
LESSON 14 ACTIVITY SHEET: Brown Bananas
PERFORM YOUR EXPERIMENT
1. Put one green banana in a paper bag. Fold the top of the bag over several times to close it.
2. Put one green banana in a plastic bag. Twist the top and fasten with a twist tie. (Leave air inside.)
3. Wrap one green banana in a few layers of plastic wrap. Seal it tightly at each end.
4. Leave the bananas for 4–5 days. (Do not open the bags or wrapping!) After 4–5 days, open the bags to observe
the results.
ANALYZE & CONCLUDE
1. In the table below, fill in your predictions and your observations about the bananas.
Paper Bag
Plastic Bag
Initial
description
Prediction of
the result
Resulting
description
You Be The Chemist®Activity
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Plastic Wrap
LESSON 14 ACTIVITY SHEET: Brown Bananas
2. In which bag or wrapping did the banana ripen the fastest? How do you know? ______________________________
______________________________________________________________________________________________________
______________________________________________________________________________________________________
3. In which bag or wrapping did the banana ripen the slowest? How do you know?
____________________________
______________________________________________________________________________________________________
______________________________________________________________________________________________________
4. What causes the bananas to ripen?
__________________________________________________________________
______________________________________________________________________________________________________
______________________________________________________________________________________________________
5. Why do the bananas ripen at different rates in the different packages? ______________________________________
______________________________________________________________________________________________________
______________________________________________________________________________________________________
______________________________________________________________________________________________________
6. Is your hypothesis valid? Why or why not? If not, what would be your next steps? ____________________________
______________________________________________________________________________________________________
______________________________________________________________________________________________________
You Be The Chemist® Activity Guide | page 186
LESSON 14 ACTIVITY SHEET: Brown Bananas
EXPAND YOUR KNOWLEDGE—ADVANCED
1. Define the following key terms. Then, provide an example of each by writing the example or drawing/pasting an
image of the example.
Term
Definition
Example (write or add image)
Enzyme
Catalyst
2. To make sure bananas are not over-ripened when they reach a grocery store, what do you think banana producers do?
______________________________________________________________________________________________________
______________________________________________________________________________________________________
______________________________________________________________________________________________________
3. Do chemical reactions in the human body use enzymes? If so, give an example. ______________________________
______________________________________________________________________________________________________
______________________________________________________________________________________________________
You Be The Chemist®Activity
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LESSON 14 ACTIVITY SHEET: Brown Bananas
ANSWER KEY Below are suggested answers. Other answers may also be acceptable.
OBSERVE & RESEARCH
Green bananas, paper bag, plastic bag, plastic wrap …
1. Write down the materials you see. ____________________________________________________________________
______________________________________________________________________________________________________
______________________________________________________________________________________________________
Bananas may be eaten. Paper bags, plastic bags, and plastic wrap may be used to hold
2. How might these materials be used? __________________________________________________________________
objects. These materials can be used to test the different rates at which a banana will ripen in each package.
______________________________________________________________________________________________________
______________________________________________________________________________________________________
3. Define the following key terms. Then, provide an example of each by writing the example or drawing/pasting an
image of the example.
Term
Definition
Physical change
A change that alters the form or appearance of a
substance but does not change its chemical
makeup or create a new substance.
Chemical reaction
A change that takes place when atoms of one or
more substances are rearranged, and the bonds
between the atoms are broken or formed to
produce new substances; also known as a chemical
change.
Diffusion
The movement of particles from an area of high
concentration to an area of low concentration.
Example (write or add image)
4. Consider whether a banana will ripen fastest in a paper bag, plastic bag, or plastic wrap and why.
Bananas will ripen the fastest if placed in a closed paper bag because oxygen gas,
uWrite your hypothesis. ______________________________________________________________
used in the ripening process, can pass through the paper bag but not through the plastic bag or plastic wrap.
______________________________________________________________________________________
______________________________________________________________________________________
You Be The Chemist® Activity Guide | page 188
LESSON 14 ACTIVITY SHEET: Brown Bananas
ANSWER KEY Below are suggested answers. Other answers may also be acceptable.
PERFORM YOUR EXPERIMENT
1. Put one green banana in a paper bag. Fold the top of the bag over several times to close it.
2. Put one green banana in a plastic bag. Twist the top and fasten with a twist tie. (Leave air inside.)
3. Wrap one green banana in a few layers of plastic wrap. Seal it tightly at each end.
4. Leave the bananas for 4–5 days. (Do not open the bags or wrapping!) After 4–5 days, open the bags to observe
the results.
ANALYZE & CONCLUDE
1. In the table below, fill in your predictions and your observations about the bananas.
Initial
description
Paper Bag
Plastic Bag
Plastic Wrap
Answers will vary
Answers will vary
Answers will vary
Prediction of
the result
Resulting
description
You Be The Chemist® Activity Guide | page 189
LESSON 14 ACTIVITY SHEET: Brown Bananas
ANSWER KEY Below are suggested answers. Other answers may also be acceptable.
The banana ripened the fastest in the
2. In which bag or wrapping did the banana ripen the fastest? How do you know? ______________________________
paper bag. The peel of this banana was the most yellow or a yellow-brown color.
______________________________________________________________________________________________________
______________________________________________________________________________________________________
3. In which bag or wrapping did the banana ripen the slowest? How do you know?
The banana in the plastic wrap ripened
____________________________
the slowest. The peel of this banana remained mostly green.
______________________________________________________________________________________________________
______________________________________________________________________________________________________
4. What causes the bananas to ripen?
The ripening process is triggered by the hormone ethylene. Ethylene is a gas that speeds up
__________________________________________________________________
various chemical reactions in the plant, which causes the fruit to ripen. Oxygen is needed for the plant to produce ethylene.
______________________________________________________________________________________________________
______________________________________________________________________________________________________
Fruit uses oxygen gas to produce ethylene, so the
5. Why do the bananas ripen at different rates in the different packages? ______________________________________
amount of oxygen the fruit is exposed to will affect the rate of ripening. If the banana does not receive oxygen, it will not ripen. The paper bag
______________________________________________________________________________________________________
allows oxygen to reach the banana and also keeps the ethylene from escaping into the air. These processes cause the banana to ripen the
______________________________________________________________________________________________________
fastest in the paper bag. On the other hand, the plastic wrap keeps out the most oxygen.
______________________________________________________________________________________________________
6. Is your hypothesis valid? Why or why not? If not, what would be your next steps? ____________________________
Answer 1: Valid because the data support my hypothesis.
______________________________________________________________________________________________________
Answer 2: Invalid because the data do not support my hypothesis. I would reject my hypothesis and could form a new one, such as …
______________________________________________________________________________________________________
You Be The Chemist® Activity Guide | page 190
LESSON 14 ACTIVITY SHEET: Brown Bananas
ANSWER KEY Below are suggested answers. Other answers may also be acceptable.
EXPAND YOUR KNOWLEDGE—ADVANCED
Have students complete this section if you used the advanced differentiation information, or challenge them to find the answers to these
questions at home and discuss how these terms relate to the experiment in class the next day.
1. Define the following key terms. Then, provide an example of each by writing the example or drawing/pasting an
image of the example.
Term
Definition
Enzyme
A type of protein found in living cells that acts as
catalyst by increasing the rate of a chemical
reaction in living organisms.
Catalyst
A substance that helps to change the rate of a
reaction but is not consumed or changed during the
reaction.
Example (write or add image)
2. To make sure bananas are not over-ripened when they reach a grocery store, what do you think banana producers do?
Banana producers pick the fruit before it is ripe in order to allow the bananas to ripen while being transported.
______________________________________________________________________________________________________
______________________________________________________________________________________________________
______________________________________________________________________________________________________
Yes, many chemical reactions in the
3. Do chemical reactions in the human body use enzymes? If so, give an example. ______________________________
human body use enzymes. The process of respiration and metabolic processes (used to break down food for energy) need enzymes. Without
______________________________________________________________________________________________________
enzymes, these reactions would occur too slowly, and we could not survive.
______________________________________________________________________________________________________
You Be The Chemist® Activity Guide | page 191