Plant hormones are signals that tell plants what to do, like when to grow bigger or make more fruits. When we understand how plant hormones work, we can help plants grow better and give us more food to eat!

Does one bad apple spoil the whole bunch?  How might one ripening fruit signal others to begin to ripen?  What might cause synchrony?  Plants use hormones to communicate among tissues.  In this experiment, students are introduced to a technique used to evaluate the ripeness of fruit.   They design experiments to test hypotheses about the role of hormones in synchronizing fruit ripening in apples.

Have you ever noticed that apples ripen at the same time? In this project, you'll explore the science behind why this happens. You'll use a special iodine solution to test the ripeness of apples and investigate the role of hormones in synchronizing fruit ripening.

One Bad Apple: Synchrony in ripening fruit

Grade Levels: 6-8; 9-12

Abstract: Does one bad apple spoil the whole bunch?  How might one ripening
fruit signal others to begin to ripen?  What might cause synchrony?  Plants use
hormones to communicate among tissues.  The ripeness of fruit will be evaluated and experiments will be done to test the role of hormones in synchronizing fruit
ripening in apples.


Background: 
   Does one bad apple spoil the whole bunch?  Does it require direct contact? 
Contact through the air?  If so, what sort of mechanism accounts for the
communication that occurs among the apples?
    In general, plant tissues communicate using classes of compounds called
hormones.  These are defined as substances produced in one location that have an
effect on target cells in a non-adjacent location.  In plants, germination,
growth, development, reproduction, and environmental response are all
coordinated through hormones.  Although most of the main plant hormones are
transported in the vascular system of the plant, one class of hormones is
transferred in gaseous phase.  This class includes the plant hormone ethylene.  
    Ethylene is manufactured and released by rapidly growing tissues (i.e.,
meristems) in roots, senescing flowers, and ripening fruit.  For example, the
darkened spots on a ripe banana release great amounts of ethylene.  Ethylene has
many effects on plants including being responsible for the stunting of plants in
high winds or when repeatedly touched.   In addition, ethylene promotes fruit
ripening.  Like many hormones, it does so at very low concentrations.  Apple
growers take advantage of this by picking fruit when it is not ripe, holding it
in enclosed conditions without ethylene, and exposing it to ethylene right
before taking it to market.  This process is why we have newly ripened apples
grown in temperate North America even in the spring and summer (apples ripen in
the fall).
    During the process of ripening, apples convert stored starch into sugar.  In
apples and many other commercial fruit, the sweet portion of the fruit evolved
as a reward for animal seed dispersers.  When seeds are ripe and ready for
dispersal, the fruit converts stored starch, which does not taste sweet, into
sugar.  The hormone ethylene initiates the metabolic pathways that lead to this
conversion.  The iodine staining procedure you use in this activity tests for
the presence of starch.  Iodine turns black in the presence of starch.  So when
the fruit is not ripe, starch is present, and the apple will stain black.  As
ripening proceeds and starch is converted to sugar, the apple will no longer
stain black.  This is best visualized in the Ripeness Chart.

Materials:

 * McIntosh or red delicious apples 
 * Potassium Iodide (KI) 
 * Iodine (I) crystals 
 * Shallow glass or plastic trays at least 5 cm (approx. 2 ") deep.
 * Knife and cutting board for cutting apples/pears
 * Students are asked to design their own experiments using common supplies such
   as:
   * other fruit like bananas, oranges, pineapples; perhaps at different stages
     of ripeness
   * plastic and paper bags
   * apple fragrance in shampoo or other perfumed product
   * different sizes or varieties of apples or pears

Procedure:

 * Make the following iodine stain recipe:
   * dissolve 10 g Potassium Iodide (KI) in 10 ml of water
   * when properly dissolved, add 2.5 g of Iodine (I) Crystals; shake the
     crystals until thoroughly dissolved
   * dilute this with water to make 1.1 liters
   * this recipe should last for several days and the solution should be stored
     in brown glass bottles for longer shelf life.

 * Familiarize students with the staining procedure by having them cut and stain
   several apples or pears. 
   
   CAUTION: Be careful with the iodine stain.  It can stain your skin and
   clothing.
   
   * pour the iodine test solution into the tray to a depth of 0.5 cm. 
   * Cut the apple or pear around the middle (in cross section).  Grasp the stem
     and place the cut section into the stain.  You may want to prevent the cut
     surface from adhering to the tray bottom by propping it using glass rods or
     plastic straws.
   * Let the apple or pear soak in the stain for one minute.  
   * Take the apple or pear out and rinse the face with water.   Do not let the
     rinse water fall into the stain. 
   * Determine a quantitative ripeness score by comparing their apples or pears
     with the Ripeness Chart.  It will be important for them to be able to
     assign a numeric score for their data analysis
 * Bring in a rotten apple or pear and several ripe ones; ask students what
   would happen if these were all placed in a plastic bag together; encourage
   students to propose a mechanism that would cause the response they suggest
 * Send students to their textbooks, the library, and web resources and have
   them develop a hypothesis about how apples or pears communicate and
   synchronize their ripening; it is important that students are asked to
   provide a justification for their hypothesis, in other words, they need to
   explain why their hypothesis is reasonable in light of what they have found
   out about the biological process of fruit ripening. 
 * Have students design and conduct an experiment to test their hypotheses. 
   They may choose to test many different hypotheses; however, their experiments
   should all have a control and at least one experimental group and replication
   with at least five within each group.
 * Students need to assign numeric scores to the ripeness of fruit in their
   experiment; they should summarize their data by calculating averages.


 

Does One Bad Apple Spoil the Bunch?

Does one bad apple spoil the whole bunch?

<h1><strong>1000 Science Fair Project Ideas by Subject</strong></h1><p>Looking for a science fair project idea? Each of our science fair project idea has complete instructions with video. Get ideas for your science projects, find extra resources for your class' scientific projects, or try a fun experiment at home! It doesn't matter what grade you're in, there's something for everyone!</p><p>You can find your perfect science fair project from the different science subjects below or from our <a href="https://www.all-science-fair-projects.com/category0.html#bottom">science fair project idea lists!</a></p>

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Biochemistry is the study of the chemistry of living things. Biochemists study how different molecules like DNA and proteins work together to sustain life. The groundbreaking discoveries in biochemistry continue to lead to the discovery of new medicines and cutting-edge treatments for diseases.

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Does One Bad Apple Spoil the Bunch?

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