Search for Science Fair Projects

1000 Science Fair Projects with Complete Instructions

Attribution: This is a cached copy of a third party project. Many of these sites are from 20 years ago and the majority are no longer running. We show only the first page of the project. We do not save all pages since copyright belongs to the third-party author.
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.

   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.


* 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
* 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


* 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

* 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.