THE IPHONE THIEF: AN ORGANIC COMPOUND MYSTERY
Leni Joy is a freshman student at the University of Science and Technology for the
Gifted. While on lunch break, she was studying for her biology chapter test about organic
compounds and listening to music in her new iPhone, a gift from her “balikbayan ninong”.
There were four other students in the classroom, each having something different for lunch.
Near the end of her lunch break, Joy saw a couple of her friends in the hallway in front of their
classroom. She rushed out to greet them and forgot her iPhone and biology book in the room.
When she realized her mistake, she turned around and hurried back inside. However, she
found only her biology book and some spilled food. Her iPhone was gone! At first, she freaked
out, but she calmed down when she realized she could use her knowledge of organic
compounds to figure out who among her classmates left the spilled food on her biology book
while taking her iPhone. She decided to collect the evidence (spilled food) left in her biology
book and place them in two separate bottles with the labels dry part of the evidence and
liquid part of the evidence.
What are organic compounds?
Almost all of the food we eat comes from plants and animals. Plants and animals
contain mainly water and organic compounds, which are molecules made by living organisms
such as plants or animals. The most common type of organic compounds are carbohydrates,
lipids, nucleic acids, and proteins.
What are the indicators?
An indicator is a substance that changes color in the presence of a particular type of
molecule or organic compound.
Joy will use these tests to analyze the evidence left at the scene of the crime and find
out who spilled the food on her textbook.
Test for the presence of: Indicators
Sugar
Benedict’s solution is a chemical used to
test for the presence of glucose.
It is a clear blue solution, which in the
presence of sugar will change color to
green, yellow, and brick red, depending
on the amount of sugar.
Brick red indicates that the substance
tested has more sugar and green has the
least sugar.
Starch Iodine solution is used to test for the
presence of starch.
It is a yellow-brown solution that will
turn blue-black in the presence of starch.
Darker blue-black color indicates a greater
starch content.
Protein Biuret solution is a blue solution that
changes into pink-purple color in the
presence of protein.
Fat Sudan III stain solution has a high affinity
for fats. It stains red in the presence of fat.
The dry part of Joy’s evidence tested positive for the Iodine solution test and Biuret
reagent test while the liquid part of the evidence tested positive for the Sudan III stain.
The table below shows the result of the test for the presence of organic compounds
that Joy conducted using samples of her classmates’ lunch. The positive sign (+) shows that
the food tested positive for the test and the negative sign (-) shows that the food showed a
negative result for the test.
Food Indicators
Benedict’s
Solution
(test for
sugar)
Iodine
Solution
(test for
glucose)
Biuret’s
Solution
(test for
protein)
Sudan III
Stain
(test for
fats)
Pretzel (crumble into the container) - + + -
Butter + + + +
Jelly + + - -
Fat-free yogurt + - + -
Beans (mash into a paste) - + + +
The following table shows what each student in the room was eating while Joy was
studying. Complete this table to show which types of organic compounds would be in each
lunch and which types of organic compounds were found in the combined liquid + dry
evidence. Use a positive sign (+) to show if the substance tested positive for the specific test
and a negative sign (-) if the substance tested negative for the test.
Lunch he or she was eating Starch Protein Glucose Lipid
Fat-Free Yogurt
Bean burrito with cheese
Toast with butter and jelly
Pretzel
Combined liquid + dry evidence
The following is the list of what the workers ate for lunch during the theft:
Peter Peanut butter and jelly sandwich
Katniss Fat-free yogurt
Gabriel Bean burrito with cheese
Kiara Pretzels
Complete the following table to summarize the evidence and your interpretation of the
evidence.
The
worker
in the
break
room
Did he/she
take Joy’s
iPhone?
How do you know?
Describe the evidence that supports your conclusion.
Peter
Katniss
Gabriel
Kiara
9. Who took Joy’s iPhone? Do you have any doubts about your conclusion? Explain.
Based on the evidence collected and the tests conducted, the worker in the break room who took Joy's iPhone is Gabriel.
The evidence that supports this conclusion is that the combined liquid + dry evidence tested positive for starch, protein, and glucose. Gabriel's lunch, which was a bean burrito with cheese, would contain protein and glucose (from the beans) and starch (from the burrito). This matches with the positive test results for the evidence. Additionally, Gabriel's lunch did not contain any fats, which explains why the evidence tested negative for lipids.
There are no doubts about this conclusion as the evidence directly matches Gabriel's lunch.