What Do You Taste?
(From www.spice.centers.ufl.edu)
NAMES:
MATERIALS:
Control taste test paper (1 per student)
PTC taste test paper (1 per student)
Sodium benzoate taste test paper (1 per student)
Thiourea taste test paper (1 per student)
What do you Taste? Lab worksheet
BACKGROUND INFORMATION:
PTC and thiourea are both very bitter compounds, and those students who
can taste them will probably dislike them. Taste buds for both are likely to be on
the back of the tongue. Since these compounds are found in vegetables like
broccoli, cabbage, turnips, and kale, people who can taste thiourea or PTC usually
don’t like their veggies. Most people can taste PTC, only 25% cannot. Some people
(about 10%) are “supertasters”, meaning they taste these and other bitter
compounds very intensely, and dislike most of them. These people do not usually
like coffee of chocolate, because coffee and chocolate are bitter flavors.
The ability to taste PTC and thiourea are genetically linked, because they
are similar chemicals. Since they are not identical, there will still be some people
who can taste PTC but not thiourea, or vice versa. People who cannot taste either
compound tend to ingest more of them. Since these compounds have anti-thyroidal
activity, PTC/thiourea non-tasters are more likely to have certain thyroid
problems. However, PTC/thiourea tasters are less likely to eat vegetables;
therefore, they are at a higher risk for heart disease and cancer. Ingesting too
much PTC at once can cause thyroid damage, which is why it’s important to limit the
student’s access to the taste strips. Someone would need to taste 500 or so PTC
taste strips in order to ingest enough PTC to be toxic.
PTC genetics are Mendelian, with a dominant allele for the ability to taste
PTC. Homozygous dominants taste PTC more intensely that heterozygous
dominants. Supertasters have a rare allele on a different gene that increases the
intensity of many tastes, not just PTC.
Sodium Benzoate is a preservative found in many foods. It is also a
compound that some people cannot taste. Those who can taste it do not always
taste the same thing. It can taste bitter, sweet, sour, or salty, depending on your
individual genetic makeup. Since the inheritance of tasting sodium benzoate is
more complicated than straightforward mendelian genetics, it is not a good trait to
use for teaching genetics. However, it drives home the point that we are all very
diverse, and that much of our diversity is genetic.
1)
Use the background information to write a hypothesis about the
differences in taste ability. Remember to use the “If, Then, Because”
format.
2)
For each lab group member, follow this procedure to find out which
compounds you can taste:
a)
Take one control taste test strip from the bag marked “control”.
b)
Place the taste strip on your tongue. Be sure to test all the regions of
your tongue. You should not taste anything. If you taste something,
it should taste like paper. Remember what it tastes like
c)
Remove the taste test strip from your mouth, and immediately throw
it in the trash cup. Do not place it on your lab bench
or desk!
d)
Take one PTC taste test strip from the bag marked
“PTC”.
e)
Place the taste strip on your tongue. Be sure to test all the regions of
your tongue. Do you taste anything?
f)
Remove the taste test strip from your mouth, and immediately throw
it in a trash can. Do not place it on your lab bench or desk!
g)
Record whether or not you taste PTC in your data table. If you
tasted nothing, or if it tasted the same as the control test, you are a
non-taster. Otherwise, you are a taster.
h)
Repeat steps 4-7 using the thiourea taste test strips.
i)
Repeat steps 4-6 using the sodium benzoate taste test
strips
j)
Record whether or not you taste sodium benzoate in your
chart. If you tasted it, record whether you tasted
something sweet, salty, sour, or bitter.
3)
Data Table: Create a data table for your group below.
4)
5)
6)
Data Table: Insert your group’s data into the data table for Ms. Meny’s
classes here. Do not erase anyone else’s data!!
Graph: Design a graph to show the class data. Remember TAILS. You
may use Excel or graph paper.
Using your group data answer below:
a) In general, could those tasting PTC also taste thiourea? Is this evidence
for or against your hypothesis?
b) In general, could those tasting PTC also taste sodium benzoate? Is this
evidence for or against your hypothesis?
c) Was there a lot of variety in your classmate’s ability to taste? Is this
evidence for or against your hypothesis?
d) Is there a relationship between the ability to taste one bitter substance
and the ability to taste another?
e) Overall, do you think your hypothesis was supported? What would you
conclude about the variety in people’s ability to taste? Make a conclusion
about both the amount diversity and the source of the diversity.