Sample Bio Lab Report - Hamilton College
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In this experiment we tested the ability of the blowfly Sarcophaga bullata to taste
different sugars and a sugar substitute, saccharin. Because sucrose is so sweet to people, I
expected the flies to taste lower concentrations of sucrose than they would of maltose and
glucose, sugars that are less sweet to people. Because saccharin is also sweet tasting to
people, I expected the flies to respond positively and feed on it as well.
METHODS
We stuck flies to popsickle sticks by pushing their wings into a sticky wax we
rubbed on the sticks. Then we made a dilution series of glucose, maltose, and sucrose in
one-half log molar steps (0.003M, 0.01M, 0.03M, 0.1M, 0.3M, and 1M) from the 1M
concentrations of the sugars we were given. We tested the flies’ sensory perception by
giving each fly the chance to feed from each sugar, starting with the lowest concentration
and working up. We rinsed the flies between tests by swishing their feet in distilled water.
We counted a positive response whenever a fly lowered its proboscis. To ensure that
positive responses were to sugars and not to water, we let them drink distilled water before
each test. See the lab handout Taste Reception in Flies (Biology Department, 2000) for
details.
RESULTS
Flies responded to high concentrations (1M) of sugar by lowering their probosces
and feeding. The threshold concentration required to elicit a positive response from at
least 50% of the flies was lowest for sucrose, while the threshold concentration was highest
for glucose (Fig. 1). Hardly any flies responded to saccharin. Based on the results from all
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