Sample Bio Lab Report - Hamilton College
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the lab groups together, there was a major difference in the response of flies to the sugars
and to saccharin (Table 1). When all the sugars were considered together, this difference
was significant (t = 10.46, df = 8, p < .05). Also, the response of two flies to saccharin was
not statistically different from zero (t = 1.12, df = 8, n.s.).
DISCUSSION
The results supported my first hypothesis that sucrose would be the most easily
detectable sugar by the flies. Flies show a selectivity of response to sugars based on
molecular size and structure. Glucose, the smallest of the three sugars, is a
monosaccharide. The threshold value of glucose was the highest in this experiment
because a higher concentration of this small sugar was needed to elicit a positive response.
Maltose and sucrose are both disaccharides but not with the same molecular weight or
composition. It has been shown that flies respond better to alpha-glucosidase derivatives
than to beta-glucosidase derivatives (Dethier 1975). Because sucrose is an alpha-
glucosidase derivative, it makes sense that the threshold value for sucrose occurs at a lower
concentration than that for maltose. This might also be the reason why sucrose tastes so
sweet to people.
My other hypothesis was not supported, however, because the flies did not respond
positively to saccharin. The sweetener people use is actually the sodium salt of saccharic
acid (Budavari, 1989). Even though it tastes 300 to 500 times as sweet as sucrose to
people (Budavari, 1989), flies taste the sodium and so reject saccharin as a salt. Two flies
did respond positively to saccharin, but the response of only two flies is not significant,
and the lab group that got the positive responses to saccharin may not have rinsed the flies
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