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SAMPLE LAB REPORT
Perception of Different Sugars by Blowflies
by Alexander Hamilton
Biology 101 October 24, 2009
Lab Partners: Sharon Flynn, Andi Alexander
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To feed on materials that are healthy for them, flies (order Diptera) use taste receptors on their tarsi to find sugars to ingest. We examined the ability of blowflies to taste monosaccharide and disaccharide sugars as well as saccharin. To do this, we attached flies to the ends of sticks and lowered their feet into solutions with different concentrations of these sugars. We counted a positive response when they lowered their proboscis to feed. The flies responded to sucrose at a lower concentration than they did of glucose, and they didn’t respond to saccharin at all. Our results show that they taste larger sugar molecules more readily than they do smaller ones. They didn’t feed on saccharin because the saccharin we use is actually the sodium salt of saccharin, and they reject salt solutions. Overall, our results show that flies are able to taste and choose foods that are good for them.
INTRODUCTION All animals rely on senses of taste and smell to find acceptable food for survival. Chemoreceptors are found in the taste buds on the tongue in humans (Campbell, 2008), for example, for tasting food. Studies of sensory physiology have often used insects as experimental subjects because insects can be manipulated with ease and because their sensory-response system is relatively simple (E. Williams, personal communication). Flies are able to taste food by walking on it (Dethier, 1963). Hollow hairs around the proboscis and tarsi contain receptor neurons that can distinguish among water, salts, and sugars, and flies can distinguish among different sugars (Dethier, 1976). These traits enable them to find necessary nutrition.
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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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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...