Aim for FiveBiology

Scientific investigation

Fruit flies and the smell of fruit

  • Unit 8
  • 4 points
  • About 10 minutes

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A short question about a described lab investigation. You describe a concept behind it, identify part of the method such as a control or a variable to hold constant, state a null hypothesis or predict a result, and justify a prediction. On the exam: Question 3 of 6 in Section II; about 10 minutes suggested.

The question and its sources

Fruit flies feed and lay their eggs on ripe and rotting fruit. Students investigated whether the odor of ripe banana affects where adult fruit flies go.

Investigation

The students built a choice chamber from two clear tubes joined at the middle. At the far end of one tube they placed a cotton ball soaked in banana extract. At the far end of the other tube they placed a cotton ball soaked in the same volume of water. The chamber was kept in the dark at 24°C.

The students released 20 flies at the middle of the chamber. After 10 minutes, they counted the flies in each half. They repeated this with six groups of new flies, switching which side held the banana extract each time.

Source: Hypothetical study

Suggested time: 10 minutes

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Part (a)

1 point

Describe how responding to the odor of ripe fruit could increase a fruit fly's fitness.

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Part (b)

1 point

Identify an additional treatment the students should run as a control to show that the flies do not prefer one side of the chamber for some reason other than the banana odor.

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Part (c)

1 point

State the null hypothesis for this investigation.

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Part (d)

1 point

The students also test flies with a mutation that prevents them from making a functional receptor protein that binds odor molecules from ripe fruit. They predict that these flies will be found in about equal numbers on the two sides. Justify this prediction.

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