Question

All octopi dream every night, and sometimes change colour while dreaming. A student hypothesises that octopi change colour only when they dream about the food they ate that day. To test this hypothesis, the student conducts an experiment with two treatments that are randomly ordered, and separated by 2 days. In one treatment, she places 10 octopi in individual tanks in captivity and provides each one with a large crab to eat during the day. She then records the dream state colour of these octopi that night. Which one (or more) of the following would be an appropriate NEGATIVE control to test this hypothesis?

• A. Provide the same 10 octopi with the same food source (crab), and then record their colour that night when they are dreaming.
• B. Provide the same 10 octopi with a new food object (e.g. sea stars) and record the colour that night when they are dreaming.
• C. Provide the same 10 octopi with a non-food object (e.g. rock), and record their colour that night when they are dreaming.
• D. Provide 10 squid with the same food source (crab) and record the colour that night when they are dreaming.

Hint:

A negative control ensures that any observed changes in the dependent variable are due to the experimental variable, and not to other unrelated factors.

Answer 1

The Correct Option is C

A negative control is used to establish a baseline response where no expected effect occurs. The purpose of a negative control is to demonstrate that the change in the dependent variable (in this case, colour change in octopi) is not due to external factors unrelated to the hypothesis.

Step 1: Analyzing the options.
- (A) Provide the same 10 octopi with the same food source (crab), and then record their colour: This option is not a negative control because the experiment is already testing the hypothesis that octopi change colour based on the food they eat.
- (B) Provide the same 10 octopi with a new food object (e.g. sea stars): This is a variation of the treatment group, not a negative control. It would test the hypothesis but wouldn't establish a baseline where no expected effect occurs.
- (C) Provide the same 10 octopi with a non-food object (e.g. rock): This option is the appropriate negative control because it ensures that the observed colour change is not due to factors unrelated to the food, as the octopi would have no expected reason to change colour in response to a non-food object.
- (D) Provide 10 squid with the same food source (crab): This is not a negative control either, as it tests the hypothesis on a different species.

Step 2: Conclusion.
Thus, the correct negative control is option (C), where the octopi are provided with a non-food object, and no colour change is expected.

Final Answer: \boxed{(C)}