Answer: Control: In the first experiment where Homer is testing his idea that salt won't lower his heart rate, the control would be his normal diet, including all the food he loves. This means he continues to eat salty food as usual.
Manipulated (Independent) Variable: In the second experiment, where Homer spends a week not eating any salty food, the manipulated variable is the absence of salty food in his diet.
Responding (Dependent) Variable: The responding variable in both experiments is Homer's heart rate, measured in beats per minute (bpm).
Conclusion: Based on the results of the experiments, Homer can conclude that reducing his salt intake (by not eating any salty food) results in a lower average heart rate (95 bpm) compared to his normal diet (average heart rate of 115 bpm). Therefore, it suggests that reducing salt intake may indeed help lower his heart rate.
Independent Variable: The independent variable in Tina's experiment is the presence or absence of caffeine. Specifically, Test 1 serves as the control group without caffeine, and Test 2 serves as the experimental group with caffeine applied to the earthworm's skin.
Dependent Variable: The dependent variable in Tina's experiment is the heart rate of the earthworm, measured in beats per minute (bpm).
Hypothesis for Tina's experiment: "If caffeine is applied to the earthworm's skin, then its heart rate will increase compared to when no caffeine is applied."