in his second experiment, what should he da different. in the same science fair, tina asks the question "does caffeine increase the heart rate of an earthworm?" in test 1, she measures the heart rate by looking at the earthworm under a microscope, the earthworm has a heart rate of 50 bpm (beats per minute). in test 2, she places a few drops of caffeine on the earthworm's skin and measures the rate again. in this test, the heart rate is 68 bpm.