Water fleas (Cladocera) are small freshwater crustaceans. They are filter feeders can are about 3-5mm long. The outer carapace o
f a water flea is transparent so the internal organs can be observed. Caffeine raises the heart rate of humans. Hanna predicts caffeine will have the same effect on other organisms. She uses the water flea as her test subject in an experiment. Hanna introduces varying amounts of caffeine to water flea populations. Using a microscope, she measures the heart rate in beats per second of sample water fleas. She records the data in a table. As the concentration of caffeine increases, Hanna observes the water flea heart rate also increases. What is the hypothesis in Hanna’s experiment? A) Caffeine raises the heart rate of humans. B) Water fleas prefer caffeine over plain water. C) Caffeine increase the heart rate of the water flea. Eliminate D) The effects of caffeine are the same on all organisms.
