Jason conducted an experiment to study the effect of temperature change on the heart of Daphnia, transparent aquatic invertebrates commonly known as water fleas. Jason heated three different beakers of water containing Daphnia to a different temperature: 30 oC, 32 oC, and 34 oC. He used a microscope to observe Daphnia in each sample. He counted the number of heartbeats in one minute and averaged his results. Which could be a step in a replication of this experiment?