Two students are planning an experiment that will test how planaria (aquatic flatworms) respond to different environments. They will conduct two investigations—one that tests the worms’ responses to different water temperatures and one that tests the worms’ responses to different levels of acidity. Student 1 wants to buy two groups of flatworms and use a different group for each investigation. Student 2 thinks the same group of worms should be used for both investigations.

Do you think either student’s method would give more accurate results? Why or why not?