2. A student observes two identical fish tanks. Each tank has three guppies
and several live plants. Two people are in charge of changing the water in
the tanks every week. One person forgets to change the water in one tank
(Tank B). Next week, the plants in Tank B seem to be growing faster than
those in Tank A. The student hypothesizes that nutrients from fish waste,
which are primarily a result of the breakdown of proteins, are helping the
plants in Tank B grow better. To test this hypothesis, what should the
student test for?
