40 to test acidity levels of water, scientists test the ph. as acid rain falls, the ph levels in lakes and streams decrease. while certain animals can tolerate low ph levels, others are extremely sensitive to the effects of acid rain and cannot live under the conditions. students in maria's class know, based on the chart, the ph range tolerated by specific organisms living in the ponds surrounding their school maria and several other students are anxious to design an experiment to investigate this topic.