A bioassay is an experiment that uses living things to test the toxicity of chemicals. 

Duckweed

Environmental Inquiry provides a collection of background information, experiments, reports, and other curricular materials for high school students. Check out their Toxicology Bioassays section, which has experiments using Duckweed and Daphnia. Each teacher will receive a copy of the book Assessing Toxic Risk, which has additional materials for teaching. 

Daphnia

Observing Daphnia Heart Rate