Lichens make surprisingly precise pollution sensors. Each type reacts differently to acidic conditions, so placing all three in the same environment reveals whether acid rain is present. Fruticose and foliose lichens shrink and turn brittle under a vinegar-water mist that mimics acid rain, while crustose lichens survive the same conditions remarkably well. That split response is exactly what makes them useful as bioindicators — the contrast between healthy and stressed samples tells you what the habitat is carrying.

Hydra live in ponds and respond quickly to changes in water quality, which makes them useful living pollution detectors. In this project, groups of hydra are placed in two sealed chambers — one receiving automobile exhaust stored in a tire inner tube, the other holding normal room air as a control. Every 24 hours you examine both groups under a stereo microscope, recording changes in body shape, feeding behavior, and survival. The differences that accumulate over several days reveal whether car exhaust can harm freshwater life even in small doses.