Light and dark bottles for an aquatic primary productivity study. The dissolved oxygen (D.O.) of the bottles is being measured using a sensor interfaced to a laptop. Changes in D.O. will reveal the extent of photosynthesic production of organic miolecules (primary productivity) by the algae in the water. The dark bottle (wrapped in foil) will reveal the extent of cellular respiration that consumes organic molecules, while the light bottle will show the rate of gross productivity (photosynthesis and respiration). The experiment is part of a high school biology lab.