Photosynthesis STEM Case (Gizmo)
Hypothesis: Diuron is painted on the bottom of boats in order to kill algae, but when released
into the water, can kill the algae that feed coral. This inhibits Photosystem 2, which is the first
step in photosynthesis. Decreasing the ATP made as a result of PS2 will lower the
concentrations of NADPH, and sugar, explaining why all 3 levels decreased.
Background: Coral is not a plant, but an animal, so it cannot produce its own food. It's
immobile, meaning it cannot hunt for food, so algae (which produces food through
photosynthesis), feeds the coral. When algae is killed in the ocean, it loses its color and can no
longer feed the color, bleaching it.
Initial Observations: Water from the GBR had 2 factors affecting the coral (more specifically the
algae that grow on the coral). High water temperatures had some part in the bleaching, but the
real suspect was diuron. Diuron affected the first stage in photosynthesis, more specifically
photosystem 2. With the decreasing levels of ATP, the levels of NADPH and sugars have to
decrease, since they don't have the adequate reactants to carry out normal function.
Experimental Data: Paraquat caused the inhibition of NADPH production. This caused and
increase in ATP and a decrease in the other 2. We know this wasn't the culprit of the coral
bleaching because the GBR sample showed a decrease in all 3, including ATP.
Conclusions I: I know that diuron caused the coral bleaching because all 3 of the factors
matched the sample; ATP, NADPH, and sugars. The diuron inhibited the production of ATP,
causing a decrease in the latter two, just like the sample.