1. A week after returning from a backpacking trip, four teenagers developed nausea and severe diarrhea. All had consumed untreated water from a stream which doctors concluded was infested with the organism, Giardia. Think about the symbiotic relationships that you studied in this unit. What type of relationship exists between the teens and the organism?

2. As humans burn fossil fuels for energy, the percent of carbon stored in fossils is reduced while the carbon in the atmosphere is increased. If green plants are also being removed, how might the carbon cycle and greenhouse effect be influenced?

3. How are decomposers critical to the carbon cycle?