ANSWERS
QUESTIONS

1. Where did the algal mat that grew over your microscope slides come from?
   (The algae were already living in the fish tank. The slides offered a fresh substrate for colonization. Microscopic spores and cells floated onto the slide and grew into an observable colony.)
2. Was it necessary to expose the beakers and their contents to light? Explain.
   (Yes. The algae require light to meet their photosynthetic needs. Without light, the algae could not survive.)
3. Where did the oxygen required by the snails come from?
   (the gas was replenished in the fresh water. It was also released by the plants during photosynthesis)
4. Suppose the snails were predators and not grazers. Would this affect the results of the experiment?
   (Yes. If they were predators, they would not feed upon the algae. The snails would starve and the algae would grow without this biological control.)
   

PART TWO

QUESTIONS

1. Why was it necessary to remove all of the snails and other organisms from the transferred aquarium plants?
   (To insure a reliable control, you needed to limit the introduction of snails or other grazers into the control environment.)
2. Was it necessary to expose the beakers and their contents to light? Explain.
   (Yes. The algae required light to meet their photosynthetic needs. Without light, the plant will die.)
3. Why were both aquarium plants and algae-covered slides used in this experiment? How is this representative of the concerns raised by the use of biological control?
   (Both were used to find out if snails might also eat the "good plants" as well as algae. Although it is preferable to have them graze on the unwelcome algae, they can easily destroy Elodea and other desired plants. This is a common concern when introducing biological control mechanisms to an invaded region.)