Arcella is an amoeba that lives in a shell made of chitin, the same material that makes up the exoskeleton of insects. It eats bacteria and small algae. You can obtain a culture of harmless bacteria, such as Enterobacter aerogenes (a normal inhabitant of the human gut) to serve as food. Divide the Arcella population into several batches, and add bacteria to half of them. After several days, use a microscope to observe a sample drop from each batch that is placed on a microscope slide and a cover slip added. Which Arcella are growing best?

Obtain cultures of Didinium, Paramecium caudatum (which lacks green algal symbionts), and Paramecium bursaria (a species that contains many green algal cells). Split the Didinium culture into several batches. Add Paramecium caudatum to half the batches, and Paramecium bursaria to the other half. After a few days, observe samples from each batch with the microscope. In which batches is Didinium most abundant and healthy? Which Paramecium is more tasty to the Didinium (which is the antelope and which is the spiny anteater of the protoplankton world)? Does having symbiotic algae make a difference?

If your microscope has a videocamera attachment, you can capture Didinium's taste tests.