The evolutionary branch leading to Closterium , the bright green alga cell seen in our gallery, may have split from the yellow pigmented diatoms as far back as two billion years ago. The line leading to ciliated protists such as Blepharisma or Stentor probably branched even earlier. Although amoebas share the characteristics that their cell membrane is flexible, there is even a great diversity among this protist group. Evidence from molecular biology studies shows that some amoebas are much more closely related to Euglena than they are to the classic textbook amoeba, Amoeba proteus . A close study of Paramecium with a student microscope allows for the observation of phagocytosis, digestion, water balance, ciliary action, cell excretion and a variety of responses to stimuli.
Paramecium is easy to culture and can be studied without specialized laboratory equipment.
In our work developing teaching media for cell biology, we regularly film and photograph live protists to demonstrate the biology of the living cell. See our video program series Visualizing Cell Processes , where we mix animations with live photo-microscopy to demonstrate how the cell works. Well, for one thing, without bacteria no fish, no frogs, no birds, no pretty pond lilies, cat tails, or sedges would survive. Bacteria are essential because they break down dead organic material, allowing raw materials once locked up in animal and plant bodies to recycle through the pond community. The bacteria themselves, become food for protozoans such as Paramecium and Vorticella , and these organisms, in turn, feed the insects, crustaceans, and baby fish, building up food chains and creating a pond community.