|A Drop of Life|
|A Drop of Life|
Article and Photomicrographs by Bruce J. Russell
Protists, Single Cells That Do It All
An amazing world exists just beyond the naked eye. Pond water is one place to investigate this landscape of single cells that behave as independent organisms. Biologists have named this group the protists.
Protist were around long before plants and animals appeared. Fossil protists have been found in rocks dated at more than 1.8 billion years old. In fact, your local pond is a very good place to find protists very similar to those that started the lines of multicellular life — and these organisms seem relatively unchanged from that ancient time. The transition from single cell life to multicellular life is one of the most fascinating questions of modern biology. This step is exemplified by the colonial alga Volvox. All animal life is now thought to have evolved from a simple colonial organism that lived over 700 million years ago. To probe this topic further, see our video/CD-Rom programs, The Domains of Life. We have also posted a annotated list of web links on this topic.
Ancient Branching of the Tree Of Life
Protists represent some of the most diverse branches in the tree of life. 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. Compared to these diverse lines of protist life, we animals are actually more closely related to our cousins, the fungi.
Have a Look at How Life Works
Single-celled pond life gives us a unique chance to study the processes of life right in the living cell! 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 program series VISUALIZING CELL PROCESSES and INSIDE THE LIVING CELL where animations and live photo-microscopy demonstrate how the cell function.
Why Study Pond Microlife?
Right, what are all those little things really good for? 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. The green and yellow algae (diatoms) seen in our gallery shots are examples of microscopic producers that convert solar energy into complex molecules that can be passed on to consumers. The same principles apply to a forest, grassland, or ocean. The simple fact is that microorganisms create the ecological foundation for life on planet earth — a foundation that supports humans and all other living things.
For more about single cell life see Guide to Microlife, published by Franklin Watts, a division of Grolier Publishing, ISBN 0-531-11266-7. This informative text includes color photomicrographs by Bruce J. Russell.