Build a Maintenance-Free Ecosystem
By Melissa Hodges
Product Manager, Zoology, Microbiology, and Botany
Carolina Biological Supply Company
When asked to picture a local ecosystem, your students are likely to think of conspicuous animals and plants, but they may not consider the microscopic organisms found in freshwater sources. While it may be inconvenient to take students to sample ponds and streams, you can easily re-create an exciting and diverse aquatic community in your classroom. Students can observe, sample, and test the ecosystem for as long as you care to keep it. If you do not have time to collect a balance of aquatic producers and consumers and set them up in a small tank, try the Carolina™ Minipond Ecosystem Kit. This kit provides opportunity for students to identify many typical aquatic organisms and to study the habitat as a whole. You can incorporate this model ecosystem into a variety of topics:
- Environmental issues (e.g., water quality, biodiversity)
- Influence of biotic and abiotic ecological factors
- Stability and succession
After you create a minipond, your students can observe and sample it just as if they were visiting a local pond or stream. Have them get a drop of pond water with a pipet, add it to a microscope slide, and cover it with a coverslip. If they find that some protozoans move too fast to be observed clearly under the microscope, they can add a drop of Protoslo® Quieting Solution to the next slide before covering it. Protoslo® does not harm the organisms, but its viscosity slows their movement enough to keep them in focus and in the field of view. Students can then observe their structures and their method of locomotion.
Challenge students to sketch 3 to 5 different organisms in enough detail that the sketches can be used later for identification. Students can compare their sketches and see what others are seeing. To help students identify the various microorganisms, download our free illustrated key to common freshwater microorganisms.
For discussion and further exploration
- The Carolina™ Minipond Ecosystem Kit includes a typical mix of microorganisms found in any nonpolluted body of freshwater. Take the opportunity to discuss human influence on local watersheds. What if a local water source were tested and no living microorganisms were found, or there were very many of only 1 or 2 types? Ask what factors may have caused these effects. Look for local or national news stories that might be integrated into your discussions about water pollution and water quality.
- Compare the structures and features of the aquatic protists that you observe with those of animals and plants. For example, animals have muscle tissue that contracts to move body parts, and some protozoans have contractile strands called myonemes that operate in a similar way to move cell parts. The terminology for protozoan anatomy includes terms such as "cell mouth," "cell anus," and "cell pharynx" because of the similarity in function between these cell parts and corresponding animal structures. Algae have various types of plastids (including chloroplasts) and perform photosynthesis as plants do. The comparisons of protists to animals and plants can also lead to discussion of the role and balance of autotrophs (producers) and heterotrophs (consumers) in an ecosystem.
- Discuss the classification of the protists that you observe. The protist kingdom itself is a grab bag of subgroups and is the least valid taxonomic kingdom in terms of interrelatedness of its members. In fact, it is almost certain that some of its members are more closely related to organisms in other kingdoms than to some in their own. Discuss what defines the kingdom. Also discuss the features of some of the groups within it (e.g. ciliates, diatoms). Note the variety among the algae that you observe and try to place them in their taxonomic groups.
- Sample various parts of the minipond (surface, bottom detritus, open water) and note any differences in the types of organisms found or in their population proportions. Discuss niches and adaptation.
- Keep the minipond over several months and sample it occasionally to check for any changes in the population makeup. Discuss succession.
- Alter an abiotic factor (e.g., adding a tiny amount of plant food, placing the pond where it gets a little more or less light, or adding some sediment) and see whether the ecosystem is affected. Discuss real-world analogies such as fertilizer runoff from farms or suburbs, loss of shade due to removal of tree cover, and sedimentation from construction project erosion.
Tips on using microorganism cultures
Need to make your activities using microorganism cultures easier? Here are a few quick ideas.