It may be necessary to grow large amounts of green algae (and other microorganisms) to be used for microscopic observations in schools. A soil culture allows you to enrich various types of algae.
Materials: A large glass jar, fresh and unfertilized garden soil, water, hot plate, celophane foil
- Fill the glass jar with a few centimeters of the garden soil.
- Add non-chlorinated tap water to the soil and fill the jar with the water (3/4 full).
- Boil the soil-water mixture for about 30 min. This will kill off bacteria in the soil and will extract nutrients from the soil. Bacterial spores may survive the boiling, as they are heat-resistant. This is not a problem, though. These bacteria will serve as a food for other microorganisms later on.
- Cool the water to room temperature and let the soil settle to the bottom of the glass jar. Do not filter the soil away. The soil will continue to supply nutrients and will act as a buffer.
- Add a small amount of pond water which contains algae. Do not add too many algae. You may want to scrape off some algae from rocks or take a few algal filaments floating in a pond.
- Cover the jar with celophane foil. This will allow for gas exchange and prevent dirt and dust falling into the water. It also reduces evaporation.
- Wait a few weeks for the algae and ciliates to develop. With a bit of luck, paramecia will grow and form white clouds in the water. The color of the water may also change, an indicator for algal growth.
- Store the jar in a bright place but not in direct sunlight.
- Using a pipette, extract some of the microorganisms to be observed under the microscope.
- Microorganisms do not form: This is probably due to the fact that there were none or not enough in the pond water which was added.
- The water starts to smell bad: This may be due to the system becoming anaerobic. Make sure that enough oxygen is able to enter the water. Paramecia and other ciliates are probably dead by now…..