- Preparation of the nutrient growth medium:
- Dissolve beef cube and sugar in a glass of water until it boils. Add gelatin and mix until it dissolves. Cover and wait until it cools down.
- Pour into clear (if possible sterile) pots or foil muffin cups, cover by using transparent wrap and place in the refrigerator.
- Take a trip to nearby streams and take water samples.
- Using sterile swabs inoculate water samples onto the nutrient growth media surfaces and place each of them into a separate plastic bag (for protection in case that some dangerous bacteria develops).
- Incubate until visible colonies of microorganisms appear. Be careful how you handle the samples, because some bacteria may be dangerous.
Discuss your findings. Explain to students that microbes are the smallest living systems on the planet, and the communities they form can be found everywhere. They play many important roles in our lives, and they also play an essential role in cleaning aquatic ecosystems.
- How microorganisms contribute to cleaning aquatic ecosystems? (By feeding on nutrients dissolved in water, which contributes to the self-purification ability of river systems.
- Can we see them with a naked eye? (These organisms can be seen only with the help of a microscope, so we call them microorganisms. In rivers, we can also see them as a part of biofilms on the surface of stones called periphyton, which is composed of various species of bacteria, algae, and other microorganisms.)
The idea for the experiment is taken from: http://www.instructables.com/id/Homemade-Nutrient-Agar/
Materials and equipment
For field sampling of water:
- sterile specimen (urine) cup with lid – for the sampling of river water
For preparing the nutrient growth medium:
- 1 glass of tap water
- 12 g of gelatin
- 4 beef broth cubes
- 2 small spoons of sugar
For working in a lab:
- sterile swabs
- samples of river water
- nutrient growth mediums
- small plastic bags with ziplock