Development of teaching materials for junior and senior high school science classes related to organic matter decomposition by microorganisms modeled on food decomposition

• Published in: Japanese Journal of Biological Education Vol. 64; no. 3; pp. 185 - 196
• Main Authors: Suzuki, Akira, Kimizuka, Shota, Fukuda, Tatsuya
• Format: Journal Article
• Language: Japanese
• Published: The Society of Biological Science Education of Japan 2023; 一般社団法人 日本生物教育学会
• Subjects: bacteria; biological education; food materials; mold; nutrient-poor medium
• ISSN: 0287-119X; 2434-1916
• DOI: 10.24718/jjbe.64.3_185

We attempted to develop cultural teaching materials for “Science Division II” in junior high and “Fundamental Biology” in high school classes in units related to organic matter decomposition by microorganisms, in Japan. Seventeen kinds of foodstuff (processed foods and fruits and vegetables) fragment (s) were separately placed on nutrient-poor agar plate media [plain agar medium and 10-fold diluted PDA medium (1/10 PDA)] in Petri dishes by aseptic manipulation. Thereafter, in one series of experiments, the Petri dishes were sealed by a piece of parafilm, and in another series of experiments, the foodstuff fragments were exposed to air-contaminant bacteria and fungi for 30 seconds prior to the sealing. All cultures were incubated at 20°C for 24 days. The exposure did not affect the growth of bacteria and mold on the surface of most foodstuff pieces. The decomposition dynamics of the foodstuff fragments during cultivation on the nutrient-poor media were able to chase at an interval of two to five days by the naked eye observation for at least 17 days. This is because the growth rates of bacteria and mold that appeared from the foodstuff pieces on the nutrient-poor media became suitable for the time-series observation. In most cultures of the fruits and vegetables, both bacteria and molds grew vigorously. On the other hand, bacteria predominated in the culture of processed animal foods. The advantage of this teaching material based on food decomposition as a model can be carried out easily and safely by the students because it does not require strict aseptic manipulation as long as the sterile agar plate media are prepared by the teacher. Namely, students prepare the foodstuff fragment (s) and put them separately on the agar plate media without strict aseptic manipulation and are able to chase the decomposition dynamics of animal and plant organic substances caused by bacteria and/or fungi from outside of the Petri dish without opening the lid of the Petri dish containing the culture.