Activity: Useful Decomposers (40 min over 2 days) Students compare aerobic and anaerobic decomposition and identify products in their homes and daily lives that are direct or indirect products of each kind of decomposition. Resources Provided Decomposers Worksheet (1 per student) Materials needed Large container for boiling water Tongs 1 pint glass jar with lid per student or pair of students Milk – 1 cup per student or pair of students Saucepan for heating milk Food-safe thermometer 1 quart container of unpasteurized yogurt Incubator set at 37o C or warm, not drafty corner of room Setup Print one copy per student of Useful Decomposers Worksheet. Directions 1. Students read and discuss text in Section 1 of Useful Decomposers Worksheet. Have students read and discuss Section 1 of the worksheet. Possible discussion questions include: what have students experienced? How can these microbe-laden products be safe? Which kind of decomposition, aerobic or anaerobic, is more likely to be smelly? 2. Students check all decomposition products they think they have in their homes and discuss findings. This step can be given as homework, allowing students to go home and investigate. The class can compile their data. How many students have each product? Are they using more aerobic or anaerobic decomposition products? 3. Students follow directions to setup milk yogurt mixture and leave for next day. 4. Students read and discuss text in Section 2 of Useful Decomposers Worksheet. Possible discussion questions include: why do powerful antibiotics often lead to digestive problems? What other animals besides cows have digestive systems that are able to break down tough plant fibers? (Ruminants such as deer and goats, termites) 5. Students check all indirect decomposition products they think they have in their homes and discuss findings. This step can be given as homework, allowing students to go home and investigate. The class can compile their data. How many students have each product? Are they using more aerobic or anaerobic decomposition products? Assessment Assessment for this activity is meant to happen through discussion. Tips Important Safety Note: If students are interested in tasting their yogurt, inspect their results first to make sure it is safe. Stirring the yogurt before trying it is recommended as there will be some liquid that separates from the solids. Students should taste less than a teaspoonful. If the milk is still mostly liquid on the following day, it is not safe to consume and should be completely discarded. While successful attempts will produce something that looks like yogurt, it will not taste like the yogurt that most students are accustomed to. Most store-bought yogurts are high in added sugars, and so the yogurt produced in this lab will taste much more sour and not sweet at all as a result. Students should be warned of this in advance or they may reflexively spit out the yogurt when they try it. The lab can be made to be more inquiry-based by offering students a couple of options for store-bought yogurt to use as their starting culture or store-bought dry yogurt cultures (available in health food stores). Dairy food manufacturers invest a large amount of money, time, and effort into finding bacterial cultures that produce consistent results, and different yogurt brands may be more or less successful. Students may make predictions about what brands or types might be more effective (e.g. name-brand vs. store-brand; regular vs. Greek, etc.). (On a side note, CRISPR was actually discovered by Danisco yogurt microbiologists, which is a testament to the amount of research that still occurs in dairy foods). Extending the Learning - Digging Deeper Other useful microbial decomposers Students can research other useful microbial decomposers. Some possibilities are: Antibiotic producing molds and bacteria Decomposers that can break down crude oil or plastics to help with oil spills or plastic in landfills Disease causing vs helpful intestinal bacteria Health benefits of probiotics (or lack thereof)
