We began the day by revisiting the grass/cow/hamburger slide from yesterday, Students were challenged to apply their understanding of the food web by figuring out how much grass a cow has to eat to produce a hamburger. Understanding that grass is at the bottom of the food chain (like halobacteria in the Great Salt Lake), and recognizing that cows eat grass (like brine shrimp eat halobacteria), students reasoned that it would take 10 times as much mass in grass to produce one hamburger. If a hamburger has a mass of 100 grams, then a cow would have to eat 1000 grams of grass to produce the hamburger. Several students wondered how much land is required to produce 1000 grams of grass, and I encourage all of my students to research that question for extra credit!
We continued our discussion of the food web game by analyzing group results, assembling a table of class results, and calculating the average number of organisms at each level of the food chain. Students observed the 10-fold decrease in organism mass as we move up the food chain, and we connected the concept of biomass with energy. The results for each class period are reported at the end of the slide deck. We also discussed the variables involved in the food web game activity, with students identifying distance from the seed-trading space, number of students per group, and the efficiency with which groups worked as key variables contributing to how many higher-level organisms a group obtained.
After the slide deck and discussion, students worked in groups to complete the back side of the worksheet from yesterday. Students learned that while the amount of matter in a system stays constant, the amount of energy in a given level decreases as we move up the food chain. This is not always obvious, especially because organisms at the bottom of the food chain tend to be very small (yet great in number).