Second in a series of five lessons, this instructional activity encourages preteens to consider cities as urban ecosystems. First, they keep a food diary for a few days. They visit the Natrional Agricultural Statistics Service website for current data on food production. They take a virtual tour of ancient Mesopotamia and discuss how the improvement of food production is related to the development of cities. Standing alone, this instructional activity does not stand out. Check out the other lessons in the series though. You may find the mini-unit valuable. for upper elementary world history.