Like so many topics teachers have to deal with, feedback loops seem pretty simple on the surface, but kids don’t come in with any understanding of what they are.
Possible pitfall: feedback is either positive or negative, and when kids hear that, they think “good” or “bad”. So it’s a good idea to address that right away. Feedback loops, both positive and negative, are composed of many processes that, in an organism, help maintain homeostasis. But positive feedback “steps on the gas”, enhancing or increasing a result, while negative feedback “steps on the brakes”, curtailing or redirecting a process. Most feedback loops in the body are the negative kind, acting to reverse a process that is upsetting equilibrium. A good example is control of body temperature. Other examples include control of blood sugar levels, and control of water loss in urine. As you describe one of these feedback examples, you might ask the students: “Is this positive feedback or negative feedback?”
Further, you might say, “If you are too cold, what would be the outcome of a positive feedback loop acting on your body temperature?”
A few feedback loops in the body are positive feedback. These are in situations where a culminating event is desired. An excellent example is the process of labor and delivery. Describe the feedback factors at work, and ask students, “Why is positive feedback desirable here?”
We can also interpret some kinds of human interactions as examples of positive or negative feedback. The courting process is one of those.
As we go up the levels of organization in biology, we can also see feedback at work , even on the level of biosphere. For example, as global warming progresses, the permafrost in the tundra melts, releasing methane. As methane levels rise, warming is increased.
Our last environmental example of feedback is one we see when water is polluted with excess nitrogen. It is described by the graphic in this student worksheet, and an answer key follows.
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Eutrophication, a Positive Feedback Loop–Student Worksheet
When the nitrate amount is high, eutrophication may happen. In eutrophication, too much plant food (fertilizer) like nitrate gets into the water and makes too much algae grow. Use arrows on the picture below to show what can happen.
Eutrophication Worksheet Answer Key