How I teach the digestive system structure (without PowerPoint )

The fundamental insight to the digestive system is how it functions to meet the needs of the whole organism. To address this, we must contrast it with other systems; we have to see what we're not to see what we are. I'll show you how I did this by co-constructing the knowledge with my students bit by bit. See the benefits of teaching without PowerPoint here.

Contrasting fungi, cnidarians, and humans.

First, I drew the fungus and explained the term secretion. (As I draw, students draw). To get an idea of a life lived this way, we watched this video of a slime mould. I then wrote the two fundamental steps below the image and took advantage of the possibility to recall examples of organic molecules.

Next I moved on to animals and the example of Hydra.

I searched for images of Hydra on google to show how these species—as with other cnidarians—have a primitive digestive system without an anus. I made explicit how the examples of fungi and Hydra, show the same concept.

But here, there are more questions. Fungi and animals are both heterotrophs, but one has an digestive system, while the other doesn't? Why?

I had students discuss in pairs why it was beneficial to have a digestive system. Then we discussed it as a class. If you could move, and therefore take a digesting meal with you. Animals may be less vulnerable while digesting food, and that they could have specialised organs for digesting.

Finally, I added the diagram of the animal with an anus and the interesting question now pertained to the ecological evolution of the anus. "What's it good for?" I asked the students.

Some students came to the answer—with more or less guidance depending on the class—of how an anus allows several meals to be processed at once, at different stages. Without an anus, it's one meal at a time.

They also saw how Hydra's simple system was a generalist. Having a mouth and anus has favoured the evolution of specialist organs that can process foods in different ways in sequence. This means that the system can have a larger variety of ways of processing the food than the generalist cnidarian system. With this higher complexity, it can have a more complex diet, which in turn affords the organism with more adaptability. This is an application of the law of requisite variety that I explain in Difference Maker.

With this in mind, we moved on to the human digestive system.

The key from here was to have students see the fundamental pattern—of secretion, digestion, and absorption—in the digestive tract. We began with a drawing of the digestive tract and noted where secretion of enzymes occurred, and where absorption happened.

However, often students can get lost in the idiosyncratic details of organs. I wanted them to see the pattern in an abstracted form: a diagram of the system, which clearly showed my understanding of its structure and principal functioning. Therefore, I drew a stock and flow diagram.

I began by drawing the principal stocks and flows: mouth, stomach, small intestine and large intestine. However, I only named the first one (nutrients in the mouth) and asked the students to name the others (in pairs).

I then focused on the glands. I drew the stocks and flows (in red) and asked students to name them using the previous diagram to help them.

Finally, I added the stock of the blood and asked students to identify it before labelling it myself. This completed the diagram and I was able to make explicit the pattern of secretion, digestion, and absorption in the human digestive tract.

From here, I asked students to carry out self-explanation, one of Fiorella and Mayer's eight generative learning strategies (2015). This activity involves students explaining the diagrams to themselves as if they were explaining it to a classmate who had missed a lesson. I have them do this individually and in silence, but another option I sometimes use is peer-explanation (in pairs). I then asked students what doubts they had and answered their questions. Learn more about teaching this way in: Difference Maker.

References

Fiorella, L., and Mayer, R. 2015. Learning as a Generative Activity: Eight learning strategies that promote understanding. UK: Cambridge University Press.