In My Classroom: Going Bananas for Phenomenon Based Teaching

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I originally drafted this “In my classroom” as a way to talk about this cool lab that I used to begin talking about the role of biological molecules in living things.  I originally intended to end this with talk of how it was a great lab experience for my students and made for a good model to explain how living things utilize biological molecules.  This was all before the recent NABT conference when I learned about the work being done by teachers in Illinois to create phenomenon based storylines as a way to teach concepts and practices from the NGSS.  I still intend to say all of those things, but the ending has really just sparked a thousand new fires in my head.  Brad’s use of the lighting of the beacons from The Return of the King is in full effect, and I am seemingly humming the score as I type away.

A few years ago, an inquiry idea got posted in the October 2015 ABT about utilizing bananas as a model for learning about biochemistry.  This year, I decided to utilize the model in my classroom as a way to introduce biological molecules and begin talking about cells and cellular processes.  I started with the bananas in class, giving groups of my students (both AP and General) very ripe, somewhat ripe, and unripe bananas.  I asked them to use their chalk markers and record as many observations as they could, comparing and contrasting the bananas.  I got some predictable responses like their coloration was different, but most made great observations about the texture, mass, and taste of the bananas.  My favorite interaction was when one adventurous student informed the class of the taste and consistency of all the banana peels, pointing out that the unripe banana appeared to have a higher water content in the peel compared to the riper specimens.

So after all these observations and in class discussion, I directed students to use the two chemicals I had provided them (iodine and Benedict’s solution) and create an assay to observe how they affected the various bananas.  We made some observations, and recorded our qualitative data from what we saw.  This lead to me revealing that Iodine serves as an indicator for starches and Benedict’s for sugars.  At this point we talked about carbohydrates and their overall structure, pointing out that polysaccharides like starches are formed from sugar monomers like glucose.  We could see clearly that one banana was strongly positive for the presence of starches while the other was more strongly positive for sugars.  This lead to me posing a question.  How did all those starches seemingly disappear, and the sugars replace them?  

My students sat on this for a second.  I had to prove that I had not injected them with sugar.  Students teetered around an answer, but I eventually had a student in each class suggest that the starches are being digested.  I had one student go so far as to name drop amylase.  This lead to us talking about chemical reaction that are occurring to break these polymers up into simpler pieces.  We modeled what they looked like and investigated the role and structure of proteins, particularly amylase.  With the last few minutes of class, we broke out the microscopes and identified cells that had been stained with iodine to indicate the location of starches in the cells.  My students were super engaged with the whole process.  We had a small writeup to summarize and model the processes we had observed.  But that was kind of the end. We still talked about these things in class, but I left a pretty cool phenomenon just hanging there.

A student slide of unripe banana stained with iodine to highlight the presence of starch (in this case amylose).

As previously stated, I got to see some awesome phenomenon based teaching from my experiences at NABT, and am looking at next steps with my students.  Jason Crean from the Illinois Association of Biology Teachers has formulated these NGSS storylines in his class following specific organisms and phenomena.  His phenomena are very heavily focused on real data from collaborations with zoologists and some of his work can be found at http://www.xy-zoo.com/.   His focus is on how all of the content standards in the NGSS connect to each other in an engaging and coherent storyline, all sparked by an investigation into a particular phenomenon.  

While thinking about writing this post, it occurred to me that the banana lab seems like a great piece in the puzzle to start my own conceptual storyline unit on how “We are what we eat.” In my head, this will be something that delves into why some people have trouble processing certain foods and how malnutrition affects us.  I have shared a little bit about this idea already on a Facebook post, and am now looking into a collaboration to produce some conceptual storylines that follow phenomenon, not just the order the standards are packaged and delivered to us.  I realize there is safety there, but safety has never been fun.

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