Best of the Week 2018-2019: Excellence in College Prep


This week in Mrs. Amanda Nugent's SL Biology class, juniors and seniors learned about the different macromolecules that make up all living things, particularly carbohydrates. To further explore this lesson in-depth, students looked more closely at how bananas store energy as starch during fruit formation, which are then converted into sugar as they ripen. Fruit bearing plants normally take sugar from their leaves and convert it into starch which is then stored in developing fruits. As the fruit ripens, it breaks down the starch into simple sugars, which is what gives fruit its naturally sweet taste.

After spending several classes studying macromolecules and their specific properties, Mrs. Nugent conducted a lab for her students to see firsthand what happens during the ripening process inside a banana. "The original idea was presented to me in a journal I read from 'The American Biology Teacher,' and was adapted by several Biology teachers I work with in a virtual community," says Mrs. Nugent. "This lab was a way for my students to visualize the properties that are unique to carbohydrates, required a great deal of conceptual understanding prior to conducting the experiment and gave students more opportunity to practice lab techniques, like preparing slides and using micropipettes to mix liquid samples, that they'll use in college-level laboratory courses."

Students were given samples of a new, ripe and unripe banana and an indicator - iodine - which, when in the presence of starch, will turn from a yellow to a dark-brown color and, when in the presence of simple sugars, will not change color at all. After making observations between new, ripe and overripe bananas, students then took samples of each and added iodine, recording the differing results in color. As an added step to the experiment, students placed separate samples of banana in water and then added the iodine. Once the mixture was shaken, students extracted a drop of the banana/iodine mixture and created their own slides to view the color changes on a cellular level. These slides of the banana cells gave a microscopic view of how different cells store starch. These cells, in particular, had small plastids which, when holding starch, turned brown and, when holding simple sugars, remained clear. Observing this reaction demonstrated to students the ongoing process that breaks starch down into simple sugars.

"Throughout this lab, students really had to think about what was going on at various levels (tissue, cellular and organelle), which can be challenging to conceptualize," says Mrs. Nugent. "Overall, the students really enjoyed making their own slides, and seeing their work on a cellular level is always int