In the Classroom: Biology 2

Elizabeth Aldrich’s Bio 2 students illustrate a microscopic process with eggs.
Sometimes all that’s needed to demonstrate a physical scientific process is to illustrate it. That’s what Elizabeth Aldrich’s Biology 2 class did for their homework on Monday night. Eighteen hours earlier, Lizzy placed two eggs in flasks containing two very different substances: water and corn syrup. The eggs had had their shells dissolved in vinegar to allow them to expand or contract, and students were tasked with illustrating what the eggs would look like after soaking in the solutions overnight, and explain how the hypothesized reaction had occurred and why.

The goal was to visually demonstrate the process of osmosis, the process by which molecules move across a permeable membrane into the region of higher solute concentration, and illustrate the difference between a hypotonic reaction, where water is retained, and a hypertonic reaction, where water is expelled. When the students came back to class the next day, the egg in the water solution had swollen to an immense size, while the egg in corn syrup had shriveled up. They were then tasked with explaining why. Students came up to the board to draw diagrams illustrating the cause of each reaction.

The assignment allowed students to observe what had previously been an abstract reaction, infer details based on the observed reaction, and draw their own conclusions based on the material shown.

Leave a Reply