Students seem to have difficulty sorting through the different types of cell transport, because it’s such an abstract concept. Even after reading the textbook, taking notes, and doing different activities, my students didn’t understand the difference between diffusion, osmosis, and active transport. I created a handout for my students to use as part of our review for the test that had them visually explain what was happening during each process.
The basic format is one of the formative assessments Paige Keeley sets out in her book, Science Formative Assessment (volume 2). She calls them “B-D-A Drawings”. Rather than do each process separately, I created one document to compare the three processes. It was a spur-of-the-moment creation, so I hand-drew the drawings for the “before” panels. One benefit of giving students the “before” drawings is that they’re all using the same basic shapes for solute and water, and the same number of molecules, and I can set it up to guide them toward what their “during” and “after” drawings will contain.
I did a jigsaw activity for this handout – I counted off students as 1, 2, or 3, then put each number at a separate table. Each table was assigned one drawing to complete. As each table worked on their drawings, I circulated through the room to answer questions they had, or to ask groups questions to prompt them to think about what would happen for their assigned process. When the group working on diffusion seemed stuck, I did a quick demo with a beaker of water and some food coloring. The osmosis group had the right idea about water moving (instead of solutes), but when I saw that their drawings did not change the water level, I asked them what would happen to the water level on each side.
Students used their science notebooks to help them think through their processes. It took them about 5-10 minutes to discuss what they thought would happen and draw the “during” and “after” diagrams. It also prompted a good discussion about equilibrium – how it would be different for each process, and how the active transport process wouldn’t reach equilibrium.
After each group had completed their set of diagrams, I regrouped students so there was one person with each diagram at a table group. Each student had to explain their diagrams to their tablemates and answer any questions. After each student had explained their process, students had to complete the diagrams for the two processes they didn’t have.
Overall, this activity gave students a visual explanation of the differences between diffusion, osmosis, and active transport. With larger classes, you could create multiple groups for each process to keep group size small enough to keep students focused on the work.