“Good morning!” greeted Upper School science teacher Sallie Mathis as Class 9 students entered Room 804.
As they settled in at their desks, Ms. Mathis informed her class that they would be working in groups of three to write their own lab procedures. “You’ll be testing whether or not certain molecules can pass through a cell membrane,” she stated.
In the written documents provided, Ms. Mathis explained that living things, whether huge and multicellular or tiny and unicellular, require a flow of materials into and out of cells and these materials must pass through the cell membrane. Much of the movement of molecules between cells occurs by means of diffusion, which is the movement of molecules from a region of higher concentration to a region of lower concentration. Diffusion occurs spontaneously and does not require the expenditure of energy (ATP).
Since Ziploc bags are “porous,” having, though imperceptible, small spaces or holes, they were to be used to simulate the outer membrane of the cell since they are selectively permeable. The students’ experiment was meant to investigate and simulate the diffusion of glucose and starch across this membrane.
The instructions stopped there. Thus, the ninth-grade scientists immediately dove into their research to determine how to best execute their goal. “It’s trial and error, using all of your data is a huge part of science,” Ms. Mathis encouraged.
Collaboration and creativity abounded as students debated how to construct their cell model. With limited materials – distilled water, glucose solution, starch solution, iodine, Benedict’s solution and Ziploc bags – their teacher encouraged the students to think outside the box.
Ms. Mathis also provided a list of questions to ponder such as ‘Which molecules are most or least likely to diffuse through the bag and why?’ and ‘Since the bag cannot choose what will enter or exit, what is the determining factor that will allow some molecules to diffuse?’
“What is an indicator and what is it for?” she prompted one group. “What does it indicate the presence of?”
“Iodine is an indicator for starch!” The students said, beaming as they began putting their pieces together.
Once Ms. Mathis approved their procedures, they could conduct their lab. After clearing off their lab tables and securing their safety equipment, they grabbed graduated cylinders, beakers and test tubes and got to work!
“Remember to write down how many drops, milliliters, and so on that you use,” remarked Ms. Mathis, noting that if someone wanted to replicate their unique lab, they’d need the exact measurements.
After creating their simulation, students hypothesized which molecules would be too large or small enough to pass through the membrane. Next, they measured their model and placed it into a beaker of solution of their choosing and left it overnight for diffusion to occur.
The following class, the scholars examined their results and discussed their outcomes – feeling confident and proud of their hard work.