Title: Diffusion in Gummy Bears
Student prior knowledge: Students need to know that the cell membrane is semipermeable and how the difference in concentration gradients can affect the direction water moves through the membrane.
Explanation: Students should be able to see the gummy bear in the salt solution shrink in volume. There was a higher concentration of water and lower concentration of NaCl inside the gummy bear compared to the lower concentration of water and higher concentration of NaCl outside the gummy bear in the cup filled with the supersaturated salt solution. Thus, the water moved from an area of higher concentration to an area of lower concentration, to reach equilibrium.
Also, the gummy bear in the water solution swells up because the concentration of solutes is higher inside of the gummy bear than outside of the gummy bear. Thus, the water travels into the gummy bear.
Questions & Answers: 1. Explain how the gummy bear swelling up relates to a red blood cell (RBC)immersed in pure water swelling up? Answer: The gummy bears model a cell with the outside of the gummy bear representing the semipermeable membrane of a cell. Red Blood cells, as well as gummy bears, have solutes on the inside. When immersed in water, the concentration of solutes is significantly higher inside the gummy bear and RBC. Water will travel into the the gummy bear/ RBC to decrease the difference in concentration across the membranes.
2. What would happen if we immersed a gummy bear in a solution that has the same amount of solutes as the gummy bear? Explain your reasoning. Answer: Ideally the gummy bear would have no change in volume, because there is no concentration gradient.
3. If we were to take the gummy bear from the water solution in day two and immerse in a supersaturated salt solution would it shrink, swell, or stay the same? Answer: The gummy bear would be expected to shrink because there would be more solute outside of the gummy bear than inside of the gummy bear. Also, the gummy bear had gone through an increase in water content on the inside so the decrease in volume would be greater.
Applications to Everyday Life: It is crucial for the bloodstream to maintain balanced ion concentrations in the plasma and inside of the red blood cell (RBC), in order to maintain a regular shape. If the plasma is too diluted the RBC may swell up, which will affect their efficiency.
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