Show slide 13 of the PPT and ask students to compare their results to the results for Ms. Angle’s class.

- Explain to students that the data from the video (or from Ms. Angle’s class) showed that the potato lost 0.66 g and the mealworms gained only 0.37 g. So overall the system lost 0.29 g. Remind students that atoms are forever, so this mass must have gone somewhere. Students may have some ideas about where the mass went. Tell students that you will discuss this missing mass later in the unit.
- Potatoes lose mass both because mealworms eat them and because water evaporates from the potatoes themselves. We checked to see how much mass potatoes lose to evaporation by leaving potatoes in a container without mealworms. In 24 hours they lost about 0.5% of their mass to evaporation—considerably less than the difference between what the mealworms ate and the weight they gained (about 3% of the potato mass). If your students are concerned about evaporation, we can suggest a couple of strategies:
- Try what we did: Put some potato slices in a container as a control.
- Discuss with the students whether they think that evaporation is the ONLY process that is causing the system to lose mass.

The remainder of the unit is based on the assumption that your class results are similar to those of Ms. Angle’s class and the Mealworms Eating video. If your class results are significantly different for any reason, after a conversation about why that may have happened, decide whether to have students conduct the investigation again or to refer to Ms. Angle’s data as they work through the remainder of the unit.