Investigation 3.1: Learning How To Test For Sugar and Starch

I am hoping to have a video for this investigation uploaded soon.

The investigation had two goals:

The first was to revisit the important pieces of our investigations.  We will need to practice our skills of identifying our focus question, a prediction, independent and dependent variables, and controls, so that we can design our own investigations down the road.

The second was to gain experience with two indicators: Benedict's solution, which is an indicator for simple sugars, and Lugol solution, which is an indicator for starch.  Once we understand how these indicators work, we can use them to gather evidence to support claims related to other foods, and connect these ideas to our bigger explanation about the digestive system.

The first day, we were only able to get part of the investigation done.  We got close to finishing maybe the first test with Benedict's solution, but that was it.  Most of the period was spent doing preparation of our samples.

You may notice the worksheet for this investigation is in a new format.  I am trying to provide us with an easy way to review the major parts of an investigation, so that as we move forward we can practice building these pieces ourselves.  Please let me know if you have any questions!

Worksheet for Investigation 3.1

After completing the investigation, we looked at the data from every group in every class to compare our group's results with the total results.  What we expected to see is that our results were similar to everyone else's.  But this sometimes doesn't happen.  Sometimes, we get unexpected results.  When this happens, we need to discuss what might have happened to result in a different outcome.  What is important to not here is that this does not mean that your group obtained the "wrong" result or a "bad" outcome!  It's very possible that your group was one of the only ones (or maybe the only one) to get an accurate result!  But we need to try to determine what happened.  First we make an observation.  Was our result similar to the one obtained by a majority of the groups?  If not, how could we possibly explain the reason our results were different?  One common explanation was contamination.  For a sample such as distilled water, for example, we logically expect that it will test negative for starch.  But if it tests positive for starch, that is unexpected, and what are the possible explanations?

Many, many students said that they felt the appropriate action would be to redo the test several times to see if maybe it was a mistake or a contamination, and that multiple trials would help to support this claim.  That is very true – we rarely do experiments only once in science.  As my wife says, "that's why they call it research.  Get it?  RE - search!"

Unfortunately, due to limited class time, we can't repeat a lot of our investigations.  We try to use everyone else's result as a simulation of us repeating the experiment.  It's not perfect, but for classroom purposes, it will have to do.  We will revisit this idea of how to handle outliers and unexpected results after Investigation 4.1.