Penny Density in Physical Science

One of the labs we did this year in Physical Science when we were studying density was one called "Coin Operated" from our textbook, Holt Science & Technology: Physical Science. Lab groups are given a set of 10 carefully chosen pennies that they mass individually and are asked to divide into two groups. (Their masses give a big hint about how to divide them.) They also use the water displacement method to determine the volume of the pennies. Students find the density for each set of 5 pennies and then are asked to determine what element they are likely to be made of. In an ideal world, one set will be close to the density of copper and the other close to zinc. Then students are tasked with figuring out how they could divide the pennies without an electronic scale. Eventually, students realize that older pennies (pre-1982) are made of copper and new pennies (post-1982) are made of zinc.

Our first test included a lab practical section and I wanted students to find the density of a penny and use that information to determine if the penny was from before 1982 or after 1982.  Of course, how do you hide the date from the students?  Fortunately, one of the few souvenir items my husband and I  let our kids get when we go somewhere special are those squished pennies with the logo of whatever place we are at. One of my daughters helped me round up four of these squished pennies so I could have four test lab stations going at once. Believe it our not, it turned out that two of them are pre-1982 and two are post-1982. Since the test, I've found two more, both post-1982.

Working with Enzyme Models

I love to have models that students can work with to help understand a concept. So much of what we do in AP Bio is too small to see--even with a microscope.  We can talk about how these small things work, but I find it more meaningful if we can get our hands on it. We do complete the AP enzyme lab and get to experiment with what factors affect the rate of the enzyme catalyzed reaction of peroxidase with hydrogen peroxide and guaiacol.  Fortunately, before the lab we did two activities to give them some concrete pictures of what is happening with enzymes.

The first exercise we did involved using pool noodles as models of enzymes, substrate, and inhibitors (both competitive and allosteric).  I got this idea from a blog post on We Teach High School and got the directions from Mr. Mohn's blog (Toucan Play That Game). Students use pool noodles to demonstrate what is happening in 4 different scenarios.  Here is the document I put together for my students to use from those two blogs.

I loved this activity.  "Allosteric" sounds so esoteric, but when you can push a wedge of a pool noodle into another pool noodle and watch the active site change, it suddenly becomes real.

I found the Need For Speed lab on Pinterest.  I modified it to use in my classroom.  After doing the activity this week, I've decided that I want to modify it even more.  Since the students had already worked with competitive inhibitors with pool noodles, I think we can skip that part with the pennies and instead focus on changes in the rate of reaction when enzyme and substrate concentrations change.