One of the labs that we do that students have to most fun with is our enzymes lab. I have done the toothpick-ase lab before; I prefer to keep using liver. Why would I bother with liver when toothpicks are easier and create less of a mess? The kids love it! It is messy and gross and all the things that they think make a great lab. Plus, I think the visual production of bubbles is an easier way to communicate the differences in the reactions.
I found this lab YEARS ago and have heavily edited it to make it work in my class. I think the original may have come from The Biology Corner, but I don’t really know anymore. I have it set up in two files because it works for me. The first are the lab instructions, I make a class set of these to leave out at the lab stations. The second is a lab data table. This is where the write their data (duh), answer questions, and write the answers to the follow up questions. Each student gets their own data table.
Here are some things I do to make this go a little smoother:
- I keep the container of liver out of the fridge during the day, but keep it covered. I cut up pieces of liver for students to collect; this saves time for the students not having to do this.
- Cut up the apple and potato for the students as well, but don’t leave them sitting out for long.
- Make sure your yeast is fresh. I just put some in a beaker and mix it into warm water. You might tell them not to put too much in the test tube. They think more is better.
- I set up the “cold peroxide” and “cold liver” and keep those in the fridge (or freezer for short term) until we need them. Students just get the test tubes and mix them. I do not warm the liver over a hot plate; I’ve burned it too many times. I set up the test tubes and keep them in a warm bath, but I just keep replacing it with heated water. Pre-boiling the liver is great because that makes sure you got it really hot. One year, I over heated the “warm liver” and under heated the “boiled liver!”
- I would also let you know that I have not had success with testing acids and bases. Most of the ways I’ve tried it, the reaction appears to go faster, not slower, but I think that is the reaction between the acid or base and the peroxide. Have any of had success with testing the effect of pH on enzymes?
- This is a great time to teach your students about the importance of lab clean up! I have them wash and dry all of the test tubes they used. I just collect the ones I need back to set up Part C for them.
I had read someone say that they blended up the liver to make it a liquid. I tried that this past year with my G/T classes and it worked out ok, but it wasn’t something I was crazy about. Part of it was the liver smoothie we ended up with that was too gross, even for me. I also had some slight technical issues with it clogging the pipettes and distorting some of the data. I’m just going to stick with cutting up the liver.
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