We're doing this DNA extraction lab today. I have 2 groups of 7th graders, so I am doing the same lab as yesterday and think I have learned a couple of things about how to make it better. We're extracting DNA from bananas, papaya seeds, liver, and candle wax (hopefuly not finding any DNA in the candle wax). The first step is to blend up the stuff with a healthy pinch of salt added to about 200 mL of cold water. Then the strained "goop" has some (about 30 mL) of liquid detergent (I tried both liquid dishwashing detergent and liquid laundry detergent and it didn't seem to make a difference) added to it, swirl it around, and let it sit for about 10 minutes.
Yesterday I blended up all the "goop" and the kids added the detergent, but they could not wait the 10 minutes. They were on to the next steps (adding a pinch of meat tenderizer and slowly layering isopropyl alcohol on top) immediately.
Today I thought I had it figured out. I blended up 3 mixtures of goop (banana, papaya, and wax) and in front of the class added the liquid detergent. I then asked them (each team having to come up with the right answer) , "What is the only substance (goop) you are going to add liquid detergent to?" They all answered the liver. I then asked "How long will you wait after you add the detergent to the liver?" They all told me 10 minutes. Then I blended the liver and put them to work sorting their test tubes and going through the steps.
Of the 4 teams of 4 in the class, how many teams would you guess added detergent to all 4 goop mixtures? 2!
How does that happen?
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