MATERIALS
- Some tubes for the possible repetition of the operation;
- tubes holder;
- icy alcohol (kept in a freezer).
METHOD
- Slowly, pour in the tube of the previous step some icy alcohol by avoiding it mix with the filtrate;
- the volume of the alcohol has to be about the same of that of the solution;
- let the tube rest for 5 minutes to allow to the DNA to precipitate and accumulate in the tube.
Now, at the interface between alcohol and the filtrate you should be able to see a milky substance, which tends to increase in volume as time progresses. This milky substance is the DNA of the banana. Unfortunately, inside this milky little mass, you may observe numerous tiny bubbles. The presence of these bubbles is due to the property that the solubility of gases in a cold liquid is higher than in a warm one. While alcohol was in the freezer it likely absorbed some gases that are expelled as the liquid is warmed up.