The only real purpose I can see to these labs is to de-mystify DNA a little and generate a little excitement at the same time about it. There's something neat about being able to "see" this stuff and know that it came from your cells and it's just this substance found naturally in all living things. It's not magic powder, it's this goopy, clumpy, stringy white stuff in our cells. My hope is that they will be really intrigued and want to know more about how this funky-looking material determines our traits.
I gave students a choice of following the wheat germ protocol or the cheek cell. It was kind of nice to have the two being followed at the same time for comparison, but it certainly complicated the distribution of materials and discussion of the two protocols.
What administrators don't understand about teaching science
I teach in a school that is probably not unlike many others. We have no real science labs, science is taught in whatever rooms are available for the programmer to put us in. We are a large school: In my grade (8) there are about 5 teachers with about 4 classes each (on average - in reality we teach a split schedule between grade 8 plus at least one other grade, but that's another story. The point is there are about 5 grade-8 teachers and about 20 grade-8 classes!). There are a small number of classrooms (about 3) for each grade that were originally designed as science rooms, but the science part (running water, gas lines, lab stations, etc) were dismantled many years ago. Nonetheless, because they are near the science supply rooms and relatively large, they are at least more desirable than other classrooms in the building. Unfortunately most of those rooms are in fact not used for science but rather as regular classrooms for English, Math, or Social Studies classes. One of the supply rooms was turned into an administrative office. I am lucky enough to teach in one of the "science" rooms.
I'm also lucky enough to be teaching regents biology which provides some guidelines, specific content objectives, and some required labs. It is still not what I consider a "curriculum" and demands a tremendous amount of planning from teachers. The labs, being at a higher level than many of the middle school labs, also require a lot of prep time and a lot of materials, some rather specialized. The DNA lab needs water within a somewhat narrow temperature range (50 - 60 Celsius), test tubes with covers, long stirring sticks, alcohol, and a few other items. All need to be prepared in such a way that 30 students (yes, 30 students) can use them at 5 different tables with a minimum about of spillage or breakage. On top of that, materials usually have to be distributed AFTER students arrive, because the room is used throughout the day by other classes and cannot be arranged at the tables before students enter. Likewise, materials have to be collected at the end of the period because the classroom will again be used by another teacher (for social studies or English) with another class. Now think about making sure all the tables are cleaned after doing cheek cell labs and other biology related activities! For my 7th grade class I have to travel to three other rooms on a different floor. This is pretty typical this year for most of my colleagues, in fact my program is great compared to others. Not exactly my idea of an ideal working environment for science teachers. As you might suppose, we have an incredibly high turnover rate for teachers in general, and - it seems to me at least - science teachers are particularly difficult to find and keep.
Back to the DNA Extraction Labs
If you are thinking of doing one of these labs, don't sweat the details. I used saltwater for the mouth rinse, which may have been unnecessary: I misread the protocol and I remembered using saltwater in a class when I did the cheek cell extraction, so I guess I didn't read that part too carefully. I must say it gave me some perverse pleasure to see the students suppressing their gag responses to the saltwater! I also tried following the correct protocol using tap water as the mouthwash and adding saltwater later. Both methods yielded neat samples of DNA. I was pretty imprecise with the liquid detergent, and didn't have any problems. Wheat germ does indeed give oodles of DNA.
The biggest problem my students had was following the protocol alone and not waiting for me to tell them what to do, or insisting I tell them at every step if it was OK now to do the step. I will take some blame for that. It isn't that often that I give them written assignments or open-ended activities and let them struggle through it on their own. (Note to self...)
The other problem was pouring the alcohol into the test tube gently without letting it mix into the saliva or the wheat germ mixture. The cups I gave them for pouring didn't work so well, probably because of the low surface tension(?) of the alcohol which leads it to spill easily, even from beakers - in trying to avoid spills they poured too fast and mixed everything up. It was a bit of a messy lab, but I think a lot of fun for the kids, and I hope a nice starting point for getting into the details of DNA in the coming couple of weeks.
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