Lesson 2: Ethanol Production and the Pros and Cons of Biofuels
This lesson will entail the students gaining an understanding of "Carbon Neutrality", and how biofuels could reduce the carbon emissions associated with motor fuel. First I will introduce them to the equations for photosynthesis and combustion, so they can see that they are inversely related. We will discuss the energy requirements for photosynthesis and relate this to the energy that is contained in biofuel. They will find that the biofuels are basically just stored sunlight energy.
The class will have already been presented on articles and data surrounding the effects of corn farming in the mid-west on environmental issues such as the "Dead Zone" in the Gulf of Mexico.
Activity 1: The Pros and Cons of Corn Ethanol
We will revisit the concept of Environmental Unity, and they will have to write some sort of opinion paper on the issues discussed in class. One possible activity is to have the class debate the merits of corn ethanol. Having debates is a good way to get students to research and understand both sides of an issue. One of the articles that students will read centers on the EROI of corn ethanol. We will discuss the energy efficiencies discussed, and pose questions regarding the use of corn ethanol.
Activity 2: Enzymatic Degradation of Cellulose
The last activity in this part of the lesson will involve the students attempting to degrade cellulose using cellulase, a common enzyme available from most biological supply companies. Students will use the enzyme on two different forms of cellulose; processed cellulose (white paper), and unprocessed cellulose (Switchgrass stalks). I will provide each group with the supplies, including glucose test strips. Since cellulose is a polymer of glucose subunits, once the cellulose is degraded the glucose test strips will indicate the presence of sugars. The glucose test strips are commonly available at most drug stores, or from biological supply companies.
The basic procedure that I have developed is as follows:
1) Prepare 200-300 ml of a 5% cellulase stock solution.
2) Give each group of students 2 vials with caps. Vials should each hold about 20 ml of solution. Have students mark the vials appropriately.
3) Provide each group with a few strips of printer paper, or the "dots" from a paper punch, as well as a few stalks of switch grass or corn husk.
4) Students should put paper in one vial and switchgrass in the other, taking care to put approximately the same amount in each.
5) Students should add about 20 ml of the cellulase solution, and test both vials for glucose concentration using the glucose test strips.
6) Let the vials sit for about 2 days. Then have students record visual data, as well as glucose concentration from a second set of glucose test strips.
I will show the students an electron microscope image of the cellulose in ordinary sheets of printer paper, and have them view ordinary printer paper through a light microscope to demonstrate the processed nature of the cellulose in paper products. We will also discuss in class the methods used in the paper industry to create paper from wood pulp. I will give them an article about paper processing so they can relate it to the processing of cellulose for ethanol.
This activity will also present a good opportunity to reinforce good scientific technique, with the inclusion of control groups, etc. I may also extend the lesson and demonstrate the denaturation of an enzyme by heating a small sample and using it on a sample of the paper strips. This will be a good springboard to explain the relatively fragile nature of some enzymes, which will eventually lead to our final lesson concerning biobuanol and its production.
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