Renewable - But Is It Sustainable?

Carol Burton, Bellevue Community College

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This page first made public: Oct 9, 2012


Students learn about ethanol production and participate in a class discussion of the different energy inputs and environmental consequences involved in producing ethanol from corn. Students produce mini-posters to illustrate the issue and their conclusions regarding the question: Renewable - But is it sustainable?

Learning Goals

Students will be able to:

  • Define the differences between renewable and sustainable.
  • Identify the different energy inputs involved in the production of ethanol from corn.
  • Discuss the pros and cons of corn ethanol and other biofuels as alternative energy.
  • Describe the role of photosynthesis, cellular respiration and the Laws of Thermodynamics as they apply to biofuels production
  • Evaluate the "value" of biofuels in terms of sustainability.
  • Document research sources correctly.

Big Ideas:

Sustainability - Renewable and non-renewable resources; Systems thinking; Ecosystem functions; Ecological footprint; Global warming

Biology - Energy flow; Nutrient cycles; Ecosystem functions; Society and technology

Additional Outcomes for Biology 101 and Majors:

Describe the processes by which carbon dioxide, oxygen, water, nitrogen, and phosphorus move in and out of plants.
Explain where and how carbon is sequestered in plants
Discuss the difference in carbon sequestration in woody vs. herbaceous plants e.g. trees vs. grass.

Context for Use

The primary rationale is to for students to think about what the term sustainability means and all the different factors involved in energy flow using ethanol from corn as an example. Production of biofuels as an alternative energy source is not as simple as the media portray. This exercise enables students to practice critical thinking skills in evaluating the "value" of biofuels - a somewhat ambiguous concept. Though not primarily part of this assignment, you could introduce energy conservation as way to approach declining reserves of fossil fuels. The popular idea of using biodiesel in your sports utility vehicle (SUV) is not the way to go.

This is an exercise that could be done with non-majors, Biology 101, or with majors. The difference would be the amount of detail and depth.

This could be used as an activity in a study skills/ learning strategies class as an exercise in critical thinking and information literacy. There are economic and social components that could be used in those disciplines.

Description and Teaching Materials

Timeframe: Prior to the day of assignment you should talk about energy flow and materials cycling, including the 1st and 2nd Laws of Thermodynamics, carbon dioxide emissions, and carbon sequestration. Also other nutrient needs, soils and soil structure. With both 101 and majors you will have talked about photosynthesis, cellular respiration and movement of materials. You may also want to plant a few ideas about energy and environmental consequences, including the less obvious ones such as transportation, soil degradation, pollution, food costs. The discussion could be done in one 50 minute class period, especially if you kept the groups on track and focused. Give them time limits (15 - 20 minutes each) on the small groups and class discussion, leaving 10 minutes to do the mini-poster. If you wanted to do it in a two hour lab period, then expand the time frame accordingly.

The article evaluation and any follow up assignments are done as homework, out of class.


Give students an article to read, something on ethanol from corn or other biofuels production (see Resource list of possible articles below). Have them turn in answers to article evaluation questions at start of class (see Questions to Answer Student Handout for article evaluation below). Make sure they know that this completed assignment is their ticket into the discussion in class. That way (we hope) they will have read the article, and are prepared for the discussion. If you have two (2 hour) periods, you could spend some time talking about the words or terms that students didn't know. Read some of the answers to this question and ask the class how they understand the terms. Or you could do this one day before the class discussion.

Use the article evaluation to assign groups of three to four students. Those who did not complete the homework put in a separate group, and they don't get points for the homework. Have each group discuss and list the different energy inputs and outputs, and environmental consequences involved in production of ethanol from corn. The list can include economic and social impacts as well as biological. Then open up the discussion to whole class. Keep this short - it's a way of ensuring that the groups have explored the possibilities adequately. The discussion will most likely move into other biofuels, and energy conservation, which is OK.

Have each group produce a mini-poster on the issue, showing inputs and outputs, pros and cons. The mini-poster could be part of an assessment - does it include all energy and environmental impacts? Are positive and negative impacts included? For majors, an alternative is to have each group diagram a tree showing inputs and outputs of various molecules, with modes of transport, destination, energy inputs and outputs.

Materials needed: Flip charts for mini-posters, colored markers.

Questions to Answer Student Handout (Microsoft Word 26kB Oct26 11)

Teaching Notes and Tips

I haven't used this particular assignment with a class, but have done similar assignments with other topics. The main problem is keeping students on track during the discussion, as you know they can wander off into other discussions. I have found opening the discussion to the whole class after the small group discussion is helpful here, but keep that brief.

Variations - you could do a jigsaw exercise looking at various energy sources, their pros and cons in terms of sustainability. A quiz on this the day after the exercise helps to keep students listening to their group members. Another idea is looking at carbon footprint using one of the many online calculators.


  • Answers to article evaluation
  • Mini-poster showing inputs and outputs, pros and cons of ethanol from corn +/- other biofuels.
  • Information literacy - find other sources on the issue, research the "experts" quoted in article. Citations should be complete and formatted correctly - you should designate a particular format if this is important to you e.g. MLA, APA, Science Editors.
  • Short paper (individual assessment) on the "value" of biofuels as alternative energy source, with pro and con arguments. Arguments should be supported with evidence even if you do not require formal citations.
  • For 101 and majors, essay or short answer questions on next exam/quiz: e.g. where does CO2 go in the plant? i.e. other molecules, make ATP, storage. What other elements are needed? Where do they come from? How do they get into plant? How long is carbon sequestered in plant? Is this different with different plant types? Which processes require energy? 'Follow" molecules of carbon dioxide and water through photosynthesis and cellular respiration, including the transport processes, and sites of reactions.

References and Resources

Possible Articles to Use - not intended to be a comprehensive list. Pick articles that have some controversy or ask questions that could stimulate a discussion.

Aldhous, Peter. Genes for Greens. New Scientist 5th January 2008: 28-31.

Brooks, Michael. Less is More. New Scientist 2nd February 2008: 33 -36

Caterinicchia, Dan. New Ethanol Goal offers Challenge, Opportunity. Seattle Times 19th December 2007: C1

Fargione, Joseph, Jason Hill, David Tilman, Stephen Polasky, and Peter Hawthorne. Land Clearing and the Biofuel Carbon Debt. Published online 7 February 2008 [DOI: 10.1126/science.1152747] (in Science Express Reports)

Pacific Northwest National Laboratory. 2008. Key to using local resources for biomass may include waste. accessed 4/7/08. Press release for larger study on use of waste as energy resource, link to study is in article (pdf file).

Righelato, Renton and Dominick V. Spracklen. Carbon Mitigation by Biofuels or by Saving and Restoring Forests? Science 17 August 2007 317: 902 [DOI: 10.1126/science.1141361]

Rosenthal, Elisabeth. Biofuels Deemed a Greenhouse Threat. 8th February 2008, New York Times.

Scharlemann, Jorn P. W. and William F. Laurance. How Green Are Biofuels?
Science 4 January 2008 319: 43-44 [DOI: 10.1126/science.1153103]

Searchinger, Timothy, Ralph Heimlich, R. A. Houghton, Fengxia Dong, Amani Elobeid, Jacinto Fabiosa, Simla Tokgoz, Dermot Hayes, and Tun-Hsiang Yu. Use of U.S. Croplands for Biofuels Increases Greenhouse Gases Through Emissions from Land Use Change. Published online 7 February 2008 [DOI: 10.1126/science.1151861] (in Science Express Reports)