Academic journal article The American Biology Teacher

Teaching Cellular Respiration & Alternate Energy Sources with a Laboratory Exercise Developed by a Scientist-Teacher Partnership

Academic journal article The American Biology Teacher

Teaching Cellular Respiration & Alternate Energy Sources with a Laboratory Exercise Developed by a Scientist-Teacher Partnership

Article excerpt

[ILLUSTRATION OMITTED]

   Students often resort to memorization and recall when learning
   about cellular respiration. The concepts of glycolysis, Krebs
   cycle, and the electron transfer chain are abstract with multiple
   steps that are difficult to follow. The electron transport chain is
   the major workhorse for creating ATP in living organisms, and yet
   there are very few ways to clearly illustrate the electron
   transport chain in the laboratory.

The above comment started a conversation between a high school biology teacher and scientists from the local university who were participants in a National Science Foundation (NSF)-funded teacher-scientist partnership program. This conversation led to a collaboration that developed this laboratory exercise demonstrating cellular respiration.

Cellular respiration is the process of obtaining biochemical energy (stored as ATP) from fuel molecules (sugars). There are three major reactions that occur in cellular respiration: glycolysis, the Krebs cycle, and the electron transport chain (ETC). The ETC is the final step in cellular respiration and produces the most ATE In eukaryotes, the ETC is on the mitochondrial membrane; however, prokaryotes do not have a mitochondria and thus the ETC is on the plasma membrane. In addition, eukaryotes are only capable of respiring on oxygen (glucose + [O.sub.2] [right arrow] C[O.sub.2] + [H.sub.2]O), called aerobic respiration. When oxygen is not present, eukaryotes can perform the less efficient fermentation reactions. Fermentation produces less ATP than aerobic respiration because it does not use the Krebs cycle and the ETC. However, in the absence of oxygen, prokaryotes have the ability to ferment as well as use the ETC (anaerobic respiration). For example, some bacteria are able to respire on solid phase iron (glucose + [Fe.sup.+3] [right arrow] C[O.sub.2] + [Fe.sup.+2]). Respiration on multiple elements gives microbes an advantage in harsh environments where oxygen is not present. In addition, microbial respiration on solid phase compounds can be exploited to produce electricity.

Microbial fuel ceils are a current research area that harvests electricity from bacteria capable of anaerobic respiration (Holmes et al., 2004; Liu et al., 2004; Logan et al., 2005). Graphite is an electrically conductive material that bacteria can respire on, thus it can be used to capture electrons from bacteria. When bacteria transfer electrons to graphite, an electrical potential is created that can produce electricity when in a circuit. A sediment battery is a simple circuit that uses graphite and anaerobic bacteria naturally found in dirt. The electrical potential produced by bacterial respiration on the graphite can be measured on a voltmeter and thus can be used as a visual aid for teaching cellular respiration.

The combination of the need for a new learning tool and the expertise of the scientists led to the development of the laboratory exercise described here. It uses student-designed sediment batteries to better visualize and measure electron transfer in living cells. This exercise satisfies National Science Education Teaching Standards A and B, and Content Standards A, B, and C.

* Background

Chemical Batteries

A battery uses chemicals to produce electrons. One common battery is a zinc/carbon battery, which has two terminals: a positive (cathode) and negative (anode). At the negative terminal, a zinc rod is placed in sulfuric acid. The sulfuric acid dissolves the zinc rod at the surface. A zinc atom will leave the rod as a [Zn.sup.+2] ion leaving two electrons on the rod; thus electrons are built up at the anode. When the battery is incorporated into a circuit, the electrons are allowed to travel from the anode to the cathode. In the cathode, the electrons travel through the carbon into sulfuric acid to produce hydrogen gas. The production and movement of electrons in a battery can power a device. …

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