This activity provides students an interactive demonstration of the electron transport chain and chemiosmosis during aerobic respiration. Students use simple, everyday objects as hydrogen ions and electrons and play the roles of the various proteins embedded in the inner mitochondrial membrane to show how this specific process in cellular respiration produces ATP. The activity works best as a supplement after you have already discussed the electron transport chain in lecture but can be used prior to instruction to help students visualize the processes that occur. This demonstration was designed for general college biology for majors at a community college, but it could be used in any introductory college-level or advanced placement biology course.

This activity/simulation is designed to give students a first-hand, interactive view of the functioning of the electron transport chain and chemiosmosis that occurs during aerobic respiration. It takes a few simple materials to set up and will help students visualize some relatively complex processes that may otherwise be quite confusing in the absence of the concrete example provided here.

The Electron Transport Chain & Chemiosmosis

The electron transport chain is one of the many processes in cellular respiration that can be very confusing for students in both high school and college. Chemical processes such as this are very abstract to students; they have a difficult time visualizing the various steps and, consequently, develop a less-than-complete understanding of these types of processes. Similarly, the process of chemiosmosis can be very challenging to teach and to visualize. Both of these processes are critical to cellular functioning, so it is critical that students leave an introductory biology course with a proficient understanding of these metabolic pathways.

Materials

  • Keys (these represent the electrons from NADH)

    • ∘ An alternative object is a potato

  • Markers (these represent the hydrogen ions)

    • ∘ Any object could be substituted here, such as marbles, bottle caps, etc.

  • Red and yellow 6 × 2 Lego pieces or something similar

    • ∘ These represent ADP and inorganic phosphate for the purpose of synthesizing ATP

Procedure

This demonstration works best in a room in which there are at least two rows of tables. The front row of tables represents the inner mitochondrial membrane (cristae), and the back row of tables represents the intermembrane space of the mitochondrion (see Figure 1). Students sitting at the front row of tables represent the various cytochromes and enzymes embedded in the inner mitochondrial membrane. In this simulation, the student on the far left side of the front row of tables is the first cytochrome. The student second from the far right of the front row of tables represents oxygen. The student on the far right of the front row represents ATP synthase. Students in the back row of tables represent the intermembrane space of the mitochondria. The teacher (with the keys) represents NADH. Providing nametags or some other indicator of the roles the students and the teacher are playing might be an additional help for students in visualizing the process.

Figure 1.

Table and classroom setup.

Figure 1.

Table and classroom setup.

Introduce the simulation by telling the students that they will be role-playing the electron transport chain and chemiosmosis. Start by giving each student in the front row of tables (except the one who represents oxygen) a marker or other object. These objects represent hydrogen ions (H+) floating around in the matrix of the mitochondrion. In the following outline, statements and questions from the teacher are indicated by italics.

  • Stand next to the student on the far left of the front row of tables (the first cytochrome). Take out the keys, shake them, and tell the students that you are NADH and the keys are the electrons that NADH possesses.

  • Ask the students to identify where the electrons came from (the answer is glucose or pyruvate). Hand the keys to the first person in the front row. Ask them what happens to them and to NADH (the teacher) chemically when electrons are transferred (the student/cytochrome is reduced and the teacher/NADH is oxidized; review oxidation and reduction if necessary).

  • At the same time, ask the first student to hand their marker (or other object) to the student behind them, who represents the intermembrane space of the mitochondrion.

  • Have the first student in the front row hand the keys to the next person and have them state who is oxidized and who is reduced. Explain that this is active transport, using the energy of the electrons being passed down the chain to pump H+ ions through the inner mitochondrial membrane.

  • Have the second student pass their marker (or other object) to the student behind them. Remind the students that the markers represent hydrogen ions being transported across the cristae of the mitochondrion.

  • Continue doing this until all the students in the front row (except the two on the far right) have passed the keys and handed their markers to the students behind them.

  • Once the keys get to the student second from the end on the right (representing oxygen), explain to the students that the final electron acceptor is oxygen and that oxygen is reduced, along with hydrogen ions, to form water, a byproduct of cellular respiration.

  • Next, ask the students about the difference in the amount of hydrogen ions in the intermembrane space compared with the matrix, which is in front of the front row of tables.

  • Explain to them that there is an electrochemical gradient of hydrogen ions from the intermembrane space to the matrix that represent potential energy, and that based on the principle of diffusion, the hydrogen ions would normally want to diffuse across the cristae in order to achieve equilibrium.

  • In order to do so, the hydrogen ions must pass through ATP synthase. Have the students with markers line up behind the student who represents ATP synthase. One by one, have them hand their marker to the student representing ATP synthase.

  • Every time a student hands a marker to the student who represents ATP synthase, have the student representing ATP synthase take one red Lego block (which represents ADP) and attach it to one yellow Lego block (which represents an inorganic phosphate). This represents the synthesis of one ATP molecule.

  • Have the student who represents ATP synthase hand the markers (hydrogen ions) to the student who represents oxygen. This student will place the keys (electrons) and markers (hydrogen ions) in their hands, combining them to represent water.

  • Continue having students pass markers (hydrogen ions) to the student who represents ATP synthase until all the hydrogen ions have passed through. The level of detail that is discussed regarding ATP synthase function is up to the individual teacher.

  • All the above information on the processes of the electron transport chain and chemiosmosis comes from Campbell Biology (Reece et al., 2012).

A variation of this activity is to use a potato instead of keys to represent the electrons. In order to do this, obtain a raw potato and heat it in a microwave for 3–5 minutes until it becomes hot. Make sure that the potato is not too hot for the students to handle safely. Give the potato to the first person on the left of the front row of tables, and continue the demonstration as stated above. The potato will become cooler as it is passed from student to student, representing the stepwise loss of energy each time the electron is passed to a different cytochrome. Discuss with the class that the passage of electrons down a transport chain is necessary because the energy from the electrons in NADH cannot be transferred to oxygen in one reaction, because of the explosiveness of one reaction. The electron transport chain allows the stepwise transfer of energy from the electrons.

Assessment

Assessment of this demonstration is really up to the individual teacher. A variety of assessments could be done, however. Students could complete a quiz on the two processes that were addressed, they could complete a write-to-learn activity that asks them to explain the two processes, questions could be asked on a test, or the students could be asked to act out and explain the processes without help from the teacher.

Reference

Reference
Reece, J.B., Urry, L.A., Cain, M.L., Wasserman, S.A., Minorsky, P.V. & Jackson, R.B. (2014). Campbell Biology, 10th Ed. Boston, MA: Pearson.