Demonstration of the Light Dependent Reactions of Photosynthesis Using Students as Molecules

Written by Rhoda Perozzi, Virginia Commonwealth University

Adapted by Kelly A. Hogan

Learning Outcomes:

– To overcome students’ difficulties with understanding how light energy excites electrons

– To enable students to visualize the way sequential events occur in membranes

– To enable students to understand that water is split in photosynthesis to supply electrons to chlorophyll

Activity Description: Students act out the light dependent reactions of photosynthesis by passing electrons to one another from taller to shorter students. The activity uses a water molecule student as well to demonstrate how water is the source of electrons for the process. This activity has been used in classes of 20 students as well as in classes of more than 300.

Time Needed: Approximately 20 minutes

Materials Needed:

– A long sturdy table for students to stand on in the front of room (not necessary but useful)

– Seven students representing: Chlorophyll of Photosystem I, Chlorophyll of Photosystem II, NADP+, electron transport system (2-3 students), water

– Crumpled paper wad representing an electron. Nametags (large if used in large lecture hall)

Activity Instructions:

1. Ask for a few students to help with a demonstration. From them, choose the second to the tallest and ask if he/she is willing to stand on the table. Explain that the table represents a thylakoid membrane in a chloroplast. Name the first person “Chlorophyll in Photosystem II.”

2. Next, ask the tallest person to stand on the table to the far left of “Chlorophyll in Photosystem II.” This person is named “Chlorophyll in Photosystem I.” (This is ideal if they happen to be wearing green.)

3. Depending on the size of the table, ask for either two or three shorter people to stand between them. These are arranged so that the tallest person is next to “Chlorophyll in Photosystem II” and the shortest next to “Chlorophyll in Photosystem I” (see figure). These two to three people are named “Electron Transport System.”

4. Ask for a relatively tall person to stand on the floor next to “Chlorophyll in Photosystem I.” This person is named NADP+.

5. Look around the room and ask the person with the brightest blue shirt to stand on the floor at the opposite end next to “Chlorophyll in Photosystem II.” Consider “forgetting” to give the person in a blue shirt a name (this will be the water).

6. Identify yourself as “Solar Energy.”  Hand “Chlorophyll in Photosystem II” a paper wad and explain that it is an electron. Explain that ideally everyone in class would be clustered around the two chlorophylls and would be handing electrons to them, but with space being limited, they will have to imagine what that would be like.

7. Hit the paper wad in the hand of “Chlorophyll in Photosystem II,” forcing the hand to go up above the person’s head (Gently of course!). Relate this motion to the action of photons of light. (They kick the electron to an excited state. Point out that if chlorophyll were all alone on the table, the electron would simply fall back down to ground state. Since, it is in a membrane, however, the electron transport chain grabs the electron in its excited state and passes it from one electron transport molecule to the next until it reaches the chlorophyll molecule in PS I.)

8. Have the students pass the electron (from PS II to the electron transport students to the Chlorophyll student of PS II). When the electron reaches PS I, hit that person’s hand, “exciting” the electron again. The electron is then passed to NADP+.

9. Throughout this time, note the person in blue (water has not been named and has been ignored).  Now, walk back to PS II and try to excite an electron again, but demonstrate that there is no electron to excite. Ask everyone what the problem is. (Students should have no problem seeing that chlorophyll has lost its electron.)

10. Ask students where another electron will come from. (Someone should point out that the person in blue has not been identified.) Consider acting surprised and say something like, “Oh, of course! This is ‘Water.’” Turn to the water student and say, “You really have a very important job here. I am going to need your full cooperation. You have to split into pieces and part of you has to leave as a gas.” (The class often finds this amusing.)

11. Slip “Water” another paper wad electron, which he or she then passes to “Chlorophyll in PS II.” Point out that there is always plenty of water in cells to constantly supply electrons to chlorophyll.

12. Have the students applause their classmates that have role played. Have the participating students state their names to help form a classroom community.

Demonstration of Electron Transport and ATP Production in Aerobic Respiration Using Students and Balloons

Written by Jennifer A. Metzler, Ball State University

Learning Outcomes:

– To allow students to visualize the events allowing ATP production from electrons carried by NADH and FADH2

– To demonstrate what the role of oxygen as the terminal electron acceptor really means

Activity Description: Students act out the electron transport chain and role of ATP synthase. Electrons and H+ are represented by different colored labeled balloons and each student representing a protein is labeled with a large piece of paper. This activity can work with any size class and is generally used as a review after the topic has been explained in class.

Time Needed: Approximately 15 minutes

Materials Needed:

– Eight student volunteers representing: Complex I, II, III, IV, oxygen, NADH, FADH2, and ATP synthase

– Three balloons representing H+, one balloon representing an electron, and a balloon to represent ATP

– Labels for all the “proteins” and molecules involved

Activity Instructions:

  1. Ask eight students to volunteer and give them a label randomly.
  2. Then ask the rest of the class to arrange the Complexes, oxygen, and ATP synthase in the appropriate positions.
  3. Ask the class how the balloons representing electrons, H+, and ATP should be distributed.
  4. First demonstrate ATP production from the electrons of NADH.
  5. Have students in the class indicate which complex (I, II, III or IV) that the NADH should pass its electron balloon to. Then have them explain how the electron should be passed, ultimately ending up at oxygen.
  6. Then have the class indicate which complexes should pump an H+ and have them move their balloon across “the membrane.”
  7. Finally, have the class indicate where the pumped protons should go to produce a molecule of ATP. Be sure to have your ATP synthase student spin to indicate the molecular machine that ATP synthase is.
  8. Then repeat the same procedure for the electrons of FADH2.
  9. Applaud for all of the hardworking volunteers.

Cell Respiration: Pair and Share

Written by Kelly A. Hogan, University of North Carolina at Chapel Hill

Learning Outcomes:

– To practice explaining the individual parts of cellular respiration

– To appreciate that teaching is an important study tool

Activity Description: Students are given worksheets that have unlabeled figures of cellular respiration in three parts. Students label the images and take notes as part of lecture or on their own. They then pair off with a neighbor and teach each part.

Time Needed: Approximately 50 minutes

Materials Needed: Worksheet with unlabeled figures from your textbook

Activity Instructions: I have had much success using the unlabeled figures as the guideline to lecture. For example, we spend 10 minutes filling out the glycolysis portion of the outline. Students then break into pair-share partners. (One student explains the figure to their partner. The partner can make corrections if necessary. Then the partner explains it back to the original student.) We repeat with the citric acid cycle and oxidative phosphorylation. The room is noisy, but the students appreciate the time to explain back a challenging topic to a partner. Before moving on, ask for questions from the students. After time to chew and digest the material this way, there are always questions!

After completing this activity, be sure to summarize all three sections and ask a few questions. Students are amazed after this that they really understand the material. Also stress the importance of studying this way. Students often have an “aha” moment about studying after this activity.

Potential questions: (You can easily make these into clicker questions or add them to their worksheets.)

  1. Which stage of cellular respiration makes the most reduced coenzymes? (Citric acid)
  2. Which stage makes the most ATP? (Oxidative phosphorylation)
  3. How does breathing in oxygen and breathing out carbon dioxide relate to this process? Where are those molecules made or needed? (Oxygen for accepting electrons and carbon dioxide as a product of acetyl co-A formation and the citric acid cycle.)
  4. What does it mean that NAD+ is reduced? (It gains two electrons and becomes NADH.)
  5. Water is a product of cellular respiration. Explain how it is made. (Electrons from NADH and FADH2 ultimately reduce oxygen, which joins with hydrogen ions to form water.)

Photosynthesis and Respiration: Are They Similar?

Written by Kelly A. Hogan, University of North Carolina at Chapel Hill

Learning Outcomes:

– To compare and contrast two challenging topics: photosynthesis and cell respiration

– To appreciate that comparing and contrasting topics is an important study tool

– To promote discussion and questions from students about where they are confused

Activity Description: After students have already had lectures on cell respiration and photosynthesis, they are asked to compare and contrast these topics. This could be a very open-ended activity or can be done with a quick worksheet.

Time Needed: Activity should take about 15 minutes but could go on longer with much discussion and review

Materials Needed: Copies of the worksheet below

Activity Instructions: After students have learned about both processes, allow students time to compare and contrast photosynthesis and cell respiration. Students often get confused by the similarities of the topics but can’t always pinpoint where they are similar or different. This activity will open up discussion to find out where students are having trouble.

Worksheet: Photosynthesis and Cellular Respiration Worksheet

Students, Design Your Own Enzyme-Catalyzed Reaction

Written by Kelly A. Hogan, University of North Carolina at Chapel Hill

Learning Outcomes:

– To practice using terms related to enzyme-catalyzed reactions

– To address a misconception that enzymes are depleted after a reaction

Activity Description: Students are given a list of words and instructions to design their own enzyme-mediated reaction. Students work in small groups to design and then demonstrate their idea to the class (students can use simple props). The whole class can decide if the demonstration is designed well to illustrate understanding. The activity can work in a small class or a large class in which only a few groups get to demonstrate. You may also choose to simply demonstrate your own example asking students to come up with ideas as you prompt them.

Time Needed: Activity may take 40 minutes (if students do group work outside of class) and may take much longer if group time is given during class

Materials Needed: Variable depending on students

Activity Instructions:

Tell students that they will design an enzyme-catalyzed reaction (could be dehydration synthesis, hydrolysis, functional group transfer, etc.) that shows their understanding of the words/ideas below. The materials students have available can be props available in a classroom, such as classmates, paper, pens, etc. You may suggest that students work outside of the class and plan ahead to bring simple props with them. Groups will demonstrate their ideas to the class. You may want to have a panel of student judges (American Idol style).

Ideas that students can demonstrate:

A. active site

B. substrate

C. product

D. enzymes are used over and over.

E. enzymes can be inhibited at their active site or their allosteric site.

F. enzyme activity is affected by environmental conditions.

Example: I place a bowl of wrapped candies on my table. I tell them that I am unwrappase. The substrate is wrapped candy and the product is unwrapped candy. My hands are the active site. A single me can unwrap many candies (enzymes are used over and over and are unchanged). The rate of me producing unwrapped candies would slow down if pistachio nuts were mixed into my bowl because the pistachio nuts would temporarily bind to my active site. Pistachios would be competitive inhibitors. If a scarf was tied around my elbows to connect them behind my back, the active site would be altered because my hands would open up and I would have trouble holding the candy. The scarf would be an allosteric inhibitor. Ideally, I work best at room temperature. If the heat was turned way up or way down my activity might be slowed by these environmental conditions, and I might be cranky and produce less product.

Using Diabetes as the Story to Discuss the Secretory Pathway of Proteins

Written by Kelly A. Hogan, University of North Carolina at Chapel Hill

Learning Outcomes:

– To use insulin as an example secretory protein

– To examine an analogy that the cell is a protein factory analogous to a manufacturing factory

– To learn about an important disease students may know little about

Activity Description: Students act out an interpreted case study and discuss answers to the questions. Lecture or animations may be interspersed in the discussion.

Time Needed: Approximately 50 minutes

Materials Needed: Copies of the case study and questions, 3 x 5 index cards

Activity Instructions: Choose 6 students to play the roles. Intersperse lecture, BioFlix animations, and discussion as needed. I always play the role ofLena, so that I can still play a “teaching role” and pull up animations while I say my lines.

OPTIONAL: The animation that could be shown to the class is located at:

For question 8, I have my students write their answers on 3 x 5 index cards. I ask them to swap cards several times with classmates. When I ask for people to read from their cards, I get a much better response. We then discuss whether the analogy is a good one or not.

Worksheet: Diabetes Case Study and Role Play Worksheet

Reviewing Macromolecules

Written by Kelly A. Hogan, University of North Carolina at Chapel Hill

*Adapted from an activity presented by Dawn Tamarkin, Springfield Technical Community College at the National Association for Biology Teacher (NABT) Conference 2010.

Learning Outcomes:

– To review nomenclature related to macromolecules

– To practice organizing and making connections between concepts

Activity Description: Students are given a sheet of paper covered with words related to macromolecules. They will first cut the words out (like flashcards) and organize them into piles with a partner. Students are encouraged to discuss different ways to group the same set of words.

Time Needed: Approximately 25 minutes

Materials Needed: Worksheets and scissors for each group

Instructions:

  1. Have the students cut out the words.
  2. Let them organize them into piles without telling them how the organization should be done.
  3. Allow them time to see how other groups grouped their words. Allow time for questions and discussion about the different ways to group words.

Worksheet: Reviewing Macromolecules Worksheet

Appreciating the Diversity of Primary Sequences in Protein Structure

Written by Kelly A. Hogan, University of North Carolina at Chapel Hill

Learning Outcomes:

– To gain an appreciation for the diversity of proteins in amino acid sequence and length

– To examine an internet tool utilized by research scientists

– To appreciate quantitative biology

Activity Description: A classroom demonstration involving one student and multiple pairs of mittens of different colors is used as an analogy to the 20 amino acids that can be ordered in a multitude of ways in primary protein structure. Students can then use theNationalCenter for Biotechnology Information (NCBI) website to explore real proteins.

Time Needed: The activity should take approximately 15 minutes

Materials Needed: Multiple pairs of mittens or gloves

Activity Instructions:

One student comes to the front of the room in which there are two pairs of mittens (say a red and a blue pair). The student is allowed to choose one for each hand. Ask the audience, “How many possible combinations are there?” (Answer: 4)

Students won’t need a mathematical equation to figure this out:

Right – red, Left – red or Right – red, Left – blue or Right – blue, Left – blue or Right – blue, Left –red

Next put another pair of mittens on the table for your student to choose from (there are three pairs total at this point). Ask the audience, “How many combinations are now possible?” (Some students may start forming combinations of colors. Give them time to see how difficult this can be. Others may see the need for a calculation more quickly.) This is a good time to point out that biology is quantitative (many students will not recognize at the introductory level that as biology advances it intersects with mathematics more and more.)

The equation for the two hands and three pairs of gloves is: 32 = 9

Two hands and four pairs of gloves: 42 = 16

Next ask the audience, “How many amino acids exist?” (Answer: 20). Make the analogy clear by explaining that you could bring 20 pairs of mittens to your student. And ask them, “For a dipeptide sequence, how many different combinations would be possible?” (Answer: 202 = 400).

(Be sure to note that Ala-Leu is indeed different from Leu- Ala because polypeptides have directionality with an amino end and a carboxyl end.)

Lastly, ask students how long a typical polypeptide is. Let them take guesses and then explain the variation that exists. You can let them name a few proteins they know and go to:

http://www.ncbi.nlm.nih.gov/protein

to show them how many amino acids are in their named proteins. (This is a great site to show them as a collaborative tool that scientists use in the research.)

Ask them to calculate the number of combinations in a protein with say 125 amino acids:

Answer:  20125 = 4.25352959 × 10162

Note: You can bring in this same idea again when you discuss the triplet nature of the DNA code. With 4 nucleotides and a triplet sequence there are 43 = 64 combinations or codons.

A Student “Bully” Demonstrates the Polar Covalent Bond

Written by Jennifer Wiatrowski, Pasco-Hernando Community College

Learning Outcomes:

– To help students visualize the relationship that exists between atoms in a polar covalent bond

Activity Description: Three students use paper to demonstrate how electrons are equally shared in non-polar covalent bonds and unevenly shared in polar covalent bonds. This works well in a class of any size.

Time Needed: A few minutes

Materials Needed: Five pieces of paper and 3 students

Activity Instructions: I usually look for a large male student to be “oxygen” and then two smaller students to be “hydrogen.”  I have the students stand in a row with oxygen in the center. Between each hydrogen and the oxygen, I have them hold a piece of paper with two large dots on it. These represent the shared pairs of electrons. I have them start out holding the electron pairs at equal distance from one another (like in a non-polar relationship). But, then I tell oxygen to be the “bully” and pull those electrons closer to his body. I then hold signs over their heads indicating partial positive and partial negative charges. (A more creative person could probably come up with some funny hats representing the charges for the students to wear.)