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Photosynthesis and Cellular Respiration Cycle

Run the Photosynthesis-Respiration Cycle Fullscreen
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About This MicroSim

This step-through animation makes the invisible exchange of gases and energy between producers and consumers visible. A green plant on the left performs photosynthesis while a deer on the right performs cellular respiration. Labeled arrows show the continuous flow of molecules between them: O2 from plant to deer, CO2 from deer to plant, and glucose flowing through the food chain. The sun provides energy input to the plant, while heat waves leaving the deer show energy dissipation.

Students can walk through six stages one at a time: sunlight energy input, plant absorption of CO2 and H2O, plant production of glucose and O2, deer consumption of glucose and O2, deer production of CO2, H2O, and ATP, and finally the full cycle view with all arrows animating. Molecule counters at each stage show concrete quantities (6 CO2 + 6 H2O yields 1 glucose + 6 O2), helping students move beyond memorizing equations to understanding the actual molecular exchange.

A "Show Molecule Counts" toggle lets students switch between a simplified view and a detailed quantitative view. The speed slider and play/pause controls allow self-paced exploration, making this suitable for both initial instruction and review.

How to Use

  1. Click Next Step to advance through the six stages of the photosynthesis-respiration cycle one at a time.
  2. Read the step description that appears, explaining what is happening at each stage.
  3. Watch the molecule arrows animate between the plant and deer, showing the direction of each substance.
  4. Toggle Show Molecule Counts to see the specific quantities of CO2, H2O, O2, and glucose at each stage.
  5. Click Previous Step to go back and re-examine any stage.
  6. Click Play Cycle to see the entire loop animate continuously.
  7. Adjust the Speed slider to slow down the animation for detailed study or speed it up for an overview.
  8. Click Reset to return to the beginning.

Iframe Embed Code

You can add this MicroSim to any web page by adding this to your HTML:

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<iframe src="https://dmccreary.github.io/ecology/sims/photosynthesis-respiration-cycle/main.html"
        height="582px"
        width="100%"
        scrolling="no"></iframe>

Lesson Plan

Grade Level

9-12 (High School Biology / Environmental Science)

Duration

40 minutes

Learning Objectives

  • Explain how photosynthesis and cellular respiration form a complementary cycle
  • Trace the flow of energy and the cycling of matter (CO2, O2, glucose, water) between producers and consumers
  • Compare the inputs and outputs of photosynthesis and cellular respiration

Prerequisites

  • Basic understanding of atoms and molecules
  • Introduction to the concepts of producers and consumers
  • Familiarity with chemical equations at a conceptual level

Standards Alignment

  • NGSS HS-LS1-5: Use a model to illustrate how photosynthesis transforms light energy into stored chemical energy
  • NGSS HS-LS1-7: Use a model to illustrate that cellular respiration is a chemical process whereby the bonds of food molecules are broken and the bonds in new compounds are formed
  • AP Environmental Science: Topic 1.1 -- Energy Flow in Ecosystems

Activities

  1. Equation Matching (5 min): Write the photosynthesis and respiration equations on the board. Ask: "What do you notice about the inputs and outputs?" Students identify that one's outputs are the other's inputs, foreshadowing the cycle concept.

  2. Step-Through Exploration (15 min): Walk through all six stages as a class with molecule counts enabled. At each step, students record the inputs, outputs, and energy changes in a two-column table (photosynthesis side vs. respiration side). By step 6, students should see the cycle is complete.

  3. Molecule Tracking Challenge (10 min): Students pick a single oxygen atom and trace it through the entire cycle: from CO2 in the atmosphere, through photosynthesis into O2, inhaled by the deer, used in respiration, and released as CO2. They write the journey as a narrative from the atom's perspective.

  4. Energy Flow Discussion (10 min): Discuss the key difference: matter cycles but energy flows. Where does the energy enter the cycle? (Sunlight.) Where does it leave? (Heat from the deer.) Why must the sun continuously supply energy? Connect to the first and second laws of thermodynamics.

Assessment Questions

  1. Explain why photosynthesis and cellular respiration are described as complementary processes. Include the chemical inputs and outputs of each.
  2. A sealed terrarium with plants and small animals survives for months without opening. Using the photosynthesis-respiration cycle, explain how the organisms inside can continue to survive.
  3. If all photosynthetic organisms on Earth disappeared, what would happen to atmospheric O2 and CO2 levels over time? Explain using the cycle model.

References

  1. Campbell, N.A., & Reece, J.B. (2017). Biology (11th ed.). Pearson. Chapters 8-9.
  2. Raven, P.H., Evert, R.F., & Eichhorn, S.E. (2013). Biology of Plants (8th ed.). W.H. Freeman.
  3. Chapin, F.S., Matson, P.A., & Vitousek, P.M. (2011). Principles of Terrestrial Ecosystem Ecology (2nd ed.). Springer. Chapter 5.