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Activity (Hands-On)Grades 6 - 8

Counting Atoms: How Not to Break the Law of Conservation of Matter

A photograph shows a group of students gathered around a classroom table and using a molecular model set to model the photosynthesis reaction.How can we demonstrate the law of conservation of matter is true using molecular models?

Students explore the science of microbial fuel cells (MFCs) by using a molecular modeling set to model the processes of photosynthesis and cellular respiration—building on the concept of MFCs that they learned in the associated lesson, “Photosynthesis and Cellular Respiration at the Atomic Level.” Students demonstrate the law of conservation of matter by counting atoms in the molecular modeling set. They also re-engineer a new molecular model from which to further gain an understanding of these concepts.

To design MFC-based sensors, engineers must understand the chemical mechanisms of photosynthesis and cellular respiration that occur within organisms such as yeasts, algae or bacteria. Engineers must understand how electron transport pathways are generated via photosynthesis and cellular respiration if they wish to harvest electrons for electrical power generation. However, one limitation to understanding these concepts is the small scale at which these chemical interactions take place. Therefore, engineers often model scientific phenomena and practice manipulating atomic variables in order to better understand what is happening within these processes.

After this activity, students should be able to:

  • Describe the processes of photosynthesis and cellular respiration.
  • Write the balanced chemical equations for the processes of photosynthesis and cellular respiration.
  • Explain the relationship between cellular respiration and photosynthesis and their connection to the cycling of matter and energy in Earth’s ecosystem.
  • Prove that the law of conservation of matter holds true by balancing the chemical equations for the processes of photosynthesis and cellular respiration and counting the atoms present on the reactant sides and the product sides of the equations.
  • Engineer a better teaching model than existing molecular models to better understand the processes.

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