Tracing Matter and Energy

Biologists can investigate the steps in metabolic processes (synthesis and breakdown) by feeding extremely small (or trace) amounts of radioactively labeled matter to laboratory organisms. This labeled matter undergoes changes in molecular structure during chemical reactions within the organism that consumed it. But the label remains detectable. The labeled matter continues to be traceable through transfers between the organisms. As these changes and transfers occur, the scientists can collect samples. In this way, they can trace the course of events by following the radioactivity.

In this activity, you will trace the path of twoimaginary, radioactively labeled carbon atoms through the various molecules in which they are organized. Both atoms will begintheir journey as part of a carbon dioxide molecule. One of the molecules you trace should end up as an organic part of a muscle protein in a human arm. The second carbon atom will travel through several cycles and end up back in the atmosphere as CO2. Your task is to use the knowledge that you gained in Cell Energetics (Cellular Respiration and Photosynthesis) to draw a diagram of what happens to the atoms during their journey. Make sure the Carbon atom stands out- remember it’s radioactive! Then you will label and explain the source of energy for these events.

  1. Construct a diagram or other visual aid to show a plausible set of events that could explain how labeled carbon atoms in molecules of atmospheric carbon dioxide ends up either in a human muscle protein or back in the atmosphere.
  • There is more than 1 possible scenario. But you must show a sequence that actually occurs in nature. You must be able to justify and explain the sequence that you choose.
  • You will be working on this with ONE other person or by yourself, so choose wisely. We will not have much time to work on this in class so you must be able to work with this person outside of school.
  • Your work (yourself and your partner) must turn in original work, meaning not the same as another group.
  • This assignment will be counted as a summative lab/project grade.
  • Your project needs to be neat, labeled and colored.
  1. Label your diagram so that it explains the sequence of events that you have illustrated. Clearly state the following:
  2. The type of metabolic process in each step (breakdown or biosynthesis)
  3. The energy source for each step (ATP, sunlight, NADH, etc)
  4. The matter source for each step (must show reactants and products)
  5. The names of the metabolic processes that occur in the sequence: cellular respiration, photosynthesis, etc.