Assess students' understanding of the global carbon cycle: key natural processes (photosynthesis, respiration, decomposition, ocean uptake), major reservoirs (atmosphere, biosphere, lithosphere/sediments, oceans), typical flux directions and relative magnitudes/residence times, and how human activities (fossil fuel combustion, land-use change) alter fluxes and atmospheric CO2. Tasks should include explaining mechanisms, interpreting simple flux/reservoir diagrams, making qualitative flux balances, and evaluating mitigation or management implications.