Solution:
The series of processes by which carbon compounds are interconverted in the environment, involving the incorporation of carbon dioxide into living tissue by photosynthesis and its return to the atmosphere through respiration, the decay of dead organisms, and the burning of fossil fuels. And the oxygen cycle is a biogeochemical cycle that describes the movement of oxygen within the earth's three main reservoirs which are the atmosphere (air), the hydrosphere (water), and the lithosphere (land).
Both mix in one cycle because of these:
The C2 oxidative photosynthetic carbon cycle plus the C3 reductive photosynthetic carbon cycle coexist. Both are initiated by Rubisco, use about equal amounts of energy, must regenerate RuBP, and result in exchanges of CO2 and O2 to establish rates of net photosynthesis, CO2 and O2 compensation points, and the ratio of CO2 and O2 in the atmosphere. These concepts evolved from research on O2 inhibition, glycolate metabolism, leaf peroxisomes, photorespiration, 18O2/ 16O2 exchange,CO2 concentrating processes, and a requirement for the oxygenase activity of Rubisco
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