Final answer:
During photosynthesis, plants absorb carbon dioxide from the atmosphere and convert it into glucose. The ratio of 14CO2 to 12CO2 in the atmosphere determines the ratio of these isotopes in the plant. However, when the plant dies, it no longer absorbs carbon dioxide and the concentration of 14CO2 decreases over time due to radioactive decay, while 12CO2 remains stable.
Step-by-step explanation:
The process not involving radioactive decay for which 14CO2 would behave differently from 12CO2 is the process of photosynthesis. During photosynthesis, plants absorb carbon dioxide from the atmosphere and convert it into glucose. The ratio of 14CO2 to 12CO2 in the atmosphere determines the ratio of these isotopes in the plant. However, when the plant dies, it no longer absorbs carbon dioxide and the concentration of 14CO2 decreases over time due to radioactive decay, while 12CO2 remains stable. This difference in behavior can be used in carbon dating to determine the age of organic material.