How is the proportion of Carbon 14 kept relatively constant in living orgasnisms?

The proportion of Carbon-14 in living organisms is kept relatively constant through the process of photosynthesis and respiration. Carbon dioxide in the atmosphere contains a stable ratio of Carbon-14 to Carbon-12, which plants absorb during photosynthesis. Animals then obtain Carbon-14 by consuming these plants or other animals. As long as an organism is alive, it continuously exchanges Carbon with its environment, maintaining the equilibrium of Carbon-14.