Explain why the ratio of carbon-14 to other carbon atoms stays constant while an organism is alive

If the level is constant, living plants ❤✌and animals should also maintain a constant carbon-14 level in them. The reason is that, as long as the organism is alive, it replaces any carbon molecule that has decayed it's nitrogen

Explanation:

But when gas exchange is stopped, be it in a particular part of the body like in deposits in bones and teeth, or when the entire organism dies, the ratio of carbon-14 to carbon-12 begins to decrease. The unstable carbon-14 gradually decays to carbon-12 at a steady rate. And that's the key to radiocarbon dating

idk i’m struggling too