The 6 electrons make it carbon, and give it its chemical properties. Some carbon has more or fewer neutrons. One of its protons became a neutron. There is a fairly constant amount of radiation from space, mainly from the sun. And so, C-14 is being produced at a fairly constant rate.
Plants take in carbon dioxide and water, and produce carbohydrates and oxygen.
This process is called photosynthesis. This means that it gives off radiation. That also means that C-14 automatically changes into something else. This is called radioactive decay. And the amount of the radiation would also drop to half in 5730 years.