Can someone please explain how the carbon cycle and nitrogen cycle works

Explanation:

Humans have changed the natural carbon cycle by burning fossil fuels, which releases carbon dioxide into the atmosphere. The nitrogen cycle begins with nitrogen gas in the atmosphere then goes through nitrogen-fixing microorganisms to plants, animals, decomposers, and into the soil.

during the process of dna replication, brdu can replace thymidine and incorporate into the newly synthesized dna, cell proliferation thus can be reflected in the extent of brdu incorporation.