Examples of organic matter in the nitrogen cycle?

Question

Protein? Excretory matter ie urea?

Answer 1

Both of those would be good examples.

Protein has amino acids, and the amine group is NH2.

Urea is nitrogenous excretory product, as are urine and uric acid.

You could even go so far as to include DNA, because it has nitrogenous bases.

Eventually, these would be converted to ammonia (NH3) or ammonium (NH4) .