During the cell cycle,
a) dna is replicated once before mitosis and again before cytokinesis.
b) dna is replicated during mitosis.
c) dna is replicated before mitosis begins.
d) dna is replicated directly after the completion of mitosis.

step 1: nitrogen fixation- conversion of atmospheric no₂ into forms useful to plants by lightning, bacteria, and cyanobacteria.

step 2: nitrification-process of converting ammonia to nitrite or nitrate.

step 3: assimilation-plant roots absorb new form of nitrogen.

step 4: ammonification-conversion of organic nitrogen to ammonia by bacteria involved in decomposition.

step 5: denitrification-bacteria turns the decomposed matter back into n₂o, which is released into atmosphere; repeat cycle.