Why do plants need nitrogen? How do plants obtain nitrogen?

(N/A) Step $1$: Plants require nitrogen as an essential nutrient to synthesize proteins, nucleic acids, vitamins, and other structural compounds.
Step $2$: Although nitrogen is abundant in the atmosphere, plants cannot absorb it directly as $N_2$ gas.
Step $3$: Plants obtain nitrogen from the soil in the form of inorganic salts such as nitrates $(NO_3^-)$ or nitrites $(NO_2^-)$.
Step $4$: These compounds are formed by nitrogen-fixing bacteria (e.g., $Rhizobium$) that convert atmospheric nitrogen into usable forms.