Question

select the correct answer.
how does the usable form of nitrogen enter our bodies?
a. by breathing in air
b. by consuming plants
c. by consuming water
d. by burning fuel

Explanation:

Plants take up nitrogen in the soil (in the form of nitrates) and incorporate it into their tissues. When we consume plants, we obtain this usable form of nitrogen.

• Air contains nitrogen gas ($N_2$), but humans cannot directly use this form as it is very stable and our bodies lack the enzymes to break the triple bond in $N_2$.
• Water ($H_2O$) does not contain nitrogen in a form that is directly usable for our body's nitrogen - containing biomolecules (like proteins, nucleic acids).
• Burning fuel is an industrial or combustion process and has no direct relation to nitrogen entering the human body in a usable form.

Answer:

B. by consuming plants