Question

how do humans get the nitrogen they need?
a. through photosynthesis
b. through cellular respiration
c. by breathing
d. by eating plants

Explanation:

Plants take up nitrogen - containing compounds from the soil and convert them into organic nitrogen compounds. Humans obtain nitrogen by consuming plants or other animals that have eaten plants. Photosynthesis is for making food using light energy, cellular respiration is for energy - release, and breathing mainly exchanges oxygen and carbon dioxide. Nitrogen in the air we breathe is in an inert form ($N_2$) that our bodies can't use directly.

Answer:

D. By eating plants