How do animals obtain the nitrogen they use to make proteins and nucleic acids?
a. by consuming plants or other animals
b. by absorbing ammonia from bacteria growing in the roots of plants
c. by breathing the nitrogen present in the atmosphere
d. by absorbing nitrogen found in the soil

I think it would be A. Because plants have bacteria on their roots that take the free nitrogen in the air from the soil and turn it into usable nitrogen. Animals could get usable nitrogen from eating plants since they have bacteria that make it. Then if an animal eats an animal that ate the plant, then it could get that nitrogen. But i am not completely sure though. I just learned this recently. I hope this helped :)

In the air and in the lower fre ah water