Once bacteria have fixed nitrogen, it can be taken up by plants and animals,?

Question

where it is used in the production of

a. nitrogen oxides

b. carbohydrates

c. proteins

d. energy

Answer 1

Proteins are an assemblage of amino acids which are built of nitrogen (and also carbon and oxygen).  Proteins and amino acids are needed by all living organisms (example: in DNA).

Answer 2

Animals do not need nitrogen. Plants do. This website has more information on the role of nitrogen in plant health:

"Nitrogen is an essential component of all proteins, and as a part of DNA, it is essential for growth and reproduction as well. Nitrogen deficiency most often results in stunting."