Animals are totally dependent on plants and microorganisms for nitrogen fixation and nitrate assimilation because animals: a. do not have the reducing power (nadph) to fix nitrogen. b. lack the enzyme aminotransferase. c. lack the enzymes to reduce n2 and no3- to nh4+. d. lack carbamoyl-phosphate synthetase i. e. lack glutamate dehydrogenase.

C. lack the enzymes to reduce N2 and NO3- to NH4+

Explanation:

Nitrogen fixation is a process by which atmospheric nitrogen (N2) is converted into ammonia (NH3) so that can be used in metabolic pathways (e.g. biosynthesis of macromolecules). Nitrogen fixation is performed by Archea and bacteria such as Azotobacter (usually in symbiosis with Leguminosa plants).

Nitrogen assimilation is a process in which organic compounds are made from inorganic nitrogen.

this protocol provides a detailed procedure for chromatin immunoprecipitation (chip) to study the dna-protein interactions.

answer: substrate concentration. enzymes work best when there is a high enough substrate concentration for the reaction they catalyse.