Cholesterol is synthesized by all animal cells and is mainly synthesized in the liver. cholesterol also serves as a precursor for several important biological compounds including all, except a. insulin b. vitamin d c. bite salts d. testosterone

The correct answer is A insulin

Explanation:

Cholesterol is a complex lipid which act as precursor for the synthesis of steroid compounds such as vitamin D a lipid soluble vitamin,testosterone a steroid hormone and bile salt helps in fat digestion.

     Insulin is a peptide hormone it is composed of amino acids linked with each other by peptide linkages .As a result insulin cannot be synthesized from cholesterol.

explanation:

b,bacteria convert nitrates

into nitrogen gas.

d,plants and animals take in

and use nitrogen compounds.

e,bacteria break down waste    

products and return nitrogen  

to the soil.

a,bacteria convert atmospheric

nitrogen to ammonia.

c,bacteria convert ammonia

to nitrites and nitrates.

it creates acid rain