DNA gel electrophoresis begins with using enzymes that do what

separate DNA fragments according to their size.

Explanation:

Gel Electrophoresis of DNA demonstrates how DNA can be specifically cut into fragments by restriction enzymes and then can be separated by fragment size on an agarose gel.

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.