plant physiologists set out to grow roots by themselves in solution in laboratory flasks.
The scientists found that the nutrition of isolated roots was quite simple.They required sugar and t heusual minerals and vitamins.
However, they did not require organic nitrogen compounds. These roots got along fine on mineral inorganic nitrogen.
Roots are capable of making their own protiens and other organic compounds.These activities by roots require energy, of couse. The process of respiration uses sugar to make the high energy compound ATP. Which drives the biochemical reactions.Respiration also requires oxygen.Highly active roots require a good deal of oxygen.