Questions

The  plant  growth  regulators  are small,  simple  molecules  of  diversechemical composition. They can be in   form   of   indole   compounds, adenine   derivatives,   carotenoids derivatives,terpenes  or  gases  like ethyleneetc.The   plant   growth regulators  are  bifurcated  into  two groups according to their functions in  a  living  plant  body.First  group of   plant   growth   regulators   are found   in   growth   activities,   for instance,  cell  division,  flowering, fruiting  and  seed  formation.The second   group   of   Plant   growth regulators   are   involved   in   plant responses  to  wounds  and  stresses of biotic and abiotic origin.

Error is in third part. Since “doing” was used in second part it should be followed by “doing” in third part as well instead of using “done”. Such repetitive figure of speech is used in
English grammar to create emphasis. This sentence indicates that a thing that is worth doing is also worthy of doing well. Here worth is the noun that must be followed by the verb doing.