Genetic adaptability is very important to the survival and adaptability of any specie. This is because, in a diverse population, the possibility of finding individuals with the right genetic adaptability to the changing environment is higher, the population will have more possible adaptations.
Physical change only change the appearances of a substance, not it’s chemical composition. Chemical changes cause an entirely new substance with new chemical formula.
Tryptophan self-controls its synthesis. If we have a large amount of tryptophan in the sense that it exceeds, tryptophan would act as a co-repressor which prevents synthesis of more enzymes for its production. Hope this answers the question.