Rhodobacter cells perform photosynthesis in the presence of light and grow heterotrophically in the dark. after being cultured in total darkness for multiple generations, phenotypic and genotypic changes occur. what phenotypic changes occur and what evolutionary processes are driving them?

Phenotypic changes:

When Rhodobacter is cultured in total darkness for multiple generations, the ability to produce it's own photopigment reduces with time with little or no ability to undergo its own photosynthesis due to absence of enzymes or pigment for photosynthesis.

It becomes expensive for the Rhodobacter to undergo photosynthesis. This allows mutants that can grow in the dark to take over from the culture grown in the dark.

Evolutionary processes:

It's natural selection that allows the fittest organism to survive. As in the case of the mutants

i believe it would cause an increase of percipitation, though i could be wrong. so i would say b is the answer.