    Sentence 1: What _was the secondary  ‘endosymbiotic event?    Sentence 2: While primary chloroplasts have a  double pee tear i their cyanobacterial  ancestor, secondary chloroplasts. have  additional membranes outside of the isk  two,.as a_result. of the secondary  endosymbiotic. event, when a  nonphotosynthetic eukaryote. engulfed a  chloroplast-containing alga but failed to digest  it-much like,..:the cyanobacterium at the  beginning of this story.