A biologist ground up some plant leaf cells and then centrifuged the mixture to fractionate the organelles. Organelles in one of the heavier fractions could produce ATP in the light, whereas organelles in the lighter fraction could produce ATP in the dark. The heavier and lighter fractions are most likely to contain, respectively, .a. peroxisomes and chloroplasts. b. mitochondria and peroxisomes. c. chloroplasts and peroxisomes. d. mitochondria and chloroplasts. e. chloroplasts and mitochondria.