Carboxysomes are polyhedral inclusion bodies that contain enzyme ribulose- 1,5-bisphosphate carboxylase/oxygenase (RuBisCO). This is responsible for the fixation of carbon dioxide in cyanobacteria. Carboxysomes have evolved as a consequence of the increase in oxygen concentration in the ancient atmosphere.
Thus, <em>carboxysomes are not energy reserves</em>, unlike another offered answers.
