The endosymbiotic theory proposes that mitochondria and chloroplasts evolved as a result of which cellular process?
a. symbiosis
b. phagocytosis
c. endosymbiosis
d. photosynthesis

The answer is B. phagocytosis

Phagocytosis is a process in which cell ingests large fragments of matter, for example, bacteria. According to the endosymbiotic theory, a host cell ingested symbiotic bacteria (through phagocytosis). Ingested bacteria later specialised into mitochondria or chloroplasts. The evidence for this theory is that mitochondria and chloroplasts similarly to bacteria have their own circular DNA and their own transcriptional and translational machinery.