A NASA scientist receives satellite data indicating that a newly discovered planet contains no oxygen gas in its atmosphere. From this information she concludes that complex multicellular organisms are UNLIKELY to exist on that planet. This is because_______________.

a. unicellular organisms consume multicellular organisms when oxygen levels are low
b. other electron acceptors (like iron) are unlikely to be widely available and abundant
c. endosymbiosis requires high oxygen concentrations for evolution to proceed
d. complex multicellular life cannot exist once photosynthesis has evolved

Endosymbiosis is an hypothesis which stipulates that complex organelles like mitochondrion and chloroplast evolved as a result of symbiotic relationship between aerobic, single cell prokaryotes in which an aerobic organism ingest an anaerobic organism in an atmosphere containing oxygen.

The oxygen in the atmosphere is like a poison to the anaerobic prokaryote and the ingestion by aerobic prokaryote protects it from the toxic effects of oxygen and in return, the ingested organism offers some benefit to its host resulting in a beneficial relationship.

Hence, the presence of oxygen is important for endosymbiosis and eventual evolution of complex organelles in multicellular organisms.

The correct option is c.