What is a eukaryote and when do it first arise

A eukaryote is an organism that belongs to the domain Eukaryota. Therefore, unlike a prokaryote, the eukaryote has a nucleus and organelles. The first eukaryotes appeared during the Proterozoic eon (2.1-1.6 billion years ago). The first organisms that appeared about 3.5 billions years ago were prokaryotes. At the moment, the conditions on Earth without oxygen were not hospitable for eukaryotes which needed oxygen to survive. Thanks to the first prokaryotes capable of performing photosynthesis that appeared about 2.7 billion years ago, the early Earth atmosphere could be changed so that first eukaryotes that were not able to perform photosynthesis could arise.

The answer is option a.

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