Question

The endosymbiotic theory states that chloroplasts and mitochondria evolved as a result of

Answer 1

a prokaryotic cell engulfing a bacterial cell.

Answer 2

A Eukaryotic cell engulfing a bacterial cell.

You may want to know that the bacteria which used to photosynthesise , after they have been engulfed by an eukaryotic cell , they evolved into Chloroplasts .
However for the bacteria which used to respire , they have evolved into mitochondria.

Hope this helps :) Good Luck !