Question

according to the theory of endosymbiosis, a mitochondria or chloroplast may have been a prey species and was engulfed by a cell or it could have been a parasite that entered the cell. why do scientists think that the cell did not destroy or remove these structures?
because they competed with the cell
because the structures benefited the cell

Explanation:

The endosymbiotic theory suggests that mitochondria and chloroplasts (once independent organisms) were engulfed by a host cell. For the cell to retain them, there must be a mutual benefit. If they competed, the cell would likely destroy them. But since mitochondria produce energy (ATP) and chloroplasts do photosynthesis (in plants), they benefit the cell, so the cell kept them. The first option (competed) is illogical as competition would prompt removal, while the second (benefited) aligns with endosymbiosis logic.

Answer:

because the structures benefited the cell