Answer:
Photosynthetic lamellae
Step-by-step explanation:
The cyanobacteria were the first successful photosynthetic cells present on the Earth which were able to convert the light energy into the chemical energy.
The endosymbiosis theory suggested that these cyanobacteria were engulfed by the eukaryotes and the cyanobacteria get transformed into the chloroplast.
The region of the chloroplast that was formed in the cyanobacteria before the endosymbiosis happened was the photosynthetic lamellae which contained the chlorophyll molecule and thus is the correct answer.
Thus, Photosynthetic lamellae are the correct answer.