Answer:
An Endoplasmic reticulum
Explanation:
A living organism can either have prokaryotic or eukaryotic cells.
Eukaryotic cells have a defined nucleus and other membrane bound organelles whereas prokaryotic cells lack membrane bound organelles such as mitochondrion and chloroplast.
Endoplasmic reticulum are membranous system that forms a system of flattened sacs in the cytoplasm.
These organelles can only be found in eukaryotic cells and not prokaryotic cell.
