Answer:
Nucleus and membrane-delimited organelles
Step-by-step explanation:
The prokaryotic cell includes bacteria and Archaea cells and generally lack nuclei and membrane-bound organelles like mitochondrion, vacuole, and chloroplast (found in plant cells). Their genetic materials lie freely within the cytoplasm without any structure delimiting them.
The eukaryotic cell, on the other hand, includes plant, animal, fungi, and protists cells. They have nuclei and other membrane-bound organelles such as the mitochondrion, vacuole, and chloroplast.
Hence, a scientist observing a eukaryotic cell and a prokaryotic cell would find that cell organelles like the nucleus and other membrane-delimited structures are only present in the eukaryotic cell.