Answer: The given statement can be completed as-
The main difference between a prokaryotic cell and a eukaryotic cell is the presence of a true nucleus in eukaryotes.
Eukaryotes are those organisms, which possess a membrane bound nucleus ( true nucleus in the cell) that contains the genetic material ( DNA) of the living organisms. The eukaryotic cells also contain membrane bound subcellular organelles like endoplasmic reticulum, golgi complex, mitochondria.
Example- Plants and animals.
Prokaryotes are those organisms that do not possess a membrane bound true nucleus and subcellular organelles. The genetic material lies in the cytoplasm of the cell.
Example- Bacteria like E.coli.