Final answer:
Prokaryotes have their genetic material not enclosed in a nucleus, whereas eukaryotic cells have a true nucleus.
Step-by-step explanation:
The statement that is true of prokaryotes but not eukaryotes is that their genetic material isn't enclosed in a nucleus. Both prokaryotic and eukaryotic cells have a plasma membrane, cytoplasm, and ribosomes where protein synthesis occurs. However, in eukaryotic cells, the DNA is surrounded by a membrane forming a true nucleus. Additionally, mitochondria, which are responsible for ATP production through cellular respiration, are present only in eukaryotic cells.