What distinguishes prokaryotic from eukaryotic cells?

• A. Eukaryotic cells have smaller genomes than prokaryotic cells.
• B. Both cell types contain a nucleus.
• C. Prokaryotes lack a nucleus and membrane-bound organelles, while eukaryotes have both.
• D. Prokaryotes use mitochondria for energy.

Answer: (C)

The key idea is how the cell’s internal organization differs, especially where the genetic material is stored and whether membrane-bound compartments exist. Eukaryotic cells keep their DNA inside a membrane-bound nucleus and contain other membrane-bound organelles such as mitochondria, endoplasmic reticulum, and Golgi. Prokaryotic cells do not have a nucleus; their DNA sits in the cytoplasm in a region called the nucleoid, and they lack membrane-bound organelles. This difference in internal organization is what distinguishes prokaryotes from eukaryotes.

Genome size isn’t a reliable rule, since it varies within each group. And it’s not true that both types have a nucleus, or that prokaryotes use mitochondria for energy—prokaryotes lack mitochondria altogether and carry out energy processes in other parts of the cell.