1.2.6—Prokaryotes vs eukaryotes
- Syllabus
- 9700–2028–2029
- Objective
- 1.2.6
- Level
- AS
The prokaryote–eukaryote contrast is about organisation, not just size
Prokaryotes and eukaryotes both have a cell-surface membrane, cytoplasm, DNA and ribosomes. The key structural contrast is that eukaryotes organise DNA and many cell processes inside membrane-bound organelles, whereas prokaryotes do not.
| Structural feature | Prokaryotes | Eukaryotes |
|---|---|---|
| Cell organisation | Usually unicellular; no membrane-bound organelles | May be unicellular or multicellular; membrane-bound organelles present |
| Genetic material | Circular DNA in the cytoplasm, not enclosed by a nucleus | Linear chromosomes inside a nucleus |
| Ribosomes | 70S | 80S in the cytoplasm; 70S in mitochondria and chloroplasts |
| Typical size | Usually about 1–5 µm in diameter | Often larger; plant cells may be about 10–100 µm across |
| Cell wall, when present | Peptidoglycan | Cellulose in plants or chitin in fungi |
The eukaryotic nucleus and other compartments keep different reactions in controlled local conditions. A prokaryote’s simpler organisation leaves its circular DNA in the cytoplasm and has no double-membrane organelles. These are structural patterns to compare together, not a single size test.
Both cell types contain DNA, ribosomes and a membrane. A large bacterium can still be prokaryotic, and a unicellular yeast cell can still be eukaryotic; identify the cell type from DNA location, ribosome type and organelle organisation rather than apparent size alone.
ConceptA-Level CAIE Biology AS