Explain why prokaryotic cells, such as bacteria, are different from eukaryotic cells in terms of their subcellular structures.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Model answer (5 marks)
Prokaryotic cells lack membrane‑bound organelles, so structures such as mitochondria, endoplasmic reticulum and a true nucleus are absent. Their DNA is not enclosed in a nucleus; instead it is a single, circular chromosome that floats freely in the cytoplasm. Prokaryotes also possess plasmids – small, circular DNA molecules that are not usually found in eukaryotes. Consequently, a prokaryotic cell contains only a cell wall, a plasma membrane, cytoplasm and plasmids, whereas a eukaryotic cell has a nucleus and a range of membrane‑bound organelles.
Examiner tips
- Use the word ‘lack’ to show absence of organelles. Mention the chromosome’s location (cytoplasm). Include plasmids as a distinguishing feature. Keep each point brief to fit the 5‑mark limit.
Common mistakes
- Confusing the absence of a nucleus with the absence of DNA. Forgetting to mention plasmids. Using vague terms like ‘organelles’ without specifying membrane‑bound ones.
Mark scheme (5 marks)
- Prokaryotic cells do not contain membrane-bound organelles (whereas eukaryotic cells do)
- Prokaryotic cells do not contain a nucleus / their genetic material is not enclosed in a nucleus
- In prokaryotic cells, genetic material (bacterial DNA) moves freely in the cytoplasm
- Prokaryotic cells contain plasmids (circular loops of DNA), which are not typically found in eukaryotic cells
- Eukaryotic cells (plant and animal cells) contain a nucleus and membrane-bound organelles such as mitochondria, whereas prokaryotic cells only have a cell wall, cell membrane, cytoplasm and plasmids
Key terms in this question
prokaryotic cell · eukaryotic cell
Related
- All Eduqas A-Level Biology revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
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