Eukaryotes and Prokaryotes
Revise Eukaryotes and Prokaryotes for GCSE Biology with this free worksheet and full mark scheme — Foundation and Higher exam-style questions with worked answers for AQA, Edexcel and OCR. Remember that prokaryotic cells have no nucleus — their single loop of DNA sits free in the cytoplasm, often alongside smaller rings called plasmids.
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Topic overview
All living things are made of cells, and those cells fall into two types: eukaryotic and prokaryotic. The difference is where the genetic material sits.
Eukaryotic cells keep their DNA enclosed inside a nucleus. All animal and plant cells are eukaryotic, and so are fungi and protists. These cells are relatively large and contain membrane-bound organelles such as mitochondria.
Prokaryotic cells have no nucleus. Their DNA sits free in the cytoplasm as a single loop, and they may also carry small rings of DNA called plasmids. Bacteria are prokaryotic, and they are much smaller than eukaryotic cells — typically a hundredth of the volume.
Revision notes
Eukaryotic cells
A eukaryotic cell has its genetic material enclosed within a nucleus, and it contains membrane-bound organelles.
Animal cells, plant cells, fungi and protists are all eukaryotic. Typical sizes are 10–100 μm, which is large enough to see clearly with a light microscope.
Prokaryotic cells
A prokaryotic cell has no nucleus. Its single loop of DNA lies free in the cytoplasm, and it has no membrane-bound organelles.
Bacteria are the example you need. They are typically 1–5 μm across, and many also carry plasmids — small circular pieces of DNA separate from the main loop.
Comparing the two
Both types have a cell membrane, cytoplasm and ribosomes, so those features cannot be used to tell them apart.
The reliable differences are the nucleus, the presence of membrane-bound organelles, the form of the DNA, and the size. Plasmids occur only in prokaryotes.
Key points
- Eukaryotic cells have a nucleus; prokaryotic cells do not.
- Animal, plant, fungal and protist cells are eukaryotic.
- Bacteria are prokaryotic.
- Prokaryotes have a single loop of DNA and may have plasmids.
- Prokaryotic cells are much smaller than eukaryotic cells.
- Both types have a cell membrane, cytoplasm and ribosomes.
Worked examples
Example 1
Give one difference between a eukaryotic cell and a prokaryotic cell. [1 mark]
Model answer
A eukaryotic cell has its genetic material enclosed in a nucleus, whereas a prokaryotic cell does not — its DNA is free in the cytoplasm (1 mark).
Example 2
Describe two ways in which the genetic material of a bacterium differs from that of an animal cell. [2 marks]
Model answer
Bacterial DNA is a single loop that lies free in the cytoplasm rather than being enclosed in a nucleus (1 mark). Bacteria may also carry plasmids, which are small rings of DNA separate from the main loop, and animal cells do not (1 mark).
Example 3
A student states that ribosomes can be used to tell eukaryotic and prokaryotic cells apart. Explain why the student is wrong. [2 marks]
Model answer
Ribosomes are found in both eukaryotic and prokaryotic cells (1 mark), so their presence does not distinguish between the two types — a feature such as the nucleus, which only eukaryotes have, would be needed instead (1 mark).
Common mistakes
Saying prokaryotes have no DNA.
They have DNA, but it is a single loop free in the cytoplasm rather than enclosed in a nucleus.
Using ribosomes or a cell membrane as a difference.
Both cell types have these, so they cannot be used to tell them apart.
Confusing plasmids with the main loop of DNA.
Plasmids are small additional rings of DNA, separate from the single main loop.
Thinking all small cells are prokaryotic.
Size is a general guide, not a definition. The nucleus is what settles it.
Exam tips
- Name the nucleus as the key difference — it is the most reliable single answer.
- Do not offer features shared by both cell types as differences.
- Use the correct units when comparing sizes: μm for cells.
- Learn bacteria as your prokaryotic example.
Key terms
- Eukaryotic
- A cell with its genetic material enclosed in a nucleus.
- Prokaryotic
- A cell with no nucleus, whose DNA is free in the cytoplasm.
- Plasmid
- A small ring of DNA in a prokaryotic cell, separate from the main loop.
- Organelle
- A specialised structure within a cell.
Related topics
Written and reviewed against the current AQA, Edexcel and OCR specifications. Spotted an error? Let us know.