OCR · A-Level · Biology
Course version: H420 · Version from Sept 2025
(k) the similarities and differences in the structure and ultrastructure…
Full specification wording
Cell structure: (k) the similarities and differences in the structure and ultrastructure of prokaryotic and eukaryotic cells.
Prokaryotic and eukaryotic cells share some features but differ in structure and ultrastructure.
Checked against the OCR H420 specification (opens in a new tab) on .
- Point 10 of 10
- 4 key terms
Study notes
From the checked teaching notes for this specification point.
The idea
Prokaryotic and eukaryotic cells share some features but differ in structure and ultrastructure. Both have a cell surface membrane, cytoplasm, ribosomes and genetic material (DNA). Differences: eukaryotic cells have a nucleus enclosing DNA, membrane-bound organelles such as mitochondria and endoplasmic reticulum, and are generally larger. Prokaryotic cells have no nucleus; DNA is a circular loop in the cytoplasm plus small circular plasmids. They lack membrane-bound organelles but have a cell wall (not cellulose), a capsule sometimes, and may have flagella or pili. Prokaryotic ribosomes are smaller (70S) than eukaryotic ribosomes (80S). A strong answer compares like with like, stating a feature and how it differs, rather than listing features of one cell only.
What earns the marks
- States that both cell types have a cell surface membrane, cytoplasm, ribosomes and DNA.
- States that eukaryotic cells have a nucleus enclosing DNA, whereas prokaryotic cells have DNA as a circular loop in the cytoplasm (plus plasmids).
- States that eukaryotic cells have membrane-bound organelles (e.g. mitochondria, endoplasmic reticulum) that prokaryotic cells lack.
- States that prokaryotic cells have a cell wall (not cellulose) and may have a capsule, flagella or pili.
- States that prokaryotic ribosomes are smaller (70S) than eukaryotic ribosomes (80S).
- States that eukaryotic cells are generally larger than prokaryotic cells.
Common mistakes and how to put them right
Listing features of only one cell type.
Put it right by making direct comparisons of the same feature.
Claiming prokaryotes have no ribosomes.
Put it right by noting they have smaller 70S ribosomes.
Saying prokaryotic DNA is in a nucleus.
Put it right by stating it is a circular loop in the cytoplasm with plasmids.
Exam tips
- Structure answers as paired comparisons: 'both have... whereas...'.
- Name specific organelles and ribosome sizes to gain precision.
- Distinguish plasmids from the main circular DNA loop.
Try the lesson
The start of the Cell structure: (k) the similarities and differences in the structure and ultrastructure of prokaryotic and eukaryotic cells. lesson, made from checked teaching notes for this specification point.
Have a go first
Which feature is present in a eukaryotic cell but absent from a prokaryotic cell?
Listen
Prokaryotic and eukaryotic cells share some features but differ in structure and ultrastructure. Both have a cell surface membrane, cytoplasm, ribosomes and genetic material (DNA). Differences: eukaryotic cells have a nucleus enclosing DNA, membrane-bound organelles such as mitochondria and endoplasmic reticulum, and are generally larger. Prokaryotic cells have no nucleus; DNA is a circular loop in the cytoplasm plus small circular plasmids. They lack membrane-bound organelles but have a cell wall (not cellulose), a capsule sometimes, and may have flagella or pili. Prokaryotic ribosomes are smaller (70S) than eukaryotic ribosomes (80S). A strong answer compares like with like, stating a feature and how it differs, rather than listing features of one cell only. A strong answer earns marks for these points. States that both cell types have a cell surface membrane, cytoplasm, ribosomes and DNA. States that eukaryotic cells have a nucleus enclosing DNA, whereas prokaryotic cells have DNA as a circular loop in the cytoplasm (plus plasmids). States that eukaryotic cells have membrane-bound organelles (e.g. mitochondria, endoplasmic reticulum) that prokaryotic cells lack. States that prokaryotic cells have a cell wall (not cellulose) and may have a capsule, flagella or pili. A common slip: Listing features of only one cell type. Instead, making direct comparisons of the same feature. Exam tip: Structure answers as paired comparisons: 'both have... whereas...
Key words
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Ultrastructure
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Prokaryotic vs eukaryotic
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Organelles and ribosomes
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Cell structure
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See every definition
- Ultrastructure
- The fine structure of prokaryotic and eukaryotic cells, which can be compared to show similarities and differences.
- Prokaryotic vs eukaryotic
- A comparison of two cell types that share a cell surface membrane, cytoplasm, ribosomes and DNA but differ in structure and ultrastructure.
- Organelles and ribosomes
- Eukaryotic cells have membrane-bound organelles such as mitochondria and endoplasmic reticulum, which prokaryotic cells lack, and prokaryotic ribosomes are smaller (70S) than eukaryotic ribosomes (80S).
- Cell structure
- Prokaryotic cells have no nucleus, with DNA as a circular loop in the cytoplasm plus small circular plasmids, and have a cell wall (not cellulose).
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