Compare Archaea and Bacteria
Compare the two prokaryotic domains using membrane lipids, ribosomal RNA and cell-wall composition.
A Level; Cambridge International Biology 9700, 2028–2030. Written responses are self-checked; this does not certify supervised fieldwork or practical competence.
Before you begin
- Classification compares shared characteristics; populations occupy environments and contain variation.
Work on paper. Try each question before revealing help, and explain why your method works.
Quick readiness check
Name one specified difference between Archaea and Bacteria.
What you will learn
- State that Archaea and Bacteria are prokaryotes
- Compare them using the three specified biochemical features
Build the explanation
Archaea and Bacteria both lack a membrane-bound nucleus, but they differ in membrane lipids, ribosomal RNA sequences and cell-wall composition. Bacterial cell walls commonly contain peptidoglycan; archaeal walls do not contain bacterial peptidoglycan. Their membrane lipids also have different chemical linkages, and rRNA sequence comparisons support their separation into distinct domains.
Use evidence within scope
Do not infer a domain from one vague feature such as small size. Use the named molecular or cell-wall evidence; cell-wall composition is not identical across every member of either domain.
Pause and explain
A report compares the rRNA sequences and wall chemistry of two prokaryotes. Explain why the features are useful together.
Worked example
A prokaryote has a cell wall without bacterial peptidoglycan and a membrane lipid chemistry characteristic of Archaea. Which domain is supported?
Show the worked solution
- Use both specified chemical comparisons.
- The evidence is consistent with Archaea.
Answer Archaea, based on the stated cell-wall and membrane-lipid evidence.
Try a topic test
Choose Easy, Normal or Difficult. Save your answers and open worked review after finishing.
Test this topic →From guided practice to a new situation
Write your answer and reasoning first. Use a hint only if you are stuck. The model solution is for self-checking; your written work is not automatically marked.
A cell lacks a nucleus. What additional evidence could distinguish Archaea from Bacteria?
Give me a hint
Identify the required evidence and sequence the reasoning.
Compare my reasoning
- Compare the membrane lipids.
- Examine rRNA or cell-wall composition.
Use differences in membrane lipids, ribosomal RNA or cell-wall composition; absence of a nucleus identifies prokaryotic organisation but not the domain.
Look for these in your work
- Relevant evidence selected
- Reasoning linked to conclusion
Why is “no nucleus” insufficient to identify a bacterium?
Give me a hint
Use the supplied example or data to justify a conclusion.
Compare my reasoning
- Archaea also lack a membrane-bound nucleus.
- Use a feature that differs between the domains.
Both domains are prokaryotic, so the absence of a nucleus is shared. Compare their membrane lipids, rRNA or wall composition instead.
Look for these in your work
- Concept applied
- Limit or assumption stated
A report compares the rRNA sequences and wall chemistry of two prokaryotes. Explain why the features are useful together.
Give me a hint
Apply the concept in a new context and qualify its limits.
Compare my reasoning
- They represent independent molecular and structural evidence.
- Agreement strengthens classification.
rRNA sequence and cell-wall chemistry provide different evidence types. Agreement between them supports the classification more strongly than a single general feature.
Look for these in your work
- New context handled
- Conclusion appropriately bounded
Common mistakes
- Saying all prokaryotes have identical walls
- Confusing membrane lipid differences with the presence of a nucleus
What can you explain now?
Name one specified difference between Archaea and Bacteria.
Compare with the explanation
Membrane lipids, rRNA or cell-wall composition
These are the comparison features in this syllabus outcome.
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Make it stick
Which three features distinguish Archaea from Bacteria in the syllabus?
If you needed the solution, close it and solve the problem again from a blank page. A correct answer is stronger when you can explain the reason for each step.