Describe virus structure and host dependence
Identify genetic material and a protein coat without treating a virus as a small bacterial cell.
Section 1.3 · Features of organisms
Extended only (Supplement); Biology 0610, 2026–2028. Use the stated specimen features and evidence. Diagrams are schematic. Written practice is self-checked
Before you begin
- Read the stated observations before choosing a group.
Work on paper. Try each question before revealing help, and explain why your method works.
Quick readiness check
Which structures form the required virus description?
What you will learn
- State the required virus structures.
- Distinguish virus structure from cellular organisation.
The syllabus structural minimum
The required description of a virus is genetic material surrounded by a protein coat. The genetic material can be DNA or RNA, depending on the virus; do not assume every virus contains both. Some viruses have additional envelopes, but an envelope is not required in this structural minimum.
A virus is not a tiny bacterial cell. It lacks the full cellular organisation and independent metabolic machinery of a bacterium. Its protein coat is not a plant or fungal cell wall, and it does not contain a membrane-bound nucleus.
Connect structure with the limit of independence
Viruses reproduce using host cells. They do not independently perform the complete collection of cellular life processes in the way an organismal cell does. This is why they are considered separately from the five cellular kingdoms in the stated comparison.
For a diagram question, label the coat and genetic material and state their locations. A geometric sketch is schematic, not a scale drawing or a claim that all viruses have the same shape. Detailed infection mechanisms are beyond the structural requirement of this lesson.
Pause and explain
Which statement about virus genetic material is accurate?
Worked example
A schematic shows an outer protein layer enclosing a strand of genetic material. Name the required virus features.
Show the worked solution
- Identify the outer layer as protein coat.
- Identify the internal strand as genetic material.
- Avoid adding a nucleus or bacterial cell structures not shown.
Answer Protein coat surrounding genetic material.
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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.
Label an outer protein boundary and an internal genetic strand in a virus schematic.
Give me a hint
Keep the labels structural.
Compare my reasoning
- Outer boundary: protein coat.
- Internal strand: genetic material.
- Do not call the coat a cell wall.
Protein coat; genetic material.
Look for these in your work
- Both labels correct.
- Correct locations.
A description says a virus has DNA inside a protein coat. Must RNA also be added? Explain.
Give me a hint
Different viruses use different genetic material.
Compare my reasoning
- The supplied virus uses DNA.
- The required description allows DNA or RNA.
- Both are not required for every virus.
No; the supplied genetic material is DNA, and the coat-plus-genome description is sufficient here.
Look for these in your work
- Respect the supplied genome.
- Reject the both-required claim.
A student places a virus among bacteria because both are small. Correct the classification reasoning.
Give me a hint
Size does not establish cellular organisation.
Compare my reasoning
- Bacteria are prokaryotic cells.
- Viruses have genetic material and a coat without full cellular machinery.
- Host dependence and structure distinguish them.
Small size is insufficient; viruses are distinct from bacterial cells in this scheme.
Look for these in your work
- Compare structures.
- Avoid size-only classification.
Common mistakes
- Genetic material is DNA or RNA depending on the virus, not necessarily both.
- A protein coat is not a nucleus or cellulose wall.
What can you explain now?
Why should a virus not be labelled a prokaryotic cell?
Compare with the explanation
It lacks the full organisation of a bacterial cell.
Prokaryotes are cellular; the virus structural description is different.
After trying it yourself, choose your next review. This is your self-assessment.
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Make it stick
Draw a virus schematic with two required labels, then explain why it is not a bacterial cell.
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.