Viruses are non-cellular, obligate intracellular parasites; nucleic acid (DNA or RNA) + protein coat. Viroids: free RNA, no protein (potato spindle tuber). Prions: infectious protein particles (mad cow). Lichens: symbiosis between fungi (mycobiont) + algae/cyanobacteria (phycobiont).
-- NCERT Class 11 Biology, Ch. 2, p. 19Viruses Viroids Lichens
8 MCQs9-step worked example
Source: NCERT Diversity in Living WorldPYQ coverage: NEET 2023, 2026Official key: NTA-verifiedLast updated: 27 Sep 2026
Viruses Viroids Lichens, explained for NEET
Viruses, viroids, prions, and lichens occupy a unique conceptual space in NEET biology — they don't fit neatly into the Five Kingdom classification, and that ambiguity is exactly what NTA exploits.
Viruses are non-cellular, obligate intracellular parasites. They possess either DNA or RNA (never both), surrounded by a protein coat (capsid). Outside a host, they are inert crystallisable particles (as demonstrated by Stanley's crystallisation of TMV). They reproduce only inside living cells using the host's machinery. Key trap: viruses are NOT placed in any kingdom because they lack cellular organisation.
Viroids are smaller than viruses — free RNA without a protein coat. Discovered by T.O. Diener (1971), they cause diseases in plants (e.g., potato spindle tuber disease). The critical distinction from viruses: viroids lack a capsid entirely; they are naked RNA molecules of low molecular weight.
Prions are infectious protein particles — no nucleic acid at all. They cause neurodegenerative diseases (e.g., mad cow disease/BSE, Creutzfeldt-Jakob disease in humans). The trap: prions are proteins that cause disease, not organisms.
Lichens are symbiotic associations between a fungus (mycobiont) and an alga or cyanobacterium (phycobiont). The fungus provides shelter, absorbs water and minerals; the alga provides food via photosynthesis. Lichens are pollution indicators — they do not grow in polluted areas (especially SO₂-rich environments).
NEET watch-out: Questions frequently test the structural hierarchy (virus > viroid > prion in decreasing complexity of genetic material) and the symbiotic nature of lichens. Confusing viroid with virion, or forgetting that prions lack nucleic acid entirely, costs marks reliably.
NCERT Class 11 Biology Chapter 2, page 11 covers these acellular entities as exceptions to the biological classification system.
Can you answer these Viruses Viroids Lichens MCQs?
Select an option to see the explanation. Wrong answers show why your choice was tempting — and name the exact trap it exploits.
MCQ 1Easy RecallPractice
Which of the following statements about viroids is correct?
Show answer and why every option is right or wrong
Answer: A. Viroids are free RNA without any protein coat, discovered by T.O. Diener (1971). They are smaller than viruses and cause plant diseases. NCERT Class 11 Biology Chapter 2, page 21.
Why B is wrong: B confuses viroids with viruses — viroids specifically LACK a protein coat; that is their defining distinction from viruses.
Why C is wrong: C describes prions, not viroids. Prions are infectious proteins lacking nucleic acid; viroids ARE nucleic acid (RNA).
Why D is wrong: D describes neither viroids nor any known infectious agent accurately — viroids are naked RNA, not DNA, and lack any envelope.
MCQ 2Concept TrapPractice
In a lichen, the phycobiont (alga) is experimentally removed and the mycobiont (fungus) is kept alive on its own. Based on the division of roles between the two partners, which outcome is most likely, and why?
Show answer and why every option is right or wrong
Answer: B. In a lichen the alga (phycobiont) is autotrophic and prepares food by photosynthesis, while the fungus (mycobiont) is heterotrophic and instead provides shelter and absorbs water and mineral nutrients for its partner. Because the mycobiont cannot photosynthesise, removing the phycobiont removes its only food source, so it cannot sustain itself long-term. NCERT Class 11 Biology, Chapter 2, page 21.
Why A is wrong: A reverses the nutritional roles — NCERT states the fungal partner (mycobiont) is heterotrophic, not autotrophic, so it depends on the alga's photosynthesis for food and cannot survive unaided once separated.
Why C is wrong: C swaps which partner does what — NCERT states the alga prepares food for the fungus, while the fungus provides shelter and absorbs water and minerals for the alga, not the reverse, so it is the fungus (not the alga) that loses its food source on separation.
Why D is wrong: D mistakes lichen symbiosis for a facultative relationship — NCERT describes it as a mutually useful association so close that the two organisms function almost as one, meaning the heterotrophic fungus is metabolically dependent on the alga's food production.
MCQ 3Easy RecallPractice
The causative agent of Creutzfeldt-Jakob disease is:
Show answer and why every option is right or wrong
Answer: C. Creutzfeldt-Jakob disease is caused by prions — misfolded infectious protein particles that lack any nucleic acid. NCERT Class 11 Biology Chapter 2, page 21.
Why A is wrong: A is incorrect — viroids cause plant diseases (e.g., potato spindle tuber disease), not mammalian neurodegenerative diseases.
Why B is wrong: B is incorrect — retroviruses are RNA viruses with reverse transcriptase (e.g., HIV); CJD involves no viral particle.
Why D is wrong: D is incorrect — bacteriophages are viruses that infect bacteria, unrelated to human neurodegenerative disease.
MCQ 4Easy RecallPractice
In a lichen, the fungal component is called:
Show answer and why every option is right or wrong
Answer: D. The fungal partner in a lichen is the mycobiont (myco = fungus); the algal/cyanobacterial partner is the phycobiont. NCERT Class 11 Biology Chapter 2, page 21.
Why A is wrong: A is the algal component (phyco = alga), not the fungal component. This is the most common swap error in NEET questions on lichens.
Why B is wrong: B refers specifically to a cyanobacterial partner (a subset of phycobionts) — still the photosynthetic component, not the fungus.
Why C is wrong: C is a general term for the photosynthetic partner and is essentially synonymous with phycobiont, not the fungal partner.
MCQ 5Direct ApplicationPractice
Which of the following features is shared by viroids and prions?
Show answer and why every option is right or wrong
Answer: D. Viroids and prions are both acellular infectious agents, and NCERT places both in the closing section of the chapter rather than in any of the five kingdoms. What they do NOT share is composition: a viroid is free RNA with no protein coat, a prion is protein with no nucleic acid — so neither "both have RNA" nor "both lack a protein coat" holds. NCERT Class 11 Biology, Chapter 2, page 21.
Why A is wrong: A is incorrect — prions contain NO nucleic acid at all (neither RNA nor DNA); only viroids are composed of RNA.
Why B is wrong: B is incorrect, and it is the trap here. Viroids are indeed smaller than viruses — NCERT calls the viroid RNA 'of smaller size than viruses' — but prions are not: NCERT says of the scrapie agent, 'The agent was similar in size to viruses.' A size claim that is true of one and false of the other cannot be what the two share.
Why C is wrong: C is incorrect — viroids cause plant diseases, but prions cause animal/human neurodegenerative diseases (BSE, CJD), not plant diseases.
MCQ 6Direct ApplicationPractice
A scientist isolates an infectious agent from a diseased potato plant. The agent is found to be a low molecular weight RNA molecule without any protein coat. This agent is most likely a:
Show answer and why every option is right or wrong
Answer: C. The description — low molecular weight free RNA, no protein coat, causing plant disease — matches viroids exactly. T.O. Diener's discovery of potato spindle tuber viroid (PSTVd) fits this scenario. NCERT Class 11 Biology Chapter 2, page 21.
Why A is wrong: A is incorrect — retroviruses are full viruses with an RNA genome, reverse transcriptase, capsid, and envelope; they are not 'naked RNA'.
Why B is wrong: B is incorrect — prions are infectious proteins with no nucleic acid; this agent IS nucleic acid (RNA).
Why D is wrong: D is incorrect — bacteriophages are DNA or RNA viruses that infect bacteria, not plants, and they possess a protein coat.
MCQ 7Direct ApplicationPractice
Which of the following correctly arranges infectious agents in decreasing order of structural complexity?
Show answer and why every option is right or wrong
Answer: B. Virus (nucleic acid + protein coat ± envelope) > Viroid (naked RNA only) > Prion (protein only, no nucleic acid). This represents decreasing complexity of components. NCERT Class 11 Biology Chapter 2, page 20.
Why A is wrong: A reverses the order completely — prions are the LEAST complex (just protein), not the most.
Why C is wrong: C incorrectly places viroid above virus; viruses have both nucleic acid AND protein coat, making them more structurally complex than naked RNA viroids.
Why D is wrong: D incorrectly places prion above viroid; prions (just protein) are simpler than viroids (RNA molecule) in terms of genetic information content.
MCQ 8CalculationPractice
Consider the following statements:
(i) Viruses can be crystallised.
(ii) Viroids have DNA as genetic material.
(iii) The__(phycobiont) in lichens is always a green alga.
(iv) Prions are resistant to nuclease treatment.
Which of the above statements are correct?
Show answer and why every option is right or wrong
Answer: B. Statement (i) is correct — W.M. Stanley crystallised TMV. Statement (iv) is correct — prions contain no nucleic acid, so nucleases (which degrade DNA/RNA) cannot inactivate them. Statement (ii) is wrong — viroids have RNA, not DNA. Statement (iii) is wrong — phycobionts can be green algae OR cyanobacteria. NCERT Class 11 Biology Chapter 2, page 20.
Why A is wrong: A includes statement (ii) which is incorrect — viroids are composed of RNA, not DNA.
Why C is wrong: C includes both incorrect statements — (ii) is wrong (viroids = RNA) and (iii) is wrong (phycobiont can be cyanobacteria, not exclusively green algae).
Why D is wrong: D includes statement (iii) which is incorrect — the phycobiont in lichens may be a cyanobacterium (e.g., Nostoc), not always a green alga.
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How do you solve a Viruses Viroids Lichens question? A worked example
- 1
Given
Four matching statements about acellular entities and symbiotic associations.
- 2
Required
Identify the correctly matched pair.
- 3
Concept
Viruses, viroids, prions, and lichens each have specific defining characteristics that NTA tests through matching-type questions. The key distinguishing features are: presence/absence of nucleic acid, presence/absence of protein coat, host type, and nature of association.
- 4
Formula/Rule
• Virus = nucleic acid (DNA OR RNA) + protein coat; obligate intracellular parasite; non-cellular• Viroid = naked RNA only; no protein coat; infects plants• Prion = protein only; no nucleic acid; causes animal/human diseases• Lichen = mutualistic (not parasitic) association; fungus + alga/cyanobacterium
- 5
Substitution (evaluate each option)
• A: Viroid — protein coat present ✗ (viroids LACK protein coat), infects animals ✗ (viroids infect plants)• B: Lichen — parasitic ✗ (lichens are mutualistic, not parasitic)• C: Prion — infectious RNA ✗ (prions are proteins, no RNA), causes plant diseases ✗ (causes animal diseases)• D: Virus — non-cellular ✓, obligate intracellular parasite ✓
- 6
Calculation/Analysis
Options A, B, and C each contain two factual errors. Option D correctly states both defining features of viruses.
- 7
Final answer
D. Virus — non-cellular, obligate intracellular parasite
- 8
Common trap
Students confuse the mutualistic nature of lichens with parasitism (option B seems plausible if you forget that both partners benefit). Similarly, the word "infectious" in option C tempts students who vaguely recall prions are infectious — but the error is calling them "RNA."
- 9
Similar NEET-style question
Which of the following is an incorrect statement?• A. Viroids lack a protein coat and infect plants• B. Prions are infectious agents made of abnormal proteins• C. Lichens are sensitive to sulphur dioxide pollution• D. Viruses contain both DNA and RNA as genetic material
(Answer: D — viruses contain either DNA or RNA, never both.)
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What to remember before solving Viruses Viroids Lichens questions
More in Diversity in Living World: 16 exam traps and mistakes · 1 question pattern from its other lessons.
Viruses Viroids Lichens questions from past NEET papers
3 questions from NEET 2023, 2026. Answers verified against NTA official keys.
NEET 2026
Symbiotic association between fungi and algae are called
1lichens
2sponges
3mycorrhiza
4chrysophytes
NTA Answer: Option 1(final)
NEET 2026
Mad cow disease is caused by ______.
1prions
2viroids
3Aspergillus sp.
4Mycoplasma sp.
NTA Answer: Option 1(final)
NEET 2023
1Both Statement I and Statement II are false.
2Statement I is true but Statement II is false.
3Statement I is false but Statement II is true.
4Both Statement I and Statement II are true.
NTA Answer: Option 4(final)
All 59 past-paper questions from Diversity in Living World →
Sources
NCERT refs: Class 11 Biology Chapter 2, p.11
Page numbers are the ones printed in the current NCERT textbook (2023 rationalised edition), unless marked pre-2023. The books are free at ncert.nic.in.
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