A virus is genetic material (RNA or DNA) wrapped inside a protein coat. A viroid is just a tiny, free piece of RNA with NO protein coat, and its RNA is low molecular weight. So the one big difference: viroids have no protein coat, viruses do. Memory hook: "vir-OID = RNA void of a coat."
A virus has genetic material (RNA or DNA) enclosed in a protein coat and is larger; a viroid is only free low-molecular-weight RNA with no protein coat and is smaller. The missing coat is the key NEET difference.
Your doubts, answered
How are viroids different from viruses in one line?
Viroids are free RNA with NO protein coat. Viruses always have a protein coat (capsid) around their genetic material. This is the single most-tested difference in NEET. NCERT says the viroid "lacked the protein coat that is found in viruses, hence the name viroid."
Do viroids have a protein coat or not?
No. Viroids do NOT have a protein coat. The name "viroid" itself comes from this fact. A virus, on the other hand, has a nucleic acid core enclosed in a protein coat. If a NEET option says a viroid "lacks a protein coat," that statement is CORRECT.
Is viroid made of RNA or DNA?
A viroid is made of RNA only, never DNA. It is a free RNA of LOW molecular weight. Viruses can have either RNA or DNA. Watch the NEET trap: if an option says viroid RNA is of "high molecular weight," that is WRONG (it is low).
Which is smaller, a viroid or a virus?
A viroid is smaller than a virus. In 1971 T.O. Diener found an infectious agent smaller than viruses that caused potato spindle tuber disease and named it a viroid. So remember: viroid = smaller + free RNA + no coat.
Do viroids cause infections like viruses?
Yes. Viroids do cause infections (mainly plant diseases, e.g. potato spindle tuber disease). Do not mark "viroids cannot cause infection" as correct in NEET. Both viroids and viruses are infectious; the difference is structure (coat vs no coat), not whether they infect.
What is the difference between viroid, virus and prion?
Virus = nucleic acid (RNA or DNA) + protein coat. Viroid = free RNA, low molecular weight, no coat. Prion = abnormally folded protein with NO nucleic acid (causes mad cow disease). One-word tags: virus = coated nucleic acid, viroid = naked RNA, prion = bad protein.
⚠️ The NEET trap ✗ Viroids differ from viruses because viroid RNA is of high molecular weight. ✓ Viroid RNA is of LOW molecular weight, and the key difference is that viroids have free RNA WITHOUT a protein coat (viruses have a coat). 🧠 NEET flips one word: "low" becomes "high." NCERT clearly states "The RNA of the viroid was of low molecular weight." If you see "high molecular weight," that option is the wrong (answer) statement.
Real NEET questions
2017
Viroids differ from viruses in having:
A · DNA molecules with protein coat
B · DNA molecules without protein coat
C · RNA molecules with protein coat
D · RNA molecules without protein coat ✓
Solution: A viroid is a free RNA that lacks the protein coat (capsid) found in viruses. Viruses have a nucleic acid (RNA or DNA) enclosed in a protein coat, so viroids differ by being free RNA WITHOUT a coat. NCERT: "a free RNA; it lacked the protein coat that is found in viruses."
2016
Which of the following statements is wrong for viroids?
A · They lack a protein coat
B · They are smaller than viruses
C · They cause infections
D · Their RNA is of high molecular weight ✓
Solution: The wrong statement is (D). Viroid RNA is of LOW molecular weight, not high. Viroids do lack a protein coat, are smaller than viruses, and do cause infections (e.g. potato spindle tuber disease), so those three statements are correct.
2019 · 2021 · ReNEET 2026
Which of the following statements is incorrect?
A · Viroids lack a protein coat.
B · Viruses are obligate parasites.
C · Infective constituent in viruses is the protein coat. ✓
D · Prions consist of abnormally folded proteins.
Solution: Incorrect statement is (C). In viruses the infective part is the genetic material (nucleic acid), NOT the protein coat. Viroids lack a protein coat, viruses are obligate parasites, and prions are abnormally folded proteins, so those are correct.
Solved Biological Classification NEET PYQs
Try the real previous-year questions from this chapter — each with the answer and a full solution.
T.O. Diener discovered viroids in 1971. He found an infectious agent smaller than viruses that caused potato spindle tuber disease.
Why is it called a viroid?
Because it is like a virus but lacks the protein coat found in viruses. The RNA is "free" (naked), so it was named viroid to show it is a coat-less, virus-like agent.
What disease does a viroid cause?
Viroids mainly cause plant diseases. The classic NCERT example is potato spindle tuber disease. Viroids are important plant pathogens.
Is a viroid living or non-living?
Like viruses, viroids sit on the border of living and non-living. They have no cell structure and cannot reproduce on their own; they need a host cell to multiply.
What is the easiest way to remember viroid vs virus for NEET?
Virus = nucleic acid (RNA or DNA) + protein coat. Viroid = free RNA only, low molecular weight, no coat, smaller. Remember "viroid = void of coat."
