Viroids: Definition, Structure, Characteristics, Examples and Difference Between Virus and Viroids

Viroids: Definition, Structure, Characteristics, Examples

and Difference Between Virus and Viroids

🌊Introduction🌊

Viroids are tiny infectious particles that mainly infect plants. They consist only of circular RNA and lack a protein coat, which makes them different from viruses. Viroids were discovered by T.O. Diener. In this article, you will learn about the definition, structure, characteristics, examples, and difference between virus and viroids.

What are Viroids?

** Definition: Viroids are the smallest infectious agents composed of circular single-stranded RNA and lacking a protein coat, which mainly infect plants.

** Discovery by T.O. Diener

** Small infectious RNA particles

Structure of Viroids:

** Circular single-stranded RNA

** No protein coat

** Simplified diagram

Characteristics of Viroids

** Infect plants

** Smallest infectious agents

** No capsid

** No DNA

Examples of Viroids:

** Potato spindle tuber viroid

** Citrus exocortis viroid

Difference Between Virus and Viroids:

Although viruses and viroids are infectious agents, they differ in structure, composition, and host range. The following table shows the major differences between viruses and viroids.

Virus	Viroids
DNA or RNA	Only RNA
Protein coat present	No protein coat
Larger in size	Smaller than viruses
Infect plants, animals, bacteria	Mainly infect plants
Example: Tobacco Mosaic Virus (TMV)	Example: Potato Spindle Tuber Viroid (PSTVd)

NCERT / NEET Important Points:

✔️ Viroids are the smallest infectious agents.
✔️ They consist only of circular single-stranded RNA (ssRNA).
✔️ Viroids lack a protein coat (capsid).
✔️ They mainly infect plants.
✔️ The term “viroid” was introduced by T.O. Diener in 1971.
✔️ Potato Spindle Tuber Viroid (PSTVd) is a well-known example of a viroid.
✔️ Unlike viruses, viroids contain only RNA and no protein coat.

Conclusion

In conclusion, viroids are the smallest infectious agents that mainly infect plants and consist only of circular RNA without a protein coat. Their simple structure distinguishes them from viruses. Learning about viroids, their characteristics, examples, and differences from viruses is essential for students preparing for NCERT and NEET Biology.

FAQs About Viroids

Q1. What are viroids?
Answer: Viroids are the smallest infectious agents composed of circular single-stranded RNA and lacking a protein coat. They mainly infect plants.

Q2. Who discovered viroids?
Answer: Viroids were discovered by T.O. Diener in 1971.

Q3. How are viroids different from viruses?
Answer: Unlike viruses, viroids contain only RNA and do not possess a protein coat (capsid).

Q4. Do viroids infect humans?
Answer: No, viroids mainly infect plants and are not known to infect humans.

Q5. What is an example of a viroid?
Answer: Potato Spindle Tuber Viroid (PSTVd) is a common example of a viroid.

Q6. Do viroids have a protein coat?
Answer: No, viroids lack a protein coat and consist only of circular RNA.

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MCQs on Viroids (NEET/NCERT)

1. What are viroids composed of?
   A) DNA only
   B) Protein only
   C) Circular single-stranded RNA
   D) DNA and protein
   
   
   Answer: C) Circular single-stranded RNA


2. Who discovered viroids?
   A) Watson
   B) T.O. Diener
   C) Darwin
   D) Mendel
   
   
   Answer: B) T.O. Diener


3. Viroids mainly infect which organisms?
   A) Animals
   B) Humans
   C) Plants
   D) Bacteria
   
   
   Answer: C) Plants


4. Which of the following is absent in viroids?
   A) RNA
   B) Protein coat
   C) Genetic material
   D) Circular structure
   
   
   Answer: B) Protein coat


5. Viroids are considered the ______ infectious agents.
   A) Largest
   B) Smallest
   C) Most complex
   D) Harmless
   
   
   Answer: B) Smallest


6. Which of the following is an example of a viroid?
   A) TMV
   B) HIV
   C) Potato Spindle Tuber Viroid
   D) Influenza virus
   
   
   Answer: C) Potato Spindle Tuber Viroid


7. Unlike viruses, viroids do not possess:
   A) RNA
   B) Circular shape
   C) Protein coat
   D) Infectious nature
   
   
   Answer: C) Protein coat


8. In which year were viroids discovered?
   A) 1950
   B) 1965
   C) 1971
   D) 1980
   
   
   Answer: C) 1971


9. Which nucleic acid is found in viroids?
   A) DNA only
   B) RNA only
   C) Both DNA and RNA
   D) Neither DNA nor RNA
   
   
   Answer: B) RNA only


10. Viroids differ from viruses because they lack:
    A) RNA
    B) Infectivity
    C) Protein coat (capsid)
    D) Circular structure
    
    
    Answer: C) Protein coat (capsid)