Chapter: Biological Classification
Sub-topic: Virus
Lead Question 2016 (Phase 1): 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
Answer: D) Their RNA is of high molecular weight
Viroids consist of low molecular weight circular RNA without a protein coat. Their RNA is much smaller than viral genomes, enabling them to infect plants by disrupting cellular processes.
1. Viroids differ from viruses because they:
A) Have a protein coat
B) Lack a protein coat
C) Contain DNA
D) Infect animals
Answer: B) Lack a protein coat
Unlike viruses, viroids do not possess a protein coat, consisting only of naked RNA. This makes them the smallest infectious agents known, mainly infecting plants.
2. The genetic material of viroids is:
A) Double stranded DNA
B) Single stranded circular RNA
C) Double stranded RNA
D) Single stranded linear RNA
Answer: B) Single stranded circular RNA
Viroids contain a single stranded circular RNA molecule that is highly stable and capable of autonomous replication within host plant cells.
3. Which disease is caused by a viroid?
A) Tobacco Mosaic Disease
B) Potato Spindle Tuber Disease
C) Influenza
D) AIDS
Answer: B) Potato Spindle Tuber Disease
This disease is caused by the Potato Spindle Tuber Viroid (PSTVd), one of the first identified viroids affecting plants by causing abnormal growth.
4. Viroids primarily infect:
A) Animals
B) Plants
C) Bacteria
D) Fungi
Answer: B) Plants
Viroids are plant pathogens that interfere with cellular metabolism, causing various diseases and crop damage.
5. The size of viroids compared to viruses is:
A) Larger
B) Smaller
C) Equal
D) Variable
Answer: B) Smaller
Viroids are much smaller than viruses, typically only a few hundred nucleotides long, lacking the protein capsid that viruses have.
6. Assertion-Reason:
Assertion (A): Viroids do not have a protein coat.
Reason (R): Viroids are composed only of a short strand of RNA.
Options:
A) Both A and R are true, and R explains A
B) Both A and R are true, but R does not explain A
C) A is true, R is false
D) A is false, R is true
Answer: A) Both A and R are true, and R explains A
Viroids consist solely of a short RNA strand without a protein coat, which explains their lack of capsid and their unique infection mechanism.
7. Match Column A with Column B:
Column A Column B
1. Viroid A. Infectious RNA without protein coat
2. Virus B. Protein coat with DNA or RNA
3. Bacteria C. Prokaryotic unicellular organism
4. Fungus D. Eukaryotic decomposer organism
Answer: 1 → A, 2 → B, 3 → C, 4 → D
Viroids are infectious naked RNA, viruses have nucleic acid plus protein coat, bacteria are unicellular prokaryotes, and fungi are eukaryotic decomposers.
8. Diagram-based MCQ:
The structure shown lacks a protein coat and consists of a circular RNA molecule. What is this infectious agent?
A) Virus
B) Viroid
C) Bacterium
D) Prion
Answer: B) Viroid
The lack of a protein coat and presence of circular RNA identifies this agent as a viroid, which infects plants causing disease.
9. Fill in the blank:
Viroids are ______ infectious agents that infect plants.
A) DNA-based
B) Proteinaceous
C) RNA-based
D) Virus-like
Answer: C) RNA-based
Viroids consist of RNA alone, without any protein coat, distinguishing them from viruses and other infectious agents.
10. Passage-based MCQ:
Passage: Viroids are the smallest known infectious pathogens. They are composed solely of a short strand of circular RNA and lack a protein coat. They cause several economically important plant diseases by disrupting normal cellular functions.
Which of the following is true about viroids?
A) They contain DNA and infect animals
B) They have a protein coat and infect bacteria
C) They are smaller than viruses and cause plant diseases
D) They are proteinaceous infectious agents