Sample 1Easy
Viroids, discovered by T.O. Diener, were found to be the causative agent of
- A
tobacco mosaic disease
- B
mumps
- C
potato spindle tuber disease
- D
foot and mouth disease
Show the answer
The answer is C.In 1971 T.O. Diener discovered a new infectious agent smaller than viruses that caused potato spindle tuber disease. It was a free RNA lacking a protein coat and was named a viroid.
- A.
Tobacco mosaic disease is caused by a virus, TMV.
- B.
Mumps is a viral disease of humans.
- D.
Foot and mouth disease of cattle is caused by a virus.
NCERT: Class 11 Biology, Chapter 2 (Biological Classification), Viruses, Viroids and Lichens
Sample 2Medium
A figure shows a virus made of a polyhedral head (A) sitting on a tubular sheath (B). The sheath ends in a plate that carries thin tail fibres (C), and the tail fibres are attached to the wall of a bacterial cell. Which statement about this virus is correct?
- A
It is a bacteriophage whose genetic material is single-stranded RNA without any protein coat
- B
It is a plant virus like TMV, with single-stranded RNA in A
- C
It is a bacteriophage; its genetic material in A is usually double-stranded DNA, enclosed in a protein coat called the capsid
- D
It is an infectious agent made of protein alone, with no nucleic acid
Show the answer
The answer is C.A virus with a head, a tail sheath and tail fibres that infects a bacterium is a bacteriophage. Bacteriophages are usually double-stranded DNA viruses, and the nucleic acid is protected by a capsid made of capsomeres.
- A.
A free RNA with no protein coat describes a viroid. Bacteriophages are usually double-stranded DNA viruses with a capsid.
- B.
The virus is attached to a bacterial cell, so it is a bacteriophage, not a plant virus. TMV is a rod-shaped helical virus with no tail fibres.
- D.
Viruses always contain a nucleic acid, DNA or RNA, inside the protein coat. The coat alone is not infectious.
NCERT: Class 11 Biology, Chapter 2
Sample 3NEET level
Assertion (A): Lichens are very good pollution indicators. Reason (R): Lichens do not grow in polluted areas. Choose the correct answer from the options given below.
- A
Both A and R are true and R is the correct explanation of A
- B
Both A and R are true but R is not the correct explanation of A
- C
A is true but R is false
- D
A is false but R is true
Show the answer
The answer is A.Lichens are symbiotic associations of algae and fungi that do not grow in polluted areas. Their absence from an area therefore indicates pollution, so R explains A.
- B.
R is the very reason lichens indicate pollution, so it does explain A.
- C.
R is true: lichens do not grow in polluted areas.
- D.
A is true: lichens are good pollution indicators.
NCERT: Class 11 Biology, Chapter 2 (Biological Classification), Lichens