Free Biodiversity and Variety of Life MCQs with Answers

651. Viruses differ from bacteria by:

• A. Having capsid
• B. Having DNA
• C. Having RNA
• D. Having small size

Explanation: The correct option is A. A capsid is a protein coat that surrounds the genetic material of a virus. It is only present in viruses and not bacteria. Both viruses and bacteria are microscopic organisms having DNA or RNA as their genetic material.

652. It is not true about viruses:

• A. Capsid has capsomeres
• B. Both DNA and RNA together as genome
• C. Some are enveloped
• D. Many infect animals

Explanation: Viruses cannot have both DNA and RNA as their genome because each type requires a completely different replication strategy and enzymes. DNA viruses depend on DNA polymerases, while RNA viruses use RNA-dependent RNA polymerases, and these systems are not compatible within a single genome. Carrying both would be inefficient and unstable, so viruses are classified strictly as either DNA or RNA viruses, never both.

653. Which of the following statements are true about the viruses?

• A. Free living
• B. Obligate parasites
• C. Both A and B
• D. None of the above

Explanation: Option B is correct. Viruses are obligate parasites. This means that they can only survive and reproduce inside living cells. They are not able to exist on their own outside of a host cell (free-living).

654. Which factors may help determine the antigenicity of a virus?

• A. Capsomeres
• B. Size of virus
• C. Whole capsid
• D. Internal proteins

Explanation: The antigenicity of a virus is mainly determined by its whole capsid, as the capsid surface exposes epitopes recognized by the immune system. Capsomeres only contribute indirectly by forming the capsid structure. The size of the virus has no role in antigenicity, while internal proteins are generally hidden and do not significantly influence immune recognition.

655. Which of the following has the morphology of a helical virus?

• A. TMV
• B. T4 Phage
• C. Poxvirus
• D. Herpes virus

Explanation: Tobacco mosaic virus (TMV) is a well-studied plant virus that belongs to the Tobamovirus genus. It is characterized by its rod-like or filamentous appearance. The structure of TMV consists of a long, cylindrical particle with helical symmetry. The viral particle is made up of a single type of protein subunit, arranged in a helical fashion around the RNA genome. The rod-shaped appearance is due to the helical arrangement of these protein subunits.

656. The structure that is located between the nucleocapsid and the envelope is the:

• A. Capsid
• B. Matrix protein
• C. Envelope
• D. Nuclear capsid

Explanation: In viruses, the matrix protein is a structural protein located between the nucleocapsid and the viral envelope. It helps maintain the shape of the virus, links the envelope to the nucleocapsid, and plays a key role in virus assembly and budding from the host cell. Matrix proteins are especially important in enveloped viruses, such as influenza and HIV, for organizing viral components during the formation of new viral particles.

657. What type of viruses are the polioviruses?

• A. DNA-enveloped virus
• B. RNA-enveloped virus
• C. DNA naked virus
• D. RNA naked virus

Explanation: The correct option is D.An RNA-naked virus is a virus that has an RNA genome but no envelope. The RNA genome is directly exposed to the environment. RNA naked viruses are more common than DNA naked viruses. Some examples of RNA viruses include poliovirus and rhinovirus.

658. Which of the following viruses possesses an envelope?

• A. Herpes virus
• B. Reovirus
• C. Polio virus
• D. Papillomavirus

Explanation: Among all of the above options, only herpes is an enveloped virus. All the rest are non-enveloped.

659. What does an icosahedral capsid consist of?

• A. Hexagonal capsomeres
• B. Pentagonal capsomeres
• C. Triangular Capsomeres
• D. Both A and B

Explanation: An icosahedral shape, common in viral capsids, is made of protein subunits called capsomeres, which can be pentameric (five subunits) or hexameric (six subunits). Pentamers occupy the 12 vertices of the icosahedron, while hexamers fill the faces and edges, creating a stable, closed shell. This arrangement follows the principle of quasi-equivalence, allowing subunits to adapt slightly to form either pentamers or hexamers. The combination of these capsomeres gives the icosahedral capsid structural stability and enough internal space to enclose the viral genome.

660. Viruses are limited in their host range because

• A. Can only replicate in certain types of cells.
• B. Certain cells are susceptible to viral infection.
• C. They can only enter cells that have proper/specific receptors.
• D. They can only enter cells with glycoproteins.

Explanation: Viruses have a limited host range because they cannot infect all cells. While they need specific cellular conditions for replication (Option A) and not all cells are equally susceptible (Option B), the key factor is the presence of the right cell surface receptors (Option C) that allow viral entry. Option D is only partly correct, since not all viral receptors are glycoproteins. Therefore, the limitation of host range is primarily due to receptor specificity.