Free Biodiversity and Variety of Life MCQs with Answers

631. Which of the following statements explains why viruses are only able to multiply in living cells?

• A. Their binary fission is controlled by host cell genes.
• B. Virus do not possess the necessary components for self-replication.
• C. DNA is only able to replicate inside living cells
• D. They have only enough genetic information for DNA replication.

Explanation: Viruses can only multiply inside living cells because they lack the cellular machinery and enzymes needed to reproduce on their own. They depend entirely on host cells to provide the tools for replication, protein synthesis, and assembly of new viral particles. Other options are either factually incorrect or misleading.

632. A chemical component that is found in all viruses is

• A. Protein
• B. DNA
• C. Lipids
• D. RNA

Explanation: Every virus has a protein coat called a capsid that protects its genetic material. While viruses may have DNA or RNA and sometimes lipids, protein is the one component found in all viruses.

633. A common polyhedral capsid shape of viruses is a _.

• A. Complex
• B. Spherical
• C. Icosahedral
• D. Helical

Explanation: Among viruses, the most common polyhedral capsid shape is icosahedral, which consists of 20 triangular faces forming a highly stable and efficient structure. Helical viruses, although common, have a spiral structure rather than flat faces. Spherical viruses appear round due to their envelope, not because of a true polyhedral capsid. Complex viruses, such as bacteriophages, have mixed structural features that do not fit simple polyhedral forms. Therefore, when considering a classic polyhedral capsid, the correct answer is icosahedral.

634. Identify the true fact about the virus:

• A. The viruses were discovered 2 billion years ago.
• B. The viruses came from outer space.
• C. Viruses evolved before bacteria.
• D. They can infect all types of cells.

Explanation: The true fact about viruses is that c) viruses evolved before bacteria. The other options (a, b, and d) are not accurate statements. Viruses were not discovered 2 billion years ago; there is no scientific evidence to support that they came from outer space, and they have specific host ranges and cannot infect all types of cells.

635. What are the subunits of capsids?

• A. Capsomere
• B. Flagella
• C. Hyphae
• D. Septa

Explanation: Capsomeres are tiny subunits that make up the protein coat, referred to as the capsid. Capsomeres are known as capsid subunits, which are the outer protective covering of proteins that protect the virus's genetic material. TMV is also known as the tobacco mosaic virus. It is a type of single-stranded RNA virus.

636. What is the viral envelope composed of?

• A. Proteins
• B. Glycoproteins
• C. Lipids and proteins
• D. All of the above

Explanation: The viral envelope is a lipid-based layer that surrounds some viruses, derived from the host cell's membrane during viral replication. It is not made entirely by the virus but is borrowed from the host, with embedded viral glycoproteins that protrude from its surface. These glycoproteins are crucial for the virus to recognize and attach to specific receptors on host cells, allowing entry and infection. The envelope also helps the virus evade the host immune system, as the host-derived lipids can mask viral components, making it less visible to immune defenses.

637. It refers to the final changes within an immature virion that result in a virus particle

• A. Assembly
• B. Coating
• C. Integration
• D. Maturation

Explanation: The question specifically asks about the final changes within an immature virion that make it infectious. While assembly is the step where viral components come together to form the virion, the particle at that stage is usually not yet infectious. Maturation is the process that converts the immature virion into a fully infectious virus, which matches the description in the question perfectly.

638. All of the following descriptions concerning viral multiplication and nucleic acids are true EXCEPT that:

• A. Viruses contain DNA or RNA, not both
• B. Viruses replicate only in living cells
• C. Viruses use the cell's biosynthetic machinery to synthesize copies of themselves
• D. Viral mRNA,viral tRNA, and viral ribsomes are used in viral replication

Explanation: Option A: Viruses contain either DNA or RNA, but not both, due to their small genome size. The type of genome determines how the virus replicates and infects host cells.Option B: Viruses are obligate intracellular parasites and rely on host cells for energy, enzymes, and machinery to replicate their genome and produce new viral particles.Option C: After entering a host cell, viruses hijack the cell's machinery to synthesize viral proteins and replicate their genome, assembling new virus particles until the host cell is destroyed.Option D: Viral replication depends on polymerases suited to their genome type, such as RNA-dependent RNA polymerase for RNA viruses. Poliovirus uses RdRp to replicate its positive-sense ssRNA genome, making this the correct option.

639. Which of the following is not true for virions?

• A. Reproduce independently
• B. Contain DNA
• C. Contain RNA
• D. Extracellular

Explanation: Virions, which are individual virus particles, do not reproduce independently. Viruses are obligate intracellular parasites, meaning they require a host cell to replicate and reproduce. The virion itself is essentially the extracellular form of a virus, consisting of genetic material (either DNA or RNA) surrounded by a protein coat called a capsid.

640. What is the approximate diameter of a retrovirus?

• A. 150 nm
• B. 100 nm
• C. 200 nm
• D. 250 nm

Explanation: The diameter of retroviruses typically ranges from approximately 80 to 120 nanometers (nm). Retroviruses are a family of enveloped viruses characterized by their use of reverse transcriptase to convert their RNA genome into DNA upon entering host cells. The viral particles consist of an outer lipid envelope, viral glycoproteins, and an inner core containing the RNA genome and viral enzymes. The size of retroviruses can vary slightly depending on the specific type of retrovirus.