Free Biodiversity and Variety of Life MCQs with Answers

591. The virus was first discovered by:

• A. K. M. Smith
• B. Twart
• C. M. Stanley
• D. Ivanowsky

Explanation: The discovery of viruses dates back to the late 19th century, when scientists were investigating diseases in plants that could not be explained by known bacteria. In 1892, Russian scientist Dmitri Ivanovsky first identified the existence of a new type of infectious agent while studying tobacco mosaic disease. He found that the disease could be transmitted by sap from infected plants, even after the sap was passed through a porcelain filter fine enough to remove all known bacteria. Later, in 1898, Dutch microbiologist Martinus Beijerinck confirmed Ivanovsky's findings and described the agent as a "contagium vivum fluidum" (a contagious living fluid), coining the concept of a virus as something fundamentally different from bacteria. This discovery marked the beginning of virology, the study of viruses, and laid the foundation for understanding these unique infectious agents.

592. Which of the following is true for viruses?

• A. Multiply only in host cells
• B. Behave as if they are plants
• C. They are made up of proteins only
• D. It occurs only inside bacteria

Explanation: Viruses are unique infectious agents with certain defining features, and among the given statements, the correct one is that they multiply only in host cells. The claim that viruses occur only inside bacteria is incorrect, because although some viruses specifically infect bacteria (bacteriophages), many others infect plants, animals, fungi, and humans. The idea that they are made up of proteins only is also wrong, as all viruses contain genetic material in the form of either DNA or RNA in addition to a protein coat, and some also have a lipid envelope. Similarly, the statement that they behave as if they are plants is misleading, since viruses do not carry out plant-like functions such as photosynthesis. The only accurate description is that viruses multiply only inside host cells, as they are obligate intracellular parasites and depend entirely on the machinery of living cells to reproduce.

593. The genetic material of retroviruses (AIDS virus) is:

• A. Single-stranded RNA
• B. Double-stranded RNA
• C. Double-stranded DNA
• D. Single-stranded DNA

Explanation: The genetic material of retroviruses, including the AIDS-causing Human Immunodeficiency Virus (HIV), is single-stranded RNA (ssRNA). Unlike most viruses, retroviruses use a special enzyme called reverse transcriptase to convert their RNA into DNA once inside the host cell. This viral DNA then integrates into the host's genome, allowing the virus to replicate using the host's cellular machinery. This unique replication strategy is a key feature of retroviruses and is central to the persistence and progression of HIV infection.

594. Interferons are produced in response to infection of:

• A. Fungi
• B. Tapeworms
• C. Viruses
• D. Bacteria

Explanation: Interferons are produced mainly in response to viral infections because host cells recognize viral nucleic acids, such as double-stranded or unusual single-stranded RNA, through specialized receptors. These signals trigger interferon production, which helps block viral replication, activate natural killer cells, and boost immune defenses. In contrast, fungi, tapeworms, and bacteria do not produce such viral nucleic acids; instead, they stimulate other immune responses like antibody production or phagocytosis. This is why interferons are specific to viral infections.

595. Most RNA viruses carry a gene for an enzyme that uses viral RNA as a template in the synthesis of more viral RNA. This enzyme is

• A. RNA primase
• B. Reverse transcriptase
• C. RNA polymerase
• D. Viral nuclease

Explanation: The correct option is RNA polymerase. Most RNA viruses carry a gene for the enzyme RNA-dependent RNA polymerase (RdRp), which uses viral RNA as a template to synthesize new RNA molecules. This enzyme is essential because host cells cannot normally replicate RNA directly from an RNA template. RdRp allows RNA viruses to produce both complementary RNA strands and multiple copies of their genome, enabling them to replicate and spread within the host. Other enzymes listed, such as viral nuclease, reverse transcriptase, and RNA primase, serve different functions and are not responsible for RNA-to-RNA synthesis in RNA viruses.

596. Which of the following statements is correct?

• A. RNA is the primary genetic material in bacteria
• B. RNA is the genetic material for all viruses
• C. DNA is the genetic material for the majority of living organisms
• D. Some viruses use RNA as their genetic material

Explanation: Some viruses use RNA as their genetic material. Viruses can contain either DNA or RNA, depending on the type. Examples of RNA viruses include the influenza virus, HIV, and SARS-CoV-2.Option A: Bacteria use RNA as their genetic material. This is incorrect because bacteria always use DNA, not RNA, as their hereditary material.Option B: All viruses use RNA as their genetic material. This is incorrect because many viruses, such as herpesvirus or adenovirus, have DNA genomes instead.Option C: DNA is the genetic material for most living organisms. While true in general, this statement does not specifically address viruses, so it does not answer the question in context.

597. Which of the following types of virus is illustrated in the diagram?

• A. Animal virus
• B. Plant virus
• C. Bacteriophage
• D. Viroid

Explanation: The correct option is an animal virus. HIV is a retrovirus that infects human immune cells (CD4+ T cells) and causes AIDS. It has a spherical shape with an RNA genome enclosed in a protein capsid and surrounded by a lipid envelope with glycoprotein spikes, which help it attach to host cells.The options are incorrect: A plant virus, such as Tobacco Mosaic Virus, infects plants and usually has a rod-like or helical shape, not the spherical, enveloped structure seen in HIV. A viroid is even simpler, consisting only of circular RNA without a protein coat, and infects plants, not animals. A bacteriophage has a head-and-tail structure and specifically infects bacteria, which looks very different from HIV. Therefore, the diagram represents an animal virus (HIV).

598. The enzyme reverse transcriptase, essentially found in all retroviruses, is

• A. DNA-dependent RNA polymerase
• B. DNA-dependent DNA polymerase
• C. RNA-dependent RNA polymerase
• D. RNA-dependent DNA polymerase

Explanation: Reverse transcriptase is an enzyme found in all retroviruses that enables them to replicate by converting their RNA genome into complementary DNA (cDNA). This DNA is then integrated into the host cell's genome, allowing the virus to use the cell's machinery for producing viral proteins and new virus particles. By reversing the normal flow of genetic information (RNA → DNA), reverse transcriptase is essential for viral survival and has also become an important tool in molecular biology research.

599. Bacteriophages kill:

• A. Fungi
• B. Parasites
• C. Bacteria
• D. Viruses

Explanation: Bacteriophages, or phages, specifically kill bacteria because they are viruses that are highly specialized to infect only bacterial cells. They recognize and attach to unique receptors found on the surface of bacteria, inject their genetic material, and use the bacterial machinery to replicate, eventually causing the bacterial cell to burst. Fungi, parasites, and viruses, however, do not have the same surface receptors or cellular structures that phages require to attach and replicate. Since phages are host-specific, their infection process cannot occur in these other organisms, which is why they are harmless to fungi, parasites, and viruses and target only bacteria.

600. Which of the following are intracellular obligate parasites?

• A. Bacteria
• B. Viruses
• C. Slime moulds
• D. Cyanobacteria

Explanation: Viruses are obligate intracellular parasites because they lack the cellular structures and metabolic machinery needed to grow and reproduce independently. They cannot carry out essential life processes like energy production or protein synthesis on their own, so they must invade a host cell and hijack its machinery to replicate. In contrast, bacteria, slime moulds, and cyanobacteria are true living organisms with cellular organisation, enzymes, and metabolic pathways that allow them to survive, grow, and reproduce independently in suitable environments. This fundamental dependence on host cells for survival is what makes viruses obligate intracellular parasites, unlike bacteria, slime moulds, and cyanobacteria.