Free Biodiversity and Variety of Life MCQs with Answers

2681. How many molecules of reverse transcriptase are found in HIV?

• A. 2
• B. 3
• C. 4
• D. 1

Explanation: Each HIV virion contains two molecules of reverse transcriptase. This enzyme is essential for converting the viral RNA genome into complementary DNA after the virus enters a host cell. HIV carries two identical strands of RNA, and the presence of two reverse transcriptase molecules ensures that reverse transcription occurs efficiently and accurately. The enzyme exists as a heterodimer composed of two subunits, known as p66 and p51, which work together during the synthesis of viral DNA. This precise number of enzyme molecules supports the virus's ability to replicate effectively within the infected host cell.

2682. About the tail of the T4 phage, which one is not true:

• A. The core, or tube, is made up of distinct proteins
• B. The core or tube is enclosed in a sheath
• C. The core and sheath are made of the same type of protein
• D. The Core and Sheath are made of another type of protein

Explanation: The answer is "Core and sheath are made of the same type of protein."Explanation: The core of the tail is made up of a rigid and inflexible protein, whereas the sheath is made up of a flexible and contractile protein. The core is the genetic material of the phage, which is made up of DNA. The sheath is a protein coat that surrounds the core and protects it from the environment. The sheath also helps the phage to attach to the host cell.

2683. The volume of the T4 phage is about _ times shorter than that of the host

• A. 1
• B. 10
• C. 100
• D. 1000

Explanation: The volume of the T4 phage is about one-thousandth (1/1000th) of the volume of its bacterial host, E. coli. This reflects the large size difference between the virus and the host cell.

2684. The word "virus" was generally referred to as a poison associated with disease and death at the time of:

• A. Louis Pasteur and Charles Chamberland
• B. Ivanowsky
• C. Louis Pasteur and W.M. Stanley
• D. Louis Pasteur and Robert Koch

Explanation: The correct answer is Louis Pasteur and Robert Koch. During the late 19th century, the term 'virus' was primarily used to describe infectious agents and was often associated with the concept of poison, particularly in relation to diseases. Pasteur's work on vaccines and Koch's postulates laid the foundation for understanding pathogenic organisms, including viruses. The other options are incorrect because while they include notable scientists, they do not accurately reflect the historical context of the term 'virus' as a poison associated with disease. Charles Chamberland, for example, focused on filtration methods rather than the terminology, and Ivanowsky's work, although significant in virology, did not establish the term in the same context.

2685. Choose the wrong statement regarding AIDS:

• A. AIDS is an immunodeficiency disease.
• B. It is caused by the retrovirus HIV.
• C. HIV selectively infects and kills B-lymphocytes.
• D. Retroviruses have RNA genomes that replicate a DNA intermediates.

Explanation: HIV (Human Immunodeficiency Virus) is a retrovirus that primarily targets the immune system, leading to immune deficiency. Being a retrovirus, HIV carries single-stranded RNA as its genetic material and uses the enzyme reverse transcriptase to convert its RNA into DNA after entering a host cell. This viral DNA is then integrated into the host genome, allowing the virus to replicate and produce new viral particles. HIV mainly attacks CD4+ T lymphocytes, macrophages, and dendritic cells, which are central to immune coordination, leading to a progressive decline in immune function and susceptibility to opportunistic infections.The option stating that HIV attacks B-lymphocytes is incorrect. While B cells are important for antibody production, they do not express CD4 receptors, so HIV cannot directly infect them. The immune deficiency seen in HIV infection occurs indirectly, because the loss of CD4+ T cells impairs the activation and regulation of B cells, reducing the body's ability to mount effective antibody responses. Thus, HIV targets the immune system primarily through CD4+ T cells, not B-lymphocytes.

2686. Which one of the following statements about viruses is correct?

• A. Viruses possess their own metabolic system
• B. Viruses contain either DNA or RNA
• C. Viruses are facultative parasites
• D. Viruses are readily killed by antibiotics

Explanation: The correct statement about viruses is that they contain either DNA or RNA as their genetic material, but never both, which is essential for their classification and replication. The other statements are incorrect. Viruses are not readily killed by antibiotics because antibiotics target bacterial cellular processes that viruses lack. They are also not facultative parasites; instead, they are obligate intracellular parasites, meaning they cannot reproduce or carry out life processes outside a host cell. Additionally, viruses do not possess their own metabolic system and entirely depend on the host cell's machinery for energy and replication. Thus, the presence of DNA or RNA is the defining feature of viruses.

2687. Viroids differ from viruses in having:

• A. DNA molecules without a protein coat.
• B. RNA molecules with a protein coat.
• C. RNA molecules without a protein coat.
• D. DNA molecules with a protein coat.

Explanation: RNA molecules without a protein coat: This is the correct description of viroids. Viroids are small, circular RNA molecules that lack a protein coat. They are unique infectious agents that can cause disease in plants.

2688. Attachment of HIV DNA with host DNA is done via action of:

• A. Integrase
• B. Protease
• C. Reverse transcriptase
• D. DNA polymerase

Explanation: The integration of HIV DNA into the host's DNA is performed by the viral enzyme integrase. Reverse transcriptase first makes DNA from RNA, protease helps in viral protein processing, and DNA polymerase belongs to the host but does not integrate viral DNA.

2689. HIV can be transmitted by all of the following sources except:

• A. Blood transfusion
• B. Sexual contact
• C. Breastfeeding
• D. Mosquito bite

Explanation: HIV spreads through blood transfusion, unprotected sexual contact, and breastfeeding, but not through mosquito bites. The virus requires specific routes involving body fluids for transmission and cannot be spread by insects or casual contact.

2690. Which one of the following organisms is scientifically correctly named, correctly printed according to the International Rules of Nomenclature, and correctly described?

• A. Musca domestica-a common reptile
• B. Plasmodium falciparum-a protozoan pathogen causing the most serious type of malaria.
• C. Felis tigris-the Indian tiger, well protected in Gir forests
• D. E. coli-full name Entamoeba coli, a commonly occurring bacterium in the human intestine

Explanation: Plasmodium falciparum is a protozoan parasite and the most dangerous cause of malaria in humans. Its digenetic life cycle occurs in two hosts: humans, where the asexual cycle takes place, and the female Anopheles mosquito, where the sexual cycle occurs and infective sporozoites are formed. Transmission to humans happens through the bite of an infected mosquito. In humans, the parasite multiplies asexually, producing fever every 48 hours, and the disease, known as malignant tertian malaria, can be fatal as it often affects the brain. The scientific names of some common organisms are house lizard - Hemidactylus, housefly - Musca domestica, Indian tiger - Panthera tigris, and E. coli - Escherichia coli.