All Free Biology MCQs with Answers

2911. T.O. Diener discovered a:

• A. Free infectious DNA
• B. Infectious protein
• C. Bacteriophage
• D. Free infectious RNA

Explanation: 1. Free infectious DNA-Avery, MacLeod, and McCarty (1944) indeed demonstrated that DNA is the "transforming principle," proving it carries genetic information. This was a landmark in molecular genetics. 2. Infectious protein (prion)-Stanley Prusiner (1982, Nobel Prize in 1997) introduced the term "prion" and demonstrated that certain diseases are caused by protein-only infectious agents. 3. Bacteriophage - Frederick Twort (1915) first observed a "filterable agent" that killed bacteria, and Félix d'Hérelle (1917) independently discovered and named bacteriophage. 4. Free infectious RNA-This concept is best represented by viroids (discovered by Theodor Diener in 1971), which are small circular RNAs that infect plants. Some RNA viruses also highlight RNA as infectious material, but unlike DNA, there wasn't a single definitive early experiment attributed to just RNA.

2912. In what sense are viruses comparable to isolated chromosomes in terms of being "non-living"?

• A. They require both RNA and DNA.
• B. They both need food molecules.
• C. They both require oxygen for respiration.
• D. Both require the environment of a cell to replicate.

Explanation: The correct answer is that both isolated chromosomes and viruses require the environment of a host cell to replicate because viruses, like isolated chromosomes, cannot replicate or carry out their life cycle independently and rely on a host cell to do so. All other options are incorrect.

2913. What is the genetic material in the influenza virus?

• A. dsDNA
• B. ssRNA
• C. Single helix DNA
• D. None of these

Explanation: The genetic material in the influenza virus is single-stranded RNA. Influenza viruses are RNA viruses responsible for causing the flu in humans and other animals. This RNA serves as the blueprint for the replication and transcription of viral genes during the infection process. All other options are incorrect.

2914. _ capsomeres are present in the capsid of the herpes virus.

• A. 32
• B. 252
• C. 162
• D. 262

Explanation: Option C is correct. The capsid of viruses is made up of protein subunits known as capsomeres. The number of capsomeres is characteristic of a particular virus. i.e., the herpes virus has 162 capsomeres, the adenovirus has 252 capsomeres, and polio has 32 capsomeres in its capsid.

2915. The major cell infected by HIV is

• A. Leukocyte
• B. Monocyte
• C. Helper T-lymphocyte
• D. B-lymphocyte

Explanation: The correct answer is helper T-lymphocytes (option C). Leukocytes are white blood cells involved in immunity, including neutrophils, eosinophils, basophils, monocytes, and lymphocytes. Monocytes are phagocytic cells that engulf pathogens and produce cytokines. B-lymphocytes produce antibodies when activated by helper T-lymphocytes. Helper T-lymphocytes coordinate the immune response by producing cytokines that activate other immune cells, and HIV specifically targets these cells, leading to AIDS.

2916. Chemically, viruses are made up of

• A. Nucleic acid only
• B. Protein only
• C. Nucleic acid and protein
• D. Lipoproteins

Explanation: The correct answer is option C, which states that viruses are made up of both nucleic acid and protein. This dual composition is crucial for their functionality. The nucleic acid, which can be either DNA or RNA, houses the genetic information necessary for the virus to replicate and infect host cells. The protein components, primarily the capsid, protect the nucleic acid and facilitate the virus's interaction with host cells.Options A and B are incorrect as they only consider one component of viral structure, neglecting the essential presence of the other. Option D is misleading because while some viruses do have a lipid envelope, it is not a characteristic applicable to all viruses, making nucleic acid and protein the fundamental components.

2917. AIDS is caused by:

• A. Bacteria
• B. Virus
• C. Fungi
• D. Algae

Explanation: Option B is correct. Yes, AIDS is caused by a virus. The virus is called the human immunodeficiency virus (HIV). HIV is a retrovirus, which means that it carries its genetic material in the form of RNA. The RNA is reverse transcribed into DNA by the virus's reverse transcriptase enzyme. The DNA is then integrated into the DNA of the host cell, where it can be replicated and transcribed into new viral RNA. It is not caused by bacteria, fungi, or algae.

2918. In viruses, a combined structure formed by the core (nucleic acid) and the capsid is:

• A. Nucleocapsid
• B. Envelope
• C. Capsomeres
• D. Prions

Explanation: Option A is correct. A nucleocapsid is the complex of viral nucleic acid (genome) and protein coat (capsid) that protects the genome and directs replication. Option B, the viral envelope, is a lipid bilayer derived from the host cell membrane and not the nucleocapsid. Option C, a capsomere, is just a protein subunit of the capsid, not the entire nucleocapsid. Option D, prions, are infectious proteins without nucleic acids and thus unrelated to nucleocapsids.

2919. The capsid, the protective coat of a virus, is made up of _ subunits known as capsomeres.

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

Explanation: Option B is correct. Chemically, a virion is made up of a core of genetic material: either DNA or RNA surrounded by a protective coat called a capsid, which is made up of protein. The capsid of viruses is made up of protein subunits known as capsomeres. The number of capsomeres is characteristic of a particular virus. The capsid is not made up of lipids, RNA and DNA.

2920. Members of which of the following groups are all parasites?

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

Explanation: Option A is correct. All viruses are obligate intracellular parasites, meaning they can only replicate inside living host cells because they lack metabolism and ribosomes. In contrast, not all fungi or algae are parasitic-some species are free-living, while others may cause disease. Bacteria are also not strictly parasites; they are independent single-celled organisms that can live freely or in association with hosts. Thus, viruses are the best example of true obligate parasites.