Free Biodiversity and Variety of Life MCQs with Answers

221. Reverse transcriptase is used to make DNA copies of:

• A. Host RNA
• B. Viral RNA
• C. Host DNA
• D. Viral DNA

Explanation: Option B is correct.HIV is equipped with various enzymes and among them: reverse transcriptase is of great importance. It takes HIV genomic dsRNA as template and reverse transcribe it to form viral dsDNA in the cytoplasm of the infected cells. The following steps take place in the reverse transcription process: 1) Initiation: Reverse transcriptase binds to the HIV RNA genome and recruits a primer, which is a short piece of RNA that is used to start DNA synthesis. 2)Elongation: Reverse transcriptase uses the primer to synthesize a DNA copy of the HIV RNA genome. 3) Termination: Reverse transcriptase terminates DNA synthesis when it reaches a specific sequence in the HIV RNA genome. Host RNA and host DNA are not used as templates by reverse transcriptase. The reverse transcriptase enzyme works in a few steps:The enzyme binds to the viral RNA.Then it unzips the RNA molecule, exposing the single-stranded RNA.The enzyme then uses the single-stranded RNA as a template to synthesize a DNA copy.The enzyme uses the single-stranded RNA as a template to synthesize a DNA copy.The reverse transcriptase enzyme works in a few steps:The enzyme binds to the viral RNA.Then it unzips the RNA molecule, exposing the single-stranded RNA.The enzyme then uses the single-stranded RNA as a template to synthesize a DNA copy.The enzyme uses the single-stranded RNA as a template to synthesize a DNA copy.

222. Which of the following cells are mainly infected by HIV?

• A. T-killer lymphocytes
• B. T-helper lymphocytes
• C. B-plasma cells
• D. B-memory cells

Explanation: Option B is correct.A)T-killer lymphocytes, also known as cytotoxic T-cells, are a type of T-cell that is responsible for killing infected cells. They are a part of the adaptive immune system and play a role in cell-mediated immunity. T-killer lymphocytes are derived from T-cells that mature in the thymus gland. In the thymus, T-cells are exposed to a variety of antigens, which helps them to develop the ability to recognize and respond to specific invaders. HIV attacks on helper T-lymphocytes so this option is incorrect.B)Helper T-lymphocytes, also known as CD4+ T-cells, are a type of T-cell that helps other immune cells to fight infection. They are a part of the adaptive immune system and play a role in cell-mediated immunity. Helper T-lymphocytes are derived from T-cells that mature in the thymus gland. In the thymus, T-cells are exposed to a variety of antigens, which helps them to develop the ability to recognize and respond to specific invaders. This is the correct answer.C)B-plasma cells are mature B-cells that produce antibodies. They are found in the bone marrow and lymph nodes. B-plasma cells are responsible for the humoral immune response, which is the part of the immune system that fights infection using antibodies. HIV attacks on helper T-lymphocytes so this option is incorrect.D)B-memory cells are a type of B-cell that is produced during the primary immune response. They are long-lived cells that can survive for many years. B-memory cells are important for the secondary immune response, which is the faster and more robust immune response that occurs when a person is exposed to an antigen that they have been exposed to before.HIV attacks on helper T-lymphocytes so this option is incorrect.

223. HIV is classified as:

• A. Bacteriophage
• B. Oncovirus
• C. Retrovirus
• D. Icosahedral virus

Explanation: Option C is correct.A)A bacteriophage, also known as a phage, is a virus that infects and replicates within bacteria. Phages are typically much simpler than other viruses, consisting of only a protein coat and a nucleic acid genome. The genome of a bacteriophage can be either DNA or RNA, and it can be single-stranded or double-stranded. It is not HIV virus so it is not correct.B) An oncovirus is a virus that can cause cancer. Oncoviruses are a type of retrovirus, which means that they carry their 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 HIV virus so it is not correct.C) Retrovirus are a type of viruses that uses RNA as its genetic material. After infecting their host cells, the retrovirus uses an enzyme called reverse transcriptase to convert its genomic RNA into DNA. The retrovirus then integrates its viral DNA into the DNA of the host cell, which allows the retrovirus to replicate. One typical example of retrovirus is HIV.So, this option is the correct one. D) An icosahedral virus is a virus that has a protein shell that is made up of 20 triangular faces. The icosahedral shape is the most common shape for viruses, and it is found in a wide variety of viruses, including poliovirus, rhinovirus, and adenovirus. It is not HIV virus so it is not correct.

224. Cilia and flagella are absent in:

• A. Viruses
• B. Bacteria
• C. Protists
• D. Lower animals

Explanation: Cilia and flagella are absent in in viruses other organisms may contain these structures.1. **Viruses**: Viruses are acellular entities, consisting of genetic material (either DNA or RNA) enclosed in a protein coat (capsid). They lack cellular structures, including cilia and flagella. Viruses do not possess the machinery for movement.2. **Bacteria**: While some bacteria have flagella for locomotion, not all bacteria possess cilia or flagella. Many bacteria move using other mechanisms, like twitching or gliding. The presence of cilia or flagella varies among bacterial species.3. **Protists**: Many protists, which are eukaryotic microorganisms, have cilia or flagella. These structures are commonly used for locomotion and feeding in protists. However, there are exceptions, and not all protists have cilia or flagella. Some may use other structures for movement, such as pseudopods.4. **Lower Animals**: Cilia and flagella are often present in lower animals, including protozoans and various simple multicellular organisms. These structures are used for movement and other functions. Lower animals exhibit a wide diversity in their use of cilia and flagella.In summary, the presence of cilia and flagella varies among different organisms. While they are generally absent in viruses, their presence or absence in bacteria, protists, and lower animals can vary depending on the specific organism and its evolutionary adaptations.

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

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

Explanation: Option A is correct.A)A nucleocapsid is the protein coat that surrounds the nucleic acid of a virus particle. It is made up of one or more types of proteins that are specifically encoded by the virus genome. The nucleocapsid protects the nucleic acid from damage and helps to direct the replication of the virus.It is made of nucliec acid(genome) and protein coat (capsid).It is the correct option.B) A virus envelope is the outermost layer of some viruses. It is made up of a lipid bilayer that is derived from the host cell membrane. The envelope contains viral proteins that help the virus to attach to and enter host cells. This option is incorrect.C) A capsomere is a protein subunit that makes up the capsid, an outer covering of protein that protects the genetic material of a virus. Capsomeres self-assemble to form the capsid.The capsomeres protect against physical, chemical, and enzymatic damage and are multiply redundant; having a few protein subunits that are repeated. This option is incorrect.C) A capsomere is a protein subunit that makes up the capsid, an outer covering of protein that protects the genetic material of a virus. Capsomeres self-assemble to form the capsid.The capsomeres protect against physical, chemical, and enzymatic damage and are multiply redundant; having a few protein subunits that are repeated. C) A capsomere is a protein subunit that makes up the capsid, an outer covering of protein that protects the genetic material of a virus. Capsomeres self-assemble to form the capsid.The capsomeres protect against physical, chemical, and enzymatic damage and are multiply redundant; having a few protein subunits that are repeated. D)Prions are infectious agents that are composed of misfolded proteins. Prions are not like other infectious agents, such as viruses or bacteria, because they do not contain any nucleic acids. Instead, they are simply misfolded proteins that can induce other proteins to fold abnormally. This can lead to the accumulation of misfolded proteins in the brain, which can cause damage and eventually death.This option is incorrect.

226. Capsid, the protective coat of a virus is made up of _ subunits known as capsomers.

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

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

227. _ enzyme is not found in human immunodeficiency virus.

• A. DNA polymerase
• B. Reverse transcriptase
• C. RNA polymerase
• D. Ligase

Explanation: Option B is correct.HIV contains three enzymes that are essential for its replication:1)Reverse transcriptase: Reverse transcriptase is an enzyme that is responsible for converting the RNA genome of HIV into DNA. This DNA can then be integrated into the host cell's genome, where it can be replicated and expressed. 2)Protease: Protease is an enzyme that is responsible for cleaving the HIV polyprotein into its functional proteins. These proteins are then used to assemble new HIV virions. 3)Integrase or ligase: Integrase is an enzyme that is responsible for integrating the HIV DNA into the host cell's genome. This integration allows the HIV DNA to be replicated and expressed by the host cell. The ligase in HIV is called integrase. Integrase is a very important enzyme for HIV replication.So, HIV particles are equipped with reverse transcriptase or DNA polymerase, integrase or ligase and proteases while RNA polymerase is absent in HIV. RNA polymerase is an enzyme that is used by cells to make RNA from DNA. It is not found in HIV, because HIV does not need to make RNA from DNA. Instead, it uses the RNA that it already has to make new copies of the virus.

228. The filterable agents were first purified in 1935, when Stanley was successful in crystallizing the _

• A. Polio virus
• B. Tobacco mosaic virus
• C. Hepatitis virus
• D. Influenza virus

Explanation: Option B is correct.Karl Landsteiner and Erwin Popper discovered the poliovirus in 1908. Landsteiner was an Austrian-American pathologist and immunologist, while Popper was an Austrian physician. They isolated the virus from the spinal cord of a child who had died of poliomyelitis. Stanley was the first scientist who crystallized tobacco mosaic virus in 1935.TMV is transmitted from infected plant to healthy plant through contact, such as by touching an infected leaf or by using the same tools on both infected and healthy plants. TMV can also be transmitted through the air, but this is less common.Baruch Blumberg, who discovered the hepatitis B virus (HBV) in 1967. Blumberg was an Australian-American physician and immunologist who was awarded the Nobel Prize in Physiology or Medicine in 1976 for his discovery. Wilson Smith, Christopher H. Andrewes, and Patrick P. Laidlaw are credited with the discovery of the influenza virus in 1933. They were working at the National Institute for Medical Research in London, England, when they isolated the virus from the throat washings of a patient with influenza.

229. Tobacco mosaic virus was discovered by:

• A. Stanley
• B. Pasteur
• C. Lwanowsky
• D. D' Herelle

Explanation: Option C is correct. Stanley was the first scientist who crystallized tobacco mosaic virus in 1935.TMV is transmitted from infected plant to healthy plant through contact, such as by touching an infected leaf or by using the same tools on both infected and healthy plants. TMV can also be transmitted through the air, but this is less common. Lwanowsky was a Russian scientist who worked on tobacco mosaic virus. He ground diseased leaves of tobacco plants and filtered them using porcelain filter. He put this filtrate on healthy leaves and they got disease. This showed tobacco plants were not infected by bacteria but by viruses. Félix D'Hérelle was a French-Canadian microbiologist who is credited with the discovery of bacteriophages, viruses that infect bacteria. In 1917, he observed that certain bacteria cultures would clear up spontaneously, and he hypothesized that a virus was responsible for the clearing. He named the virus a bacteriophage, from the Greek words for "bacteria" and "eater." Louis Pasteur was a French chemist and microbiologist who is considered the father of microbiology. He made many important discoveries in the field of microbiology, including the germ theory of disease, pasteurization, and vaccines against rabies and anthrax.

230. Animal viruses cannot replicate in:

• A. Blood Plasma
• B. Skin cell
• C. Plant cell
• D. All of these

Explanation: One of the most important features of viruses is that they can reproduce unity in living cells, where they reproduce by replication. Viruses cannot replicate in blood plasma. Blood plasma is the liquid part of blood that does not contain cells. It is made up of water, proteins, sugars, and other nutrients. Viruses need a host cell in order to replicate, and they cannot do so in blood plasma. Also Viruses cannot replicate in skin cells. Skin cells do not have the machinery that viruses need to replicate, such as the ribosomes that are needed to make proteins. Additionally, the skin is covered in a layer of dead cells that acts as a barrier to viruses. Viruses cannot replicate in plant cells. Viruses need to hijack the host cell's machinery in order to replicate, and plant cells have different machinery than animal cells. This is why plant viruses have evolved to specifically infect plant cells.