All Free Biology MCQs with Answers

3081. HIV mainly attacks:

• A. CD4 site of T cells
• B. B cells
• C. White blood cells
• D. None of these

Explanation: HIV mainly attacks the CD4 site of T cells. T cells are a type of white blood cell that is important for the immune system. They help the body fight off infection by recognizing and destroying foreign invaders.

3082. The viral genome is integrated into the host genome by which of the following enzymes?

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

Explanation: The viral genome is integrated into the host genome by the integrase enzyme. Integrase is an enzyme that is found in retroviruses, such as HIV. It is responsible for inserting the viral DNA into the host cell's DNA. This allows the viral DNA to be replicated along with the host cell's DNA and to be passed on to daughter cells when the cell divides.

3083. HAV is transmitted by:

• A. Faeces
• B. Sexual contact
• C. Sharing needles and syringes
• D. All of these

Explanation: HAV, or hepatitis A virus, is a virus that can cause hepatitis, an inflammation of the liver. HAV is transmitted through the faecal-oral route, which means that it can be spread through contact with contaminated faeces.

3084. When did experimental administration of the HIV vaccine begin?

• A. 2001
• B. 1999
• C. 2005
• D. 2000

Explanation: By 2001, several early-phase clinical trials (Phase I and II) of experimental HIV vaccines were underway. These trials were carefully controlled and involved volunteers who were HIV-negative, but they were not exposed to the virus. Instead, vaccines used weakened viral components, viral proteins, or DNA/RNA sequences to safely provoke an immune response.

3085. Pigs are related to:

• A. HEV
• B. HAV
• C. HBV
• D. HCV

Explanation: In pigs, swine hepatitis E (HEV) causes microscopic lesions in the liver without any clinical presentation. It is considered important, being a zoonotic disease (spread between animals and humans). Humans can be infected by exposure to infected pigs or by consuming improperly cooked meat. The hepatitis E virus is prevalent in pigs worldwide.

3086. Which of the following statements correctly describes the tobacco mosaic virus (TMV)?

• A. RNA virus
• B. DNA virus
• C. Bacteriophage
• D. dsDNA virus

Explanation: Option (a) states that the tobacco mosaic virus (TMV) is an RNA virus. This statement is correct. TMV is a positive-sense, single-stranded RNA virus that infects plants. It belongs to the family Virgaviridae and the genus Tobamovirus. Its genome consists of a single-stranded RNA molecule, and it replicates using RNA-dependent RNA polymerase.

3087. Poxvirus is different from all others due to:

• A. Structure
• B. Size
• C. Nucleic acid
• D. All of above

Explanation: The answer is all of the above. Poxviruses are different from all other viruses in terms of their structure, size, and nucleic acid.

3088. The genetically engineered vaccine is available for which of the following hepatitis viruses?

• A. HBV
• B. HAV
• C. HCV
• D. Options A and B are correct

Explanation: Option (d) suggests that both the Hepatitis B virus (HBV) and the Hepatitis A virus (HAV) have genetically engineered vaccines available. This statement is correct. As explained earlier, genetically engineered vaccines are available for both HBV and HAV.

3089. Poxvirus has:

• A. Double stranded DNA
• B. Single stranded DNA
• C. Double stranded RNA
• D. Both A and C

Explanation: Poxviruses have double-stranded DNA. They are the only known viruses with this type of genome. Poxviruses are also enveloped viruses, meaning they have a lipid membrane surrounding their capsid. This makes them more resistant to harsh environments, such as heat and drying. Therefore, option A is the correct answer.

3090. For attachment, the rabies virus binds to a:

• A. Complement receptor
• B. Integrin ICAM-1
• C. Acetylcholine receptor
• D. Epidermal growth factor receptor

Explanation: To clarify, the attachment of the rabies virus to host cells involves interactions between viral glycoproteins and specific receptors, and in the case of the rabies virus, one of the receptors used for attachment is the nicotinic acetylcholine receptor (nAChR). This receptor is normally associated with nerve signal transmission but is repurposed by the virus for attachment, facilitating its entry into host cells.