All Free Biology MCQs with Answers

3091. Where does the AIDS virus infect?

• A. RBCs
• B. Platelets
• C. Helper T lymphocytes
• D. None of these

Explanation: The human immunodeficiency virus (HIV) infects leukocytes, also known as white blood cells. These cells are part of the body's immune system and help fight infection. HIV targets a specific type of leukocyte called a CD4+ T cell. CD4+ T cells help the body fight infection by signalling other immune cells to attack the invading organism.

3092. Which specialized enzyme do retroviruses have?

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

Explanation: Retroviruses have a specialized enzyme called reverse transcriptase. Reverse transcriptase is an enzyme that can transcribe RNA into DNA. This is unique to retroviruses, as most other viruses can only replicate their DNA into RNA.

3093. What is hepatitis D also known as?

• A. Serum hepatitis
• B. Infectious hepatitis
• C. Bacterial hepatitis
• D. Delta hepatitis

Explanation: Hepatitis A is also called "infectious hepatitis."Hepatitis B is called "serum hepatitis," and it is a highly contagious virus.Hepatitis D, also known as "delta hepatitis," is a liver infection caused by the hepatitis D virus (HDV).Therefore, option D is correct.

3094. How is HIV transmitted?

• A. Sexual contact
• B. Blood
• C. Breast feeding
• D. All of the above

Explanation: HIV is a sexually transmitted disease that spreads to the blood, especially in target cells of the immune system known as T-cells; thus, the virus can also be transmitted through blood transfusions. Since the virus is very small in size, it can also pass from mother to child through breast milk. Hence, option D is the correct answer.

3095. Which of the following is not a component of HIV?

• A. RNA
• B. Ribosomes
• C. Envelope
• D. Matrix

Explanation: Ribosomes are not a component of HIV. HIV is a retrovirus, which means that it has RNA as its genetic material. Ribosomes are not found in viruses, as they are only found in cells.

3096. HIV differs from many viruses because it has high genetic_

• A. Sensitivity
• B. Complexity
• C. Variability
• D. Viability

Explanation: HIV is best described by genetic variability, not sensitivity, complexity, or viability. Its high mutation rate produces diverse viral variants, making treatment and vaccine development difficult. This genetic diversity is a key challenge in managing the virus.

3097. SIV is the abbreviation of

• A. Simian immunodeficiency virus
• B. Silurian immunodeficiency virus
• C. Siberian immunodeficiency virus
• D. Both A and C

Explanation: SIV stands for Simian Immunodeficiency Virus, which is a retrovirus that infects non-human primates such as monkeys and chimpanzees. It is closely related to the Human Immunodeficiency Virus (HIV) and is considered its precursor, as cross-species transmission of SIV from primates to humans is believed to have led to the emergence of HIV-1 and HIV-2. Like HIV, SIV attacks the immune system, particularly CD4+ T cells, leading to immunodeficiency in its hosts.

3098. All of the following are the current preventive methods of HIV infection, except

• A. Safe and protected lifestyle.
• B. Use of sterile injections and needles.
• C. Use of available vaccines.
• D. Safe blood transfusion methods.

Explanation: HIV (human immunodeficiency virus) is a virus that attacks the body's immune system. If HIV is not treated, it can lead to AIDS (acquired immunodeficiency syndrome). There is currently no effective cure; hence, there are no available vaccines for it.

3099. Influenza is caused by:

• A. Adenovirus
• B. Pox virus
• C. Influenza Virus
• D. Herpes virus

Explanation: Influenza is caused specifically by the influenza virus because it belongs to the Orthomyxoviridae family, which has unique properties - it is an enveloped, negative-sense RNA virus with a segmented genome that determines the typical flu symptoms (fever, cough, sore throat, body aches). Other viruses you mentioned - herpesviruses (DNA viruses), variola virus causing smallpox (Poxviridae, DNA virus), and adenoviruses (DNA viruses) - belong to completely different viral families with distinct structures, replication strategies, and disease profiles. They cause illnesses like cold sores, chickenpox/shingles (herpes family), smallpox (variola), or respiratory and eye infections (adenovirus), but not influenza. In short, disease causation is tied to the specific virus family and its biology, so only influenza viruses can cause flu.

3100. This locks the HIV genome into the capsid:

• A. Gag protein
• B. Env protein
• C. Pol protein
• D. All of these

Explanation: The HIV Gag protein is responsible for packaging and locking the viral genome inside the capsid because its nucleocapsid (NC) domain specifically binds the RNA packaging signal (Ψ) and tethers the genome during assembly, while its capsid (CA) domain polymerizes to form the protective shell. In contrast, Pol encodes enzymes (protease, reverse transcriptase, and integrase) that are co-packaged but do not mediate genome encapsidation, and Env forms the envelope glycoproteins for viral entry, playing no role in capsid assembly or RNA packaging.