All Free Biology MCQs with Answers

3071. What does an icosahedral capsid consist of?

• A. Hexagonal capsomeres
• B. Pentagonal capsomeres
• C. Triangular Capsomeres
• D. Both A and B

Explanation: An icosahedral shape, common in viral capsids, is made of protein subunits called capsomeres, which can be pentameric (five subunits) or hexameric (six subunits). Pentamers occupy the 12 vertices of the icosahedron, while hexamers fill the faces and edges, creating a stable, closed shell. This arrangement follows the principle of quasi-equivalence, allowing subunits to adapt slightly to form either pentamers or hexamers. The combination of these capsomeres gives the icosahedral capsid structural stability and enough internal space to enclose the viral genome.

3072. Viruses are limited in their host range because

• A. Can only replicate in certain types of cells.
• B. Certain cells are susceptible to viral infection.
• C. They can only enter cells that have proper/specific receptors.
• D. They can only enter cells with glycoproteins.

Explanation: Viruses have a limited host range because they cannot infect all cells. While they need specific cellular conditions for replication (Option A) and not all cells are equally susceptible (Option B), the key factor is the presence of the right cell surface receptors (Option C) that allow viral entry. Option D is only partly correct, since not all viral receptors are glycoproteins. Therefore, the limitation of host range is primarily due to receptor specificity.

3073. Viruses do not replicate on their own due to:

• A. Too small
• B. Lack metabolic machinery
• C. Have no cell wall
• D. All of these

Explanation: Option B is correct. Viruses do not replicate on their own because they are not living organisms and lack the metabolic machinery. In order for a virus to replicate, it needs to infect a host cell. The virus's genetic material is then injected into the host cell, and the host cell's machinery is used to replicate the virus's genome and produce new virus particles.

3074. It is incorrect about the virus:

• A. Acellular nature
• B. DNA
• C. RNA
• D. Metabolism

Explanation: Option D is correct. Viruses do not replicate on their own because they are not living organisms and lack the metabolic machinery. In order for a virus to replicate, it needs to infect a host cell. The virus's genetic material is then injected into the host cell, and the host cell's machinery is used to replicate the virus's genome and produce new virus particles. Viruses are acellular. This means that they are not made up of cells. They are simply pieces of genetic material (DNA or RNA) that are wrapped in a protein coat.

3075. In which year was the AIDS virus named?

• A. 1986
• B. 1981
• C. 1983
• D. 1990,

Explanation: In 1981, AIDS was first recognized as a new disease, but the virus was unknown. By 1983, the virus was discovered independently by French and American scientists and was temporarily called LAV and HTLV-III. Finally, in 1986, the official name HIV was adopted to avoid confusion. Later, in the 1990s, more details about the virus and its types (HIV-1 and HIV-2) were uncovered, but the name HIV remained standard.

3076. The herpes virus is responsible for which of the following types of herpes?

• A. Simplex
• B. Quadruplex
• C. Triplex
• D. Duplex

Explanation: The correct answer is option A. The herpes virus is responsible for the simplex type of herpes. Simplex means "single" or "uncomplicated." The herpes simplex virus (HSV) is a double-stranded DNA virus that can cause a variety of diseases, including cold sores, genital herpes, and shingles.

3077. Which of the following molecules facilitates the entry of HIV into the human body?

• A. Liposomes
• B. Glycoprotein
• C. Polysaccharides
• D. Lipopolysaccharides

Explanation: Option B is correct, as glycoprotein acts as a receptor molecule, to which the attachment proteins on the enveloped viruses bind, to allow a virus entry into a cell. Other molecules are not responsible for the entry of viruses into a human cell. Explanations are given under each option.

3078. Prominent symptoms of AIDS:

• A. Pneumonia
• B. Rapid weight loss
• C. Extreme and unexplained tiredness.
• D. All of these

Explanation: AIDS, or acquired immunodeficiency syndrome, is the most advanced stage of HIV infection. It is characterized by a severely weakened immune system that leaves the body vulnerable to opportunistic infections and cancers. The most common symptoms of AIDS include pneumonia, extreme tiredness, and unexplained weight loss.

3079. Which of the following is more virulent?

• A. HIV-2
• B. HIV-1(a)
• C. HIV-1
• D. HIV-2(a)

Explanation: HIV-2 is less virulent, has a slower disease progression, and is mostly confined to West Africa, with limited global spread. HIV-1(a), a subtype of HIV-1, is more virulent than HIV-2 and contributes significantly to worldwide infections, showing faster progression. HIV-2(a), a subtype of HIV-2, remains less virulent and follows the same pattern of slower transmission and disease development as HIV-2 in general. HIV-1, overall, is the most virulent type, responsible for the majority of HIV infections worldwide, with rapid progression to AIDS if untreated. Therefore, HIV-1 is considered more virulent than HIV-2.

3080. There is no vaccine against HIV. What is the possible reason for this?

• A. Virus mutates rapidly
• B. Vaccine is very expensive
• C. Vaccines can be controlled by changes in hygiene.
• D. None of these

Explanation: The correct answer is "virus mutates rapidly." HIV is a retrovirus, which means that it reverse transcribes its RNA into DNA. This allows the virus to integrate its genetic material into the host cell's DNA, which makes it very difficult for the body's immune system to fight off.