All Free Biology MCQs with Answers

2371. The three stages of HIV infection are

• A. Acute infection➝ Chronic infection➝ AIDS
• B. AIDS ➝ Acute infection ➝ Chronic infection
• C. Chronic infection ➝ AIDS ➝ Acute infection
• D. Acute infection ➝ AIDS ➝ Chronic infection

Explanation: HIV infection progresses through three main stages. The first stage is acute HIV infection, which usually occurs 2-4 weeks after exposure. During this period, the virus replicates rapidly, causing a very high viral load, and many people develop flu-like symptoms such as fever, rash, sore throat, fatigue, and swollen lymph nodes, although some may not notice any symptoms. Because of the high viral load, individuals are highly infectious at this stage. The second stage is chronic HIV infection, also called the clinical latency or asymptomatic stage. This stage can last for 10 years or longer without treatment, though it may progress more quickly in some people. During this time, the virus continues to replicate at lower levels while the immune system works to control it. Many people do not have symptoms or only experience mild ones, such as fatigue or recurrent minor infections. With effective antiretroviral therapy (ART), individuals can stay in this stage indefinitely and live a near-normal lifespan. The final stage is AIDS (Acquired Immunodeficiency Syndrome), which occurs when the immune system is severely damaged. This is diagnosed when the CD4 T-cell count falls below 200 cells/mm³ or when certain opportunistic infections or cancers develop. Symptoms in this stage may include chronic fever, weight loss, night sweats, persistent diarrhea, and frequent or severe infections. Without treatment, survival after reaching AIDS is typically around three years, but with ART, progression to this stage can often be prevented.

2372. AIDS is caused by which viruses?

• A. Human immunodeficiency virus
• B. Retroviruses
• C. Influenza virus
• D. Paramyxoviruses

Explanation: Option: A AIDS is caused by the human immunodeficiency virus (HIV). AIDS is the name used to describe potentially life-threatening infections and illnesses that happen when the immune system has been severely damaged by the HIV virus. Option C: The influenza virus causes influenza. Option D :Paramyxoviruses cause mumps and measles.

2373. In icosahedral, the capsomeres are arranged in _ triangles:

• A. 100
• B. 200
• C. 1000
• D. None of these

Explanation: The correct option is D (None of the above), as the capsomeres are arranged in 20 equilateral triangles in icosahedral viruses. An icosahedron is a polyhedron with 20 faces, each of which is an equilateral triangle.

2374. For the synthesis of mRNA, HIV uses the:

• A. Cytoplasmic RNA polymerase
• B. None of these
• C. Host RNA polymerase
• D. Viral RNA polymerase

Explanation: The synthesis of HIV mRNA does not occur through a cytoplasmic RNA polymerase or a viral RNA polymerase. Instead, HIV depends entirely on the host's RNA polymerase II after integration of its DNA into the host genome. Therefore, the correct option is Host RNA polymerase.

2375. Chimpanzees have _ instead of HIV.

• A. SIV
• B. CIV
• C. HBV
• D. HIV-2

Explanation: Chimpanzees have SIV, or simian immunodeficiency virus, instead of HIV. SIV is a closely related virus to HIV, and it can infect humans.

2376. The average diameter of large viruses is approximately

• A. 100 to 160nm
• B. 100 to 200nm
• C. 100 to 360nm
• D. Always below than 100nm

Explanation: Most viruses vary in diameter from 20 nanometers (nm; 0.0000008 inch) to 250-400 nm; the largest, however, measure about 500 nm in diameter and are about 700-1,000 nm in length. Only the largest and most complex viruses can be seen under the light microscope at the highest resolution.

2377. The shape of the tobacco mosaic virus is:

• A. Spring shape
• B. Rod shape or helical shape
• C. Comma shape
• D. Spherical shape

Explanation: This is factual recall from the chapter of acellular life which states that TMV is a helical virus that appears rod shaped so option B is most suitable.

2378. It is very stable and allows viruses to exist in water, air, and the ground.

• A. Nucleoproteins
• B. Nucleocapsid
• C. Tail of virus
• D. Capsid

Explanation: a. Nucleoproteins-Proteins bound to nucleic acids; important for genome function but not for environmental stability.b. Nucleocapsid-Viral genome plus capsid; protects the genome, but stability mainly comes from the capsid.c. Tail of virus-Found in some bacteriophages; used for attachment and injection, not for stability.d. Capsid (Correct Answer)-Protein shell protecting the viral genome; crucial for stability and survival in water, air, and soil.

2379. Viroids lack:

• A. RNA
• B. Enzyme
• C. Protective protein coat
• D. All of these

Explanation: The correct option is C. Viroids lack a protein coat. Viroids are the smallest known infectious agents. They are composed of a single-stranded RNA molecule that is circular in shape. Viroids do not have a protein coat, which is a protective layer that surrounds the genetic material of other viruses.

2380. The numbers of capsomeres found in adenovirus capsid is?

• A. 162
• B. 200
• C. 252
• D. 155

Explanation: The adenovirus particle consists of an icosahedral protein shell surrounding a protein core that contains the linear, double-stranded DNA genome. The shell, which is 70 to 100 nm in diameter, is made up of 252 structural capsomeres. 162 capsomeres are found in herpes virus. So, option C is correct.