Free Biodiversity and Variety of Life MCQs with Answers

2671. Tobacco mosaic virus is a tubular filament of size?

• A. 100 × 150 nm
• B. 150 × 250 nm
• C. 300 × 20 nm
• D. 300 × 180 nm.

Explanation: The Tobacco Mosaic Virus (TMV) is a rod-shaped (tubular) filament measuring about 300 nanometers (nm) in length and 20 nanometers (nm) in diameter, with a central hollow core of about 4 nm.

2672. Tobacco mosaic virus was discovered by:

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

Explanation: Stanley was the first scientist to crystallize the tobacco mosaic virus (TMV) in 1935. TMV spreads mainly through contact between infected and healthy plants or contaminated tools. Ivanowsky, a Russian scientist, discovered that TMV could pass through filters that trapped bacteria, proving it was caused by a virus. Félix D'Hérelle discovered bacteriophages, viruses that infect bacteria, in 1917. Louis Pasteur, the father of microbiology, developed the germ theory of disease and created vaccines for rabies and anthrax.

2673. HIV is classified as?

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

Explanation: Option B is correct. Retroviruses use RNA as their genetic material and employ reverse transcriptase to form DNA, which integrates into the host genome for replication. HIV is a classic example. In contrast, bacteriophages infect bacteria, hepatitis is liver inflammation often caused by viruses (A-E), and icosahedral viruses have a capsid with 20 triangular faces, as seen in poliovirus and adenovirus.

2674. When a virus is in the lysogenic cycle, which of these will occur?

• A. Viral DNA becomes incorporated into the host chromosome.
• B. The host cell produces many new viruses before it breaks apart.
• C. The viral DNA replicates, and it is separated by the cell's spindle apparatus.
• D. Antiviral defenses of the cell expel the viral DNA.

Explanation: In the lysogenic cycle, the viral DNA integrates into the host cell's chromosome and becomes part of the host genome, forming a prophage (in bacteriophages) or provirus (in animal viruses). At this stage, the viral genes remain dormant and do not direct the host to produce new viruses. The other statements-production of many new viruses (lytic cycle), separation by the spindle apparatus, or expulsion by host defences-do not correctly describe the lysogenic cycle. The correct event is that viral DNA becomes incorporated into the host DNA.

2675. HAV is transmitted through:

• A. Blood transfusion
• B. Oro-faecal route
• C. Insect bites
• D. Sexual contact

Explanation: Hepatitis A is primarily transmitted through the faecal-oral route, which occurs when food or water contaminated with faeces from an infected person is consumed. This makes poor sanitation and hygiene key factors in its spread. Other routes, such as blood transfusion or insect bites, do not play a role in transmission. While sexual contact can occasionally contribute, it is not a major cause. Overall, maintaining proper hygiene and ensuring clean food and water are the most effective ways to prevent hepatitis A infection.

2676. Poliomyelitis affects:

• A. Sensory neuron
• B. Interneurons
• C. Motor neuron
• D. Autonomic neurons

Explanation: Poliomyelitis mainly targets the motor neurons responsible for voluntary muscle movement, leading to muscle weakness and paralysis. Sensory neurons remain unaffected, so sensation is usually preserved. Interneurons and autonomic neurons are generally not directly attacked by the virus, though severe cases can sometimes interfere with vital functions if the brainstem is involved. Overall, the destruction of motor neurons is the key cause of the characteristic paralysis seen in polio.

2677. Which one is not an opportunistic disease related to HIV infection?

• A. Destruction of the body's immune system
• B. Recurrent pneumonia
• C. Pulmonary tuberculosis
• D. Toxoplasmosis

Explanation: This statement is a general characteristic of HIV infection but not a specific opportunistic disease. HIV gradually destroys the immune system, particularly T helper cells, leading to immunodeficiency.

2678. Pick the false statement about AIDS:

• A. HIV infection
• B. Reverse transcription in the HIV particles
• C. Destruction of T cells
• D. Cure after proper medication

Explanation: The false statement is D) Cure after proper medication, as there is currently no cure for HIV/AIDS. While antiretroviral therapy (ART) can control the infection, it does not provide a cure.

2679. The major cell infected by HIV is

• A. Leucocyte
• B. Monocyte
• C. Helper T-lymphocyte
• D. B-lymphocyte

Explanation: Leukocytes, or white blood cells, are immune system cells that defend the body against infections. They include neutrophils, eosinophils, basophils, monocytes, and lymphocytes. Monocytes are phagocytic leukocytes that mature in the blood, engulf pathogens, and produce cytokines to regulate immune responses. Lymphocytes include helper T-lymphocytes and B-lymphocytes. Helper T-lymphocytes coordinate the immune response by producing cytokines that activate B-lymphocytes and cytotoxic T-lymphocytes; they are the primary target of HIV, whose attack on these cells leads to AIDS. B-lymphocytes, activated by helper T-cells, produce antibodies that specifically recognize and neutralize foreign antigens

2680. The most important measure to prevent AIDS and HIV is

• A. Avoiding intravenous drugs
• B. Avoiding intracellular drugs
• C. Avoiding use of syringes
• D. Avoiding direct contact with HIV

Explanation: The most important measure to prevent AIDS and HIV is avoiding direct contact with HIV. While avoiding intravenous drug use and the use of shared syringes are crucial steps, as these are major routes of transmission, the primary focus should be on preventing direct contact with the virus itself.