All Free Biology MCQs with Answers

3111. These viruses usually occur in two structural forms:

• A. HIV
• B. HCV
• C. Bacteriophage
• D. COVID-19

Explanation: Bacteriophages, like other viruses, usually occur in two structural forms: cuboidal (icosahedral) and helical. In many bacteriophages, these two forms are combined into a characteristic head-and-tail structure. The head, which is icosahedral in shape, contains the viral DNA, while the tail is helical, functioning as a tube through which the nucleic acid is injected into the bacterial host. For example, the T-even phages (T2, T4, and T6) have a large icosahedral head and a long contractile helical tail, giving them the appearance of a tadpole. In contrast, some other phages like T3 and T7 are simpler and mostly icosahedral with only a very short, non-contractile tail. Thus, bacteriophages illustrate how the two fundamental viral structural types-cuboidal (icosahedral) and helical-can exist either separately or in combination, depending on the type of phage.

3112. What type of phage is a T2 phage?

• A. ssDNA phage
• B. ssRNA phage
• C. dsDNA phage
• D. dsRNA phage

Explanation: T2 phage is more properly called Enterobacteria phage T2. It is a virulent bacteriophage that infects Escherichia coli bacteria. It contains linear "double-stranded DNA" and is covered by a protective protein coat.

3113. What is the function of lysozyme released by bacteriophages?

• A. Injecting DNA
• B. Replication
• C. Dissolve bacterial cell wall
• D. All of these

Explanation: The lysozyme released by bacteriophages plays a crucial role in the infection cycle. Its main function is to break down the bacterial cell wall, specifically the peptidoglycan layer. This enzyme is usually present in the tail region of bacteriophages, and during infection, it helps the phage inject its DNA into the host cell by locally degrading the cell wall at the site of attachment. Later, at the end of the lytic cycle, lysozyme is again involved in breaking open (lysing) the bacterial cell wall to release the newly formed phage particles. Thus, lysozyme is essential both for entry of the viral genome into the host and for the release of progeny phages during cell lysis.

3114. When was the tobacco mosaic virus successfully crystallized?

• A. 1935
• B. 1930
• C. 1932
• D. 1920

Explanation: The tobacco mosaic virus (TMV) was first successfully crystallized in 1935 by the American biochemist Wendell Meredith Stanley.This work was groundbreaking because it showed that viruses could be isolated and crystallized like chemicals, which challenged the prevailing view of viruses as "living organisms" and helped establish virology as a scientific field. Stanley was awarded the 1946 Nobel Prize in Chemistry for this achievement.

3115. Which virus is complex in structure?

• A. Influenza virus
• B. Herpes virus
• C. T4 virus
• D. All of these

Explanation: The T4 bacteriophage is a complex virus with a highly specialized structure. Its icosahedral head houses double-stranded DNA, while the tail functions like a syringe, using a contractile sheath to inject DNA into the host. The baseplate and long tail fibers help the virus recognize and attach to E. coli, and short spikes pierce the cell wall to enable genome delivery. This intricate design makes T4 much more advanced than simple helical or icosahedral viruses, acting as a molecular machine for efficient infection.

3116. Which of the following shows a coiled RNA strand and capsomeres?

• A. Polio virus
• B. Tobacco mosaic virus
• C. Measles virus
• D. Retrovirus

Explanation: Tobacco Mosaic Virus fits the description you provided. Tobacco mosaic virus is an RNA virus that causes tobacco mosaic disease. It has a single-stranded coiled RNA molecule as its genetic material, a part of which hangs outside the protein coat. The protein coat consists of approximately 2130 capsomeres, which are helically arranged to form a hollow cylinder of about 4 nm diameter.

3117. Which one of the following statements is correct regarding sexually transmitted diseases (STDs)?

• A. A person may contract syphilis by sharing milk with one already suffering from the disease.
• B. Hemophilia is one of the STDs.
• C. Genital herpes and sickle cell anemia are both STDs.
• D. The chances of a 5-year-old boy contracting an STD are very little.

Explanation: STDs are primarily transmitted through sexual contact, so the likelihood of a 5-year-old boy contracting an STD is very low due to the absence of sexual activity at that age. Option A is incorrect because syphilis cannot be contracted through sharing milk. Option B is incorrect because hemophilia is a genetic disorder, not an STD. Option C is incorrect because, while genital herpes is an STD, sickle cell anemia is a genetic disorder.

3118. A common cold differs from pneumonia in that

• A. The common cold is a mild viral illness, while pneumonia is a serious infection that affects the lungs.
• B. The common cold mainly affects the digestive system, while pneumonia only affects the heart.
• C. The common cold is caused by bacteria, while pneumonia is always caused by viruses.
• D. The common cold is usually treated with antibiotics, while pneumonia never requires them.

Explanation: In conclusion, the main difference between the common cold and pneumonia is that the common cold is a mild viral infection of the upper respiratory tract, while pneumonia is a potentially serious infection that affects the lungs and may be caused by bacteria, viruses, or fungi. The incorrect options confuse organ systems, causes, and treatments, but only Option A correctly states the key difference.

3119. Which one of the following statements is correct with respect to AIDS?

• A. HIV can be transmitted through eating food together with an infected person.
• B. Drug addicts are least susceptible to infection.
• C. AIDS patients are being fully cured cent percent with proper care and nutrition.
• D. The causative HIV retrovirus enters helper T-lymphocytes, thus reducing their numbers.

Explanation: HIV is a retrovirus that infects helper T-lymphocytes (CD4⁺ cells), which are essential for coordinating the immune system. The virus binds to CD4 receptors and enters the cell, where it converts its RNA into DNA and integrates it into the host's genome. As HIV multiplies, it destroys the T-cells, leading to a gradual decline in their numbers. With fewer helper T-lymphocytes, the immune system becomes weaker and less able to fight infections, eventually resulting in AIDS.

3120. In five-kingdom system, the main basis of classification is

• A. Mode of nutrition
• B. Mode of reproduction
• C. Complexity of behavior
• D. Number of chromosomes

Explanation: In Whittaker's five-kingdom system of classification, the main basis is mode of nutrition, which distinguishes autotrophs (plants), heterotrophs by ingestion (animals), heterotrophs by absorption (fungi), and mixed types (protists, monerans). Other factors like mode of reproduction, complexity of behavior, and number of chromosomes were not used as the primary basis, since they are either variable, not universal, or less significant at the kingdom level.