All Free Biology MCQs with Answers

3101. In what year did the WHO declare that smallpox was completely eradicated?

• A. 1967
• B. 1975
• C. 1980
• D. 1985

Explanation: The World Health Organisation (WHO) declared that smallpox was completely eradicated in 1980. This was a major achievement in global public health, as smallpox was a highly contagious and deadly disease.

3102. _ is associated with several tumors in humans:

• A. HSV-2
• B. Varicella-zoster virus
• C. Oncoviruses
• D. Picomavirus

Explanation: Oncoviruses (also called oncogenic viruses) are viruses that can cause cancers in humans and animals. They achieve this by inserting their genetic material into host cells, altering normal regulatory pathways, and disrupting tumour suppressor genes or activating oncogenes. This leads to uncontrolled cell growth and tumour formation.

3103. Which viruses can convert normal cells into cancer cells?

• A. Retrovirus
• B. Adenovirus
• C. Poliovirus
• D. All of the above

Explanation: Retroviruses are a type of virus that can potentially convert normal cells into cancer cells. Retroviruses, like the human immunodeficiency virus (HIV), have an RNA genome that is reverse transcribed into DNA and integrated into the host cell's genome. This integration process can disrupt normal cellular genes or regulatory elements, leading to uncontrolled cell growth and potentially causing cancer.

3104. People with chronic hepatitis are at risk of?

• A. Kidney damage
• B. Liver damage
• C. Heart damage
• D. Lung damage

Explanation: People with chronic hepatitis are at risk of developing serious complications due to long-term liver inflammation and damage. The major risks include cirrhosis (scarring of the liver), liver failure, and hepatocellular carcinoma (primary liver cancer). Chronic hepatitis also increases the chance of portal hypertension, which can lead to complications such as variceal bleeding, ascites, and hepatic encephalopathy. Therefore, individuals with chronic hepatitis require regular monitoring and medical management to reduce these risks.

3105. Bacteriophages, or phages, are also known as

• A. Bacteria facilitator
• B. Bacteria eater
• C. Animal viruses
• D. Plant viruses

Explanation: Bacteriophages are viruses that infect and replicate within bacteria, not facilitators. They are sometimes called "bacteria eaters," a colloquial but descriptive term since they inject their genetic material into bacterial cells. They are distinct from animal and plant viruses, which infect animals and plants respectively.Correct Answer: b. Bacteria eater.Summary: Bacteriophages specifically infect bacteria, and the term "bacteria eater" effectively describes their role.

3106. The bacteriophage incorporates into the host genome in which phase?

• A. Lysogenic cycle
• B. Lytic cycle
• C. Both
• D. None of the above

Explanation: The bacteriophage incorporates into the host genome in the lysogenic cycle. In the lysogenic cycle, the bacteriophage DNA integrates into the host DNA and becomes a prophage. The prophage is then replicated along with the host DNA and is passed on to daughter cells when the host cell divides. The prophage can remain dormant in the host cell for many generations, or it can be triggered to enter the lytic cycle and produce new phages.

3107. What is the first step in the replication of a bacteriophage?

• A. Replication
• B. Penetration
• C. Attachment
• D. Injection

Explanation: The bacteriophage first attaches itself to the host cell. It then penetrates and injects itself into the nucleus of the host cell. It then replicates the genetic material.

3108. Where is the double-stranded DNA of the bacteriophage found?

• A. Tail fibers
• B. Bacterial cytoplasm
• C. Base plate
• D. Head

Explanation: The double-stranded DNA of the bacteriophage is found in the head (capsid). Tail fibers and the base plate are structural components for attachment, while the bacterial cytoplasm only receives the DNA after injection. Thus, the correct location before infection is the capsid.

3109. Bacteriophages have been used widely in genetic research since they are the smallest and simplest biological entities capable of what?

• A. Self replication in host cell
• B. Duplication
• C. Self duplication
• D. Multiplication in host cell

Explanation: The most accurate answer is self-replication in a host cell, since bacteriophages can reproduce only by infecting bacteria and directing the host machinery to make copies of themselves. "Multiplication in host cell" is acceptable but less precise, while "self-duplication" and "duplication" are incorrect because they do not accurately describe viral replication.

3110. Binary fission occurs in which stage of the bacteriophage life cycle?

• A. Lysogenic cycle
• B. Lytic cycle
• C. Both A and B
• D. None

Explanation: All infections of bacterial cells by phages do not result in lysis. In some cases viral DNA, instead of taking over the control of the host's machinery, becomes incorporated into the bacterial chromosome. A phage in this state is called a prophage, and this process is known as lysogeny. In this condition the bacterium continues to live and reproduce normally.