Free Biodiversity and Variety of Life MCQs with Answers

541. The mouth, lips, and skin are affected due to the infection of:

• A. Pox virus
• B. Herpes virus
• C. Paramyxovirus
• D. Adenovirus

Explanation: Herpesviruses are DNA viruses that cause lifelong latent infections, commonly producing oral and genital herpes with painful vesicles, cold sores, and sometimes encephalitis. Poxviruses are large DNA viruses responsible for diseases like smallpox and molluscum contagiosum, characterized by fever, rash, and skin nodules. Paramyxoviruses are RNA viruses that cause measles, mumps, and respiratory infections, presenting with fever, cough, conjunctivitis, Koplik spots, parotid swelling, and pneumonia. Adenoviruses are DNA viruses that often affect the respiratory tract, eyes, and gut, leading to pharyngitis, conjunctivitis, gastroenteritis, and flu-like illness.

542. Hepatitis A and E are transmitted by contact with _ from infected individuals.

• A. Serum
• B. Blood
• C. Faeces
• D. Saliva

Explanation: Hepatitis A and E viruses are enterically transmitted viruses, meaning their natural route of spread is through the gastrointestinal tract. After infection, these viruses multiply in the liver but are shed in very high concentrations in the feces, especially during the acute phase. This heavy viral shedding contaminates food and water, which then serves as the main source of transmission. In contrast, their presence in blood or saliva is either absent or very minimal and not enough to establish efficient transmission. Moreover, these viruses are non-enveloped RNA viruses, which makes them highly stable in the environment and resistant to stomach acid, allowing them to survive passage through the digestive tract. On the other hand, they are not adapted to survive or spread effectively via blood or saliva, which is why the fecal-oral route remains the primary mode of transmission for Hepatitis A and E.

543. Which one is not a living characteristic of the virus?

• A. Mutation
• B. Genome
• C. Replication
• D. Crystallization

Explanation: Viruses exhibit certain living characteristics such as mutation, replication, and the presence of a genome, but not crystallization. Their ability to mutate allows them to evolve and adapt to changing environments, while replication, though dependent on a host cell, shows their capacity to reproduce like living organisms. The presence of genetic material (DNA or RNA) further emphasizes their biological nature, as it stores and transfers hereditary information. In contrast, crystallization is a physical property that occurs when viruses are isolated and purified, reflecting their non-living aspect rather than a life process. Thus, mutation, replication, and genome represent the living characteristics of viruses, whereas crystallization highlights their non-living nature.

544. Phage attaches to the bacterial cell surface by its:

• A. Sheath
• B. Core
• C. Head
• D. Tail

Explanation: The attachment of a bacteriophage's tail to its host is a highly specific process that initiates infection. The long tail fibres of the phage first recognise and bind to particular receptor molecules present on the bacterial cell surface, such as proteins, lipopolysaccharides, or teichoic acids. This initial contact stabilises the phage and allows the short tail fibres or baseplate to firmly anchor to the host. Once anchored, the tail sheath contracts, driving the tail tube through the bacterial cell wall and membrane. This creates a passageway through which the viral genetic material is injected into the host cytoplasm, beginning the infection cycle.

545. Which processes take place during the lytic cycle?

• A. Replication
• B. Transcription
• C. Translation
• D. All of these

Explanation: The lytic cycle is a viral reproduction process where a bacteriophage infects and destroys a host cell. It begins with attachment, as the phage binds to receptors on the bacterial surface, followed by entry, where viral DNA is injected into the host. During biosynthesis, the viral genome hijacks the cell's machinery to produce viral proteins and nucleic acids. In the maturation stage, these components assemble into complete viruses. Finally, the host cell undergoes lysis, breaking open and releasing many new viruses to infect other cells. This cycle is rapid and always ends with the death of the host cell.

546. It is antiviral:

• A. Penicillin
• B. Streptomycin
• C. Tetracycline
• D. Interferon

Explanation: Penicillin, tetracycline, and streptomycin are antibiotics that specifically target structures and processes unique to bacteria, which is why they are not effective against viruses. For example, penicillin interferes with bacterial cell wall synthesis, tetracycline inhibits bacterial protein synthesis by binding to the 30S ribosomal subunit, and streptomycin also acts on bacterial ribosomes, causing errors in protein production. Since viruses lack cell walls, ribosomes, and the metabolic machinery necessary for independent life, these antibiotics have no targets to act upon within viral particles or infected host cells. In contrast, interferons are naturally occurring proteins produced by host cells in response to viral infection, and they work by enhancing the body's antiviral defenses. They do not directly kill viruses but instead stimulate nearby uninfected cells to produce antiviral proteins, inhibit viral replication, and boost the immune response by activating natural killer cells and macrophages. This fundamental difference explains why antibiotics like penicillin, tetracycline, and streptomycin are useless against viruses, while interferons play a direct role in controlling viral infections.

547. The second major form of hepatitis is

• A. Hepatitis A
• B. Hepatitis B
• C. Hepatitis C
• D. Hepatitis D

Explanation: The second most common major form of hepatitis is hepatitis B. Hepatitis B is a viral infection that affects the liver and can lead to both acute and chronic liver disease. It is caused by the hepatitis B virus (HBV) and is primarily transmitted through exposure to infected blood, unprotected sexual contact, sharing of needles, or from mother to child during childbirth. The infection can range from mild, with few or no symptoms, to severe, causing jaundice (yellowing of the skin and eyes), fatigue, nausea, abdominal pain, and dark urine. Chronic hepatitis B can result in serious complications, including cirrhosis, liver failure, and liver cancer. Fortunately, Hepatitis B is preventable through vaccination, safe practices to avoid bloodborne exposure, and early detection and treatment to manage long-term effects

548. A characteristic of viruses is:

• A. Without independent metabolism
• B. Multiplication outside living cells
• C. With independent metabolism
• D. It can be a culture in a cell-free medium

Explanation: Viruses lack the cellular machinery necessary for independent metabolism. Unlike living organisms, they cannot carry out metabolic processes such as energy production or nutrient utilization on their own. They lack the necessary organelles and enzymes to perform these functions.

549. In the case of HIV, only _ can infect host cells.

• A. Double-stranded DNA
• B. Single-stranded RNA
• C. Double stranded RNA
• D. Single stranded DNA

Explanation: While the original genetic material of HIV is single-stranded RNA, the virus undergoes a process called reverse transcription. During this process, the single-stranded RNA is converted into a complementary single-stranded DNA (cDNA) molecule. This cDNA is then integrated into the host cell's genome, forming a double-stranded DNA structure that can infect host cells.

550. Some retroviruses can convert:

• A. Cancer cells into normal cells
• B. Cancer cells into germ line cells
• C. Cancer cells into degenerated cells
• D. Normal cells into cancer cells

Explanation: Retroviruses can cause cancer by inserting their genetic material into the host cell's DNA. This insertion can disrupt the normal function of genes that control cell growth and division, potentially activating oncogenes (genes that promote cancer) or inactivating tumor suppressor genes (genes that prevent cancer). Additionally, some retroviruses carry oncogenes themselves, directly introducing cancer-causing genes into the host cell. Over time, these disruptions can lead to uncontrolled cell growth and the development of tumors.