All Free Biology MCQs with Answers

2361. During the lytic cycle, how many phages are released from the infected host cell?

• A. 100-300
• B. 100-500
• C. 100-200
• D. 100-400

Explanation: During the lytic cycle of bacteriophages, the host bacterial cell is eventually lysed (burst open), releasing numerous new phage particles into the surrounding environment. The actual number of phages produced per infected bacterium can vary, but as you mentioned, estimates often range from around 100 to 200 phages. This high burst size is a characteristic feature of the lytic cycle. The virus takes advantage of the host cell's machinery to produce a large number of progeny phages, ensuring the efficient spread of the viral infection to neighboring bacterial cells. The released phages can then go on to infect new host cells and continue the cycle.

2362. Retroviruses are characterized by:

• A. Lack envelope
• B. Have no capsid
• C. Reverse transcriptase enzyme
• D. DNA genome

Explanation: Retroviruses are a unique group of RNA viruses that can reverse transcribe their RNA genome into DNA; that's how they are characterised. They are enveloped viruses and have a capsid.

2363. Viruses that attack bacteria are called what?

• A. Virophage
• B. Lysophage
• C. Bacteriophage
• D. None of these

Explanation: A bacteriophage is a type of virus that infects bacteria. In fact, the word "bacteriophage" literally means "bacteria eater," because bacteriophages destroy their host cells.

2364. Chicken pox is caused by:

• A. Hepatitis A virus
• B. Varicella zoster virus
• C. Influenza virus
• D. HIV

Explanation: Chickenpox (varicella) is an infectious disease caused by the vancella zoster virus (VZV), a member of the herpesvirus family. The virus leads to an itchy rash and fluid-filled blisters, typically in children. The same virus can reactivate later in life as shingles.

2365. The genetically Engineered vaccine is not available for which of the following?

• A. HAV
• B. HBV
• C. HCV
• D. HDV

Explanation: Genetically Engineered vaccines are not available for "HCV" (Hepatitis C- Virus). It is due to its extreme genetic variability and the lack of small animal models for testing vaccines.

2366. Which of the following causes mad cow disease?

• A. Prion
• B. Virus
• C. Bacteria
• D. Both a and b

Explanation: Mad Cow Disease (Bovine Spongiform Encephalopathy, BSE) is a fatal neurodegenerative disorder in cattle caused by prions-misfolded proteins that damage the brain. It spreads mainly through contaminated feed containing infected nervous tissue. In cattle, symptoms include loss of coordination, behavioral changes, difficulty walking, weight loss, and death. In humans (variant Creutzfeldt-Jakob disease), it causes memory loss, confusion, personality changes, muscle stiffness, and coordination problems, eventually leading to coma and death. Prevention relies on banning contaminated animal feed, strict meat inspection, and culling infected animals.

2367. Which was the first virus to be successfully crystallized?

• A. TMV
• B. Smallpox
• C. Poliovirus
• D. Adenovirus

Explanation: TMV (tobacco mosaic virus) is the first virus to be successfully crystallized.The filterable agents were first purified in 1935, when Stanley was successful in crystallizing the tobacco mosaic virus.

2368. A remarkable feature of the poxvirus:

• A. Largest in size
• B. DNA genome
• C. Envelope
• D. None of these

Explanation: Poxviruses are the largest viruses known to science. They can be up to 200 nanometers in diameter, which is much larger than most other viruses, which are typically around 20-30 nanometers in diameter.

2369. It is true about mumps:

• A. It can affect the testes and ovaries.
• B. Passive immunisation is the only treatment.
• C. The vaccine is not available
• D. Widely spread

Explanation: Mumps was more widespread in the past, but due to widespread vaccination efforts, the incidence of mumps has significantly decreased in many parts of the world. The MMR (measles, mumps, and rubella) vaccine is highly effective in preventing mumps, and vaccination programs have contributed to controlling its spread.

2370. Which of the following diseases is sexually transmitted?

• A. Tuberculosis
• B. AIDS
• C. Dengue fever
• D. Cholera

Explanation: Acquired immunodeficiency syndrome (AIDS) is a chronic, potentially life-threatening condition caused by the human immunodeficiency virus (HIV). By damaging your immune system, HIV interferes with your body's ability to fight infection and disease. You can get HIV from contact with infected blood, semen, or vaginal fluids. Most people get the virus by having unprotected sex with someone who has HIV. Another common way of getting it is by sharing drug needles with someone who is infected with HIV. Hence, Option B is correct.Tuberculosis is caused by bacteria that spread from person to person through microscopic droplets released into the air. This can happen when someone with the untreated, active form of tuberculosis coughs, speaks, sneezes, spits, laughs, or sings. Hence, Option A is incorrect. When a mosquito bites a person infected with a dengue virus, the virus enters the mosquito. Then, when the infected mosquito bites another person, the virus enters that person's bloodstream and causes an infection. Hence, Option C is incorrect. A person can get cholera by drinking water or eating food contaminated with cholera bacteria. In an epidemic, the source of the contamination is usually the feces of an infected person that contaminates water or food. Hence, Option D is incorrect.