All Free Biology MCQs with Answers

2931. In the lytic cycle of bacteriophage, the phage is regarded as

• A. Virulent
• B. Temperate
• C. Lysogenic
• D. Latent

Explanation: Virulent phages immediately destroy their host cells through the lytic cycle. Temperate phages can choose between the lytic and lysogenic cycles, allowing them to either kill the host or remain dormant. Lysogenic phages integrate their DNA into the host genome and replicate with it without causing harm until triggered to become active. Latent phages also remain inactive within the host for some time before reactivating to produce new viruses and lyse the host cell.

2932. The bacteriophage replicates only inside a _.

• A. Animal cell
• B. Bacterial cell
• C. Fungal cell
• D. Animal and bacterial cell

Explanation: Bacteriophages are viruses that specifically infect and replicate within bacterial cells. They are composed of genetic material, either DNA or RNA, encased in a protein coat known as a capsid. Some bacteriophages may also have a lipid envelope. They utilize the host bacterium's cellular machinery for replication. While they are highly effective against bacteria, they do not infect or replicate inside animal or fungal cells. Therefore, the correct answer is a bacterial cell. The other options are incorrect because they do not represent the specific host cell type that bacteriophages target.

2933. The part of the bacteriophage that enters the host cell is

• A. Protein sheath
• B. Genome
• C. Protein coat
• D. Tail

Explanation: The genome of a bacteriophage enters the host cell. Here is the explanation of each of the options:1. Protein Sheath: The protein sheath of a bacteriophage is a structure that surrounds and protects the genetic material of the virus. It is not the part that enters the host cell.2. Genome: The genome of a bacteriophage is its genetic material, typically composed of DNA or RNA. This is the part that enters the host cell. Once inside the host cell, it directs the host machinery to replicate and produce more phage particles.3. Protein Coat: The protein coat, also known as the capsid, is the outer shell of the bacteriophage. It encases the genetic material (genome) of the virus. While the protein coat does play a crucial role in the attachment and injection of the genome into the host cell, it is not the part that directly enters the cell.4. Tail: The tail of a bacteriophage is involved in attaching to the host cell and injecting the genetic material (genome) into the host. It serves as a delivery system for the genome.

2934. Enzymes that are also present in a virus:

• A. Dehydrogenase
• B. Urease
• C. Lysozyme
• D. Arginase

Explanation: Lysozyme is a ubiquitous enzyme present in all living organisms and viruses to break down cell walls. Dehydrogenase, urease, and arginase are absent in viruses because viruses lack their own metabolism and cellular machinery. They do not carry out respiration or other biochemical reactions. Instead, viruses depend entirely on the host cell's enzymes and energy for their replication and survival.

2935. Most commonly, lesions can be seen around the mouth, lips, and at other skin sites:

• A. Influenza
• B. Polio
• C. Mumps
• D. Herpes

Explanation: Lesions around the mouth and lips are most commonly associated with herpes (specifically HSV-1). Mumps can also lead to facial swelling, but it's not considered a skin lesion in the traditional sense. Influenza and polio do not typically cause such lesions.

2936. Viral inflammation of the parotid gland is commonly associated with:

• A. Mumps
• B. Small pox
• C. Herpes simplex
• D. Influenza

Explanation: Mumps belongs to the group of paramyxoviruses. It is highly contagious, and this disease causes painful swelling of the parotid glands. Mumps is a viral infection caused by the mumps virus. It can cause swelling of the salivary glands, which are located near the jaw, and can lead to swelling of the cheeks. While mumps doesn't cause skin lesions, the swelling of the salivary glands can give the appearance of facial lesions. The other three options have diseases with different symptoms.

2937. Smallpox is caused by the poxvirus, which is:

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

Explanation: Smallpox is caused by the Variola virus, which has a double-stranded DNA genome. This type of genome allows the virus to replicate in the cytoplasm and produce complex viral particles. Other genome types, such as single-stranded DNA, double-stranded RNA, and single-stranded RNA, are found in different viruses but not in poxviruses. The double-stranded DNA structure of the Variola virus gives it stability and the ability to carry a large amount of genetic information needed for its life cycle.

2938. Pigs are reservoirs for:

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

Explanation: Hepatitis E is the correct option because pigs serve as a natural reservoir for certain genotypes of the hepatitis E virus, particularly genotypes 3 and 4, which can infect humans through zoonotic transmission. The infection often occurs when people consume undercooked pork or come into contact with infected pigs. In contrast, hepatitis A, B, and C viruses are not zoonotic and are transmitted only among humans through routes such as fecal-oral contact (hepatitis A) or exposure to infected blood and body fluids (hepatitis B and C). Therefore, pigs are specifically associated with hepatitis E and not with the other types of hepatitis viruses.

2939. The enzymes involved in viral replication are synthesized:

• A. By the host cell
• B. On the interior surface of the viral membrane
• C. On the viral ribosomes
• D. On the interior surface of the viral coat

Explanation: The enzymes involved in viral replication are synthesized by the host cell machinery after the virus infects the cell. Once the viral genome enters the host, it directs the host's ribosomes to translate viral mRNA into viral proteins, including the enzymes necessary for replication, such as polymerases and transcriptases. Thus, these enzymes are not produced in the virus but are produced by the host cell during the infection process under the control of viral genetic material.

2940. Which of the following pairs of diseases is viral?

• A. Rabies, Measles
• B. Cholera, Tuberculosis
• C. Typhoid, Tetanus
• D. AIDS, Syphilis

Explanation: Cholera, typhoid, tuberculosis, syphilis, and tetanus are bacterial diseases, while measles and mumps are viral diseases.