Free Biodiversity and Variety of Life MCQs with Answers

551. The agent causing AIDS was identified by research teams from:

• A. Pasteur Institute in the USA
• B. National Institute of Health in France
• C. Pasteur Institute in the USA and the National Institute of Health in France
• D. Pasteur Institute in France and the National Institute of Health in the USA

Explanation: The Pasteur Institute is located in France, and the National Institute of Health (NIH) is located in the USA. The correct option accurately represents the collaboration between these two institutions in identifying the AIDS-causing agent, which is the human immunodeficiency virus (HIV).

552. The following are the means of transmission of AIDS, EXCEPT:

• A. Intimate sexual contact and breastfeeding
• B. Use of common syringes and surgical instruments
• C. Blood transfusion without screening
• D. Human immunodeficiency virus

Explanation: HIV, the virus causing AIDS, spreads through specific means: intimate sexual contact, breastfeeding, shared needles or unsterilized surgical tools, and unscreened blood transfusions. The virus itself isn't a method of transmission; rather, it's the agent transmitted via these routes.

553. Now a vaccine against _ has been synthesized, and its experimental administration in humans started in South Africa.

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

Explanation: It was claimed in 2001 that a vaccine against HIV had been developed, and after successful trials, it would be on the market for consumers.

554. HIV is uncoated:

• A. Outside the cytoplasm
• B. At the surface of the host cell
• C. Inside the cytoplasm
• D. Inside the nucleus of the host cell

Explanation: After entering the host cell, HIV undergoes a process called uncoating, during which the viral capsid that surrounds its genetic material is disassembled. This step occurs after the virus fuses with the host cell membrane and releases its core into the cytoplasm. The uncoating process allows the viral RNA and essential enzymes, such as reverse transcriptase, integrase, and protease, to be released into the host cell's cytoplasm. Once uncoated, the viral RNA becomes accessible for reverse transcription, where it is converted into complementary DNA. This newly formed viral DNA is later transported into the nucleus, where it integrates into the host cell's genome, initiating the next stages of the HIV replication cycle.

555. In the infection cycle of HIV, RNA is converted into a DNA duplex by:

• A. Replication
• B. Transcription
• C. Reverse transcription
• D. Translation

Explanation: The answer is "Reverse Transcription."Explanation: RNA is converted into DNA by a process called reverse transcription. It is controlled by the reverse transcriptase enzyme.

556. In the infection cycle of HIV, after attachment, there comes:

• A. Entry
• B. Uncoiling
• C. Reverse transcription
• D. Integration

Explanation: The answer is "Entry." Explanation: In the infection cycle of HIV, V occurs after the attachment of the virus to the host cell, followed by entry, which is followed by uncoiling.

557. The CD4 receptor-bearing T lymphocyte is infected by:

• A. HIV
• B. HBV
• C. HCV
• D. HAV

Explanation: The answer is "HIV."Explanation: Viruses are intracellular obligate parasites, and they require a specific receptor site for their adsorption. The receptor site required by HIV is called the CD44 receptor site (cluster of differentiation 4). It is a cluster of specific glycoproteins that develops on the surface of T4 lymphocytes.

558. The following are true about the head of the T4 phage EXCEPT:

• A. Hexagonal structure
• B. Pyramidal structure
• C. Prism-shaped structure
• D. An oval structure

Explanation: The answer is "An oval structure."Explanation: The head of a bacteriophage is an elongated, pyramidal, hexagonal prism-shaped structure to which a straight tail is attached. The head of the T44 phage is not oval. It is a prolate icosahedron, which means that it is shaped like a sphere that has been stretched out along one axis. The head of the phage is about 50 nanometers in diameter and 100 nanometers long.

559. "Two triangular structures with a common base" is the description of the structure of _ of the T4 phage.

• A. Tail
• B. Head
• C. Collar
• D. Base plate

Explanation: "Two triangular structures with a common base" is the description of the structure of the base plate of the T4 phage. The baseplate is a complex structure located at the end of the phage's tail and plays a crucial role during infection. It serves as the site of attachment to the bacterial cell surface and coordinates the contraction of the tail sheath during DNA injection. The description "two triangular structures with a common base" refers to the characteristic arrangement of the base plate's subunits, which form a hexagonal or star-like structure that appears as two triangular parts sharing a common base when viewed in certain orientations.

560. Within the head of the T4 phage, the _ molecule is present.

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

Explanation: The T4 bacteriophage contains a double-stranded DNA genome of about 169,000 base pairs. Like all dsDNA, the strands are antiparallel and held together by hydrogen bonds between complementary bases. Inside the phage head, this DNA is packed at very high density in a spool-like, liquid-crystalline arrangement. The DNA is enclosed within a rigid protein capsid, which is made of capsid proteins arranged in an icosahedral lattice with hexamers and pentamers. This structure both protects the genome from the environment and allows efficient injection into the host cell during infection.