A patient presents with fever, myalgias, and upper respiratory symptoms. Laboratory testing identifies an infectious agent that lacks metabolic machinery and is unable to replicate outside living cells. Which statement best describes this type of pathogen?
Viruses reproduce independently through binary fission
Viruses are obligate intracellular parasites that require host cells to replicate
Viruses are unicellular organisms containing ribosomes
Viruses generate ATP through oxidative phosphorylation
Viruses are classified as eukaryotic microorganisms
The Correct Answer is B
A. Viruses reproduce independently through binary fission: Binary fission is a form of asexual reproduction used by prokaryotic cells such as bacteria. Viruses cannot reproduce independently because they lack cellular machinery and rely entirely on host cells for replication.
B. Viruses are obligate intracellular parasites that require host cells to replicate: Viruses are acellular pathogens that cannot carry out metabolism, synthesize proteins, or replicate without a host cell. They invade host cells, hijack the host's transcription and translation machinery, and assemble new virions, classifying them as obligate intracellular parasites.
C. Viruses are unicellular organisms containing ribosomes: Viruses are not cells and do not contain ribosomes, cytoplasm, or any internal organelles. They are non-living particles composed primarily of nucleic acid and protein.
D. Viruses generate ATP through oxidative phosphorylation: Viruses lack mitochondria or any energy-producing machinery, so they cannot generate ATP. Energy production is entirely dependent on the host cell’s metabolic processes.
E. Viruses are classified as eukaryotic microorganisms: Viruses are not classified as eukaryotes because they do not have a nucleus, membrane-bound organelles, or independent metabolic activity. They are a distinct category of acellular infectious agents.
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Correct Answer is B
Explanation
A. Flagella: Flagella are whip-like appendages used for motility and are commonly found in prokaryotic cells such as bacteria. They are anchored in the cell membrane and cell wall and function to propel the cell toward nutrients or away from harmful stimuli. Their presence is consistent with prokaryotic structure and physiology.
B. Nucleus: Prokaryotic cells lack a membrane-bound nucleus. Instead, their genetic material exists as a single circular DNA molecule located in the nucleoid region of the cytoplasm. The absence of a nucleus is a defining feature that differentiates prokaryotes from eukaryotes.
C. Ribosomes: Prokaryotic cells contain ribosomes, typically 70S in size, which are responsible for protein synthesis. These ribosomes are dispersed throughout the cytoplasm and facilitate translation of messenger RNA into functional proteins.
D. Cell wall: Most prokaryotes possess a rigid cell wall that maintains cell shape, provides structural support, and protects against osmotic stress. In bacteria, the cell wall is primarily composed of peptidoglycan, which differs structurally from eukaryotic cell walls.
E. Cell membrane: The plasma membrane is a phospholipid bilayer that encloses the cytoplasm of prokaryotic cells. It regulates the movement of substances in and out of the cell and houses proteins essential for energy production, nutrient transport, and signal transduction.
Correct Answer is B
Explanation
A. Ehrlich: Paul Ehrlich is known for his work in immunology and chemotherapy, including the development of the concept of the “magic bullet” and the discovery of salvarsan for treating syphilis. While his work advanced the understanding of targeted therapies, he was not the first to develop vaccines.
B. Jenner: Edward Jenner is credited with developing the first successful vaccination. In 1796, he inoculated a boy with material from cowpox lesions and demonstrated that it conferred immunity against smallpox. This pioneering work established the principle of using a related, less virulent pathogen to prevent disease.
C. Lister: Joseph Lister introduced antiseptic surgery using carbolic acid to reduce postoperative infections. His contributions advanced surgical safety but did not involve the development of vaccines or active immunization.
D. Koch: Robert Koch provided experimental proof that specific microbes cause specific diseases through Koch’s postulates. While foundational in microbiology, he did not develop vaccines.
E. Escherich: Theodor Escherich discovered Escherichia coliand contributed to bacteriology and pediatric infectious disease research. His work focused on bacterial identification, not vaccination.
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