Which observation most directly challenged the original formulation of classical cell theory?
Discovery of ribosomes as non-membranous organelles
Identification of multinucleated skeletal muscle fibers
Observation that all living organisms metabolize ATP
Recognition that membranes are composed of phospholipid bilayers
The Correct Answer is B
A. Discovery of ribosomes as non-membranous organelles: Ribosomes are intracellular structures responsible for protein synthesis and are not surrounded by membranes. While their discovery expanded understanding of cellular components, it did not contradict classical cell theory, which focuses on cells as the basic structural and functional units of life.
B. Identification of multinucleated skeletal muscle fibers: Classical cell theory posits that a cell has a single nucleus and functions as an autonomous unit. The presence of multinucleated skeletal muscle fibers, also called syncytia, challenged this notion This observation revealed that some cells can deviate from “one nucleus per cell” concept, prompting refinement of the theory.
C. Observation that all living organisms metabolize ATP: While ATP metabolism is a universal feature of living cells, this observation supports rather than challenges cell theory. It reinforces the concept that cells are the basic functional units responsible for life-sustaining biochemical processes.
D. Recognition that membranes are composed of phospholipid bilayers: Identifying the phospholipid bilayer structure of membranes clarified how cells maintain compartmentalization and selective permeability. This structural insight complements classical cell theory and does not contradict the fundamental principles regarding cellular organization.
Nursing Test Bank
Naxlex Comprehensive Predictor Exams
Related Questions
Correct Answer is A
Explanation
A. Cocci, bacilli, coccobacilli, vibrios, spirilla, and spirochetes: These are all recognized bacterial shapes. Cocci are spherical, bacilli are rod-shaped, coccobacilli are short rods, vibrios are comma-shaped, spirilla are rigid spiral-shaped bacteria, and spirochetes are flexible, corkscrew-shaped bacteria. These morphological classifications are used in microbiology to identify and categorize bacterial species.
B. Cocci, diplocytes, flagella, fimbriae, and spores: While cocci are a bacterial shape, diplocytes refers to paired cocci, flagella and fimbriae are appendages, and spores are dormant survival structures. This list mixes shapes with structures, hence does not exclusively describe bacterial morphology.
C. Bacilli, nuclei, ribosomes, mitochondria, and cocci: Bacilli and cocci are bacterial shapes, but nuclei, ribosomes, and mitochondria are cellular organelles not used to define bacterial morphology. Bacteria are prokaryotes and lack membrane-bound organelles.
D. Spirilla, cilia, capsules, and peptidoglycan: Spirilla is a bacterial shape, but cilia are eukaryotic structures, capsules are extracellular protective layers, and peptidoglycan is a cell wall component. Only spirilla refers to bacterial morphology.
E. Spirochetes, lysosomes, peroxisomes, and cocci: Spirochetes and cocci are bacterial shapes, but lysosomes and peroxisomes are eukaryotic organelles. This list is not limited to recognized bacterial morphologies.
Correct Answer is A
Explanation
Plasmids are small, circular, double-stranded DNA molecules that exist independently of the bacterial chromosome. They often carry genes that provide selective advantages, such as antibiotic resistance, virulence factors, or metabolic capabilities, allowing bacteria to adapt rapidly to environmental pressures. Plasmids can replicate autonomously and may be transferred between bacteria through processes like conjugation, promoting the spread of resistance or virulence traits. Unlike the chromosomal DNA, plasmids are not essential for basic survival but play a critical role in bacterial evolution and pathogenicity.
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