A patient with infective endocarditis has blood cultures showing cocci in clusters with a thick peptidoglycan layer. What color would this organism appear on Gram stain?
Gram-negative
Gram-positive
The Correct Answer is B
Cocci in clusters with a thick peptidoglycan layer are characteristic of Gram-positive bacteria, such as Staphylococcus species. During Gram staining, the thick peptidoglycan retains the crystal violet-iodine complex, causing the bacteria to appear purple under the microscope. This structural feature also contributes to resistance to osmotic stress and plays a role in pathogenicity. Gram-positive identification helps guide antibiotic selection, as these bacteria typically respond to agents targeting the cell wall. Gram-negative bacteria have a thin peptidoglycan layer and an outer membrane containing lipopolysaccharides. They do not retain the crystal violet stain and appear pink or red after the counterstain (safranin) is applied.
Nursing Test Bank
Naxlex Comprehensive Predictor Exams
Related Questions
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 A
Explanation
Eukaryotic cells are characterized by having a true nucleus, which houses the cell’s genetic material enclosed within a nuclear membrane. In addition, they contain various membrane-bound organelles, such as mitochondria, endoplasmic reticulum, Golgi apparatus, lysosomes, and peroxisomes, each performing specialized cellular functions. This organization allows compartmentalization of metabolic processes, efficient energy production, and regulated protein synthesis. In contrast, prokaryotic cells lack a nucleus and membrane-bound organelles, with DNA located in a nucleoid region. The presence of these features distinguishes eukaryotes from prokaryotes and is fundamental to understanding their structural and functional complexity.
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