Gram-positive bacteria have a cell wall that contains:
A thin peptidoglycan layer
A thick peptidoglycan layer
No peptidoglycan
An outer membrane only
The Correct Answer is B
A. A thin peptidoglycan layer: A thin peptidoglycan layer is characteristic of Gram-negative bacteria, not Gram-positive bacteria. In Gram-negative cells, the thin layer is located between the inner cytoplasmic membrane and the outer membrane.
B. A thick peptidoglycan layer: Gram-positive bacteria have a thick, multilayered peptidoglycan wall that provides structural strength, maintains cell shape, and protects against osmotic pressure. This thick layer also traps the crystal violet-iodine complex during Gram staining, giving Gram-positive cells their purple color under a microscope.
C. No peptidoglycan: All bacteria except mycoplasmas have peptidoglycan in their cell walls. Gram-positive bacteria rely heavily on this thick peptidoglycan layer for structural integrity, so that they have no peptidoglycan is incorrect.
D. An outer membrane only: Gram-positive bacteria lack an outer membrane. The presence of an outer membrane is a defining feature of Gram-negative bacteria, which lies outside their thin peptidoglycan layer. Gram-positive bacteria instead have a thick peptidoglycan wall often containing teichoic acids.
Nursing Test Bank
Naxlex Comprehensive Predictor Exams
Related Questions
Correct Answer is A
Explanation
A. To prevent distortion of cells: Allowing the smear to air-dry completely ensures that the bacterial cells retain their natural shape and size. If the smear is heat-fixed while still wet, the water can rapidly boil, causing cells to rupture, shrink, or burst, which distorts their morphology. Maintaining cell integrity is essential for accurate microscopic examination and identification of bacteria.
B. To speed up staining: Air-drying is not intended to speed up staining; in fact, it is a preparatory step to preserve cell structure before applying stains. Proper drying ensures that stains adhere evenly without artifacts caused by residual moisture.
C. To make the bacteria grow: Smear preparation does not promote bacterial growth. Heat fixing kills the bacteria, making them safe to handle and fixing them to the slide. Growth occurs only on appropriate culture media, not on a prepared smear.
D. To increase contrast: Contrast is primarily achieved through the staining process, such as Gram staining or simple stains. Air-drying itself does not enhance contrast; it only prepares the cells to be fixed and stained properly without distortion.
Correct Answer is C
Explanation
A. Purple: Purple indicates Gram-positive bacteria, which retain the crystal violet-iodine complex within their thick peptidoglycan cell walls during the Gram staining process. The color persists even after decolorization with alcohol or acetone.
B. Blue: Blue is not a standard color outcome in Gram staining. Gram-negative and Gram-positive bacteria are typically differentiated as purple or pink/red; blue may appear in other specialized staining techniques but not standard Gram staining.
C. Pink/Red: Gram-negative bacteria appear pink or red after Gram staining. Their thin peptidoglycan layer does not retain the crystal violet-iodine complex after decolorization. They are counterstained with safranin, which imparts the pink/red color, allowing differentiation from Gram-positive bacteria.
D. Green: Green is not a result of Gram staining. Green coloration is associated with other staining methods or pigments but is not part of the Gram stain differential process.
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