Why must the smear be completely air-dried before heat fixing?
To prevent distortion of cells
To speed up staining
To make the bacteria grow
To increase contrast
The Correct Answer is A
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.
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Related Questions
Correct Answer is A
Explanation
The fine adjustment knob on a microscope is used to sharpen or clarify the image after the initial focus has been achieved with the coarse adjustment knob. The coarse adjustment knob moves the stage or objective lens quickly over a larger distance to bring the specimen roughly into focus, which is especially useful with low-power objectives. Once the image is visible, the fine adjustment knob allows for precise, gradual adjustments to enhance the clarity and detail of the specimen, particularly under high-power or oil immersion objectives. This ensures accurate visualization of cellular structures without damaging the slide or lens.
Correct Answer is A
Explanation
Hemolysins are bacterial exotoxins that specifically target and lyse red blood cells, releasing hemoglobin into the surrounding environment. They are produced by certain pathogenic bacteria, such as Streptococcus and Staphylococcus species, and contribute to nutrient acquisition by providing iron from hemoglobin. Hemolysins can cause varying degrees of red blood cell destruction, resulting in different patterns on blood agar: alpha hemolysis (partial lysis with greenish discoloration), beta hemolysis (complete lysis with clear zones), and gamma hemolysis (no lysis). Their activity is an important virulence factor in bacterial infections.
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