The isolation streak plate technique is used to separate individual bacterial cells on an agar plate.
True
False
The Correct Answer is A
The isolation streak plate technique is specifically designed to separate individual bacterial cells on the surface of an agar plate. By streaking a loop or swab across the agar in a systematic pattern, the bacterial population is progressively diluted, allowing single cells to land apart from each other. These isolated cells then grow into distinct colonies, which can be used for identification, further testing, or pure culture development. This technique is fundamental in microbiology for obtaining pure cultures from mixed bacterial samples, ensuring accurate study of bacterial morphology, physiology, and biochemical characteristics.
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Related Questions
Correct Answer is B
Explanation
A. Their outer membrane traps the stain: Gram-positive bacteria do not have an outer membrane; this structure is characteristic of Gram-negative bacteria. Therefore, the outer membrane cannot be responsible for retaining crystal violet in Gram-positive cells.
B. Their thick peptidoglycan layer holds the crystal violet-iodine complex: Gram-positive bacteria have a thick, multilayered peptidoglycan cell wall that forms a dense network. During Gram staining, the crystal violet combines with iodine to form an insoluble complex that gets trapped within this thick peptidoglycan matrix. Even after alcohol or acetone decolorization, the complex remains, causing the cells to appear purple under a microscope.
C. They absorb the safranin more strongly: Safranin is a counterstain used to color Gram-negative bacteria red after decolorization. Gram-positive bacteria do not absorb safranin strongly because the retained crystal violet-iodine complex masks it. Therefore, safranin absorption is not responsible for the purple color of Gram-positive cells.
D. They do not undergo decolorization: While Gram-positive bacteria resist decolorization, this is not because they fail to undergo the process; it is due to the structural ability of their thick peptidoglycan to trap the crystal violet-iodine complex. The resistance is a result of the cell wall structure, not a lack of exposure to the decolorizing agent.
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.
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