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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Correct Answer is A
Explanation
A Petri dish is a shallow, cylindrical, lidded container commonly used in laboratories for culturing microorganisms such as bacteria, fungi, and cells. It is typically made of clear glass or disposable sterile plastic, which allows easy observation of microbial growth. The dish consists of two parts: a flat bottom portion that holds the growth medium and a slightly larger lid that covers it to protect the culture from contamination while still allowing gas exchange. In microbiology, the bottom of the dish is usually filled with a nutrient medium such as agar that supports microbial growth. Samples are inoculated onto the agar surface and incubated under controlled temperature conditions. As microorganisms multiply
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.
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