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Biology Questions

Qu. 1. In a sample of bacteria which stain positively with the Gram stain, not all organisms will appear stained with the same intensity. This can be because uptake of the stain was not taken up evenly by all cells, or that excessive washing out of the stain has occurred in some cells (History, 2004). It can also be due to a prolonged decolorization step in the procedure, which is the critical step for differentiating Gram-positive and Gram-negative organisms. During the Gram staining procedure, if washing or decolorizing is continued too long, all the stain may be removed from some cells, making them appear Gram-negative when they are actually Gram-positive. Most cocci are Gram-positive, and so in this case, there was probably some leaching of the stain during the washing step. Since this sample was from a pure culture, in a correctly applied Gram-stain, all cocci should have stained more or less equally.

Qu. 2. Selective media are media to which compounds have been added which will selectively inhibit the growth of certain microorganisms but not others (Growth, 2004). Differential media are media to which an indicator such as a dye has been added which allows the observer to differentiate between different organisms by their chemical reactions during growth because some of the organisms can use this ingredient but not others.

Eosin-methylene-blue (EMB) agar is both a selective and a differential medium which is often used for the isolation of Gram-negative enteric bacteria (Growth). The methylene blue in the medium inhibits the growth of Gram-positive bacteria. The mechanism by which the inhibition works is not well-understood, but small amounts of methylene blue successfully inhibit the growth of most Gram-positive bacteria. The dye eosin responds to changes in pH, changing from colorless to black under acidic conditions. EMB-agar medium contains both lactose and sucrose as energy sources, but no glucose. Lactose...

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Biology Questions. (1969, December 31). In LotsofEssays.com. Retrieved 21:26, March 28, 2024, from https://www.lotsofessays.com/viewpaper/1713191.html