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Micro 6.2

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Question
Answer
What are the two common methods of preserving bacterial cultures for long periods?   Deep-freezing and lyophilization  
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What is deep-freezing?   method where a pure culture of microbes is placed in suspending liquid and quick-frozen.  
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What's the range of temperatures for deep-freezing?   -50 to -95 degrees Celsius.  
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After deep-freezing, how long is the microbe preserved?   For several years.  
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What is lyophilization?   Freeze-drying.  
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What happens during lyophilization?   A suspension of microbes is quickly frozen and the water is removed by a high vacuum.  
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What is the temperature range for lyophilization?   -54 to -72 degrees Celsius.  
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lyophilization: what's done to the container while the water is removed by the vacuum?   The container is sealed by melting the glass with a high temperature torch.  
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How do the organisms remain after the deep-freezing process? After lyophilization?   Deep-freezing leaves a block of ice. Lyophilization leaves organisms in a powder-like residue.  
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How long can the microbes be stored after lyophilization? How are they revived?   Decades. Can be revived by hydration with a suitable liquid nutrient medium.  
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What's the definition of generation time?   The length of time it takes for a cell to divide and for its populations to double. (on multiple choice as well! Answer on there is written as simply "The length of time it takes for a cell to divide")  
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What are the 4 DIRECT methods of measuring microbial growth   Plate count, filtration, the most probable number (MPN) method, and direct microscopic count.  
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What does a plate count reflect?   the # of viable microbes. Assumes that each bacterium grows into a single colony.  
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How are plate counts reported?   as colony-forming units (CFU)  
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What are the 2 methods of doing a plate count?   1. pour plate method 2. streak plate method  
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What happens during filtration?   bacteria are retained on the surface of a membrane filter and are then transferred to a culture medium to grow and subsequently be counted.  
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What is the most probably number (MPN)? What kind of microbes can it be used for?   It's a statistical estimation that can be used for microbes that will grow in a liquid medium.  
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How are microbes counted in a direct microscopic count?   the microbes in a measured volume of a bacterial suspension are counted with the use of a specially designed slide.  
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What are the 3 INDIRECT methods of measuring microbial growth?   Turbidity, metabolic activity, dry weight.  
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What's used to determine turbidity? How does it work?   A spectrophotometer. Measures the amount of light that passes through a suspension of cells.  
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What does the metabolic activity method assume?   That the amount of metabolic product (like acid, or CO2) is in direct proportion to the # of bacteria present. (there's only as much poop as there are people, after all)  
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What do you do during the dry weight method?   Extract, filter extra material, & dry it in a desiccator. Weigh.  
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