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Micro-Exam2
Micro 6.2
| Question | Answer |
|---|---|
| What are the two common methods of preserving bacterial cultures for long periods? | Deep-freezing and lyophilization |
| What is deep-freezing? | method where a pure culture of microbes is placed in suspending liquid and quick-frozen. |
| What's the range of temperatures for deep-freezing? | -50 to -95 degrees Celsius. |
| After deep-freezing, how long is the microbe preserved? | For several years. |
| What is lyophilization? | Freeze-drying. |
| What happens during lyophilization? | A suspension of microbes is quickly frozen and the water is removed by a high vacuum. |
| What is the temperature range for lyophilization? | -54 to -72 degrees Celsius. |
| 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. |
| 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. |
| 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. |
| 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") |
| What are the 4 DIRECT methods of measuring microbial growth | Plate count, filtration, the most probable number (MPN) method, and direct microscopic count. |
| What does a plate count reflect? | the # of viable microbes. Assumes that each bacterium grows into a single colony. |
| How are plate counts reported? | as colony-forming units (CFU) |
| What are the 2 methods of doing a plate count? | 1. pour plate method 2. streak plate method |
| 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. |
| 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. |
| 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. |
| What are the 3 INDIRECT methods of measuring microbial growth? | Turbidity, metabolic activity, dry weight. |
| What's used to determine turbidity? How does it work? | A spectrophotometer. Measures the amount of light that passes through a suspension of cells. |
| 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) |
| What do you do during the dry weight method? | Extract, filter extra material, & dry it in a desiccator. Weigh. |
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