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31 Cards in this Set
- Front
- Back
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Describe a detrimental and a beneficial effect ofbiofilms. |
Detrimentaleffect is dental plaque. Beneficial effect is bioremediation and sewagetreatment. |
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Define a pure culture |
A population oforganisms that are descended from a single cell. |
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Explain what occurs during each of the five phases ofgrowth. |
Lagphase — the "tooling-up" period during which cells synthesize DNA,amino acids, and enzymes necessary for cell growth. Logphase — the period of active growth. Stationaryphase — cells are synthesizing compounds that make them more resistant tocertain environmental conditions but they are dying as fast as they aredividing. Deathphase — cells are dying faster than they are dividing. Phaseof prolonged decline - very gradual decrease in the number of viable cells onthe population. |
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Explain how the environment of a colony differs fromthat of cells growing in a liquid broth. |
Ina liquid broth, the population of cells is exposed to uniform conditions. Cellsin a colony are exposed to different conditions, depending on the location ofthe cell within the colony. |
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List the five categories of optimum temperature, and describe acorresponding environment in which a representative might thrive. |
Psychrophile — glacier lake. Psychrotroph - refrigerated food. Mesophile — surface of the humanbody. Thermophile — compost heap. Extreme thermophile — hydrothermalvent. |
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Why would botulism be a concern with canned foods? |
Obligate anaerobescan grow in improperly canned foods. |
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Explainwhy O2-containing atmospheres kill some microbes. |
Reactive oxygenspecies (ROS) including (O2-) and hydrogen peroxide aredamaging to cells. Many organisms haveenzymes that detoxify these compounds. Bacteria that cannot survive in aerobicatmospheres generally lack these enzymes. |
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Explainwhy photoautotrophs are primary producers. |
Using sunlight for energy and CO2 asa carbon source, photoautotrophs synthesize organic compounds that other formsof life require; without primary producers, humans and other animals could notexist. |
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Distinguish between a selective medium and a differential medium. |
A selective medium contains aningredient that inhibits the growth of undesired organisms; a differentialmedium contains an ingredient that allows for the visual differentiation of twospecies. A medium can be both selective and differential. |
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If the number of microorganisms in lake water were determined using botha direct microscopic count and a plate count, which method would most likely give a higher number? Why? |
The direct microscopic count would likely give the highest number because most environmental bacteria cannot be grown in culture and therefore would not be accounted for with the plate count. |
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High-performance boat manufacturers know that microbescan collect on a boat, ruining its hydrodynamic properties. Aboat-manufacturing facility recently hired you to help with this problembecause of your microbiology background. What strategies other than routinecleaning would you pursue to come up with a long-term remedy for the problem? |
The best strategywould be to find ways to coat the surface of a boat with a material thatprevents biofilm formation. You can try to develop a paint or resin that istoxic to the bacteria and does not leak out too much to harm other organisms. |
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Why would bacteria in a biofilm be more resistantto harmful chemicals? |
Because the extracellular polymericsubstances can impede the diffusion of chemicals. |
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What properties of agar make it ideal for usein culture media? |
Very few microbes can degrade it; itcan be heat-sterilized without destroying it; it remains solid over thetemperature range at which most microbes grow. |
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To identify the causative agent of a givenillness, a pure culture is often needed. How is a streak plate used to obtain apure culture? |
A series of streaks over the surfaceof an agar plate sequentially dilute an inoculum to the point at which singlecells are deposited; one cell can then multiply to form a population ofprogeny. |
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Explain the difference between the lag andexponential phases. |
In the lag phase, cells are"gearing up" to begin dividing, whereas in the exponential phase,cells are dividing at a continuous rate. |
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What is the function of the enzyme catalase? |
It detoxifies H2O2 by breaking itdown to H2O and O2 |
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Why would hydrogen peroxide be an effectivedisinfectant? |
Because it is a reactive oxygenspecies (ROS); organisms that produce catalase can break it down, butconcentrated solutions can overwhelm that capacity. |
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Why would human-made materials (such as manyplastics) be degraded only slowly or not at all? |
Because microorganisms are unlikelyto have enzymes to break them down. |
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Would bacteria that cannot use lactose beable to grow on MacConkey agar? Explain your answer. |
Becausethere are nutrients other than lactose in the medium. |
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Water that accumulates in dirty bowls anddishes left in the sink often becomes cloudy over time. Besides suspended foodparticles, what causes the turbidity? |
Bacteria growingin the water, using the nutrients in the dirty bowls and dishes. |
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Differences between pour plate and spreadplate technique. |
Spreadplate - 0.1 to 0.2 ml of cultured samples - transfer onto the surface of medium inpetri dish - spread over the surface using sterilizedbended glass rod Pour plate - 0.1- 1 ml of the diluted sample - add onto the sterilized petri dish - overlaid with molten medium; cooled to 50degrees Celsius - gently swirl plate to mix microbial cellswith medium |
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What do you understand colony forming unit(CFU) and what are the three things need to be considered for measuring CFU? |
Colony forming unit (CFU) – measureof viable cells account for the fact that microbial cells often attach to oneanother, then grow to form a single colony.In calculating CFU, three things mustbe considered 1.Number of colonies 2.The amount of sample that was diluted before plating 3.Volume platedCFU: number of viable cells per unitvolume of sample |
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If there are 103 cells per ml at the middle of log phase, and thegeneration time of the cells is 30 minutes, how many cells will there be 2hours later? |
1.6 × 104 |
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Compared with their growth in the laboratory, what would be rate of bacteriain nature? |
Moreslowly |
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Cells are most sensitive to penicillin during which phase of the growthcurve? |
Exponential |
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Lactic acid is a primary metabolite. If a company wants to harvest thiscompound from a bacterial culture, the cells should be in which growth phase? |
Exponential |
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E.coli,a facultative anaerobe, is grown for 24 hours on the same solid medium, butunder two different conditions: one aerobic, the other anaerobic. Whatcondition would be favorable for larger size of population? |
Largerwhen grown under aerobic conditions |
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Which of the following is false? a) E. coli grows faster in nutrient broth than in glucose-saltsmedium. b) Organisms require nitrogen tomake amino acids. c) Some eukaryotes can fix N2.d) An organism that grows on ham isosmotolerant. e)Blood agar is used to detect hemolysis. |
Some eukaryotes can fix N2 |
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If the pH indicator were left out of MacConkey agar, the type of mediumit would be? |
Complex |
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A soil sample is placed in liquid and the number of bacteria in thesample determined in two ways: (1) colony count and (2) direct microscopiccount. How would the results compare? |
Many more bacteria would be estimated by method |
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The concentrationof E.coli in a broth is between 104and 106 cells per ml. To determine the precise number of living cells in thesample, what method would be the best? |
Plate out an appropriate dilution of the sample onnutrient agar |
