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35 Cards in this Set
- Front
- Back
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What does microbial growth refer to?
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Growth refers to an increase in the number of cells, not an increase in cell size.
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List three physical requirements for microbial growth.
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1. Temperature
2. pH 3. Osmotic pressure |
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Psychrophiles
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Freezing to max of 20 degrees Celsius. Mostly spoil foods.
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Mesophiles
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Middle temps: 15-45 degrees Celsius. Human normal flora and human pathogens.
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Thermophiles
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45-65 degrees Celsius
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What pH do most bacteria like?
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Neutral pH (6.5-7.5)
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pH buffers
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Finite quantity of media.
-Slow down changes in pH -Reason: Buy ourselves time and allow bacteria to survive long enough so we can study them. |
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Three examples of buffers:
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1. Salt of phosphate
2. Peptone 3. Amino acids |
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What is osmotic pressure?
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It refers to the concentration of dissolved salts or sugars in an environment
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What is an isotonic environment? What happens to a cell in an isotonic environment?
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The concentration outside the cell is the same inside the cell. Equal amounts of water enter and exit the cell, so there is no net loss of water,
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What is a hypertonic environment? What happens to a cell in a hypertonic environment?
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The concentration outside the cell is greater than inside the cell. Far more water will exit the cell than will enter the cell, causing plasmolysis.
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What is plasmolysis?
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The osmotic loss of water from a cell that occurs when it is placed in a hypertonic environment.
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Genus of an extreme halophile:
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Halobacterium spp.
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What is an extreme halophile?
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A bacterium that can survive or requires high concentrations of salt.
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What is a facultative halophile?
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A bacterium that can survive high or normal salt concentrations.
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List microbial chemical requirements:
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1. Carbon
2.Nitrogen, sulfur, and phosphorous 3. Trace elements 4. Presence or absence of oxygen 5. Organic growth factors |
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Who needs carbon?
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Everyone.
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Why do you need to provide a carbon source for microbes?
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Because they need it to synthesize organic components.
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What components do nitrogen, sulfur, and phosphorous make?
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DNA, RNA, and ATP.
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Nitrogen-fixation
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The conversion of N2 to NH3 (ammonia).
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Rhizobium spp.
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Associates with legumes like soybeans, peas, lentils, etc. Turns atmospheric nitrogen into a form that plants can use.
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Trace elements
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Minerals required in small quantities (ppm or ppb). We typically get what we need when we drink water.
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Aerobes
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Require oxygen to survive
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Facultative anaerobes
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Can survive in presence or absence of oxygen; however, it grows better in the presence of oxygen.
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Obligate anaerboes
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Can't use oxygen and is poisoned in its presence.
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Aero-tolerant anaerobes
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Can't use oxygen but are not poisoned in its presence.
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Microaerophilic
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Can only survive in oxygen concentrations that are lower than that in air: 2-10% (water, soil)
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List examples of organic growth factors.
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Vitamins and enzymes that the organism cannot synthesize on its own.
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What is generation time? And what shortens or lengthens it?
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Time required for a cell to divide or the time for the population to double. Optimal environmental conditions are going to shorten generation time while adverse conditions will make generation time longer.
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Lag phase
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First growth phase. Little or no cell division but the cells are preparing to divide.
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Log phase
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Exponential increase in population. Cellular reproduction is most active in this phase and generation time is at a minimum.
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When is the best time to perform a Gram-stain?
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During log phase.
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When are bacteria most susceptible?
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During log phase.
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Stationary phase
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Number of cells produces equal the number of cells dying (exhausting nutrients and oxygen). Accumulating metabolic products result in a more acidic environment. Temperature increases.
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Death phase
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Number of cells dying outnumber the number of cells being produced.
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