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Micro chapt. 4
Prokaryote Growth
| Question | Answer |
|---|---|
| Direct Cell Counts | Do not distinguish between living and dead cells. |
| One of the most rapid methods of determining the number of cells in a suspension is | direct microscopic count. |
| Coulter counter and a flow cytometer | count cells as they pass through a minute aperture. |
| The most probable number (MPN) method | is a statistical assay based on the theory of probability and is used to estimate cell numbers |
| Turbidity of a Culture | a rapid measurement that can be correlated to the number of cells; a spectrophotometer is used to measure turbidity |
| pH indicators | can be used to monitor acid production |
| How can Gas production can be detected in blood cultures | by using a molecule that fluoresces more brightly when the pH changes slightly or by using an inverted tube in culture media to trap gas. |
| How is ATP is detected | by employing luciferase, which uses ATP to produce light. |
| Obligate anaerobes and oxygen | cannot multiply if oxygen is present |
| Microaerophiles and oxygen | require small amounts of oxygen, but higher concentrations are inhibitory |
| Most bacteria are neutrophiles so what would their ph level be? | within the pH range of 5 to 8 |
| Acidophiles grow optimally | ph below 5.5 |
| Alkaliphiles grow optimally | at a pH above 8.5 |
| If the solute concentration is higher in the medium than in the cell | water diffuses out of the cell, causing plasmolysis. |
| required elements for Heterotrophs | organic carbon |
| Chemoautotrophs | use inorganic compounds for energy and derive their carbon from CO2 |
| Photoheterotrohs | use the energy of sunlight and derive their carbon from organic compounds. |
| Chemoheterotrophs | use organic compounds for energy and as a carbon source |
| A chemically defined medium | is composed of precise mixtures of pure chemicals; an example is glucose-salts medium. |
| A selective medium inhibits | organisms other than the one being sought; examples include Thayer Martin Agar and MacConkey Agar. |
| A differential medium | contains a substance that certain bacteria change in a recognizable way; examples include blood agar and MacConkey agar |
| enrichment culture | provides conditions in a broth that enhance the growth of one particular organism in a mixed population |
| When grown in a closed system, what are the stages of growth? | population of bacteria goes through four phases - lag, log, stationary and death. |
| Lag Phase | The number of cells does not increase; during this period bacteria synthesize the macromolecules required for multiplication. |
| the exponential or log phase | the cells divide at a constant rate. Initially these bacteria synthesize primary metabolites, but they begin synthesizing secondary metabolites in the late log phase |
| stationary phase | Bacteria stop growing after they have used up a required nutrient, when oxygen is in short supply, or when toxic metabolites accumulate to high levels. |
| death phase | The total number of viable cells in the population decreases at a constant rate during the death phase. |
| How doesThe position of a single cell within a colony markedly determines its environment? | cells on the edge may be in log phase whereas those in the center may be in death phase |
| How is a biofilm established? | Cell-to-cell communication through quorum sensing appears to be important in establishing the structure of a biofilm. |
| The nitrogen in microorganisms will typically be present in what molecules? | Protein - also present in nucleic acids. |
| Why would small organic compounds affect the water content of cells? | These compounds would affect the osmotic pressure of cells and water would diffuse into cells in response to a higher concentration of these small organic compounds |
| Why would bacteria be more susceptible to antibiotics during log phase? | because bacteria are multiplying rapidly and most metabolic systems are active. When a metabolic system is active, it is most susceptible to antibiotic action |
| A method that counts only live microbes is the | plate count |
| To develop a pure culture from a mixed culture, a microbiologist may use the | streak plate |
| A microorganism isolated from the Antarctic would most likely be | a psychrophile |
| The difference in the 2 phases of the exponential phase | inital phase=activities geared toward increasing cell mass then in late log phase, stationery phase approaches with accumulation of waste products and depletion of nutrients |
| phase where primary metabolites are produced | exponential phase |
| phase of prolonged decline | many members of population are dying and releasing nutrients while few filter cells are actively multiplying |
| How does a chemostat keep cultures in constant state of growth? | manipulates the concentration of nutrients in a medium so that log phase can be continued |
| Zone of clearance in blood agar | beta hemolysis |
| Grows rapidly at 20 - 40 degrees | Mesophiles |
| Chocolate Agar | red blood cells heated to release nutrients for fastidious bacteria |
| Turbidity drawbacks | does not distinguish between dead or living |
| Enzyme(s) that can help an organism survive the toxic effects of oxygen is | catalase & superoxide dismutase |
| A differential media is used to | isolate a specific organism or group of organisms |
| Secondary metabolites are normally produced during | stationary phase |
| an enrichment media for chemolithotrophs | You grow an organism in media containing H2S and CO2 as the only sources for energy and carbon |
| A growth medium that can discriminate between two different bacterial species based on an observed change in the media is termed | a differential medium |
| During which phase of culture growth are cells not actively dividing? | Stationary, lag, death phases |
| cells increase the number of ribosomes they contain. | in the lag phase |
| A mixture of organisms is in a pool of seawater. Which organism will have a growth advantage as the water evaporates? | osmotolerant prokaryotes |
| Number of cells measured using glass slides & counting chambers | Direct microscopic count |
| Contain a substance that a particular bacteria will CHANGE in a RECOGNIZEABLE way | differential media |
| What extends lag time | warm media |
| no cell division - no death | lag time |
| unpaired electrons | dangerous |
| photoheterotrophs | use light but need organic compounds |
| complex & differentail media | can tell growth from one organisin from another |
| MPN | detects ANY growth |
| Cells are more resistant to antibiotics, radiation and harmful chemicals. | Stationery phase |
| When the number of colonies that grow are multiplied by the dilution factor to get the concentration of original culture | Spread plate method |
| Where measured culture is serialy diluted and measured in small ammount and then poured onto plate & incubated | Spread plate method |
| uses passage of a measured amount of very dilute culture and estimates the number of cells by placing filter on a plate | Filtration |
| involves diluting the sample to where dilutions contain no living cells (determined by no growth or turbidity) | MPN |
| Used to determine biomass | Dry weight |
| Aseptic conditions | absence of pathogens |
| Degermination | removal of pathogens from skin with chemicals |
Created by:
sloanie32
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