Questions and Answers
What is the primary effect of hypertonic environments on cells?
Which of the following statements accurately describes the role of nitrogen in bacterial metabolism?
What distinguishes extreme halophiles from facultative halophiles?
Which reactive oxygen species is produced by the addition of an extra electron to molecular oxygen?
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Which of the following substances is NOT known to be a source of sulfur for bacteria?
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Which trace elements are commonly required by microorganisms as enzyme cofactors?
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What is the primary function of biofilms in microbial communities?
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What process involves the introduction of microbes into a culture medium?
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What is one significant factor contributing to the increased resistance of biofilms to microbicides?
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What discovery is Louis Pasteur known for in relation to aseptic technique?
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Which of the following best describes the function of an autoclave?
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What is the primary characteristic of chemically defined media?
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Which type of media suppresses the growth of unwanted microbes?
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What is the purpose of the streak plate method?
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What temperature range is typically used for deep-freezing bacterial cultures?
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Which of the following statements about selective and differential media is correct?
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Which bacterial growth condition is associated with capnophiles?
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What method is used to preserve bacterial cultures by freezing and dehydrating in a vacuum?
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What is the optimum growth temperature range for thermophiles?
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Which environment is NOT typically associated with the growth of thermophiles?
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What defines the optimum growth temperature for hyperthermophiles?
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What is the pH range in which most bacteria grow optimally?
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What characteristic distinguishes an acid from a base?
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What type of organism is Bacillus alcalophilus?
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Which of the following substances is considered a strong base?
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Which type of microorganism can thrive in pH environments lower than 5?
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What is the main process by which prokaryotic cells reproduce?
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During which phase of bacterial growth is there a lag in cell division?
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What is the calculation for the total number of cells after a certain number of generations in binary fission?
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What is a method that involves counting the colonies on plates with a specific range of colonies?
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Which measurement technique uses a spectrophotometer to assess bacterial numbers?
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In the exponential growth phase, what is happening to the number of cells?
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What is the purpose of performing a serial dilution before counting colonies?
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Which method uses a special Petroff-Hausser cell counter for bacterial enumeration?
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Study Notes
Organic and Inorganic Elements
- Trace Elements: Essential inorganic elements required in small quantities, mainly serving as enzyme cofactors; examples include iron, copper, molybdenum, and zinc.
- Organic Growth Factors: Compounds sourced from the environment necessary for growth, including vitamins, amino acids, purines, and pyrimidines.
Biofilms
- Microbial Communities: Consist of bacteria that form protective slime or hydrogels on surfaces, facilitating cell-to-cell communication through quorum sensing.
- Nutrient Sharing: Bacteria in biofilms share nutrients and are sheltered from adverse environmental factors.
- Infection Role: Biofilms are implicated in approximately 70% of infections, commonly found on medical devices like catheters and heart valves, as well as in dental carries.
- Resistance: Biofilms exhibit 1000 times greater resistance to microbicides, found in environments including digestive systems and sewage treatment systems.
Culture Media
- Definition: A culture medium provides nutrients for microbial growth, typically prepared sterile (no living microbes).
- Inoculation: The process of introducing microbes into a sterile medium.
- Culture: Refers to the microbes grown in or on the culture medium.
Aseptic Technique
- Developed by Louis Pasteur to prevent contamination in laboratory settings, demonstrating that microorganisms originate from other microorganisms, not spontaneously.
Temperature Requirements
- Thermophiles: Heat-loving organisms with optimal growth temperatures between 50°C and 60°C; thrive in hot springs, geothermal areas, and compost heaps.
- Hyperthermophiles: Require temperatures exceeding 80°C, capable of surviving above 100°C. Found in extreme environments like hydrothermal vents.
pH Levels
- Hydrogen Ion Concentration: Indicates acidity (pH 0-6) or alkalinity (pH 8-14) of solutions.
- Bacterial Growth: Most bacteria flourish between pH 6.5 and 7.5; acidophiles thrive in acidic conditions, while alkaliphiles grow in basic environments.
Osmotic Pressure
- Hypertonic Environments: Can lead to plasmolysis in cells.
- Halophiles: Extreme halophiles require high osmotic pressures; facultative halophiles can tolerate these conditions.
Key Elements for Microbial Growth
- Carbon: Acts as a structural backbone for organic molecules; chemoheterotrophs obtain energy from organic compounds.
- Nitrogen: Vital for proteins, DNA, and ATP; bacteria can decompose proteins or utilize nitrogen fixation.
- Sulfur: Necessary for certain amino acids and vitamins; sourced primarily from protein decomposition.
- Phosphorus: Essential for DNA, RNA, ATP, and membranes; commonly sourced from inorganic phosphate (PO43-).
- Oxygen: Various reactive oxygen species (ROS) including singlet oxygen, superoxide radicals, and hydroxyl radicals pose oxidative stress, necessitating careful handling in sterile environments.
Growth of Bacterial Cultures
- Pure Culture: Contains only one species or strain; can be isolated using streak plate methods.
- Binary Fission: Primary method of bacterial reproduction resulting in two daughter cells.
Generation Time & Growth Phases
- Generation Time: Varies from 20 minutes to 24 hours, with binary fission doubling cell numbers each generation.
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Growth Curve Phases:
- Lag Phase: No growth.
- Log Phase: Exponential increase in cell numbers.
- Stationary Phase: Balance between dividing and dying cells.
- Death Phase: Logarithmic decrease in population.
Direct Measures of Microbial Growth
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Methods of Counting:
- Plate Count: Count colonies formed on agar plates (30-300 CFUs).
- Filtration: Collects bacteria from a solution for colony growth on Petri dishes.
- Most Probable Number (MPN): Statistical method assessing positive tube counts.
- Microscopic Count: Counts bacteria using specialized cell counters.
Indirect Measures of Bacterial Numbers
- Turbidity: Measures cloudiness of a solution using a spectrophotometer.
- Metabolic Activity: Assesses the amount of metabolic products as indicators of bacterial numbers.
- Dry Weight: Weighs dried bacteria for quantification, particularly in filamentous organisms.
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Description
This quiz covers the essential organic and inorganic elements necessary for microbial growth. It explores trace elements, their roles as enzyme cofactors, and the importance of organic compounds sourced from the environment. Additionally, learn about biofilms and the communication methods of microbial communities.
