128 Questions
What is the purpose of a continuous culture?
To maintain the cells in a state of exponential growth
What is the name of the equipment used to produce a steady-state culture?
Chemostat
What is the advantage of using a continuous culture?
It maintains the cells in a state of exponential growth
What is the purpose of removing equal volumes of old culture in a continuous culture?
To remove waste products
What is the characteristic of a continuous culture?
The cells are in a state of exponential growth
What is the difference between a continuous culture and a batch culture?
The way nutrients are added
Why is it desirable to maintain cells in a state of exponential growth?
For certain applications such as alcohol production
What is the purpose of a chemostat?
To maintain a steady-state culture
What is the characteristic of a steady-state culture?
The population size is constant
What is the importance of monitoring pH levels in a continuous culture?
To ensure the optimal growth of the cells
What is the characteristic of batch culture?
Conditions in the culture are continually changing
What is the purpose of measuring bacterial growth?
To determine the number of viable cells
What is the unit of measurement for bacterial growth?
Number of cells per milliliter
What is the advantage of direct methods of measuring bacterial growth?
They provide a direct count of individual cells
Which of the following is an indirect method of measuring bacterial growth?
Measuring the effects of bacterial growth
What is the most probable number method?
A statistical method of estimating bacterial growth
What is the purpose of serial dilution in measuring bacterial growth?
To estimate the number of viable cells
What is the advantage of membrane filtration in measuring bacterial growth?
It is a selective method
What is the purpose of electronic counters in measuring bacterial growth?
To count individual cells
What is the characteristic of indirect methods of measuring bacterial growth?
They measure the effects of bacterial growth
What is the stationary phase of cell growth?
When cell division decreases to the point that new cells are produced at the same rate as old cells die
What is the primary factor limiting cell growth in the stationary phase?
All of the above
What happens to the number of live cells in the stationary phase?
It remains constant
What is the result of cell division decreasing to the point that new cells are produced at the same rate as old cells die?
The number of live cells remains constant
What is the primary consequence of the stationary phase on the environment?
The environment becomes less favorable
What is the result of the oxygen supply becoming inadequate for aerobic organisms?
Cell growth decreases rapidly
What is the impact of toxic waste materials on cell growth?
It decreases cell growth
What is the significance of the carrying capacity of the environment?
It is the maximum number of cells that can grow in an environment
What is the impact of pH changes on cell growth?
It decreases cell growth
What is the result of the nutrient supply becoming limited?
Cell growth decreases rapidly
What is the phase where the organism divides at its most rapid rate?
Log phase
What is the result of the population of organisms after one generation time?
The population doubles
What is the term used to describe the growth of organisms during the log phase?
Exponential growth
What is the interval of time during which the population of organisms doubles?
Generation time
What happens to the population of organisms after 2 hours if the generation time is 20 minutes?
The population increases by 64 times
What is the term used to describe the growth of organisms in a logarithmic manner?
Logarithmic growth
What is the result of the population of organisms after 3 hours if the generation time is 20 minutes?
The population increases by 512 times
What is the main function of a spectrophotometer in microbiology?
To measure the amount of light that passes through a sample
What is the phase where the growth of organisms slows down or stops?
Stationary phase
What is the rate of growth of organisms during the log phase?
Rapid and exponential
Which of the following is an environmental factor that affects microbial growth?
All of the above
What is the term used to describe the time required for the population of organisms to double?
Generation time
What is the relationship between absorbance and the number of microorganisms?
Absorbance is directly proportional to the number of microorganisms
What is the purpose of measuring turbidity in microbiology?
To estimate the number of microorganisms present
Which of the following is a nutritional factor that affects microbial growth?
Availability of carbon
What is the effect of pH on microbial growth?
pH affects the growth rate of microorganisms
What is the purpose of measuring dry weight in microbiology?
To measure the mass of microorganisms per unit volume
Which of the following is a physical factor that affects microbial growth?
Temperature
What is the effect of radiation on microbial growth?
Radiation decreases the growth rate of microorganisms
Which of the following is a method for measuring microbial growth?
All of the above
What happens to the number of live cells during the decline phase?
It decreases at a logarithmic rate.
What occurs during the decline phase in cultures of spore-forming organisms?
More spores than vegetative cells survive.
What is the duration of the decline phase?
It is highly variable.
What happens to cells during the decline phase?
They assume unusual shapes and become difficult to identify.
What is the relationship between the decline phase and the logarithmic growth phase?
The decline phase always occurs after the logarithmic growth phase.
What happens to the growth rate of cells during the decline phase?
It decreases rapidly.
What is the main characteristic of the decline phase?
Decrease in cell population.
What is the outcome of the decline phase?
Some cells survive.
What is the significance of the decline phase?
It is a transition phase between growth and death.
What is the relationship between the decline phase and cell death?
The decline phase leads to cell death.
What is the temperature range for the growth of psychrophiles?
0°C to 15°C
Which of the following bacteria is an example of a psychrophile?
Achromobacter
What is the term for bacteria that can adjust to and tolerate a range of environmental conditions?
Facultative
What is the term for bacteria that must have a specific environmental condition to grow?
Obligate
Which of the following is a characteristic of thermophiles?
Growth at high temperatures
What is the term for bacteria that grow best at moderate temperatures?
Mesophiles
Which of the following bacteria is a concern because it can grow in refrigerated food and cause foodborne illness?
Staphylococcus aureus
What is the classification of bacteria based on their growth temperature range?
Psychrophiles, Mesophiles, and Thermophiles
Which of the following is NOT a type of bacteria?
Obligate
What is the term for the ability of bacteria to adjust to and tolerate different environmental conditions?
Facultative
What is the relationship between the nematode and the microbe?
The nematode and the microbe are in a mutualistic relationship.
What is the role of the microbe in the nematode-microbe mutualism?
To break down organic matter and provide nutrients to the nematode.
What is the benefit of the nematode-microbe mutualism to the nematode?
The nematode receives nutrients from the microbe.
What is the environment in which the nematode-microbe mutualism is found?
Soil ecosystems.
What is the result of the nematode-microbe mutualism on the ecosystem?
It decreases the amount of organic matter in the ecosystem.
What is the relationship between the nematode and the fungus?
The nematode and the fungus are in a mutualistic relationship.
What is the role of the fungus in the nematode-fungus mutualism?
To break down organic matter and provide nutrients to the nematode.
What is the benefit of the nematode-fungus mutualism to the nematode?
The nematode receives nutrients from the fungus.
What is the environment in which the nematode-fungus mutualism is found?
Soil ecosystems.
What is the result of the nematode-fungus mutualism on the ecosystem?
It decreases the amount of organic matter in the ecosystem.
What is the primary purpose of using a continuous culture?
To maintain cells in a state of exponential growth
What is the characteristic of a steady-state culture?
Cells are in a state of equilibrium
Why is it necessary to remove equal volumes of old culture in a continuous culture?
To prevent the build-up of toxic waste products
What is the advantage of using indirect methods of measuring bacterial growth?
They are less expensive than direct methods
What is the result of cell division decreasing to the point that new cells are produced at the same rate as old cells die?
The population of cells enters the stationary phase
What is the primary factor limiting cell growth in the stationary phase?
Availability of nutrients
What is the range of temperatures that microorganisms can grow?
From around freezing to above boiling point
What is the minimum temperature that permits a microbe's continued growth and metabolism?
The lowest temperature at which growth is possible
What is the impact of toxic waste materials on cell growth?
They inhibit cell growth
What is the significance of the carrying capacity of the environment?
It is the maximum population size that can be supported by the environment
What happens to enzymes when the temperature rises above the maximum temperature?
They are permanently inactivated
Why is refrigeration effective in preventing microbial growth?
Because it reduces the growth rate of microorganisms
What is the optimum temperature for microbial growth?
The temperature at which growth is fastest
What happens to lipids in the cell membrane when the temperature is low?
They harden
Why are bacteria more apt to survive extremes of cold than extremes of heat?
Because enzymes are not denatured by chilling
What is the effect of temperature on microbial growth rate?
Growth rate increases with temperature until the optimum temperature is reached
What is the purpose of refrigeration in preventing microbial growth?
To reduce the growth rate of microorganisms
What is the result of temperature rising above the maximum temperature for an extended period?
The cell will die
What is the typical temperature range for human pathogens?
30°C to 40°C
What is the characteristic of thermophilic organisms?
They grow best at temperatures from 50°C to 60°C
What is the significance of thermoduric organisms in food preservation?
They can withstand short periods of high temperatures
What is the optimal temperature range for Bacillus stearothermophilus?
50°C to 60°C
What is the typical temperature range for mesophilic organisms?
30°C to 40°C
What is the significance of inadequate heating in food preservation?
It can leave thermoduric organisms alive
What is the characteristic of thermophilic organisms in food spoilage?
They can display minimal growth at temperatures as low as 30°C
What is the ideal temperature range for the growth of mesophiles?
Between 25°C and 40°C
What is the term for the process of removing equal volumes of old culture in a continuous culture?
Dilution
What is the significance of temperature in food preservation?
It can affect the growth of all microorganisms
What is the main advantage of using a continuous culture over a batch culture?
It allows for more precise control over environmental conditions
What is the optimal temperature range for human body temperature?
37°C to 38°C
What is the characteristic of thermoduric organisms in food preservation?
They can withstand short periods of high temperatures
What is the term for the equipment used to produce a steady-state culture?
Chemostat
What is the main characteristic of a continuous culture?
It is a dynamic system with a constant flow of nutrients
What is the purpose of maintaining cells in a state of exponential growth?
To maintain a steady-state culture
What is the term for the group of organisms that include most bacteria?
Mesophiles
What is the importance of monitoring pH levels in a continuous culture?
To ensure the optimal growth of the cells
What is the term for the process of inoculating a fresh culture with a small amount of cells from a previous culture?
Subculturing
What is the main difference between a continuous culture and a batch culture?
The flow of nutrients and waste products
What is the primary function of oxygen in aerobic organisms?
To act as a terminal electron acceptor in respiratory chains
What is the characteristic of obligate anaerobes?
They are killed by free oxygen
Why do aerobes require shaking or mechanical stirring in a deep culture?
To increase oxygen availability for growth
What is the primary difference between aerobic and anaerobic organisms?
Their requirement for oxygen
What is the purpose of anaerobic chambers in culturing obligate anaerobes?
To exclude oxygen from the culture
Why is oxygen poorly soluble in water?
Due to its hydrophobic nature
What is the characteristic of aerobic organisms in a shallow layer of medium?
They can grow throughout the medium
Why do cultures of rapidly dividing cells require more oxygen than cultures of slowly dividing cells?
Because they have a higher energy demand
What is the purpose of providing sufficient oxygen to aerobic organisms in a laboratory culture?
To act as a terminal electron acceptor in respiratory chains
What is the characteristic of heterotrophic bacteria?
They obtain energy by breaking down organic matter
Study Notes
Cell Growth Stages
- Cells adapt to new environment and produce required enzymes to utilize available resources
- This allows them to undergo regular, genetically-determined division via binary fission
- This exponential growth leads to a rapid increase in cell numbers over a fixed time period, known as the generation time
- Cell population can double during each generation time under optimal conditions
Logarithmic Growth Phase
- Cells divide at their fastest rate during this phase
- Population grows exponentially, doubling with each generation time
- Provides a way to predict future cell counts based on current population
Stationary Phase
- Cell division slows to match the rate of old cell death
- Culture reaches a constant cell number
- Nutrients become limited and waste products accumulate
- Oxygen supply may become inadequate for aerobes, and pH changes can be harmful
Decline/Death Phase
- Unfavorable conditions cause many cells to lose ability to divide
- Cell population decreases logarithmically
- Many cells undergo changes in shape and structure, making identification difficult
- Spore-forming organisms may have more spores than vegetative cells survive
Generation Time
- Time required for cell population to double during exponential growth
- Predictable, genetically-determined interval
- Example: 1000 cells/mL doubles to 2000 cells/mL in 20 minutes, then 4000 cells/mL in 40 minutes
Continuous vs Batch Culture
- Continuous culture maintains cells in exponential growth phase
- Fresh medium continuously added, equal volumes of old removed
- Maintains constant nutrient levels and other conditions
- Batch culture has changing conditions as no new nutrients added
Measuring Bacterial Growth
-
Direct methods count individual cells
-
Indirect methods measure effects of growth
-
Direct methods include:
- Serial dilution and viable plate counts
- Membrane filtration
- Most probable number
- Microscopic counts
- Electronic counters### Environmental Factors Affecting Microbial Growth
-
Microorganisms can be influenced by a variety of physical and biochemical factors in their environment
-
Physical factors include pH, temperature, oxygen concentration, moisture, hydrostatic pressure, osmotic pressure, and radiation
-
Biochemical factors include availability of carbon, nitrogen, sulfur, phosphorus, trace elements, and vitamins
Temperature
- Microorganisms can grow over a wide range of temperatures, from around freezing to above boiling point
- Minimum temperature is the lowest that allows continued growth and metabolism, below this microbial activities are inhibited
- Lower temperatures slow growth as enzymes work less efficiently and lipids harden, reducing membrane fluidity
- Maximum temperature is the highest allowing growth and metabolism, above this enzymes and nucleic acids become denatured, killing the cell
- Optimum temperature range promotes fastest growth and metabolism, rarely a single point
Microbial Temperature Classification
-
Psychrophiles (cold-loving): grow best 15-20°C, some as low as 0°C
-
Mesophiles: grow best 25-40°C, include most common bacteria
-
Thermophiles: grow best at higher temperatures
-
Many bacteria tolerate a range overlapping temperature categories
-
Classified as obligate (requiring specific condition) or facultative (can adapt to different conditions)
-
Psychrophiles live in cold water and soil, examples include Achromobacter, Flavobacterium, Pseudomonas
-
Concern over Staphylococcus and Listeria that can grow in refrigerated food### Environmental Factors Affecting Microbial Growth
Temperature
- Most human pathogens have optimal growth temperatures between 30°C and 40°C (human body temperature is 37°C)
- Thermoduric organisms can survive short periods of high temperatures, but may not be killed by inadequate heating during canning or pasteurization
- Examples of heat-resistant cysts include Giardia, and spore formers like Bacillus and Clostridium
- Thermophiles (heat-loving organisms) grow best at temperatures between 50°C and 60°C
- Bacillus stearothermophilus, an obligate thermophile, grows at its maximum rate at 65°C to 75°C, but can still cause food spoilage at temperatures as low as 30°C
Oxygen
- Oxygen is present in the atmosphere (20% concentration) and most life forms depend on it for survival and growth
- Bacteria can be divided into aerobes (require oxygen to grow) and anaerobes (do not require oxygen)
- Obligate aerobes (e.g. Pseudomonas) require free oxygen for aerobic respiration, while obligate anaerobes (e.g. Clostridium botulinum, C. tetani, and Bacteroides) are killed by free oxygen
- Aerobic organisms require oxygen as a terminal electron acceptor in their respiratory chains
- In laboratory cultures, aerobes must be provided with enough oxygen to satisfy their requirements
- In shallow layers of medium (e.g. petri dishes), sufficient oxygen is available in surface moisture, but in deeper cultures (e.g. flasks of broth), aerobes will only grow in surface layers unless additional oxygen is provided (oxygen is poorly soluble in water)
- Obligate anaerobes cannot tolerate oxygen at all and are cultured in special anaerobic chambers, with oxygen excluded from all liquid and solid media
Learn about the different stages of cell growth, including adaptation, exponential growth, and logarithmic growth phase. Understand how cell populations change over time.
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