Question 1

The __________ __________ is the length of time it takes for a population of microorganisms to double in number.

Accepted Answer

The answer of The __________ __________ is the length of...

Question 2

The membranes of psychrophilic bacteria have relatively high levels of __________ fatty acids,which allow them to remain semifluid at cold temperatures.

Accepted Answer

Unsaturated fatty acids have double bonds in their carbon chain, which prevents them from packing tightly together. This results in a more fluid and flexible membrane, which is essential for psychrophilic bacteria to survive in cold temperatures. Saturated fatty acids, on the other hand, have no double bonds and tend to pack tightly together, making the membrane more rigid and less adaptable to different temperatures. Sterols and aromatics are not typically found in bacterial membranes.

Question 3

An open system in which the growth rate is maintained by the removal and addition of media at such a rate as to maintain a constant cell density is called a

Accepted Answer

A turbidostat is an open system where the growth rate is controlled by adjusting the flow of media to maintain a constant cell density, typically monitored by turbidity.

Question 4

Which of the following is considered a cardinal growth temperature?

Accepted Answer

All of the minimum, maximum, and optimum temperatures are considered cardinal growth temperatures because they represent key points in the temperature range at which a microorganism can grow. The minimum temperature is the lowest temperature at which growth can occur, the maximum temperature is the highest temperature at which growth can occur, and the optimum temperature is the temperature at which growth is fastest or most favorable for a given microorganism. Therefore, all of these temperatures are important for understanding the growth characteristics of microorganisms.

Question 5

Which of these methods can be used to determine the number of viable microorganisms in a sample?

Accepted Answer

Measuring colony forming units per ml is the most reliable method to determine the number of viable microorganisms in a sample as it counts only the live, viable cells that are able to form colonies on a solid culture medium. This method involves plating serial dilutions of the sample on a suitable medium and counting the number of colonies that grow after incubation. The other methods mentioned (light scattering in a spectrophotometer, measuring total cell mass, and counting a known volume of cells in a hemocytometer) do not differentiate between live and dead cells and may overestimate the number of viable microorganisms.

Question 6

At 4:00 p.m.a closed flask of sterile broth is inoculated with 10,000 cells.The lag phase lasts 1 hour.At 9:00 p.m.the culture enters stationary phase with a population of 65 million cells.At what time is the population half maximal?

Accepted Answer

The population is half maximal when it reaches half of 65 million, which is 32.5 million. The exponential phase of growth occurs between the end of the lag phase (5:00 p.m.) and the beginning of the stationary phase (9:00 p.m.). Since the population increases exponentially during this time, to find when the population is half of its maximum (32.5 million), we look for the midpoint in time between the start and end of this phase. Given the exponential growth, the population would reach half its maximum size just before it stops growing. Since the stationary phase starts at 9:00 p.m., the population would be half maximal shortly before this, at 8:40 p.m.

Question 7

Organisms that are damaged by the normal atmospheric levels of oxygen (20%)but require oxygen at levels of 2-10% for growth are called

Accepted Answer

Organisms that are damaged by normal atmospheric levels of oxygen but require oxygen for growth in lower levels (2-10%) are called microaerophiles. Facultative anaerobes can grow in the presence or absence of oxygen, whereas aerotolerant organisms can tolerate the presence of oxygen but do not use it for growth or metabolism. Anoxygenic organisms do not use oxygen for metabolism.

Question 8

A culture system with constant environmental conditions maintained through continual provision of nutrient and removal of wastes is called __________ culture system.

Accepted Answer

A continuous culture system, as described, involves a continual supply of nutrients and removal of waste, which allows for stable environmental conditions for the cultured organism. The other options, batch, fed-batch, and semicontinuous, involve changes in nutrient and waste levels throughout the course of the culture.

Question 9

Organisms that grow at 0^$\circ$C and have a maximum growth temperature of 35^$\circ$C are called

Accepted Answer

Organisms that grow at low temperatures (0-20°C) and have a maximum growth temperature of 35°C are called psychrotrophs. Psychrophiles are microorganisms that grow at very low temperatures (-15 to 10°C). Frigiphiles are microorganisms that thrive at extremely low temperatures, such as those found in glaciers and polar ice caps. Mesophiles are microorganisms that grow at moderate temperatures (20-45°C).

Question 10

Organisms that ignore oxygen and grow equally well in its presence or absence are called

Accepted Answer

Organisms that can grow equally well in the presence or absence of oxygen are called aerotolerant anaerobes. They do not require oxygen for growth but can tolerate its presence. Facultative anaerobes grow better in the presence of oxygen but can also grow in its absence or under anaerobic conditions. Microaerophiles grow best in environments with low oxygen concentrations. Anoxygenic organisms do not produce oxygen during photosynthesis and do not necessarily grow in the absence of oxygen.

Question 11

The growth rate of a given species of microorganism is dependent on the composition of the medium in which it is grown.

Accepted Answer

The growth rate of a microorganism is heavily influenced by the composition of the medium in which it is grown. Factors such as nutrient availability, pH, temperature, and oxygen levels can all have a significant impact on the growth rate of microorganisms. For example, some microorganisms may require very specific nutrients in order to grow, while others may be able to thrive in a wide range of different conditions. As a result, it is important to carefully tailor the growth medium to meet the needs of the specific microorganism being grown.

Question 12

An open system in which the growth rate is maintained by adding a nutrient (present in limiting quantities)at the same rate that medium containing microorganisms is removed is called a

Accepted Answer

An open system in which the growth rate is maintained by adding a nutrient at the same rate that medium containing microorganisms is removed is called a chemostat.

Question 13

Microbial __________ is an increase in cell constituents that may or may not be accompanied by an increase in cell number.

Accepted Answer

The answer of Microbial __________ is an increase in cell...

Question 14

At 4:00 p.m.a closed flask of sterile broth is inoculated with 10,000 cells.The lag phase lasts 1 hour.At 9:00 p.m.the log phase culture has a population of 65 million cells.The mean generation time is approximately

Accepted Answer

The log phase lasts from 5:00 p.m. to 9:00 p.m., which is 4 hours or 240 minutes. The population grows from 10,000 to 65 million, which is a 6,500-fold increase. Using the formula for exponential growth, the mean generation time is approximately 20 minutes.

Question 15

At 4:00 p.m.a closed flask of sterile broth is inoculated with 10,000 cells.The lag phase lasts 1 hour.At 9:00 p.m.the log phase culture has population of 65 million cells.The approximate number of generations that has occurred is

Accepted Answer

The answer of At 4:00 p.m.a closed flask of sterile...

Question 16

Which of the following can be used to estimate the number of microorganisms in a culture?

Accepted Answer

All of the choices can be used to estimate the number of microorganisms in a culture. Direct counts of microbial cells involve using a microscope or a hemocytometer to count cells. Counts of viable cells using colony growth procedures involve counting the number of colonies that grow on an agar medium. Measurements of microbial biomass involve using techniques such as dry weight measurements or turbidity measurements.

Question 17

One of the major advantages of a continuous culture system is that the cells can be maintained in the exponential growth phase for extended periods of time.

Accepted Answer

In a continuous culture system, fresh nutrients are constantly added while waste products are removed, allowing cells to maintain exponential growth for an extended period of time. This is a major advantage over batch culture systems where cells will eventually enter stationary phase and stop growing.

Question 18

Organisms that do not require oxygen for growth but grow better in its presence are called

Accepted Answer

Facultative anaerobes are organisms that can grow with or without oxygen, but they grow better in its presence. These organisms can switch between aerobic and anaerobic metabolism depending on the availability of oxygen. Microaerophiles require oxygen, but at a low concentration, and aerotolerant organisms do not require oxygen for growth but can tolerate its presence. Anoxygenic organisms do not use oxygen for respiration, but they also do not necessarily grow better in its absence.

Question 19

Organisms that grow well at 0^$\circ$C and have optimum growth temperatures of 15^$\circ$C or lower are called

Accepted Answer

Organisms that grow well at low temperatures, such as 0-20°C, and have an optimum growth temperature of 15°C or lower are called psychrophiles. Psychrotrophs also grow well at low temperatures but have an optimum growth temperature of 20-30°C. Frigiphiles are a type of psychrophile that can grow at temperatures as low as -15°C. Mesophiles have an optimum growth temperature of 20-45°C and are most commonly found in environments with a temperature range of 25-40°C, such as the human body.

Question 20

In a continuous culture system,the rate at which media is added and removed is called the __________ rate.

Accepted Answer

In a continuous culture system, a constant flow of fresh media is added to and an equal volume of spent media is removed from the reactor vessel at a fixed rate. This constant rate is known as the dilution rate. The dilution rate ensures that the microbial population remains in exponential growth phase, and helps to maintain a steady state in the culture. The other options, such as chemostatic, pass-through, and flow-through rates are not commonly used terms to describe a continuous culture system.

Quiz 7: Microbial Growth

The is the length of time it takes for a population of microorganisms to double in number.

The membranes of psychrophilic bacteria have relatively high levels of __________ fatty acids,which allow them to remain semifluid at cold temperatures.

An open system in which the growth rate is maintained by the removal and addition of media at such a rate as to maintain a constant cell density is called a

Which of the following is considered a cardinal growth temperature?

Which of these methods can be used to determine the number of viable microorganisms in a sample?

At 4:00 p.m.a closed flask of sterile broth is inoculated with 10,000 cells.The lag phase lasts 1 hour.At 9:00 p.m.the culture enters stationary phase with a population of 65 million cells.At what time is the population half maximal?

Organisms that are damaged by the normal atmospheric levels of oxygen (20%) but require oxygen at levels of 2-10% for growth are called

A culture system with constant environmental conditions maintained through continual provision of nutrient and removal of wastes is called __________ culture system.

Organisms that grow at 0^$\circ$C and have a maximum growth temperature of 35^$\circ$C are called

Organisms that ignore oxygen and grow equally well in its presence or absence are called

The growth rate of a given species of microorganism is dependent on the composition of the medium in which it is grown.

An open system in which the growth rate is maintained by adding a nutrient (present in limiting quantities) at the same rate that medium containing microorganisms is removed is called a

Microbial __________ is an increase in cell constituents that may or may not be accompanied by an increase in cell number.

At 4:00 p.m.a closed flask of sterile broth is inoculated with 10,000 cells.The lag phase lasts 1 hour.At 9:00 p.m.the log phase culture has a population of 65 million cells.The mean generation time is approximately

At 4:00 p.m.a closed flask of sterile broth is inoculated with 10,000 cells.The lag phase lasts 1 hour.At 9:00 p.m.the log phase culture has population of 65 million cells.The approximate number of generations that has occurred is

Which of the following can be used to estimate the number of microorganisms in a culture?

One of the major advantages of a continuous culture system is that the cells can be maintained in the exponential growth phase for extended periods of time.

Organisms that do not require oxygen for growth but grow better in its presence are called

Organisms that grow well at 0^$\circ$C and have optimum growth temperatures of 15^$\circ$C or lower are called

In a continuous culture system,the rate at which media is added and removed is called the __________ rate.

Quiz 7: Microbial Growth

The __________ __________ is the length of time it takes for a population of microorganisms to double in number.

The membranes of psychrophilic bacteria have relatively high levels of __________ fatty acids,which allow them to remain semifluid at cold temperatures.

An open system in which the growth rate is maintained by the removal and addition of media at such a rate as to maintain a constant cell density is called a

Which of the following is considered a cardinal growth temperature?

Which of these methods can be used to determine the number of viable microorganisms in a sample?

At 4:00 p.m.a closed flask of sterile broth is inoculated with 10,000 cells.The lag phase lasts 1 hour.At 9:00 p.m.the culture enters stationary phase with a population of 65 million cells.At what time is the population half maximal?

Organisms that are damaged by the normal atmospheric levels of oxygen (20%) but require oxygen at levels of 2-10% for growth are called

A culture system with constant environmental conditions maintained through continual provision of nutrient and removal of wastes is called __________ culture system.

Organisms that grow at 0 ∘\circ∘ C and have a maximum growth temperature of 35 ∘\circ∘ C are called

Organisms that ignore oxygen and grow equally well in its presence or absence are called

The growth rate of a given species of microorganism is dependent on the composition of the medium in which it is grown.

An open system in which the growth rate is maintained by adding a nutrient (present in limiting quantities) at the same rate that medium containing microorganisms is removed is called a

Microbial __________ is an increase in cell constituents that may or may not be accompanied by an increase in cell number.

At 4:00 p.m.a closed flask of sterile broth is inoculated with 10,000 cells.The lag phase lasts 1 hour.At 9:00 p.m.the log phase culture has a population of 65 million cells.The mean generation time is approximately

At 4:00 p.m.a closed flask of sterile broth is inoculated with 10,000 cells.The lag phase lasts 1 hour.At 9:00 p.m.the log phase culture has population of 65 million cells.The approximate number of generations that has occurred is

Which of the following can be used to estimate the number of microorganisms in a culture?

One of the major advantages of a continuous culture system is that the cells can be maintained in the exponential growth phase for extended periods of time.

Organisms that do not require oxygen for growth but grow better in its presence are called

Organisms that grow well at 0 ∘\circ∘ C and have optimum growth temperatures of 15 ∘\circ∘ C or lower are called

In a continuous culture system,the rate at which media is added and removed is called the __________ rate.

The is the length of time it takes for a population of microorganisms to double in number.

Organisms that grow at 0^$\circ$C and have a maximum growth temperature of 35^$\circ$C are called

Organisms that grow well at 0^$\circ$C and have optimum growth temperatures of 15^$\circ$C or lower are called