Microbial Growth Phases Quiz
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Questions and Answers

What is the main characteristic of the lag phase in microbial growth?

  • Cells synthesize enzymes and grow in size. (correct)
  • Cells are metabolically inactive.
  • Population size is decreasing.
  • Cells are rapidly dividing.

During which phase do microbes experience the highest metabolic activity?

  • Stationary phase
  • Lag phase
  • Death phase
  • Log phase (correct)

What happens to the number of viable cells during the stationary phase?

  • It remains constant. (correct)
  • It fluctuates wildly.
  • It decreases exponentially.
  • It increases rapidly.

Which of the following statements is true regarding the death phase of microbial growth?

<p>Cells cannot divide, leading to an exponential decrease in population. (B)</p> Signup and view all the answers

The generation time for microbial populations varies mainly due to which factor?

<p>The environmental conditions and species. (B)</p> Signup and view all the answers

What adaptations do thermophiles have to stabilize their proteins?

<p>More hydrogen bonds and use of chaperones (C)</p> Signup and view all the answers

What is the optimum growth pH range for acidophiles?

<p>pH 0.1 - 5.5 (B)</p> Signup and view all the answers

Which type of organism absolutely requires oxygen for growth?

<p>Obligate aerobes (C)</p> Signup and view all the answers

What is a key characteristic of facultative anaerobes?

<p>They can grow using both aerobic and anaerobic metabolism depending on oxygen availability (A)</p> Signup and view all the answers

How do acidophiles and alkalophiles maintain their internal pH near neutrality?

<p>By utilizing plasma membranes impermeable to protons (A)</p> Signup and view all the answers

What is the main principle behind the Most Probable Number (MPN) method?

<p>It estimates the number of cells based on fermentation of carbohydrates. (D)</p> Signup and view all the answers

Which of the following is NOT a classification of microorganisms based on their optimum growth temperature?

<p>Insectophiles (B)</p> Signup and view all the answers

What method measures the turbidity of a bacterial culture to estimate growth?

<p>Spectrophotometer (A)</p> Signup and view all the answers

Which of the following is a disadvantage of the turbidity measurement method?

<p>Cannot distinguish live and dead cells (C)</p> Signup and view all the answers

What environmental factor is NOT typically associated with bacterial growth?

<p>Magnetism (B)</p> Signup and view all the answers

Which group of microorganisms can grow at temperatures between 50 - 60°C?

<p>Thermophiles (B)</p> Signup and view all the answers

What products accumulate as bacteria multiply, reflecting metabolic activity?

<p>CO2 and acids (D)</p> Signup and view all the answers

Which method involves weighing a cell pellet to determine microbial mass?

<p>Dry weight method (C)</p> Signup and view all the answers

What is the primary purpose of a continuous culture system?

<p>To provide a constant supply of nutrients and remove wastes (C)</p> Signup and view all the answers

Which method is used to measure viable cells in a sample?

<p>Standard Plate Count (A)</p> Signup and view all the answers

What is a characteristic feature of a chemostat?

<p>It maintains a constant biomass concentration (C)</p> Signup and view all the answers

Which of the following is an indirect method of measuring microbial growth?

<p>Turbidity measurement (D)</p> Signup and view all the answers

In a direct microscopic count using a Petroff-Hausser counting chamber, which of the following is true?

<p>Cells are counted across a single fixed area (D)</p> Signup and view all the answers

What is the key advantage of membrane filtration in measuring cell count?

<p>It allows for the assessment of water purity (B)</p> Signup and view all the answers

Which of the following cultures keeps cells in log phase for extended periods?

<p>Continuous culture (A)</p> Signup and view all the answers

What is the primary method of counting larger microorganisms such as protozoa?

<p>Coulter counter (B)</p> Signup and view all the answers

What is the primary characteristic of capnophiles?

<p>Thrive in high concentrations of carbon dioxide (A)</p> Signup and view all the answers

How do aerobes protect themselves from toxic oxygen products?

<p>By producing protective enzymes like superoxide dismutase (B)</p> Signup and view all the answers

What is the role of a GasPak in an anaerobic jar?

<p>To generate hydrogen and carbon dioxide for anaerobic conditions (A)</p> Signup and view all the answers

What defines barophiles?

<p>Organisms that are killed by atmospheric pressure (B)</p> Signup and view all the answers

What does the term water activity (aw) refer to?

<p>The amount of water available for organisms to utilize (B)</p> Signup and view all the answers

Which type of microorganisms can survive in environments with very high salt concentrations?

<p>Halophiles (D)</p> Signup and view all the answers

What is a feature of extreme halophiles?

<p>Thriving at salt concentrations of 20-30% (A)</p> Signup and view all the answers

What does marine agar aim to replicate?

<p>The mineral concentration found in sea water (C)</p> Signup and view all the answers

Flashcards

Log Phase (Exponential Phase)

The period where bacterial cells are actively dividing and doubling in number. This is characterized by the highest metabolic rate and rapid growth.

Stationary Phase

The period where the number of new cells created equals the number of cells dying. This marks the end of rapid growth and often a decline in nutrient availability.

Death Phase

The period where the number of cells dying surpasses the ones being produced. This leads to a decline in the overall bacterial population due to factors like lack of resources and built-up waste products.

Lag Phase

The initial period where bacterial cells acclimate to a new environment. Little to no cell division occurs during this stage.

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Binary Fission

The process of a single bacterial cell dividing into two identical daughter cells. This is the primary mode of bacterial reproduction.

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Microbiology

Study of microorganisms including bacteria, archaea, fungi, viruses and protists.

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Microbial growth

The process of increasing in size and number of cells.

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Log/Exponential Phase

A period during microbial growth where cells are rapidly dividing and doubling in number.

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Extremophiles

Organisms that thrive in harsh conditions that would kill most other organisms, such as extreme temperatures or salinity.

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Continuous Culture

A method of cultivating microorganisms in an open system, where fresh nutrients are constantly supplied, and waste products are continuously removed. This method maintains cells in the exponential growth phase to achieve a steady-state concentration of biomass.

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Chemostat

A type of continuous culture system where the growth rate is controlled by the rate of nutrient input.

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Photobioreactor

A bioreactor specifically designed to cultivate phototrophic microorganisms (organisms that use sunlight to produce energy) by providing them with optimal light conditions.

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Standard Plate Count

A method of measuring the number of viable cells in a sample by diluting the sample and plating the dilution on a nutrient agar plate. Colonies that grow represent viable cells.

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Membrane Filtration

A method of measuring microbial populations by filtering a known volume of liquid through a membrane filter. The filter is then placed on a culture medium and incubated. Colonies that grow on the filter represent the number of microorganisms present in that volume.

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Direct Microscopic Count

A technique that involves directly counting the number of microbial cells using a calibrated microscope slide and a counting chamber. This method can distinguish between viable and non-viable cells.

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Turbidity

A method of measuring microbial growth that is based on the turbidity or cloudiness of a liquid culture medium.

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Metabolic Activity

The ability of a microbial population to utilize specific nutrients, produce metabolic products, or break down substrates. This can be used to estimate the number of microorganisms in a sample.

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Obligate aerobes

Organisms that require oxygen for growth and perform aerobic respiration (e.g., Pseudomonas sp.).

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Acidophiles

Organisms that thrive in acidic environments with optimal pH ranging from 0.1 to 5.5.

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Facultative anaerobes

Organisms that do not require oxygen for growth but can tolerate its presence and may even use it for metabolism (e.g., E. coli, Staphylococcus sp.).

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Obligate anaerobes

Organisms that do not require oxygen for growth and are actually harmed by its presence (e.g., Bacteroides sp.).

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Microaerophiles

Organisms that grow best in the presence of a small amount of free oxygen (e.g., Campylobacter sp., Helicobacter pylori).

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Capnophiles

Microorganisms that require high concentrations of carbon dioxide (CO2) for growth.

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Anaerobic jar

A sealed container used to cultivate obligate anaerobic bacteria by creating an oxygen-free environment.

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Hydrostatic pressure

The pressure exerted by the weight of water on organisms living in aquatic environments.

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Barophiles

Organisms that thrive under high hydrostatic pressure, like those found in deep ocean trenches.

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Water activity (aw)

A measure of the water available to organisms, influenced by the concentration of solutes.

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Osmotolerant microorganisms

Organisms that can tolerate a wide range of water activity, often found in environments with high salt concentrations.

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Extreme Halophiles

Organisms that require high salt concentrations (typically 20-30%) for growth. Often found in environments like salt flats.

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Barotolerant

Organisms that grow best at standard atmospheric pressure but can survive and grow in higher pressure environments.

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Study Notes

Microbial Growth

  • Microbial growth involves an increase in cell size and cell numbers.
  • Microbes reproduce by binary fission (equal division) and budding (unequal division).

Cell Division

  • Binary fission: Cells elongate, DNA replicates, cross-wall forms, and cells separate.
  • Budding: A new cell develops as a bud from the parent cell.

Phases of Growth

  • Lag phase: Little or no cell division, adaptation to new conditions, metabolic activity to synthesize enzymes, and produce ATP.
  • Log phase (exponential): Highest metabolic activity, most rapid growth, population doubles with each generation.
  • Stationary phase: Cell division slows down, number of cells produced = number of cells dying, limited nutrients, limited oxygen, and metabolic waste accumulates.
  • Death phase: Number of cells dying > number of cells produced, metabolic waste becomes toxic, cells lose their ability to divide.

Growth Curve

  • A graph showing the phases of microbial growth over time.

Measurement of Growth

  • Direct methods:
    • Standard plate count: Dilute bacterial culture, transfer dilution onto agar plate (spread/pour), measure viable cells only.
    • Membrane filtration: Filter water sample, place the filter with trapped cells onto agar plate.
    • Direct microscopic count: Petroff-Hausser counting chamber (hemocytometer), electronic counter (Coulter counter).
  • Indirect methods:
    • Turbidity: Spectrophotometric analysis (measure turbidity).
    • Metabolic activity (most probable number (MPN)): Determine fermentation of carbohydrates (e.g., lactic acid, acetic acid). Measure gas production to assess bacterial growth.
    • Dry weight: Centrifuge microbes, dry pellet, measure dry weight.

Environmental Factors

  • Most organisms grow in moderate conditions. Extremophiles tolerate harsh conditions.
  • Factors affecting microbial growth include temperature, pH, oxygen, hydrostatic pressure, water activity (aw), and radiation.

Temperature

  • Psychrophiles: Optimum growth around 15-20°C.
  • Mesophiles: Optimum growth around 25-40°C.
  • Thermophiles: Optimum growth around 50-60°C.
  • Extreme thermophiles: Live in near-boiling temperatures (e.g., hot springs).

pH

  • Acidophiles: Optimum growth at pH 0.1-5.5.
  • Neutrophiles: Optimum growth at pH 5.5-7.0.
  • Alkalophiles: Optimum growth at pH 8.5 and above (11.5).

Oxygen

  • Aerobes: Require oxygen to grow.
  • Obligate aerobes: Need oxygen for aerobic respiration.
  • Anaerobes: Can grow without oxygen.
  • Obligate anaerobes: Killed by oxygen.
  • Facultative anaerobes: Can grow with or without oxygen.
  • Aerotolerant anaerobes: Can survive in oxygen but don't use it for metabolism.
  • Microaerophiles: Grow best with limited oxygen.
  • Capnophiles: Require high concentrations of CO2.

Hydrostatic Pressure

  • Barophiles: Live under high pressure.
  • Barotolerant: Can survive in high pressure but grow best at normal atmospheric pressure.

Water Activity (aw)

  • Water activity is the availability of water to organisms; reduced by solutes (osmotic effect).
  • Osmotolerant organisms can grow over a wide range of water activities. They often use compatible solutes to increase their internal osmotic concentration.
  • Halophiles: Require high salt concentrations (e.g., seawater or Dead Sea).
  • Halotolerant: Can tolerate salt but don't require it.

Radiation

  • Ionizing radiation (x-rays, gamma rays): Disrupts molecules (DNA).
  • UV radiation: Causes thymine dimers in DNA.

Continuous Culture Methods

  • Using a continuous culture system (e.g., bioreactor, chemostat, turbidostat), microbes can maintain growth in log phase by continuously providing nutrients and removing wastes. This enables the study of microbial growth at low nutrient concentrations and interactions under certain conditions.

Microbial Growth in Natural Environments

  • Natural environments are complex and constantly changing. They often contain low nutrient concentrations (oligotrophic environments) and expose organisms to overlapping gradients of nutrients and environmental factors.

Responses to Oligotrophic Environments

  • Microorganisms become more competitive in nutrient capture and use.
  • Morphological changes can increase surface area, and the ability to absorb nutrients.
  • Mechanisms to sequester nutrients become important for survival.

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Chapter 7 Microbial Growth PDF

Description

Test your knowledge on the various phases of microbial growth including lag, log, stationary, and death phases. This quiz will challenge your understanding of microbial metabolism, conditions for growth, and classifications based on temperature and pH. Perfect for students studying microbiology or life sciences.

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