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Questions and Answers
What is the normal pH range for most bacteria to thrive?
What is the normal pH range for most bacteria to thrive?
All bacteria are unable to grow at low pH values.
All bacteria are unable to grow at low pH values.
False
What type of buffer is commonly used to maintain neutral pH?
What type of buffer is commonly used to maintain neutral pH?
phosphate buffer
Certain bacteria that require high salt concentrations for growth are known as ______.
Certain bacteria that require high salt concentrations for growth are known as ______.
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Match the following types of buffers to their pH range:
Match the following types of buffers to their pH range:
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What happens to bacteria in hypertonic solutions?
What happens to bacteria in hypertonic solutions?
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Osmophiles are organisms that require a low solute concentration for growth.
Osmophiles are organisms that require a low solute concentration for growth.
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What effect does pH have on the fate of free amino acids in the cell?
What effect does pH have on the fate of free amino acids in the cell?
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Osmotic pressure results from water diffusing across the cell membrane in response to ______.
Osmotic pressure results from water diffusing across the cell membrane in response to ______.
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Which property of bacteria makes them relatively resistant to changes in osmotic pressure?
Which property of bacteria makes them relatively resistant to changes in osmotic pressure?
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Which type of microorganism requires oxygen for growth and carries out aerobic respiration?
Which type of microorganism requires oxygen for growth and carries out aerobic respiration?
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Facultative anaerobes can grow only in the absence of air.
Facultative anaerobes can grow only in the absence of air.
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Name one example of an acidophile.
Name one example of an acidophile.
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Organisms that grow best at high pH are known as ________.
Organisms that grow best at high pH are known as ________.
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Match the following types of microorganisms with their oxygen requirements:
Match the following types of microorganisms with their oxygen requirements:
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Which of the following statements about microaerophiles is true?
Which of the following statements about microaerophiles is true?
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Strict anaerobes are sensitive to oxygen and will die upon exposure.
Strict anaerobes are sensitive to oxygen and will die upon exposure.
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What is the pH range in which most organisms grow best?
What is the pH range in which most organisms grow best?
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Most pathogenic bacteria are classified as __________.
Most pathogenic bacteria are classified as __________.
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Which of these bacteria is an example of an obligate anaerobe?
Which of these bacteria is an example of an obligate anaerobe?
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Which mechanism helps phototactic bacteria respond to changing light conditions?
Which mechanism helps phototactic bacteria respond to changing light conditions?
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Chemical substances can only act as nutrients for bacterial growth.
Chemical substances can only act as nutrients for bacterial growth.
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What is the primary effect of ultraviolet (UV) light on bacterial cells?
What is the primary effect of ultraviolet (UV) light on bacterial cells?
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Bacteria protect themselves from harmful radiation damage by synthesizing _____ and other pigments.
Bacteria protect themselves from harmful radiation damage by synthesizing _____ and other pigments.
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Match the following chemicals with their effects on bacteria:
Match the following chemicals with their effects on bacteria:
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What is a characteristic of photosynthetic bacteria?
What is a characteristic of photosynthetic bacteria?
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Bright light has a beneficial effect on all types of bacteria.
Bright light has a beneficial effect on all types of bacteria.
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What type of agents can some chemical substances act as, preventing bacterial growth?
What type of agents can some chemical substances act as, preventing bacterial growth?
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The toxicity of light on bacteria primarily depends on the _____ spectrum.
The toxicity of light on bacteria primarily depends on the _____ spectrum.
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Match the following effects with their descriptions:
Match the following effects with their descriptions:
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What is the primary role of carotenoids in bacteria?
What is the primary role of carotenoids in bacteria?
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Study Notes
Oxygen Relationships of Microorganisms
- Microorganisms are grouped based on their oxygen requirements or intolerance
- Aerobes grow in the presence of molecular oxygen
- Obligate aerobes need oxygen for growth and aerobic respiration
- Microaerophiles grow only at reduced oxygen concentrations (around 5% less than atmospheric levels)
- Microaerophiles will not grow in air
Facultative Anaerobes
- Facultative anaerobes grow in the presence or absence of air
- Many, like E. coli, switch between aerobic respiration and fermentation depending on oxygen availability
- They use fermentation in the absence of oxygen and aerobic respiration in its presence
- This group includes strictly fermentative bacteria (like streptococci) that are insensitive to oxygen
Other Bacteria and Anaerobes
- Other bacteria are anaerobes and grow only in the absence of air
- Obligate anaerobes carry out fermentative metabolism
- Various bacteria (e.g., sulfate-reducing Desulfovibrio) and archaea (e.g., methanogenic archaea) are included
- Strict anaerobes are killed by brief oxygen exposure
Effects of Acidity and pH
- Acidity or alkalinity affects microbial growth
- Most grow best between pH 6 and 8
- Internal cell pH must remain close to neutral despite external conditions
- Acidophiles grow best at low pH (e.g., Helicobacter pylori)
- Alkaliphiles grow best at high pH (e.g., Vibrio cholera)
- Most pathogenic bacteria are neutrophiles
pH of a Solution and Bacterial Growth
- pH describes hydrogen ion concentration
- Bacterial growth rates depend greatly on pH values and protein structure
- Enzymes are inactive at very high or low pH values
- Bacteria are less tolerant of high temperatures at low pH than at neutral pH
- pH values are controlled in culture media and industrial fermenters to optimize growth
Buffers and pH Control
- Buffers maintain a specific pH range, preventing large changes
- Phosphate buffers are used at neutral pH
- Borate buffers are used at alkaline pH
- Citrate buffers are used at acidic pH
- Most bacteria grow well within a pH range of 6 to 9
pH and Microbial Metabolism
- pH of the medium determines dominant carbohydrate metabolism pathways
- Amino acid fate (carboxylation or deamination) depends on pH
Effects of Pressure (Osmotic and Hydrostatic)
- Growth of all cells is affected by external and internal pressure
- Forces include osmotic and hydrostatic pressure
- Hydrostatic pressure arises from water column weight (deep ocean)
- Osmotic pressure results from water diffusion across the membrane in response to solute concentrations
- Salinity (salt concentration) is often associated with osmotic pressure
Osmotic Pressure and Salinity
- Cell walls make bacteria relatively resistant to osmotic pressure changes
- Hypertonic solutions cause shrinkage (desiccation)
- Hypotonic solutions cause bursting
- Organisms growing in high solute concentrations are osmotolerant
- Osmophiles require high solute concentrations for growth
- Salinity has a substantial effect on osmotic pressure
- Some bacteria have specific responses to salt (NaCl) concentrations, some are halophiles
Effects of Light
- Photosynthetic bacteria need light for ATP production
- They function optimally at specific light intensities and wavelengths
- Some photosynthetic bacteria exhibit phototaxis (movement toward light)
- Certain mechanisms regulate flagellar rotation with changing light intensity
- Bacteria can respond to wavelengths
- Visible and UV light can damage proteins and DNA
- Pigments (like carotenoids) protect from harmful light
- UV light can cause DNA replication issues leading to mutations
Effects of Radiation
- Light is essential for growth in photosynthetic bacteria
- Other bacteria are mostly harmed by light, especially UV radiation
- UV light toxicity is due to absorption in nucleic acids and proteins
- UV light prevents DNA replication and can cause lethal mutations
Effects of Chemicals
- Chemical substances can be nutrients or prevent bacterial growth
- Certain chemicals act as bacteriostatic agents (prevent growth) or bactericidal agents (kill bacteria)
- Some chemicals destroy cell structures (like denaturing proteins with alcohol)
Effects of Antibiotics
- Penicillin inhibits transpeptidase, affecting peptidoglycan cross-linking (prevents cell wall formation in bacteria, not eukaryotes).
- Oxacillin, bacitracin, and vancomycin are cell wall antibiotics, they inhibit cell wall biosynthesis, causing weakened cell walls, cell lysis, and death
- Actinomycin interferes with RNA synthesis by binding to DNA thus preventing transcription..
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Description
Explore the diverse oxygen requirements of microorganisms in this quiz. Learn about aerobes, obligate aerobes, microaerophiles, and facultative anaerobes, along with other anaerobes. Understand how these classifications impact their growth and metabolism.
