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Questions and Answers
What is the preferred pH range for most microorganisms?
Which group of microorganisms prefer a pH of >8.5?
What is the characteristic pH range for acidophiles?
What is the term used for solutions with higher solute concentration outside the cell compared to inside?
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Which group of microorganisms can endure very cold or even freezing temperatures?
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What is the preferred temperature range for psychrotrophs?
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What is the term used to describe organisms that prefer to live in salty environments?
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If a solution has the same concentration of solutes inside and outside a cell, what is it called?
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What happens to bacteria with rigid cell walls when placed in a hypertonic solution?
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Which type of organism is Staphylococcus aureus classified as in terms of its preference for salty environments?
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What is the process known as when a bacterial cell escapes cytoplasm due to bursting in a hypotonic solution?
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Which term describes microbes that can survive in high atmospheric pressure?
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What is the role of water in microbial growth?
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What are halophiles?
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Why can certain microbial stages like bacterial endospores survive desiccation?
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At what temperature do thermophiles grow best?
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What determines the temperature range over which an organism grows best?
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What is the optimum temperature for mesophiles to grow best?
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Study Notes
Temperature
- Psychrophiles prefer cold temperatures, such as deep ocean water
- Psychrotrophs, a type of psychrophile, prefer refrigerator temperature (4°C)
- Psychroduric organisms can endure very cold or freezing temperatures, but prefer warm temperatures
pH
- Most microorganisms prefer a neutral or slightly alkaline growth medium (pH 7.0-7.4)
- Acidophiles prefer a pH of 2 to 5
- Alkaliphiles prefer a pH of >8.5
Osmotic Pressure and Salinity
- Osmotic pressure is the pressure exerted on a cell membrane by solutions both inside and outside the cell
- Osmosis is the movement of a solvent through a permeable membrane from a lower concentration of solutes to a higher concentration of solutes
- A hypertonic solution has a higher concentration of solutes outside the cell than inside the cell
- Plasmolysis occurs when a bacterial cell is placed in a hypertonic solution, causing the cell membrane and cytoplasm to shrink away from the cell wall
- A hypotonic solution has a lower concentration of solutes outside the cell than inside the cell
- Plasmoptysis occurs when a bacterial cell bursts in a hypotonic solution, causing the cytoplasm to escape
- Isotonic solutions have equal concentrations of solutes inside and outside the cell
- Halophilic organisms prefer to live in salty environments
- Haloduric organisms can survive in salty environments but do not prefer them
Barometric Pressure
- Piezophiles are microbes that can survive in high atmospheric pressure (>14.7 psi)
Nutrients and Moisture
- All living organisms require nutrients to sustain life
- Nutrients are energy sources, and organisms obtain energy by breaking chemical bonds
- Moisture is essential for life and necessary for carrying out normal metabolic processes
- Some microbial stages (e.g., bacterial endospores and protozoal cysts) can survive drying (desiccation)
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Description
Test your knowledge on the factors that affect microbial growth, encouraging the growth of microbes in vitro, and inhibiting the growth of microbes in vitro as outlined in Chapter 8 of Burton’s Microbiology for the Health Sciences.
