GCSU (Bachoon) Microbiology Test 2 Exam Q’s and A’s
Why do we study microbial growth? - -1) to prove what causes disease
2) for antibiotic susceptibility (how to kill)
3) for research
-what are the physical aspects of microbial growth? - -- temperature
- pH
- osmotic pressure
-what are the 3 main groups microbes are classified into based on their optimum
temperature? - -1) psychrophiles
2) mesophiles
3) thermophiles
-psychrophiles - -- cold loving microbes
- don't cause disease
- (-10 deg. C to 20 deg. C)
-what is a psychrotroph? - -- organism that is capable of growth between 0 deg. C and 30
deg. C
-mesophiles - -- moderate temperature loving microbes, most common type
- (25 deg. C - 40 deg. C)
- these are human pathogens also include most of the common spoilage and disease
organisms.
- ex: 37 deg. C (the optimum temp. for many pathogenic bacteria)
-thermophiles - -- heat loving microbes
- (40 deg. C - 70 deg. C)
- many can't grow at temps below 45 deg. C
- hyperthermophiles = (70 deg. C - 110 deg. C)
-what temperature do pathogens grow at? - -- human body temp. (37 degrees celsius)
-what pH range do most bacteria grow best in? - -- a narrow pH range
- neutral (6.5 - 7.5)
- very few grow below pH 4
- foods with low pH (cheese, pickles..) don't spoil easily)
-What are some examples of bacteria that grow below pH 4? - -- sulfur oxidizers
- H. pylori
-____ have more H+ than ______ - -acids, bases
, -what is the osmotic pressure inside bacterial cells in an isotonic solution? - -- 0.85% NaCl
-What type of solution inhibits bacterial growth? - -- hypertonic solutions (solutes are
higher outside the cell)
- water leaves the cell
-what is plasmolysis? - -- the osmotic loss of water from the cell in a hypertonic
environment
- shrinkage of the cell plasma membrane - die
-What causes high osmotic pressure and can be used to preserve food? - -- salt or sugar
- causes plasmolysis
ex: salted meat, jams, jelly
-What percentage of salt and sugar are solutions that restrict growth? - -solutions that
restrict growth are:
> 5% salt
> 10% sugar
-- How do salts and sugars preserve foods?
- Why are these considered physical rather than chemical methods of microbial control? -
-- they create a hypertonic environment.
- As preservatives they don't directly affect cell structures or metabolism; instead they alter
the osmotic pressure
-What microorganisms can actually grow in salts and sugar preservatives? - --
staphylococcus aureus grow in up to 7% salt and spoils salted foods
- some fungi can grow in jelly and jams
(MOLDS are more capable of growth in high osmotic pressure than bacteria is)
-What are the chemical requirements of microbial growth? - -- carbon
- nitrogen
- sulfur
- phosphorus
- trace elements
- oxygen
-carbon - -- 50% of the dry weight of a bacterial cell
-nitrogen - -- for proteins, DNA, RNA, ATP
- 14% of the dry weight of bacterial cells
sources: decomposing proteins, NH+4, nitrates, nitrogen fixing
Why do we study microbial growth? - -1) to prove what causes disease
2) for antibiotic susceptibility (how to kill)
3) for research
-what are the physical aspects of microbial growth? - -- temperature
- pH
- osmotic pressure
-what are the 3 main groups microbes are classified into based on their optimum
temperature? - -1) psychrophiles
2) mesophiles
3) thermophiles
-psychrophiles - -- cold loving microbes
- don't cause disease
- (-10 deg. C to 20 deg. C)
-what is a psychrotroph? - -- organism that is capable of growth between 0 deg. C and 30
deg. C
-mesophiles - -- moderate temperature loving microbes, most common type
- (25 deg. C - 40 deg. C)
- these are human pathogens also include most of the common spoilage and disease
organisms.
- ex: 37 deg. C (the optimum temp. for many pathogenic bacteria)
-thermophiles - -- heat loving microbes
- (40 deg. C - 70 deg. C)
- many can't grow at temps below 45 deg. C
- hyperthermophiles = (70 deg. C - 110 deg. C)
-what temperature do pathogens grow at? - -- human body temp. (37 degrees celsius)
-what pH range do most bacteria grow best in? - -- a narrow pH range
- neutral (6.5 - 7.5)
- very few grow below pH 4
- foods with low pH (cheese, pickles..) don't spoil easily)
-What are some examples of bacteria that grow below pH 4? - -- sulfur oxidizers
- H. pylori
-____ have more H+ than ______ - -acids, bases
, -what is the osmotic pressure inside bacterial cells in an isotonic solution? - -- 0.85% NaCl
-What type of solution inhibits bacterial growth? - -- hypertonic solutions (solutes are
higher outside the cell)
- water leaves the cell
-what is plasmolysis? - -- the osmotic loss of water from the cell in a hypertonic
environment
- shrinkage of the cell plasma membrane - die
-What causes high osmotic pressure and can be used to preserve food? - -- salt or sugar
- causes plasmolysis
ex: salted meat, jams, jelly
-What percentage of salt and sugar are solutions that restrict growth? - -solutions that
restrict growth are:
> 5% salt
> 10% sugar
-- How do salts and sugars preserve foods?
- Why are these considered physical rather than chemical methods of microbial control? -
-- they create a hypertonic environment.
- As preservatives they don't directly affect cell structures or metabolism; instead they alter
the osmotic pressure
-What microorganisms can actually grow in salts and sugar preservatives? - --
staphylococcus aureus grow in up to 7% salt and spoils salted foods
- some fungi can grow in jelly and jams
(MOLDS are more capable of growth in high osmotic pressure than bacteria is)
-What are the chemical requirements of microbial growth? - -- carbon
- nitrogen
- sulfur
- phosphorus
- trace elements
- oxygen
-carbon - -- 50% of the dry weight of a bacterial cell
-nitrogen - -- for proteins, DNA, RNA, ATP
- 14% of the dry weight of bacterial cells
sources: decomposing proteins, NH+4, nitrates, nitrogen fixing
