GCSU Bachoon Microbiology Test 2 Exam Questions with Correct Answers Latest Update
2025/2026
Why do we study microbial growth? - Answers 1) to prove what causes disease
2) for antibiotic susceptibility (how to kill)
3) for research
what are the physical aspects of microbial growth? - Answers - temperature
- pH
- osmotic pressure
what are the 3 main groups microbes are classified into based on their optimum temperature? -
Answers 1) psychrophiles
2) mesophiles
3) thermophiles
psychrophiles - Answers - cold loving microbes
- don't cause disease
- (-10 deg. C to 20 deg. C)
what is a psychrotroph? - Answers - organism that is capable of growth between 0 deg. C and
30 deg. C
mesophiles - Answers - 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 - Answers - 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? - Answers - human body temp. (37 degrees celsius)
,what pH range do most bacteria grow best in? - Answers - 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? - Answers - sulfur oxidizers
- H. pylori
____ have more H+ than ______ - Answers acids, bases
what is the osmotic pressure inside bacterial cells in an isotonic solution? - Answers - 0.85%
NaCl
What type of solution inhibits bacterial growth? - Answers - hypertonic solutions (solutes are
higher outside the cell)
- water leaves the cell
what is plasmolysis? - Answers - 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? - Answers - salt or sugar
- causes plasmolysis
ex: salted meat, jams, jelly
What percentage of salt and sugar are solutions that restrict growth? - Answers 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? -
Answers - 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? - Answers -
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? - Answers - carbon
- nitrogen
- sulfur
- phosphorus
- trace elements
- oxygen
carbon - Answers - 50% of the dry weight of a bacterial cell
nitrogen - Answers - for proteins, DNA, RNA, ATP
- 14% of the dry weight of bacterial cells
sources: decomposing proteins, NH+4, nitrates, nitrogen fixing
sulfur - Answers - used to synthezie 4 amino acids
- for synthesizing sulfur-containing amino acids and vitamins such as thiamine and biotin
sources: sulfate ion SO4^2-, hydrogen sulfide H2S
phosphorus - Answers - essential for synthesis of nucleic acids and the phospholipids of cell
membranes
- also found in the energy bonds of ATP
source: phosphate ion PO4^3-
trace elements - Answers only needed in small amounts
2025/2026
Why do we study microbial growth? - Answers 1) to prove what causes disease
2) for antibiotic susceptibility (how to kill)
3) for research
what are the physical aspects of microbial growth? - Answers - temperature
- pH
- osmotic pressure
what are the 3 main groups microbes are classified into based on their optimum temperature? -
Answers 1) psychrophiles
2) mesophiles
3) thermophiles
psychrophiles - Answers - cold loving microbes
- don't cause disease
- (-10 deg. C to 20 deg. C)
what is a psychrotroph? - Answers - organism that is capable of growth between 0 deg. C and
30 deg. C
mesophiles - Answers - 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 - Answers - 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? - Answers - human body temp. (37 degrees celsius)
,what pH range do most bacteria grow best in? - Answers - 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? - Answers - sulfur oxidizers
- H. pylori
____ have more H+ than ______ - Answers acids, bases
what is the osmotic pressure inside bacterial cells in an isotonic solution? - Answers - 0.85%
NaCl
What type of solution inhibits bacterial growth? - Answers - hypertonic solutions (solutes are
higher outside the cell)
- water leaves the cell
what is plasmolysis? - Answers - 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? - Answers - salt or sugar
- causes plasmolysis
ex: salted meat, jams, jelly
What percentage of salt and sugar are solutions that restrict growth? - Answers 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? -
Answers - 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? - Answers -
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? - Answers - carbon
- nitrogen
- sulfur
- phosphorus
- trace elements
- oxygen
carbon - Answers - 50% of the dry weight of a bacterial cell
nitrogen - Answers - for proteins, DNA, RNA, ATP
- 14% of the dry weight of bacterial cells
sources: decomposing proteins, NH+4, nitrates, nitrogen fixing
sulfur - Answers - used to synthezie 4 amino acids
- for synthesizing sulfur-containing amino acids and vitamins such as thiamine and biotin
sources: sulfate ion SO4^2-, hydrogen sulfide H2S
phosphorus - Answers - essential for synthesis of nucleic acids and the phospholipids of cell
membranes
- also found in the energy bonds of ATP
source: phosphate ion PO4^3-
trace elements - Answers only needed in small amounts
