Food Microbiology Exam queries and
answers graded A+
Describe a detrimental and a beneficial effect of biofilms. - ANS✅✅-The structure of biolfilms
shields the microbes growing within it, making them very resistant to antibiotics and disinfectants.
-Many bioremediation efforts (use bacteria to degrade harmful chemicals) are enhanced by biofilms.
Define a pure culture - ANS✅✅A population of organisms descended from a single cell and
therefore separated from all other species
Explain what occurs during each of the five phases of growth. - ANS✅✅Lag phase- begin
synthesizing enzyme required for growth
Exponential (log) phase- cells divide at a constant rate. Productions of primary metabolites
Stationary phase- numbers remain constant. Some die. Others grow
Death Phase- total number of viable cells decreases. Cells die at a constant rate.
Phase of prolonged decline- some cells survive. They adapted to tolerate worsened conditions
Explain how the environment of a colony differs from that of cells growing in a liquid broth. -
ANS✅✅Liquid broth- population of cells are exposed to uniform conditions.
Colony- exposed to different conditions
List the five categories of optimum temperature, and describe a corresponding environment in
which a representative might thrive. - ANS✅✅Psychrophile- arctic and Antarctic -5 - 15
Psychrotroph- food spoilage 20 - 30
Mesophile- 25 - 45. Pathogens 35 - 40
Thermophiles- hot springs 45 - 70
Hyperthermophiles- hydrothermal vents 70 - 110
Why would botulism be a concern with canned foods? - ANS✅✅Obligate anaerobes can grow in
improperly canned foods. The most important obligate anaerobe is Clostridium botulinum which
causes the disease botulism which is deadly.
, Explain why O2-containing atmospheres kill some microbes. - ANS✅✅Reactive oxygen species are
damaging to cells. Bacteria that cannot survive in aerobic atmospheres lack enzymes that detoxify
these compounds.
Explain why photoautotrophs are primary producers. - ANS✅✅They receive energy from sunlight
and carbon from CO2. Support other forms of life
Distinguish between a selective medium and a differential medium. - ANS✅✅Selective media-
inhibits growth of certain species
Differential media- contains substance that microbes change in identifiable way
If the number of microorganisms in lake water were determined using both a direct microscopic
count and a plate count, which method would most likely give a higher number? Why? -
ANS✅✅Direct microscopic count because it calculates total microbe count. Usually cannot
distinguish between dead and live ones.
High-performance boat manufacturers know that microbes can collect on a boat, ruining its
hydrodynamic properties. A boat-manufacturing facility recently hired you to help with this problem
because of your microbiology background. What strategies other than routine cleaning would you
pursue to come up with a long-term remedy for the problem? - ANS✅✅I would find what
microbes we are dealing with. Then with that information I could see which microbes would be the
most harmful. Also maybe wax it so they couldn't stick to the boat so easily. Or have the boat sit
higher in the water so less surface can touch the water.
Why would bacteria in a biofilm be more resistant to harmful chemicals? - ANS✅✅Biofilm
structure shields microbes growing within
What properties of agar make it ideal for use in culture media? - ANS✅✅It is used to solidify. Not
destroyed by high temperatures. Few microbes can degrade it
To identify the causative agent of a given illness, a pure culture is often needed. How is a streak plate
used to obtain a pure culture? - ANS✅✅Streak-plate method yields pure cultures. Isolates colonies
because no overlap occurs using streak.
Explain the difference between the lag and exponential phases. - ANS✅✅Lag- cells do no increase
Exponential- cells divide at a constant rate
answers graded A+
Describe a detrimental and a beneficial effect of biofilms. - ANS✅✅-The structure of biolfilms
shields the microbes growing within it, making them very resistant to antibiotics and disinfectants.
-Many bioremediation efforts (use bacteria to degrade harmful chemicals) are enhanced by biofilms.
Define a pure culture - ANS✅✅A population of organisms descended from a single cell and
therefore separated from all other species
Explain what occurs during each of the five phases of growth. - ANS✅✅Lag phase- begin
synthesizing enzyme required for growth
Exponential (log) phase- cells divide at a constant rate. Productions of primary metabolites
Stationary phase- numbers remain constant. Some die. Others grow
Death Phase- total number of viable cells decreases. Cells die at a constant rate.
Phase of prolonged decline- some cells survive. They adapted to tolerate worsened conditions
Explain how the environment of a colony differs from that of cells growing in a liquid broth. -
ANS✅✅Liquid broth- population of cells are exposed to uniform conditions.
Colony- exposed to different conditions
List the five categories of optimum temperature, and describe a corresponding environment in
which a representative might thrive. - ANS✅✅Psychrophile- arctic and Antarctic -5 - 15
Psychrotroph- food spoilage 20 - 30
Mesophile- 25 - 45. Pathogens 35 - 40
Thermophiles- hot springs 45 - 70
Hyperthermophiles- hydrothermal vents 70 - 110
Why would botulism be a concern with canned foods? - ANS✅✅Obligate anaerobes can grow in
improperly canned foods. The most important obligate anaerobe is Clostridium botulinum which
causes the disease botulism which is deadly.
, Explain why O2-containing atmospheres kill some microbes. - ANS✅✅Reactive oxygen species are
damaging to cells. Bacteria that cannot survive in aerobic atmospheres lack enzymes that detoxify
these compounds.
Explain why photoautotrophs are primary producers. - ANS✅✅They receive energy from sunlight
and carbon from CO2. Support other forms of life
Distinguish between a selective medium and a differential medium. - ANS✅✅Selective media-
inhibits growth of certain species
Differential media- contains substance that microbes change in identifiable way
If the number of microorganisms in lake water were determined using both a direct microscopic
count and a plate count, which method would most likely give a higher number? Why? -
ANS✅✅Direct microscopic count because it calculates total microbe count. Usually cannot
distinguish between dead and live ones.
High-performance boat manufacturers know that microbes can collect on a boat, ruining its
hydrodynamic properties. A boat-manufacturing facility recently hired you to help with this problem
because of your microbiology background. What strategies other than routine cleaning would you
pursue to come up with a long-term remedy for the problem? - ANS✅✅I would find what
microbes we are dealing with. Then with that information I could see which microbes would be the
most harmful. Also maybe wax it so they couldn't stick to the boat so easily. Or have the boat sit
higher in the water so less surface can touch the water.
Why would bacteria in a biofilm be more resistant to harmful chemicals? - ANS✅✅Biofilm
structure shields microbes growing within
What properties of agar make it ideal for use in culture media? - ANS✅✅It is used to solidify. Not
destroyed by high temperatures. Few microbes can degrade it
To identify the causative agent of a given illness, a pure culture is often needed. How is a streak plate
used to obtain a pure culture? - ANS✅✅Streak-plate method yields pure cultures. Isolates colonies
because no overlap occurs using streak.
Explain the difference between the lag and exponential phases. - ANS✅✅Lag- cells do no increase
Exponential- cells divide at a constant rate
