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MCB 2610 exam 2 Question and answers verified to pass 2024/2025
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MCB 2610 exam 2 Question and answers verified to pass 2024/2025 MCB 2610 exam 2 Listeria monocytogenes - correct answer Gram positive rods, no spores or capsules, facultative anaerobe, only has flagella when growing below 30C it has a wide range of temperatures that it can grow in ( 1-45C)...

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  • October 17, 2024
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MCB 2610 exam 2
Listeria monocytogenes - correct answer ✔Gram positive rods, no spores or
capsules, facultative anaerobe, only has flagella when growing below 30C


it has a wide range of temperatures that it can grow in ( 1-45C)


It is a virulent food borne pathogen and intracellular parasite, that is found in
raw milk, cheeses, veggies, processed meat.


18 people died in Nova Scotia due to coleslaw contamination with sheep
manure. No current listeria recalls, but there was a recent outbreak in south
africa.


cell growth - correct answer ✔The population of cells is growing, which can
result in an increase in cell number and/or size.


the growth curve - correct answer ✔Used for batch cultures,


logarithm: cell number versus time,


has 4 distinct phases: lag, exponential, stationary, senescence, and death


batch culture - correct answer ✔culture incubated in a closed vessel with a
single batch of medium

,Lag phase - correct answer ✔Cell is synthesizing new components in order
to adapt to the new environment so that it can use the available nutrients to
grow.


This phase varies in length, and there is no change in the actual number of
cells - although they may change in size.


exponential phase (log phase) - correct answer ✔rate of growth and division
is constant and maximal.


population is most uniform in terms of chemical and physical properties during
this phase.


slope of the line will tell us how fast the organism is dividing, if the line is very
steep then it means that the organism is dividing very fast


stationary phase - correct answer ✔population growth eventually ceases,
and the total number of viable cells remains constant. This means that there is
either no more reproduction or it is being matched by the rate of death.


in this phase, all cells are doing something different: some may be dividing,
dying, or just sitting there


possible reasons for stationary phase - correct answer ✔nutrient limitation,
limited oxygen availability,
toxic waste accumulation,
critical population density reached

,balanced growth - correct answer ✔during log phase, the number of bacterial
cells doubles at a constant, exponential rate for balanced growth


unbalanced growth - correct answer ✔cells are forming at different rates
relative to each other.


This can be due to a change in nutrient levels or environmental conditions.


It shows that microbes grow under precise, coordinated control and that
organisms respond quickly to changes in environmental conditions.


Senescence and Death Phase - correct answer ✔The amount of viable cells
declines.


It can be due to cells being viable but not culturable. This means the cells are
alive but dormant. So they are capable of growth but only when conditions are
right. Or it can be due to programmed cell death, where a portion of the
population is genetically programmed to die.


stationary phase and starvation response - correct answer ✔entry into
stationary phase due to starvation and other stressful conditions activates
survival strategy.
-morphological changes (e.g., endospore formation)
-Decrease in size, protoplast shrinkage, and nucleoid condensation
-RpoS protein assists RNA polymerase in transcribing genes for starvation
proteins


starvation responses - correct answer ✔production of starvation proteins -
makes cells harder to kill
-increase cross-linking in cell wall

, -Dps protein protects DNA
-chaperone proteins prevent protein damage


cells are called persister cells
-long-term survival
-increased virulence


why do shift up and shift down experiments cause cells to go into unbalanced
growth? - correct answer ✔They have to readjust their metabolic pathways
to match those new set of conditions, so that period of unbalanced growth can
be long/short depending on how different they are and how much adjusting
the cells have to do


cell yield - correct answer ✔the highest amount of cells that are produced by
this particular set of conditions. It is usually the top at the stationary phase on
the graph.


prolonged decline in growth - correct answer ✔bacterial population
continually evolves,
process marked by successive waves of genetically distinct variants,
natural selection occurs


measuring microbial population growth - correct answer ✔Use the microbial
growth curve, which can determine the generation time, growth rate, and
growth yield


generation (doubling) time - correct answer ✔the time to double the
population in the exponential phase.

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