Mimg 100L: Midterm 2 Questions and
All Actual Answers 2026 Updated.
Describe the formation of biofilms. - Answer formation:
1. planktonic cells (reversibly) attach to substrate
2. first colonizers become irreversibly attached (sessile)
3. cells grow and divide
4. EPS forms as well as water channels
5. dispersal: cells on the periphery slough off and become planktonic, finding their own places
to colonize
Describe the characteristics of biofilms. - Answer -clusters of microorganisms in a matrix
-embedded w water channels
-extracellular polymeric substances (EPS) is secreted by the organisms in the biofilm
-hydrated gel prevents desiccation
-protects against predation from other microbes
Identify health risks associated with biofilms and describe how the characteristics of biofilms
may contribute to pathogenicity or antibiotic resistance. - Answer -biofilms can cause
infections and chronic infections
-pathogens in biofilms have higher antibiotic resistance: cells deeply embedded have a slower
metabolic rate, and are less susceptible antibiotics targeting metabolism
-EPS slows the diffusion of antibiotics
-phenotypic changes such as increased efflux pump production help extrude antibiotics
-EPS environment is ideal for gene transfer & sharing of antibiotic resistant DNA
Describe quorum sensing and its role in cell-to-cell communication and coordination of cellular
activities - Answer quorum sensing: the mechanism by which organisms in a biofilm
coordinate their activities in response to environmental stimuli
-helps microbes detect their cell density through the release of autoinducers, which can trigger
a cascade of signals that activate genes that are useful when populations are dense enough
Give an example of how quorum sensing is advantageous to bacterial cells in a given
environment. - Answer -when there is a large enough population of pathogens they can
release virulence factors to overwhelm immune defenses
-(they know there's enough of them to take over !!)
, Define fastidious organisms. - Answer organisms that can't make certain nutrients and
require them to be added to the medium
Define enrichment media. - Answer media that contains growth factors, vitamins, and other
nutrients to promote the growth of specific organisms
Compare and contrast selective and differential media. - Answer selective media: inhibits the
growth of certain organisms and supports the growth of others by supplying nutrients and
adding inhibiting factors; used to isolate microorganisms
differential media: takes advantage of biochemical properties of target organisms, often leading
to a visible change when growth of target organisms are present.
both are used to compare and contrast microorganisms
Compare and contrast defined and undefined/complex media, and explain why a microbiologist
might use one over the other in a given situation. - Answer defined media: have a completely
known chemical composition
undefined/complex media: precise chemical composition is not known due to the addition of
extracts/digests from meat, plants, yeasts
depending on price, as well as the fact that some bacteria have only been able to grow on
complex media influence the decision to use one or the other
Describe two scenarios in which microbiologists would use selective and/or differential media. -
Answer use of selective media: want to inhibit the growth of specific organisms (ie, gram
positive)
use of differential media: want to distinguish between two different bacteria (ie, beta vs gamma
hemolytic bacteria)
Describe examples of what makes a medium selective. - Answer - salt content
- pH
- antibiotics
- dyes, salts, other chemical additives
All Actual Answers 2026 Updated.
Describe the formation of biofilms. - Answer formation:
1. planktonic cells (reversibly) attach to substrate
2. first colonizers become irreversibly attached (sessile)
3. cells grow and divide
4. EPS forms as well as water channels
5. dispersal: cells on the periphery slough off and become planktonic, finding their own places
to colonize
Describe the characteristics of biofilms. - Answer -clusters of microorganisms in a matrix
-embedded w water channels
-extracellular polymeric substances (EPS) is secreted by the organisms in the biofilm
-hydrated gel prevents desiccation
-protects against predation from other microbes
Identify health risks associated with biofilms and describe how the characteristics of biofilms
may contribute to pathogenicity or antibiotic resistance. - Answer -biofilms can cause
infections and chronic infections
-pathogens in biofilms have higher antibiotic resistance: cells deeply embedded have a slower
metabolic rate, and are less susceptible antibiotics targeting metabolism
-EPS slows the diffusion of antibiotics
-phenotypic changes such as increased efflux pump production help extrude antibiotics
-EPS environment is ideal for gene transfer & sharing of antibiotic resistant DNA
Describe quorum sensing and its role in cell-to-cell communication and coordination of cellular
activities - Answer quorum sensing: the mechanism by which organisms in a biofilm
coordinate their activities in response to environmental stimuli
-helps microbes detect their cell density through the release of autoinducers, which can trigger
a cascade of signals that activate genes that are useful when populations are dense enough
Give an example of how quorum sensing is advantageous to bacterial cells in a given
environment. - Answer -when there is a large enough population of pathogens they can
release virulence factors to overwhelm immune defenses
-(they know there's enough of them to take over !!)
, Define fastidious organisms. - Answer organisms that can't make certain nutrients and
require them to be added to the medium
Define enrichment media. - Answer media that contains growth factors, vitamins, and other
nutrients to promote the growth of specific organisms
Compare and contrast selective and differential media. - Answer selective media: inhibits the
growth of certain organisms and supports the growth of others by supplying nutrients and
adding inhibiting factors; used to isolate microorganisms
differential media: takes advantage of biochemical properties of target organisms, often leading
to a visible change when growth of target organisms are present.
both are used to compare and contrast microorganisms
Compare and contrast defined and undefined/complex media, and explain why a microbiologist
might use one over the other in a given situation. - Answer defined media: have a completely
known chemical composition
undefined/complex media: precise chemical composition is not known due to the addition of
extracts/digests from meat, plants, yeasts
depending on price, as well as the fact that some bacteria have only been able to grow on
complex media influence the decision to use one or the other
Describe two scenarios in which microbiologists would use selective and/or differential media. -
Answer use of selective media: want to inhibit the growth of specific organisms (ie, gram
positive)
use of differential media: want to distinguish between two different bacteria (ie, beta vs gamma
hemolytic bacteria)
Describe examples of what makes a medium selective. - Answer - salt content
- pH
- antibiotics
- dyes, salts, other chemical additives
