MCB 2610 Lab Exam I
why is the spore stain used with bacteria such as Bacillus and Clostridium? - ✔️✔️they
develop an endospore in response to certain environmental conditions such as
depletion of nutrients
procedure for making smears - ✔️✔️1. use a wax pencil to draw a circle on the slide
2. take a loop of distilled water and smear it on the slide
3. take a very small loop of culture
4. smear it onto distilled water
5. allow to dry then heat fix, smear side up 3x
what is the purpose of aseptic technique? - ✔️✔️maintain pure cultures
what is the purpose of a T-streak? - ✔️✔️isolate and maintain single species from
mixed populations
which objective lens should never be used with immersion oil? - ✔️✔️40x
what type of stain is used for simple staining? - ✔️✔️simple crystal violet stain
if the chromophore is a positive ion, the stain is considered a(n)
______________________ stain - ✔️✔️basic
if the chromophore is a negative ion, the stain is considered a(n) __________________
stain - ✔️✔️acidic
what is the quickest and most economical method of bacterial isolation? - ✔️✔️streak
plate method
what is the mordant used in the gram stain and what does it do? - ✔️✔️iodine - it
makes the color permanent
bacteria that retain the Gram stain are classified as Gram _____________ -
✔️✔️positive
what do Gram positive bacteria have that allows them to retain the primary stain? -
✔️✔️thick wall of peptidoglycan
why are Gram negative bacteria easy to decolorize? - ✔️✔️they have an outer
membrane and a thinner layer of peptidoglycan
, do Gram negative stains retain the counterstain (safranin)? - ✔️✔️yes
T/F heat used during staining causes sporulation - ✔️✔️FALSE
Procedure for Gram Stain - ✔️✔️1. prepare a smear of bacteria
2. flood the surface with crystal violet
3. wait one minute and then pour off the excess stain
4. wash gently with water
5. flood the stain with Gram's iodine
6. wait one minute and then wash off the excess with water
7. drip alcohol on the slide and allow to decolorize until no more color is removed
8. wash with water
9. counterstain for 30-40 seconds with safranin
10. wash with water
11. blot dry
microbial growth is defined as
_________________________________________________________ - ✔️✔️an
increase in population size
what is happening during the lag phase? - ✔️✔️cells are adjusting to new conditions
and synthesizing a full complement of enzymes
what is happening during the log phase? - ✔️✔️each cell divides into two new cells -
two-fold exponential growth
what is happening during the death phase? - ✔️✔️cell death rate exceeds remaining
cell division
what causes the death phase? - ✔️✔️accumulation of toxic waste, cell damage from
environment
as bacteria grow in a liquid medium, the broth becomes ___________ turbid, which
_____________ optical density - ✔️✔️more, increases
how can we measure the change in optical density? - ✔️✔️spectrophotometer
the change in optical density is AKA __________________ - ✔️✔️absorbance
what is the generation time? - ✔️✔️the time required for the population to double in
number
why is the spore stain used with bacteria such as Bacillus and Clostridium? - ✔️✔️they
develop an endospore in response to certain environmental conditions such as
depletion of nutrients
procedure for making smears - ✔️✔️1. use a wax pencil to draw a circle on the slide
2. take a loop of distilled water and smear it on the slide
3. take a very small loop of culture
4. smear it onto distilled water
5. allow to dry then heat fix, smear side up 3x
what is the purpose of aseptic technique? - ✔️✔️maintain pure cultures
what is the purpose of a T-streak? - ✔️✔️isolate and maintain single species from
mixed populations
which objective lens should never be used with immersion oil? - ✔️✔️40x
what type of stain is used for simple staining? - ✔️✔️simple crystal violet stain
if the chromophore is a positive ion, the stain is considered a(n)
______________________ stain - ✔️✔️basic
if the chromophore is a negative ion, the stain is considered a(n) __________________
stain - ✔️✔️acidic
what is the quickest and most economical method of bacterial isolation? - ✔️✔️streak
plate method
what is the mordant used in the gram stain and what does it do? - ✔️✔️iodine - it
makes the color permanent
bacteria that retain the Gram stain are classified as Gram _____________ -
✔️✔️positive
what do Gram positive bacteria have that allows them to retain the primary stain? -
✔️✔️thick wall of peptidoglycan
why are Gram negative bacteria easy to decolorize? - ✔️✔️they have an outer
membrane and a thinner layer of peptidoglycan
, do Gram negative stains retain the counterstain (safranin)? - ✔️✔️yes
T/F heat used during staining causes sporulation - ✔️✔️FALSE
Procedure for Gram Stain - ✔️✔️1. prepare a smear of bacteria
2. flood the surface with crystal violet
3. wait one minute and then pour off the excess stain
4. wash gently with water
5. flood the stain with Gram's iodine
6. wait one minute and then wash off the excess with water
7. drip alcohol on the slide and allow to decolorize until no more color is removed
8. wash with water
9. counterstain for 30-40 seconds with safranin
10. wash with water
11. blot dry
microbial growth is defined as
_________________________________________________________ - ✔️✔️an
increase in population size
what is happening during the lag phase? - ✔️✔️cells are adjusting to new conditions
and synthesizing a full complement of enzymes
what is happening during the log phase? - ✔️✔️each cell divides into two new cells -
two-fold exponential growth
what is happening during the death phase? - ✔️✔️cell death rate exceeds remaining
cell division
what causes the death phase? - ✔️✔️accumulation of toxic waste, cell damage from
environment
as bacteria grow in a liquid medium, the broth becomes ___________ turbid, which
_____________ optical density - ✔️✔️more, increases
how can we measure the change in optical density? - ✔️✔️spectrophotometer
the change in optical density is AKA __________________ - ✔️✔️absorbance
what is the generation time? - ✔️✔️the time required for the population to double in
number
