BIOL 3150 Lab Practical 1 Exam and
All Correct Answers.
ways to avoid contamination - Answer - clean work surfaces, cleaning workstation and
washing hands before and after experiments
- proper aseptic technique applied (flaming loop after each bacterial sample, heating lip of each
tube before/after opening tube, etc)
- avoid touching the lip of a tube with a loop which contains a bacterial sample
why agitate a broth culture before obtaining a sample - Answer to ensure that the bacteria,
which was once settled at the bottom of the broth, is mixed throughout the sample
broth culture - Answer provide large numbers of bacteria in a small space and are easily
transported
slant culture - Answer used to store already purified cultures for extended periods of time
- can be sub-cultured to broths or new slants.
agar plate culture - Answer large surface area which allows for the fast drying of bacteria
- good for isolation
why are slants used to store bacterial cultures - Answer they allow for bacteria to grow slow
and live much longer
how to cool an inoculation loop - Answer placing the face of the loop on an uninoculated
area within the plate or slant
- must be done prior to removing any bacterial sample to ensure you do not kill the bacteria you
are sampling
petri dish to broth - Answer - label sterile broth with initials, date, and name of organism
- heat inoculating loop until red hot
- lift and use lid of petri dish as shield from contamination
- touching the inoculating loop to an uninoculated portion of the plate to cool
- gently touch the loop to some growth and collect a small amount
- remove loop and replace lid of petri dish
- remove lid to broth, heat mouth of tube while keeping it at an angle to avoid contamination
, - insert loop into sterile broth and mix gently, tapping the loop's face on the inside of tube
before removing the loop from the tube (to remove film within the loop)
- reheat mouth of tube at angle and replace lid to broth
- flame inoculating loop from base to tip until red hot
why streak for a culture - Answer to produce isolated colonies of an organism and better
view characteristics of such colonies
- samples can be taken from the isolated colonies
streak plate technique - Answer - section the plate into quadrants
- begin with sample of organism on inoculating loop
- streak the loop gently across the surface of the agar in a zig-zag, covering a quadrant of the
plate
- sterilize and cool inoculating loop and begin quadrant 2 by passing over the sample already
streaked in quadrant 1
- repeat same process for next quadrant
- pull 2 lines from the final quadrant (this is where you should see isolation)
why sterilize the loop between streaks? - Answer to ensure there isn't too much bacteria
present
- with each new quadrant, there should be a smaller fraction of bacteria present
smear - Answer sample of bacterial cells spread on a slide for examination under a
microscope or on the surface of a culture medium for examination
- must be flamed before it is stained to ensure that the bacteria sticks to the slide
simple stains show - Answer shape and arrangement
gram-negative vs gram-positive cell - Answer - gram-negative: no teichoic acid, thin layer of
peptidoglycan, lipopolysaccharides, outer membrane
- gram-positive: teichoic acid, thick layer of peptidoglycan, no lipopolysaccharides or outer
membrane
gram staining - Answer - crystal violet: primary stain, stains both gram-positive and gram-
negative cells purple
- iodine: mordant to fix the dye on the gram-negative and gram-positive cells, both cells remain
purple
All Correct Answers.
ways to avoid contamination - Answer - clean work surfaces, cleaning workstation and
washing hands before and after experiments
- proper aseptic technique applied (flaming loop after each bacterial sample, heating lip of each
tube before/after opening tube, etc)
- avoid touching the lip of a tube with a loop which contains a bacterial sample
why agitate a broth culture before obtaining a sample - Answer to ensure that the bacteria,
which was once settled at the bottom of the broth, is mixed throughout the sample
broth culture - Answer provide large numbers of bacteria in a small space and are easily
transported
slant culture - Answer used to store already purified cultures for extended periods of time
- can be sub-cultured to broths or new slants.
agar plate culture - Answer large surface area which allows for the fast drying of bacteria
- good for isolation
why are slants used to store bacterial cultures - Answer they allow for bacteria to grow slow
and live much longer
how to cool an inoculation loop - Answer placing the face of the loop on an uninoculated
area within the plate or slant
- must be done prior to removing any bacterial sample to ensure you do not kill the bacteria you
are sampling
petri dish to broth - Answer - label sterile broth with initials, date, and name of organism
- heat inoculating loop until red hot
- lift and use lid of petri dish as shield from contamination
- touching the inoculating loop to an uninoculated portion of the plate to cool
- gently touch the loop to some growth and collect a small amount
- remove loop and replace lid of petri dish
- remove lid to broth, heat mouth of tube while keeping it at an angle to avoid contamination
, - insert loop into sterile broth and mix gently, tapping the loop's face on the inside of tube
before removing the loop from the tube (to remove film within the loop)
- reheat mouth of tube at angle and replace lid to broth
- flame inoculating loop from base to tip until red hot
why streak for a culture - Answer to produce isolated colonies of an organism and better
view characteristics of such colonies
- samples can be taken from the isolated colonies
streak plate technique - Answer - section the plate into quadrants
- begin with sample of organism on inoculating loop
- streak the loop gently across the surface of the agar in a zig-zag, covering a quadrant of the
plate
- sterilize and cool inoculating loop and begin quadrant 2 by passing over the sample already
streaked in quadrant 1
- repeat same process for next quadrant
- pull 2 lines from the final quadrant (this is where you should see isolation)
why sterilize the loop between streaks? - Answer to ensure there isn't too much bacteria
present
- with each new quadrant, there should be a smaller fraction of bacteria present
smear - Answer sample of bacterial cells spread on a slide for examination under a
microscope or on the surface of a culture medium for examination
- must be flamed before it is stained to ensure that the bacteria sticks to the slide
simple stains show - Answer shape and arrangement
gram-negative vs gram-positive cell - Answer - gram-negative: no teichoic acid, thin layer of
peptidoglycan, lipopolysaccharides, outer membrane
- gram-positive: teichoic acid, thick layer of peptidoglycan, no lipopolysaccharides or outer
membrane
gram staining - Answer - crystal violet: primary stain, stains both gram-positive and gram-
negative cells purple
- iodine: mordant to fix the dye on the gram-negative and gram-positive cells, both cells remain
purple
