Lab Manual Questions, part 2 | CEM 255 - Organic Chemistry Laboratory |2025/2026
What types of microbes dominated in the air of your microbiology lab? (water fountain) ✔️Fungal
microbes- bacterial doesn't grow on metal and I swabbed the water fountain which consists of metal.
Why is it important to use aseptic techniques when inoculating tubes and media plates? ✔️To prevent
unwanted microorganisms from contaminating sterile inoculating tubes and media plates
How does the procedure for using the microscope differ using high dry power as opposed to low power?
✔️High- 40x magnification- fine focus
Low- 10x magnification- course focus
How does loss of light affect the resolution of a specimen? ✔️Species is not seen as easily
What is the purpose of using immersion oil? ✔️It minimizes the refraction of light
What two things can be adjusted to control the amount of light passing into a specimen? ✔️Iris diaphram
and light intensity adjuster
Describe how to properly care for a microscope after immersion oil has been used? ✔️Remove
immersion oil by using a drop of isopropanol (70%) on lens paper
Why must we stain bacteria before examining them with a microscope? ✔️Because most bacteria lack
natural pigmentation, cells are hard to visualize with out first applying a stain
What component of a stain gives bacteria their color? ✔️The dye; usually acidic or basic
What advantages does knowing the morphology and arrangement of a culture provide? ✔️Helps
diagnose the infectious organism and successfully prescribe a course of antibiotic
Why must you use water when preparing a smear from a solid culture? ✔️To evenly distribute the
culture on the slide to see it better
What is a differential stain? ✔️Method to distinguish between different types of bacteria often based on
color differences- utilizes four different reagents
How can the age of the cell culture affect the results of a gram stain? ✔️Older cultures begin to loose the
ability to retain the primary dye. Aging of the cells tends to make them become Gram Neg. even though
they are not
Which is the most critical step in the gram staining procedure? ✔️Decolorization- If you decolorize too
vigorously all cells will loose the primary stain and will appear Gram Neg.
How can the results of a gram stain on a bacterial culture help a physician decide which antibiotic to use
against that bacterium? ✔️To identify brucella spp. from blood cultures- they rely on Gram stains as a
preliminary test
, Can bacteria cell produce more than one spore? ✔️No
Why is heat required to stain endospores? ✔️Because it fixes the specimen so that it doesn't run off
when you stain it
What is the advantage to the bacteria to produce endospores? ✔️They are resistant to physical agents
(freezing temp., heat, and desiccation) and chemical agents (antibiotics/bacterides)
Can bacteria survive with a capsule ✔️yes
What advantages of a capsule to bacterial cells ✔️The capsule makes it difficult for phagocytes to ingest
the bacteria
After performing the Acid Fast Stain what is the color of cells lacking mycelia acid? ✔️Blue
How does a layer of mycelia acid contribute to these bacteria ability to cause disease? ✔️Increased
resistance to chemical damage/dehydration and prevent effective activity of antibiotics.
When performing a streak plate, why is it necessary to flame the loop between each streak pattern?
✔️So that you drag less and less bacteria with you, spreading out the colonies
How can you confirm that your isolation colony came from a single type of bacteria cell? ✔️They divide
several times forming a visible mass of growth on the surface from one organism
If you were to isolate bacteria from a water sample, which of these isolation techniques would you use
and why? ✔️Spread- able to see different colonies
When performing the spread plate technique, why is it important to burn off all of the alcohol from the
glass rod before attempting to spread the bacteria? ✔️So that you have completely sterilized the loop
What is complex media? ✔️contains nutrient-rich substances such as yeast extract, peptone, or thyptone
and therefore the precise chemical constituents are unknown
What is the primary goal of selective media? ✔️To contain a component which either inhibits the growth
of a certain group of microbes or, alternatively, supports the growth of very few microbes
Besides MacConkey Agar, what other media(s) would be useful for isolating E.Coli from a stool sample?
✔️BAP, SS, and EMB
Explain why a pH indicator can be useful in determining whether or not fermentation of a substrate has
occurred? ✔️- pH can be changed to an unfavorable growth conditions for most microbes
- Fermentation can produce lactic acid which would turn a certain color acid if the bacteria is
fermentation positive
why, particularly in clinical laboratories, are selectively differential mediums employed most often?
✔️Because time is of the essence to diagnose and identify pathogenic microbes and you can test more
than one bacteria at a time, saving time.
What types of microbes dominated in the air of your microbiology lab? (water fountain) ✔️Fungal
microbes- bacterial doesn't grow on metal and I swabbed the water fountain which consists of metal.
Why is it important to use aseptic techniques when inoculating tubes and media plates? ✔️To prevent
unwanted microorganisms from contaminating sterile inoculating tubes and media plates
How does the procedure for using the microscope differ using high dry power as opposed to low power?
✔️High- 40x magnification- fine focus
Low- 10x magnification- course focus
How does loss of light affect the resolution of a specimen? ✔️Species is not seen as easily
What is the purpose of using immersion oil? ✔️It minimizes the refraction of light
What two things can be adjusted to control the amount of light passing into a specimen? ✔️Iris diaphram
and light intensity adjuster
Describe how to properly care for a microscope after immersion oil has been used? ✔️Remove
immersion oil by using a drop of isopropanol (70%) on lens paper
Why must we stain bacteria before examining them with a microscope? ✔️Because most bacteria lack
natural pigmentation, cells are hard to visualize with out first applying a stain
What component of a stain gives bacteria their color? ✔️The dye; usually acidic or basic
What advantages does knowing the morphology and arrangement of a culture provide? ✔️Helps
diagnose the infectious organism and successfully prescribe a course of antibiotic
Why must you use water when preparing a smear from a solid culture? ✔️To evenly distribute the
culture on the slide to see it better
What is a differential stain? ✔️Method to distinguish between different types of bacteria often based on
color differences- utilizes four different reagents
How can the age of the cell culture affect the results of a gram stain? ✔️Older cultures begin to loose the
ability to retain the primary dye. Aging of the cells tends to make them become Gram Neg. even though
they are not
Which is the most critical step in the gram staining procedure? ✔️Decolorization- If you decolorize too
vigorously all cells will loose the primary stain and will appear Gram Neg.
How can the results of a gram stain on a bacterial culture help a physician decide which antibiotic to use
against that bacterium? ✔️To identify brucella spp. from blood cultures- they rely on Gram stains as a
preliminary test
, Can bacteria cell produce more than one spore? ✔️No
Why is heat required to stain endospores? ✔️Because it fixes the specimen so that it doesn't run off
when you stain it
What is the advantage to the bacteria to produce endospores? ✔️They are resistant to physical agents
(freezing temp., heat, and desiccation) and chemical agents (antibiotics/bacterides)
Can bacteria survive with a capsule ✔️yes
What advantages of a capsule to bacterial cells ✔️The capsule makes it difficult for phagocytes to ingest
the bacteria
After performing the Acid Fast Stain what is the color of cells lacking mycelia acid? ✔️Blue
How does a layer of mycelia acid contribute to these bacteria ability to cause disease? ✔️Increased
resistance to chemical damage/dehydration and prevent effective activity of antibiotics.
When performing a streak plate, why is it necessary to flame the loop between each streak pattern?
✔️So that you drag less and less bacteria with you, spreading out the colonies
How can you confirm that your isolation colony came from a single type of bacteria cell? ✔️They divide
several times forming a visible mass of growth on the surface from one organism
If you were to isolate bacteria from a water sample, which of these isolation techniques would you use
and why? ✔️Spread- able to see different colonies
When performing the spread plate technique, why is it important to burn off all of the alcohol from the
glass rod before attempting to spread the bacteria? ✔️So that you have completely sterilized the loop
What is complex media? ✔️contains nutrient-rich substances such as yeast extract, peptone, or thyptone
and therefore the precise chemical constituents are unknown
What is the primary goal of selective media? ✔️To contain a component which either inhibits the growth
of a certain group of microbes or, alternatively, supports the growth of very few microbes
Besides MacConkey Agar, what other media(s) would be useful for isolating E.Coli from a stool sample?
✔️BAP, SS, and EMB
Explain why a pH indicator can be useful in determining whether or not fermentation of a substrate has
occurred? ✔️- pH can be changed to an unfavorable growth conditions for most microbes
- Fermentation can produce lactic acid which would turn a certain color acid if the bacteria is
fermentation positive
why, particularly in clinical laboratories, are selectively differential mediums employed most often?
✔️Because time is of the essence to diagnose and identify pathogenic microbes and you can test more
than one bacteria at a time, saving time.
