Microbiology 295 Connect Lab Questions
Please select those nutritional requirements that are essential for growth, reproduction, and maintenance of a bacterial cell.
- carbon - hydrogen - nitrogen - water - vitamins and minerals
Why is the plate labeled on the bottom?
Because even if the lid is interchanged with the wrong lid, the label will still be correct
If turbidity is an indirect measure of growth, why can't you talk about turbidity when examining microbial growth on a plate?
Because growth on plates is evidenced by distinct mounds of cells on the surface
Identify the reason why the focal distance is important when the oil-immersion objective is used to observe a specimen.
Because if the focal distance is changed while using the oil-immersion objective, the objective may touch and scratch/break the glass slide.
Why do some microbiologists prefer to open and close quickly the culture tube instead of flaming its mouth prior and after transferring bacteria to or from it?
Because it eliminates the necessity of an open flame
Why is it important to moisten the sterile swab with sterile medium?
Because it provides a medium that will collect sample from a surface in a more effective way
Why do you need to discard the swab in a biohazard bag?
Because the swab is now contaminated with microbes from the environment and should not be discarded with normal trash
When is the inoculating loop sterilized during the streak plate procedure?
Before you take inoculum from culture tube and between each transfer
What is the best way to dissolve agar in a medium as you are preparing it?
Bring the medium to a boil while stirring.
When transferring an inoculum from one liquid culture to another, it is essential to use a Bunsen burner to flame the mouth of the tubes before and after opening them.
False
The genus _______ is an extremely important member of the apicomplexan group because several of its species are the causative agents of malaria.
Plasmodium
After diluting a sample of bacteria, what methods can be used to isolate colonies for counting?
Pour and spread plating
What medium is commonly used when culturing molds on agar plates?
Sabouraud's agar
Why must the entire calibration procedure be performed for each objective lens of a microscope?
The size of the field changes with increased magnification.
If after swabbing a visibly dusty surface and transferring the contents of the swab onto a plated medium, no growth is observed after incubation at 37 degrees Celsius, the most likely explanation is
The surface is not sterile but the culture conditions are not adequate to grow the microbes that may be found on it.
Which of the following CANNOT serve as a nitrogen source?
agar
Which of the following increases as the number of bacteria in a sample increase?
Absorbance
Identify the characteristic that is most related to microbial growth in a liquid culture medium.
Turbidity
Which of the following may indicate that you have correctly subcultured an organism from a plate to a slant? (Check all that apply.)
- After Gram staining a smear prepared from the slant, all of the cells have similar color and morphology under the microscope. - The slant shows only one color of growth.
When completing a quadrant streak, when do you flame the loop? (Check all that apply.)
- Before you pick up a loopful of organisms from the original culture - Before you streak quadrant two and three - Before you return the loop to the receptacle
What two items can be used to check the alignment of the annulus and phase ring in phase-contrast microscopy?
- Centering telescope - Optovar (aperture viewing unit)
Which of the following are phenotypic characteristics used to identify fungi? (Check all that apply.)
- Colony surface color - Underside pigmentation - Hyphal structure - Type of spore production
A mass of intermeshed hyphae is a _______.
mycelium
Choose the statements that are true regarding the principles of fluorescence.
- Electrons become excited when a molecule absorbs energy. - Light is emitted when electrons return to their ground state. - The ground state of an electron is a low-energy state.
Which of the following are types of algae? (Check all that apply.)
- Euglenoids - Dinoflagellates - Diatoms
Select the correct uses of the Bunsen burner when aseptically transferring organisms from one medium to another.
- Flame the mouth of a culture tube before inserting the inoculating loop. - Flame the mouth of an inoculated tube before replacing the cap. - Heat the inoculating loop prior to removal of organisms from the culture tube.
What are the distinguishing characteristics of fungi? (Check all that apply.)
- Heterotrophic - Cell walls composed of chitin - Propagate by spores
Brightfield microscopy requires specimens to be stained before observation, whereas phase-contrast microscopy does not require staining. Why is this advantageous?
- It allows for the observation of living cells. - Staining can lead to undesirable artifacts on a specimen slide.
What two adjustments can be made to the condenser?
- It can be moved up and down under the stage. - Its diaphragm can be opened/closed to regulate amount of light hitting the slide.
Which are advantages of the streak-plate method when compared to the pour-plate method?
- It requires less materials. - It is a very quick process.
How is fluorescence microscopy different from brightfield microscopy? (Check all that apply.)
- It uses UV light rays. - It uses a darkfield condenser. - It uses special filters to limit light reaching observer.
You are observing a new slide that you made using microbiological staining techniques. When you look through the eyepieces, all you see is complete darkness. Taking into account potential sources of error when operating a microscope, what should you check before calling your instructor to ask why nothing is visible? Check all that apply.
- Make sure that the light source is turned on and the microscope is plugged in. - Adjust the intensity of the light source. - Make sure that the diaphragm is open. - Check to see that an objective lens is fully set into place over the slide.
Although genetic analysis is used to determine relatedness between fungal species, traditional classification schemes rely primarily on which two of the following?
- Morphological characteristics - Reproductive mechanisms
Maximum resolution can be achieved when using the oil immersion lens by implementing what procedures?
- Move the condenser to highest position - Increase the light intensity from the source - Open the diaphragm fully
Which of the following are characteristics of bacteria? Check all that apply.
- Possess a cell wall composed of peptidoglycan - Use ribosomes to manufacture proteins - Species may use aerobic or anaerobic metabolism
What should be done before returning a microscope to its storage location? Check all that apply.
- Rotate the nosepiece to put the low-power lens into position. - Wrap the cord so it does not hang freely. - Remove oil from all lenses and the stage. - Adjust the mechanical stage to a low and centered position.
Please select all of the statements which are TRUE regarding isolated colonies.
- The colony results from a single cell or a cluster of cells multiplying into a visible mass. - The cells within the colony are all the same species. - Isolated colonies form on solid nutrient media.
What are two advantages of using a darkfield condenser for fluorescence microscopy?
- The majority of harmful UV light rays do not reach the observer's eyes. - The contrast is increased, making the specimen more visible.
Why is it necessary to use oil when viewing a specimen with the oil immersion lens? Check all that apply.
- The oil reduces the diffraction of light. - It improves the resolving power of the microscope.
What is done to limit the formation of condensation on the lid of an agar plate, therefore preventing the dispersal of inoculated organisms? (Check all that apply.)
- The plates are incubated lid down. - Agar is cooled to 50 degrees Celsius before adding to an empty plate.
After inoculating and incubating an agar slant from a culture of E. coli, which of the following would indicate an unsuccessful aseptic transfer? (Check all that apply.)
- There is no growth on the slant. - There are red, yellow, and white colonies on the slant. - There is fungal growth in the original E. coli culture tube.
heck each of the components that are found in ALL bacteriological culture media.
- energy source - water - carbon source - vitamins and minerals - nitrogen source
The mercury vapor arc lamp used in fluorescent microscopes can be dangerous because ________. (Check all that apply.)
- it can explode due to pressurized gas - it can cause serious eye damage
If the oil immersion lens is used in fluorescence microscopy, ________. (Check all that apply.)
- oil must be placed between slide and objective lens - oil must be placed between condenser and slide
The three major means of locomotion in free-living protozoa are
- pseudopodia. - cilia. - flagella.
Indicate the three preferred methods for long-term preservation of bacterial cultures.
-Freezing at -196oC in glycerol -Lyophilization -Storing cultures under a layer of sterile mineral oil
Indicate the three most important considerations in maintaining a stock culture.
-Maintaining the purity of the culture -Maximizing survival of the cells -Preventing physiological or genetic changes to the culture
Which methods of counting or estimating numbers of bacteria will likely include nonliving as well as living cells?
-Microscopic counts -Turbidimetric methods
Indicate the media in the following list that are appropriate for use in preparing fungal slide cultures.
-Sabouraud's agar -Emmons' agar -Cornmeal agar -Czapek solution agar
Indicate which of the following are important considerations when using the spectrophotometer to determine absorbance of bacterial cultures.
-Use a cuvette of sterile nutrient broth to zero the absorbance. -Be sure to properly align the cuvette each time in cuvette holder. -Handle only the top of the cuvette and carefully wipe the cuvette with Kimwipes to remove any smudges. -Shut the cuvette holder cover whenever reading absorbance or transmittance.
If 10 divisions of the ocular micrometer line up with two divisions of the stage micrometer, what is the correct mathematical calculation used in calibration?
0.02 mm/10
A total of 145 colonies were counted on the plate that received 1.0 mL of the 1:10,000 dilution of a specimen. What is the bacterial count for the original specimen?
1,450,000 colonies/mL
Each tube in the series represents a dilution factor of ______ compared with the tube before.
10
The total magnification achieved when using a 100X oil immersion lens with 10X binocular eyepieces is ________.
1000x
Which objective lens is most commonly used to observe bacteria?
1000x
A total of 75 colonies were counted on the plate that received 1 mL of a diluted specimen. After calculating, it is determined that the total bacterial count in the original specimen was 75,000,000 colonies per mL. What was the dilution factor for the plated sample?
1:1,000,000
Upon checking the pH of the medium you are preparing, you realize that the pH is 8.0 and ideally should be 7.0. Which of the following steps should be used to adjust the pH?
Add several drops of HCl and recheck the pH.
If the calibrated value for the ocular micrometer at this magnification is 2 microns, what is the total length of the yeast cell and bud on the right?
30 microns
When performing a standard plate count, what is the range for statistically valid colony counts?
30-300
When performing a Standard Plate Count, plates that contain __________________ colonies are selected for counting with the Quebec Colony Counter.
30-300 colonies
If you are using the 40x objective to observe your specimen and the ocular of your microscope is labeled "10x", what is the total magnification of your specimen?
400
If you count 50 colonies on the 1:1000 dilution plate, what would be the total calculated number of bacterial cells in 1.0 ml of the original culture?
50,000
Identify the best definition of aseptic technique.
A basic procedure used to transfer bacteria, prevent contamination of the working environment and ensure purity of bacterial cultures
What is the difference between a broth and a slant?
A broth is liquid, whereas a slant is solid.
What is a pure culture?
A culture with one organism
What is a bacterial colony?
A mound of bacteria on a solid medium that originated with a single cell
A disinfectant is used on your work surface
All of the choices are correct.
Identify the definition of a pathogen.
An organism that can cause an infection even in healthy individuals
Recall the difference between antisepsis and disinfection.
Antisepsis applies to living tissues; disinfection applies to inanimate surfaces.
What is used to count colonies from spread or pour plates?
Colony counter
Identify the correct definition of sterile.
Completely free of all lifeforms, including spores and viruses
Which of the following lenses does NOT affect the magnification of the specimen?
Condenser lens
_______ are nonmotile asexual fungal spores that form on specialized hyphae and may include phialospores, blastospores, chlamydospores, or arthrospores.
Conidia
What were previously known as "blue-green algae?"
Cyanobacteria
What type of microscope is particularly useful for diagnosing syphilis by observing living spirochaetes in a patient specimen?
Darkfield microscope
What are the sterile water tubes used for in this experiment?
Dilution of an original bacterial culture
What is being done to the inoculum as you streak from one quadrant to the next?
Dilution of sample
_______ fungi are those species that occur as either molds or yeast, depending on environmental conditions such as temperature and nutrient availability.
Dimorphic
_______ are marine algae that are responsible for "red tides" when great numbers of cells form blooms in the water.
Dinoflagellates
What is the correct way to sterilize a glass spreader rod?
Dip in alcohol and then burn off in an open flame.
Predict the effect of endospores on preservation of a bacterial culture.
Endospores will promote and enable culture preservation.
Please choose the answer that best fills in the blanks of this sentence in the correct order. Algae and protozoa are in Domain ______ and cyanobacteria are in Domain _____.
Eukarya; Bacteria
A colony of microbes contains different species of microorganisms.
False
A light microscope can be used to observe viruses.
False
It is a health concern when bacteria grow on agar that has been exposed to the skin.
False
The application of a disinfectant to the lab bench ensures that the work area is sterile before the laboratory exercise is started.
False
The coarse focus knob can be used to adjust the focus when using any of the objective lenses.
False
The distance between the lines of an ocular micrometer is exactly 0.01 mm.
False
The number of living bacteria in a liquid sample can be easily enumerated by direct methods.
False
The pour plate and spread plate methods will be used to count both living and dead bacteria from the original sample to get accurate counts of the original population.
False
The resolving power of the human eye is higher than that of the light microscope whereas the magnification of the light microscope is higher than that of the human eye.
False
The slide should be placed on the stage with the material to be viewed facing the condenser lens.
False
The total magnification capability of a light microscope is only limited by the magnifying power of the lens system.
False
Which of the following does not describe cyanobacteria?
Have bacteriochlorophyll
What is the advantage of using the streak plate method over the pour plate method?
It is quick and takes less materials.
Why is agar a useful solidifying agent in microbiology?
It is solid at room temperature, but liquid at temperatures that are tolerated by bacteria.
What advantage does the pour-plate method have over the streak-plate method?
It requires less skill.
You measure the absorbance of a bacterial culture two hours after inoculating a sterile medium, and then you continue to measure the absorbance every two hours for a total of 3 days. If you plotted the absorbance over time, what would the graph look like?
It would increase and then level off.
Which of the following stains is used for staining slide cultures?
Lactophenol cotton blue
Please choose the answer that best completes the blanks of this sentence in the correct order. ________ are fungi that contain microscopic intertwining filaments called hyphae, whereas _______ are fungi that lack hyphae.
Molds; yeast
Which method is often used to test for the presence of coliforms in drinking water?
Most Probable Number (MPN)
Which of the following would be best observed in a bacterial cell by using phase-contrast microscopy?
Motility of cells
Where should you label an agar plate before inoculating with bacteria?
On the bottom containing the agar
What does parfocal mean?
Once the image is focused in low power, it remains focused when switching to high power.
How do you position your hands when carrying the microscope to and from the laboratory bench?
One hand holding the arm, the other underneath, holding the base
Which of the following plates would be a good choice for counting?
One with approximately 100 colonies
When is a loopful of culture taken from the broth when performing a streak plate procedure?
Only before quadrant one
If a darkfield condenser causes all light rays to bypass the objective, where does the light come from that makes an object visible in the dark field?
Periphery
What might be a disadvantage of using these plating methods to enumerate bacteria?
Some bacteria may not grow on the type of medium used.
What is different about the colony growth on pour plates when compared with spread plates?
Some colonies will grow subsurface.
Which of the following is not a type of sexual fungal spore?
Sporangiospore
Which method used to determine numbers of bacteria in a sample involves the preparation of a series of dilutions of the sample in sterile water, adding measured volumes of each dilution to melted nutrient agar plates, making pour plates, incubating, counting colonies, and multiplying colony counts by dilution factors to determine the number of bacteria in the sample?
Standard Plate Count (SPC)
Which method is usually used to sterilize most agar media?
Steam autoclave
What two methods are commonly used for separating a mixed culture of bacteria?
Streak plating; pour plating
Choose the most appropriate method to freeze a bacterial culture for preservation.
Suspend bacteria in a small vial of glycerol and place in a -196oC freezer.
What is the difference between the plates used in pour plating when compared with spread plating?
The bacteria are transferred into an empty Petri dish instead of onto the surface of existing agar.
Please choose the development that led to the new three-domain system of classification.
The discovery of rRNA and its use in analyzing genetic relatedness
Suppose you forget to add oil immersion when using the oil-immersion objective. Predict what would you likely observe.
The image would look blurry and would not get into focus when the fine focus knob is turned.
Starting with the low-power lens when viewing a slide offers what advantage?
The larger field of view enables you to easily locate the specimen.
What information can be obtained from the number of colonies obtained on a plated medium?
The number of colonies indicates the number of viable cells when the sample was deposited on the medium.
How is air contamination prevented when an inoculating loop is used to introduce or remove organisms from an agar plate?
The plate lid is kept closed or lifted only slightly when inoculating.
Which other part of the instrument allows control of how much light enters the specimen?
The rheostat or voltage regulator
In which quadrant will you expect to see isolated colonies?
Third or fourth
What is the purpose of the condenser?
To allow the maximum amount of light to enter the specimen
Why should you open the plate so that it looks like a clam shell?
To prevent contamination of the culture with environmental microbes
What is the purpose of the immersion oil?
To prevent the loss of light rays
A cardioid condenser is preferred when using higher-power objective lenses in darkfield microscopy.
True
Liquid media are more suitable for producing large amounts of cells, whereas plated (solid) media are more suitable for isolation of microorganisms.
True
Most bacteria are smaller than most eukaryotic parasites.
True
Once focus is achieved at one magnification, a higher-power objective lens can be rotated into position without fear of striking the slide.
True
Only lint-free, optically safe tissue should be used to wipe off microscope lenses.
True
Which of the following correctly describes the position of your hands while carrying a microscope to and from the laboratory bench?
Use both hands with one on the base and one around the arm
Why is the 1:100 dilution used for plating the 1:1000 plate?
You are only transferring 0.1 ml to the plate so you must multiply by a factor of ten.
What would happen if you forgot to sterilize your loop in between each quadrant streak?
You would likely not dilute the inoculum enough to obtain separated colonies.
What would happen if you touched quadrant one while streaking quadrant four?
You would spread a lot of bacteria from quadrant one into quadrant four and probably not see isolated colonies.
Which of the following is not a type of asexual fungal spore?
Zygospore
The ______ the working distance of an objective lens, the ______ the magnification.
greater; lower
Specific proteins on or in a cell can be tagged with fluorochromes that have been chemically linked to
antibodies.
The goal of ______ technique is to minimize the contamination of both original and newly inoculated cultures as well as protect the laboratory handler from contamination.
aseptic
The resolving power of a microscope is a function of
both numerical aperture and wavelength of light.
Please choose the answer that best completes the blanks of this sentence in the correct order. The name of the organism should be labeled on the _______ of an agar plate, and the plate should be incubated with the lid _____.
bottom; down
A microscope that allows light to pass directly through the condenser to the eye is called a _______ microscope.
brightfield
Before the oil immersion lens is rotated into place, you should
center the object of interest and add a drop of oil to slide.
The coarse focus knob moves the stage over distances measured in
centimeters/millimeters.
The most useful adjustment for increasing image contrast under low-power magnification is
closing down the diaphragm.
When direct and diffracted light rays are brought into exact phase with each other, the result is _______, increasing the amplitude of these waves and the brightness of the object.
coincidence
A ______ is a mound of cells on a solid medium that represents the progeny from one original bacterial cell.
colony
When using a ______ microscope, the background of the field is dark and the specimen is brightly illuminated.
darkfield
A phase-contrast microscope differs from a brightfield microscope by having a
diaphragm with an annular stop and a phase plate.
Please choose the description that best fits a medium that has been designed to indicate the growth of Staphylococcus aureus based on its ability to ferment mannitol.
differential
A correctly prepared slide culture will enable the preparation of one stained slide for viewing.
false
Brain heart infusion (BHI) agar is sometimes used to grow fastidious bacteria that require a number of metabolic growth factors. This medium is an example of a chemically defined medium.
false
Methods used to preserve bacterial cultures should promote growth and metabolic activity during storage.
false
Once a standard curve has been prepared by plotting numbers of bacteria (CFU/mL) versus absorbance for one species of bacteria, this curve can be used for estimating bacterial numbers by measuring absorbance for any species of bacteria.
false
The heat filter in a fluorescent microscope is used to eliminate nonuseful, heat-generating
infrared rays.
When two light waves of equal amplitude are in reverse phase, a dark object is produced and this is called ________.
interference
The phase-contrast microscope is best suited for observing
living organisms on a slide with a cover glass.
Select the inoculating tool that is more appropriate to remove bacterial growth from a liquid culture.
loop
Bacterial cultures can be preserved by freeze-drying, also known as _________.
lyophilization
The level of microbial contamination on an agar plate is measured as the ______ of colonies.
number
A microscope that maintains the focus of a specimen even when the magnification is increased is called _______.
parfocal
Fluorescence eventually diminishes with continued exposure to UV light due to _______.
quenching
When preparing pure cultures, dilution is necessary for
reducing the number of inoculated organisms so that isolated colonies can develop.
To retrieve a sample from a culture tube with an inoculating loop, the cap of the tube is
removed and held with the fingers of the loop hand.
The barrier filter in the fluorescence microscope is kept in position to
screen out exciting light rays.
Media which contain substances such as antibiotics, dyes, and other compounds to inhibit the growth of certain types of bacteria are called ________ media.
selective
You are interested in studying the gram-negative bacteria that may be found in ground meat. You would like to use a medium that will enable the growth of most species of gram-negative bacteria, while inhibiting gram-positive bacteria. This would be a __________________ medium.
selective
An indirect method of estimating bacterial numbers is based on the turbidity of the sample. A ________ can be used to determine the turbidity by measuring absorbance.
spectrophotometer
Asexual spores that form within a thin-walled sac are referred to as ________.
sporangiospores
Please choose the answer that best completes the blanks of this sentence in the correct order. The ______ plate method involves spreading an inoculum onto the surface of a plate in a pattern that results in isolated colonies in some areas of the plate after incubation, whereas the ______ plate method involves diluting an inoculum into several melted agar tubes and then adding their contents into plates for solidification and incubation.
streak; pour
A microscope's resolving power can be defined in simple terms as
the clarity of the images it produces.
The coarse and fine focus knobs adjust the distance between
the stage and the objective lens.
The primary goal of fungal slide cultures is
to enable staining and observation of fungal sporulating structures in situ.
Purple and green sulfur bacteria get their energy from photosynthesis but their carbon source is from organic nutrients instead of carbon dioxide.
true
The majority of heterotrophic microorganisms are chemoheterotrophs that derive both energy and carbon from organic compounds.
true
Bacteria are _______, meaning that they are distributed everywhere.
ubiquitous
Darkfield microscopes are preferred over brightfield microscopes when observing
unstained living cells.
An inoculating loop or needle is sterilized in a flame
until the entire wire is bright red.
