Biol 2051 Lab Midterm Cont.

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The stains used in lab for experiment 8 were differential stains.

False, they were simple stains.

What is the magnification of the first objective you will use to initially focus on your smear?


When plates are incubated at 37°C, they should always be placed upside down to prevent condensation from pooling on the growing cultures.


Microscopes you will be using in lab to view your smears are:

•Binocular microscopes
•Delicate instruments that require care and daily maintenance
•Equipped with 100x objectives
•Compound light microscopes

Place the following in the order light travels from the light source to through the specimen (your smear) to your eye: a - light source; b - ocular lens; c - condenser; d - objective; e - smear; f - slide on the stage; g - your eye. (write your answer with no spaces or punctuation between the letters)

light source, condenser, slide on the stage, smear, objective, ocular lens, my eye

Preparing a smear is done using which of the following pieces of equipment?

inoculating loop. microscopic slide, bunsen burner or hot plate

When using the microscope, which of the following statements are true?

•You focus on the smear using the 10X objective first using the course adjustment knob.
•After you've focused with the 10X objective, you switch objectives to the 100X objective and use only the fine adjustment knob for focusing.

Which of the following most accurately describes how you should heat fix a smear if no slide warmer is available?

After letting smear air dry, quickly pass the slide over a flame


long, thin structures used by many microorganisms for locomotion.

You should only use immersion oil with the 100X objective lens.


You are trying to view your simple stains using a microscope. When you are switching the objective lens from 10X to 100X, you should grab the objective lens to turn the nosepiece.

False, you should turn the revolving nosepiece to switch from the objective 10x to 100x.

What is the smallest size cell you can see with the light microscopes in lab?

0.2 microns

In daily lab techniques and microscope care, you should follow the procedures in the lab manual. You will lose points if you:

•Clean your microscope lenses with paper towels
•Forget to clean your microscope with lens paper
•Leave your bunsen burner lit and leave the room
•Use the coarse focus with the 100X objective

Which of the following terms are used to describe the location of flagella?


What is the first thing you should do if you suspect the broth culture given to you is not a pure culture that might give you a hint that it is not pure by showing you the cell morphology or morphologies present in the culture?

stain a smear of the broth culture

You observed a stained slide under the microscope, and found some cells were random and rod shaped and the other cells were coccus shaped in chains. This smear was made from a pure culture.


If most of the cells on your smear look randomly arranged, but you find one grouping of cells that appears to be in a strepto arrangement, then this is sufficient evidence to conclude that your organism has a strepto cell arrangement.


The structure and function of the bacterial flagella are the same as the eukaryotic flagella.


What characteristic of cells does the Gram stain differentiate?

Cell wall structure

Which of the following are used for a Gram stain?

•95% Ethanol
•Gram's Iodine
•Crystal violet

A low agar concentration is used to test motility b/c:

Motile bacteria can move easier when agar concentrations are low

You look carefully at your simple stain of the culture for experiment 10 and see all purple rod-shaped bacteria, but some appear larger than others. You begin to think your culture is mixed. Which of following will give you more information than what you already have and help you determine if the culture is mixed?

streak plate and gram stain

Tetrazolium salt is colorless until oxidized by bacteria.


Place the following in order of occurrence in performing a Gram stain: a - make a thin smear; b - cover smear with crystal violet for 1 min; c - cover smear with Gram's iodine for 1 min; d - cover with safranin for 1 min; e - heat fix the smear; f - rinse with ethanol for a few seconds; g - rinse with water; h - blot dry

make a thin smear, heat fix the smear, cover smear w/ crystal violet, rinse w/ water, cover smear w/ gram's iodine for 1 minute, rinse w/ water, rinse w/ ethanol for a few seconds, rinse w/ water, cover w/ safranin for 1 minute, rinse w/ water, blot dry

Polar flagella are attached at one or both ends of the cell, and peritrichous flagella are inserted at many locations around the cell surface.


gram stain

•depends on bacteria differing in the amount of peptidoglycan
•is a differential stain

Bacterial endospores

•can be killed by autoclaving
•are problematic to the food industry b/c the bacteria that germinate and grow from the spores if ingested can produce deadly toxins.
•can survive heating, freezing, drying, exposure to various chemicals, radiation, and boiling water

Which of the following organisms did you see in lab that tested positive for motility?

•Enterobacter aerogenes
•Pseudomonas putida
•Escherichia coli
•Bacillus megaterium

In preparing the smear for the acid-fast stain, you

add egg albumin to help disperse the Mycobacterium

Red tetrazolium salt could be seen radiating out from the stab line of the motile organism.


You did a simple stain and streak plate from a broth culture to try to determine if it is a pure culture. From what you saw you concluded the culture was pure. What information did the streak plate provide?

only one colony morphology was present

Place the organisms below in order from the hottest optimum growth temperature to coldest optimum growth temperature.

Thermophile, mesophile, psychrophile

Bacillus sphaericus

terminal endospore

Bacillus megaterium

central endospore

For experiment 17B, Saccharomyces cerevisiae will be dispensed into

a single tube of each pH

The Bacillus cultures used for the endospore stains were grown on

slants lacking essential nutrients

Which of the following will you experimentally test for experiment 17A?

the ability of a bacterium to survive at a certain temperature for a brief period of time

To prepare your agar plate for experiment 17C you

swab your assigned bacteria over the entire agar surface

As a hospital lab technician you are given a blood culture from a patient and asked to determine if they have an active infection by Mycobacterium tuberculosis. How would you determine this?

an acid-fast stain

Describe the appearance of the Mycobacterium on a plate. With what cell component does this correlate?

compact, dry, wrinkled; mycolic acids in the cell wall

Which of the following statements regarding micropipettors is/are true?

•the pipette w/ the blue button should be used only for volumes b/t 200 and 1000ul. The pipettes w/ the gold button can accurately measure 20 - 200ul
•When picking up liquid the pipette plunger must be depressed to the first stop and slowly released. To dispense the liquid the plunger should be pushed to the first stop and then past to expel all of the liquid
•A fresh tip must be used for every transfer and the used tip must be ejected into the jar of vesphene on top of the bench

What do Bacillus sphaericus, Mycobacterium smegmatis, and Escherichia coli have in common?

rod-shaped bacteria

A bacteria that can survive exposure to a temperature can also divide and grow at that temperature.


You are given a culture of Pseudomonas fluorescens which is psychrotolerant mesophilic bacterium to conduct experiment 17A.What temperatures do you expect it to survive?

0°C, 4°C, 37° C

Which of the following would be considered an "extremely high salt concentration"?

25% NaCl

Deinococcus radiodurans can survive UV exposure because it:

Has an extraordinary ability to repair its UV damaged DNA

Put the following in order from the lowest to highest pH ranges.

Acidophile; neutrophile; basophile

What type of media will you be using for exp 17D?

plates with low, medium, high, very high amounts of salt

Ultraviolet radiation penetrates poorly and therefore cannot penetrate the lid of a Petri dish in order to reach the bacteria on the agar surface.


What method for enumerating bacteria will you use for experiment 15?

Viable plate count

What prevents most bacterial cells from lysing in a hypotonic environment?

cell wall

Which of the following is a disadvantage of the direct microscope count?

•it counts all cells, both live and dead.
•It requires the use of a hemacytometer

Which is the correct order of use of the three parts of the most probable number technique?

Presumptive, Confirmed, Completed

At which salt concentrations should you expect the halophile Vibrio natriegens to grow?

5% and 10%

Salt "cured" fish

represent hypertonic environments in which most microbes cannot grow

Which series of dilutions would give you an overall dilution of 10-7.

•10^-2, 10^-2, 10^-3
•10^-3, 10^-4

You will be inoculating 15 lauryl sulfate lactose broths (5 double strength and 10 single strength) for the presumptive MPN test.


You look at your plate from experiment 15 and find that your 10-4 plate contains 43 colonies. What is the cfu/ml ?

4.3 X 10^5

The term countable plate refers to a plate that has

between 30 and 300 colonies

Which of the following statement(s) is/are true about the Most Probable Number Technique?

•Escherichia coli is used as the indicator organism for fecal contamination in the United States. •The selective component in the presumptive test is lauryl sulfate
•Coliforms ferment lactose and produce carbon dioxide within 48 hours of incubation.
•Many enteric diseases are transmitted from person to person via fecally-contaminated water.

You are using biosafety level 1 related species of 2 genera of human pathogenic bacteria for experiments 18 and 19. What are these genera?


You inoculated 1ml of a broth culture of E. coli into a bottle containing 99ml of sterile water. You then transfered 0.1ml onto a TSA plate. What is the overall dilution of that plate?


How will you prepare your plates for experiments 18 and 19?

by covering the entire surface to create a lawn of bacteria

What is the differential component in the confirmed and completed tests of the most probable number technique?

lactose in both the confirmed and completed tests

Endospore Stain

•Primary Stain - Malachite green
•"Mordant" - heat from steam drives stain into cells
•Decolorizer - water to remove stain from vegetative cells
•Counterstain - safranin
-Red vegetative cells & Green endospores

Acid-Fast Stain

•Primary Stain - carbol-fuchsin
•"Mordant" - heat from steam drives stain into cells
•Decolorizer - acid alcohol removes the primary stain from non-acid-fast bacteria
•Counterstain - methylene blue

Vibrio natriegens


Escherichia coli

off-white, translucent, Gram -, rod-shaped, least salt tolerant, convex

Bacillus species

gram + rod, form endospores, non-motile

Staphylococcus epidermidis

yellow, opaque, Gram-positive staphylococci, in clusters, halotolerant

Spirosoma linguale

Gram-negative spirals

Deinococcus radiodurans

•does not form endospores but has radiation resistance due to incredible ability to repair DNA
•survives radiation but is sensitive to heat

B. Megaterium

should survive UV due to endospores, but vegetative cells are killed

Saccharomyces cerevisiae

eukaryote, yeast, acidophile

Alcaligenes faecalis


Halobacterium salinarium

extreme halophile (requires 25% salt); archaea

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