Chapter 3 MIcroscopy and Cell Structure

Question 1

Eukaryotic cells are

A. less complex than prokaryotic cells.

B. members of the domains Bacteria and Archaea.

C. defined by the presence of a membrane bound nucleus.

D. able to reproduce more rapidly than prokaryotes.

E. less complex than prokaryotic cells, members of the domains Bacteria and Archaea AND able to reproduce more rapidly than prokaryotes.

Answer 1

C. defined by the presence of a membrane bound nucleus.

Question 2

The two magnifying lenses found in a light microscope are the

A. basic and transverse.

B. small and large.

C. ocular and objective.

D. simple and phase.

Answer 2

C. ocular and objective.

Question 3

The resolving power of a microscope is described as the ability of the microscope to

A. separate clearly two objects that are very close together.

B. magnify an object.

C. separate the colors of an organism’s internal structure.

D. see structures at various depths in a tissue.

Answer 3

A. separate clearly two objects that are very close together.

Question 4

In viewing a microscopic specimen, oil is used to

A. increase the refraction.

B. decrease the refraction.

C. increase the reflection.

D. increase the resolution.

E. decrease the refraction AND increase the resolution.

Answer 4

E. decrease the refraction AND increase the resolution.

Question 5

The use of oil with certain high power objective lenses increases

A. magnification.

B. the amount of light that enters the objective lens.

C. resolution.

D. contrast.

E. All of the choices are correct.

Answer 5

B. the amount of light that enters the objective lens.

Question 6

If everything else is equal, the best way to observe more details in a microscopic specimen is to

A. increase resolution.

B. increase magnification.

Answer 6

A. increase resolution.

Question 7

The microscope which allows the specimen to appear 3-dimensional is the

A. phase contrast microscope.

B. interference microscope.

C. fluorescence microscope.

D. dark-field microscope.

Answer 7

B. interference microscope.

Question 8

Which of the following microscope types would be least useful in viewing unstained living cells?

A. phase contrast

B. interference

C. bright-field

D. dark-field

Answer 8

C. bright-field

Question 9

Electron microscopes differ from light microscopes in that

A. electrons replace light.

B. electromagnets replace glass lenses.

C. resolution is higher.

D. magnification is higher.

E. All of the choices are correct.

Answer 9

E. All of the choices are correct.

Question 10

Specimens can be observed at the atomic level using a(n)

A. scanning electron microscope.

B. transmission electron microscope.

C. atomic force microscope.

D. All of the choices are correct.

E. None of the choices is correct.

Answer 10

C. atomic force microscope.

Question 11

Individual atoms on the surface of prepared samples can be observed by using the

A. phase contrast microscope.

B. scanning electron microscope.

C. dark-field microscope.

D. atomic force microscope.

Answer 11

D. atomic force microscope.

Question 12

Basic dyes

A. have negative charges.

B. have positive charges.

C. are electrically neutral.

D. contain both positively and negatively charged particles.

Answer 12

B. have positive charges.

Question 13

Which of the following stains is/are considered differential?

A. capsule stain.

B. flagella stain.

C. acid-fast stain.

D. Gram stain.

E. acid-fast stain AND Gram stain.

Answer 13

E. acid-fast stain AND Gram stain.

Question 14

The Gram stain and the endospore stain both use

A. basic dyes.

B. acidic dyes.

C. safranin.

D. methylene blue.

E. basic dyes AND safranin.

Answer 14

E. basic dyes AND safranin

Question 15

The order of reagents in the Gram stain reaction are

A. safranin, alcohol, methylene blue, iodine.

B. crystal violet, iodine, alcohol, safranin.

C. methylene blue, alcohol, safranin.

D. crystal violet, alcohol, iodine, safranin.

Answer 15

B. crystal violet, iodine, alcohol, safranin.

Question 16

Which may result in Gram-positive bacteria appearing to be Gram-negative?

A. decolorizing too long

B. decolorizing too short

C. using old cultures

D. using young cultures

E. decolorizing too long AND using old cultures

Answer 16

E. decolorizing too long AND using old cultures

Question 17

The major criteria used in placing bacteria into different groups is based on differences in

A. cell wall structure.

B. cell membrane permeability.

C. presence or absence of flagella.

D. detergent susceptibility.

Answer 17

A. cell wall structure.

Question 18

In a basic staining procedure, which is the correct order?

A. fix, smear, stain

B. smear, fix, stain

C. fix, stain, decolorize

D. smear, decolorize, stain

Answer 18

B. smear, fix, stain

Question 19

The acid-fast stain

A. reflects differences in cytoplasmic membrane structure.

B. is useful for distinguishing a small group of organisms, including Mycobacterium.

C. uses crystal violet and safranin.

D. uses carbolfuchsin and methylene blue.

E. is useful for distinguishing a small group of organisms, including Mycobacterium AND uses carbolfuchsin and methylene blue.

Answer 19

E. is useful for distinguishing a small group of organisms, including Mycobacterium AND uses carbolfuchsin and methylene blue.

Question 20

Capsules

A. take up stain well.

B. may correlate with an organism’s ability to cause disease.

C. are typically “negatively” stained.

D. are stained as a wet mount.

E. may correlate with an organism’s ability to cause disease, are typically “negatively” stained AND are stained as a wet mount.

Answer 20

E. may correlate with an organism’s ability to cause disease, are typically “negatively” stained AND are stained as a wet mount.

Question 21

The endospore stain

A. is applicable to only a few groups of bacteria.

B. usually shows the spores as green structures among a background of pink cells.

C. uses crystal violet as the primary stain.

D. is an example of a negative stain.

E. is applicable to only a few groups of bacteria AND usually shows the spores as green structures among a background of pink cells.

Answer 21

E. is applicable to only a few groups of bacteria AND usually shows the spores as green structures among a background of pink cells.

Question 22

Which fluorescent stain would be useful for distinguishing between dead and living bacteria?

A. acridine orange

B. auramine

C. rhodamine

D. CTC

Answer 22

D. CTC

Question 23

Immunofluorescence

A. uses fluorescently tagged molecules.

B. makes use of the specificity in binding of antibodies.

C. utilizes acridine orange.

D. would require a special UV microscope.

E. uses fluorescently tagged molecules, makes use of the specificity in binding of antibodies AND would require a special UV microscope.

Answer 23

E. uses fluorescently tagged molecules, makes use of the specificity in binding of antibodies AND would require a special UV microscope.

Question 24

Which term(s) refer(s) to bacterial morphology?

A. Bacillus

B. coccus

C. bacillus

D. polyhedral

E. coccus AND bacillus

Answer 24

E. coccus AND bacillus

Question 25

Which is not true of the cytoplasmic membrane? A. It defines the boundaries of the cell. B. It is a semipermeable barrier. C. It consists mainly of a fixed, static phospholipid bilayer. D. It uses proteins as selective gates and sensors. E. All of the choices are true.

Answer 25

C. It consists mainly of a fixed, static phospholipid bilayer.

Question 26

Which is true of simple diffusion of water? A. Water usually enters a cell and produces a tremendous osmotic pressure. B. Water usually leaves the cell and produces negative osmotic pressure. C. Water tends to enter and leave the cell equally, resulting in no pressure in the cell. D. The diffusion ultimately relies on the selectively permeable nature of the cell membrane. E. Water usually enters a cell and produces a tremendous osmotic pressure AND the diffusion ultimately relies on the selectively permeable nature of the cell membrane.

Answer 26

E. Water usually enters a cell and produces a tremendous osmotic pressure AND the diffusion ultimately relies on the selectively permeable nature of the cell membrane.

Question 27

The cytoplasmic membrane of both eukaryotes and prokaryotes functions to A. form endoplasmic reticulum. B. produce energy. C. regulate movement of molecules which enter and leave the cell. D. form lysosomes and golgi apparatus.

Answer 27

C. regulate movement of molecules which enter and leave the cell.

Question 28

The proteins of bacteria that are involved in the movement of small molecules into the cell, are called A. transport proteins. B. permeases. C. carriers. D. peptidases. E. transport proteins, permeases AND carriers.

Answer 28

E. transport proteins, permeases AND carriers.

Question 29

Most solutes pass through the cytoplasmic membrane via A. osmosis. B. diffusion. C. transport proteins. D. secretion.

Answer 29

C. transport proteins.

Question 30

Facilitated diffusion and active transport A. both transport molecules into or out of a cell. B. are both not very specific as to which molecules are transported. C. both require a concentration gradient to function. D. both require an expenditure of energy in order to transport the molecules. E. both require a concentration gradient to function AND both require an expenditure of energy in order to transport the molecules.

Answer 30

A. both transport molecules into or out of a cell.

Question 31

The macromolecule found in the cell walls of all bacteria is A. diaminopimelic acid. B. teichoic acid. C. peptidoglycan. D. glycocalyx.

Answer 31

C. peptidoglycan.

Question 32

Which is(are) true concerning the cell wall of prokaryotes? A. It determines the shape of the bacteria. B. It prevents the bacteria from bursting. C. It contains peptidoglycan. D. It may be targeted by antimicrobials. E. All of the choices are true.

Answer 32

E. All of the choices are true.

Question 33

Which amino acid(s) is/are found only in the cell walls of bacteria? A. glycerol B. L-form of glycine C. diaminopimelic acid D. L-form of methionine E. L-form of glycine AND L-form of methionine

Answer 33

C. diaminopimelic acid

Question 34

The cell wall of Gram-positive bacteria A. contains a thin layer of peptidoglycan. B. contains a thick layer of peptidoglycan. C. is, due to its thickness, an excellent barrier to most molecules. D. contains an outer membrane containing LPS. E. contains a thin layer of peptidoglycan AND contains an outer membrane containing LPS.

Answer 34

B. contains a thick layer of peptidoglycan.

Question 35

Which molecules are associated with the cell wall of Gram-positive bacteria? A. peptidoglycan B. D-form amino acids C. teichoic acids D. LPS E. peptidoglycan, D-form amino acids AND teichoic acids

Answer 35

E. peptidoglycan, D-form amino acids AND teichoic acids

Question 36

The cell wall of Gram-negative organisms A. has a thick peptidoglycan layer. B. has a thin peptidoglycan layer. C. is more permeable to various molecules than the Gram-positive cell wall. D. is characterized by an outer membrane containing LPS. E. has a thin peptidoglycan layer AND is characterized by an outer membrane containing LPS.

Answer 36

E. has a thin peptidoglycan layer AND is characterized by an outer membrane containing LPS.

Question 37

Endotoxin A. consists of LPS. B. determines bacterial shape. C. may have different effects depending on the specific bacterial source. D. is toxic due to the effects of the peptide side chains. E. determines bacterial shape, may have different effects depending on the specific bacterial source AND is toxic due to the effects of the peptide side chains.

Answer 37

A. consists of LPS.

Question 38

Penicillin would be most effective against A. non-growing bacteria. B. growing bacteria. C. Gram-positive bacteria. D. Gram-negative bacteria. E. growing bacteria AND Gram-positive bacteria.

Answer 38

E. growing bacteria AND Gram-positive bacteria.

Question 39

Peptidoglycan A. may be digested by penicillin. B. consists of a long string of NAG coupled to a long string of NAM. C. may be digested by lysozyme. D. is used to construct a spheroplast.

Answer 39

C. may be digested by lysozyme.

Question 40

Which of the following bacteria lack a cell wall? A. Treponema pallidum B. Mycobacterium tuberculosis C. Staphylococcus aureus D. Mycoplasma pneumoniae

Answer 40

D. Mycoplasma pneumoniae

Question 41

The capsule A. may be used for protection. B. may be used to help the bacteria adhere to surfaces. C. may be involved in movement. D. may be involved in energy production. E. may be used for protection AND may be used to help the bacteria adhere to surfaces.

Answer 41

E. may be used for protection AND may be used to help the bacteria adhere to surfaces.

Question 42

The structures used for motility in both eukaryotes and prokaryotes are A. cilia. B. flagella. C. pili. D. fimbriae.

Answer 42

B. flagella.

Question 43

Movement in bacteria A. is directly to or away from a stimulus. B. relies on the beating of cilia. C. is often referred to as run and tumble. D. may involve pili. E. is often referred to as run and tumble AND may involve pili.

Answer 43

E. is often referred to as run and tumble AND may involve pili.

Question 44

Extrachromasomal DNA is found in ____________________________. A. mitochondria B. plasmids C. nucleoid D. nucleoli E. mitochondria AND plasmids

Answer 44

E. mitochondria AND plasmids

Question 45

Endospores are A. a dormant cell type. B. a form of reproduction. C. an obligate intracellular parasite. D. sensitive to damaging environmental conditions.

Answer 45

A. a dormant cell type.

Question 46

Eukaryotic cells A. are more obviously compartmentalized than prokaryotes. B. usually have a single circular supercoiled piece of DNA. C. contain peptidoglycan in the cell wall. D. have the same size ribosomes as prokaryotes. E. usually have a single circular supercoiled piece of DNA AND contain peptidoglycan in the cell wall.

Answer 46

A. are more obviously compartmentalized than prokaryotes.

Question 47

The membranes of eukaryotes and mycoplasma A. contain peptidoglycan. B. contain sterols for "strength". C. contain ergosterol. D. are fixed static structures.

Answer 47

B. contain sterols for "strength".

Question 48

Phagocytosis A. is the ingestion of particles and may be performed by animal cells. B. is the ingestion of particles and may be performed by bacteria. C. is the secretion of proteins. D. is the formation of a lysosome. E. is the ingestion of particles and may be performed by bacteria AND is the formation of a lysosome.

Answer 48

A. is the ingestion of particles and may be performed by animal cells.

Question 49

The cytoskeleton A. is a dynamic structure composed of microtubules, microfilaments and intermediate filaments. B. is a static structure that gives a rigid shape to the cell. C. consists of flagella and cilia that are internalized. D. is not necessary for movement or reproduction. E. is a static structure that gives a rigid shape to the cell, consists of flagella and cilia that are internalized AND is not necessary for movement or reproduction.

Answer 49

A. is a dynamic structure composed of microtubules, microfilaments and intermediate filaments.

Question 50

The nucleus A. is a double membrane sac containing DNA and is found in eukaryotes. B. is a single phospholipid membrane sac containing prokaryotic DNA. C. is a smaller structure contained within the eukaryotic nucleolus. D. cannot transport molecules to the cytoplasm due to the double membrane barrier.

Answer 50

A. is a double membrane sac containing DNA and is found in eukaryotes.

Question 51

Which is not true of mitochondria and chloroplasts? A. They are found in all organisms. B. They contain DNA and 70S ribosomes. C. They are capable of performing protein synthesis. D. They generate ATP.

Answer 51

A. They are found in all organisms.

Question 52

An advantage of the smaller size of prokaryotes, compared to eukaryotes, is A. high surface area relative to low cell volume. B. more rapid growth rates. C. compartmentalization of cellular processes in membrane-bound organelles. D. predators, parasites, and competitors constantly surround them. E. high surface area relative to low cell volume AND more rapid growth rates.

Answer 52

E. high surface area relative to low cell volume AND more rapid growth rates.

Question 53

Bacillus and Clostridium are medically relevant groups of bacteria that characteristically stain acid-fast.

Answer 53

FALSE

Question 54

LPS is found in the outer membrane of Gram-positive bacteria.

Answer 54

FALSE

Question 55

Penicillin affects the synthesis of phospholipids, thereby producing weak membranes and lysis of the bacteria.

Answer 55

FALSE

Question 56

Drugs that target prokaryotic protein synthesis would have no effect on eukaryotic protein synthesis.

Answer 56

FALSE

Question 57

Endospores are involved in bacterial reproduction.

Answer 57

FALSE

Question 58

Lysosomes are bags of digestive enzymes found in prokaryotic cells.

Answer 58

FALSE

Question 59

Smooth endoplasmic reticulum is involved in protein synthesis.

Answer 59

FALSE

Question 60

Mitochondria and chloroplasts are thought to have once been free living bacteria that invaded another cell.

Answer 60

TRUE

Question 61

Cilia and flagella project from the cell and are not covered by cytoplasmic membrane.

Answer 61

FALSE

Question 62

Prokaryotes may ingest particles via phagocytosis

Answer 62

FALSE

Question 63

An electron microscope must place the specimen in a vacuum within a sealed chamber. Why? A. Electrons are particles-there are also particles in air. Without a vacuum, the electrons would strike and be scattered by the atoms/particles within the air. B. Because electrons are highly radioactive, and the chamber must be completely sealed to prevent them from escaping and contaminating the lab area. C. This is the method for fixing the specimen to the slide grid for an electron microscope. Without fixing the specimen by vacuum, it would slide off and we wouldn't be able to visualize it. D. All of the above are true.

Answer 63

A. Electrons are particles-there are also particles in air. Without a vacuum, the electrons would strike and be scattered by the atoms/particles within the air.

Question 64

An electron microscope must use electromagnet 'lenses' shaped like donuts to direct the electrons onto the specimen. Why aren't they solid, like the lenses in a light microscope? A. A magnetic field cannot be applied across a completely solid object-there must be an opening within the object for the field to be applied through. B. The user has to be able to physically look through the magnets to focus the beam of electrons onto the specimen, since the metal of the magnets is opaque. Without a hole in the middle, the user wouldn't be able to see! C. The electrons would destroy the electromagnet material unless there was a physical hole for them to travel through on their way to the specimen. D. Electrons are particles, and particles cannot travel through a solid item. The hole in the middle allows them to travel from the source of the electrons to the specimen.

Answer 64

D. Electrons are particles, and particles cannot travel through a solid item. The hole in the middle allows them to travel from the source of the electrons to the specimen.

Question 65

Which microscope would be the BEST selection for examination of a virus? A. Confocal scanning laser microscope B. Atomic force microscope C. Dark-field light microscope D. Scanning electron microscope

Answer 65

D. Scanning electron microscope

Question 66

You want to examine the structure of the protein coat of a virus by microscopy. Which microscope is your best choice, and why? A. The scanning electron microscope-it has excellent resolution and magnification, much higher than a light microscope, and can clearly visualize viruses. B. An atomic force microscope-this has the highest resolution and magnification of the microscopes we discussed. Here, we want to visualize a subcomponent of the virus particles, so we need the best value for resolution and magnification we can possibly achieve. C. A fluorescent microscope-this will let us tag the protein coat with colored dyes in order to visualize it using this light microscope at 1000x. D. A bright-field light microscope-of course, we'll need to stain the viruses before we can visualize them against the bright white background at 1000x total magnification.

Answer 66

B. An atomic force microscope-this has the highest resolution and magnification of the microscopes we discussed. Here, we want to visualize a subcomponent of the virus particles, so we need the best value for resolution and magnification we can possibly achieve.

Question 67

Your instructor wants you to bring in an example of a biofilm to your lab. Which choice is the best selection for bringing in an intact biofilm for further study? A. Disconnecting and bringing in the old, mildewed showerhead from the showers in your dorm. B. Scraping the mold off of the shower curtain in your dorm's bathroom into a paper cup using a butter knife. C. Using a toothpick to scrape plaque off of your teeth and smearing it onto a slide to bring in to lab. D. Wiping a sponge across a slimy boulder in a stream in a nearby park and bringing it in to lab.

Answer 67

A. Disconnecting and bringing in the old, mildewed showerhead from the showers in your dorm.

Question 68

A newly developed antibiotic drug shows promise by inhibiting prokaryotic 70S ribosomes in initial studies. However, when animal studies are begun, it's noted that it also inhibits growth of animal cells. Aren't prokaryotic ribosomes different from eukaryotic ribosomes? How can this be happening? A. Perhaps the ribosomes aren't as different as we thought, so a drug can affect and impair both of them. B. While the proteins made in the cytosol of eukaryotic cells are, indeed, produced from the 80S eukaryotic ribosome, mitochondria and chloroplasts possess 70S ribosomes. This drug might be impairing the activity of chloroplasts in animal cells. C. While the proteins made in the cytosol of eukaryotic cells are, indeed, produced from the 80S eukaryotic ribosome, mitochondria and chloroplasts possess 70S ribosomes. This drug might be impairing the activity of mitochondria in animal cells. D. Perhaps the scientists accidently combined their cultures of animal and bacterial cells-this might indicate an impairment in growth in the culture. In reality, it's still just impairing the bacterial cells.

Answer 68

C. While the proteins made in the cytosol of eukaryotic cells are, indeed, produced from the 80S eukaryotic ribosome, mitochondria and chloroplasts possess 70S ribosomes. This drug might be impairing the activity of mitochondria in animal cells.

Question 69

A research laboratory is investigating environmental factors that would inhibit the growth of Archaea. One question they have is if adding the antibiotic penicillin would be effective in controlling their growth. What do you think the outcome would be if they tried this? A. The penicillin wouldn't affect the Archaea because it prevents crosslinking of peptidoglycan-Archaea don't have this compound in their cell walls. B. The penicillin will inhibit cell wall formation in the Archaea, killing them. C. The penicillin will slow down the growth of the Archaea by damaging the cell wall, but they will still be able to grow somewhat. D. The penicillin will enhance the growth of the Archaea by providing a rich nutrient source.

Answer 69

A. The penicillin wouldn't affect the Archaea because it prevents crosslinking of peptidoglycan-Archaea don't have this compound in their cell walls.

Question 70

A research lab is trying to produce new antibiotics. They come up with drugs that detach the hydrophilic heads from the phospholipids in plasma membranes. This drug A. would be highly toxic and completely useless for human beings-we also have plasma membranes with hydrophilic head groups! B. would be highly toxic only to bacteria, making it an excellent drug to develop and test further. Humans have a different phospholipid structure in their cell plasma membranes than bacteria. C. would generally not be toxic enough to damage Gram-negative bacteria, as their plasma membranes lie under a thick layer of peptidoglycan. D. would be highly toxic for human beings, but might be useful as a topical antibiotic skin cream. The top layer of skin cells is dead anyway, so it wouldn't matter if this damaged those cells. It could NOT be taken internally, though, by human beings.

Answer 70

D. would be highly toxic for human beings, but might be useful as a topical antibiotic skin cream. The top layer of skin cells is dead anyway, so it wouldn't matter if this damaged those cells. It could NOT be taken internally, though, by human beings.

Question 71

A new drug is developed that targets and binds to the lipid A portion of LPS from Gram-negative bacterial cells. This drug shows a high degree of activity and binding in a test tube setting against purified lipid A. Based on this information, A. we should fast track this drug and get it out to physicians immediately to help prevent toxic/septic shock in humans. B. we should do some animal testing with whole Gram-negative cells and the drug before we jump to any conclusions. C. we should next proceed by moving to testing in a test tube using whole Gram-negative cells to see if it binds with the same strength. D. we should abandon the drug entirely. Binding to lipid A won't kill the bacteria, so the drug is useless to develop further. It wouldn't help humans who have septic shock at all.

Answer 71

C. we should next proceed by moving to testing in a test tube using whole Gram-negative cells to see if it binds with the same strength.

Question 72

Another new drug is developed-this one inhibits formation of the flagellar filament by impairing production of the protein flagellin. Is this going to be a good drug? A. Potentially-it would definitely only impair bacteria, but wouldn't matter for the ones that don't use a flagellum to move around. B. Potentially-if it could be shown that it also didn't impair the production of the eukaryotic flagellum. C. No-our eukaryotic cells depend on flagella to move around in our body, and this would impair that function. D. No-bacterial flagella are produced using microtubules, not the protein flagellin. This drug would be useless in eliminating bacteria.

Answer 72

A. Potentially-it would definitely only impair bacteria, but wouldn't matter for the ones that don't use a flagellum to move around.

Question 73

simple staining

Answer 73

only a single eye is used

Question 74

staining procedures typically use what kind of charge on what kind of dye?

Answer 74

the use positive charged dyes because they are basic dyes (they collect the hydrogens and satisfy the negative charges they have)

Question 75

why are dyes basic (positive)? why is this advantageous?

Answer 75

these dyes stain cells because they are attracted to the many negatively charged cellular components. Examples of basic dyes include methylene blue, crystal violet, safranin, and malachite green.

Question 76

Although acidic dyes do not stain cells, they can be used for what??

Answer 76

negative staining- a procedure that colors the background. the cells repel the negatively charged dye, allowing the colorless cell to stand out against the background. an advantage of negative staining is that it can be done as a wet mount. this avoids the heat fixing step, a process that can distort the shape of the cells.

Question 77

Differential staining

Answer 77

used to distinguish different groups of bacteria. the 2 most frequently used differential staining techniques are the Gram stain and the acid-fast stain.

Question 78

explain the steps in the gram stain procedure?

Answer 78

1. the smear is first flooded with the PRIMARY STAIN, crystal violet in this case. the primary stain is the first dye applied in differential staining and generally stains all cells. 2. The smear is rinsed to remove excess dye and then flooded with a solution called Gram's iodine. this iodine combines with the crystal violet to form a dye-iodine complex, thereby decreasing the solubility of the dye within the cell. 3. The stained smear is rinsed, and then a DECOLORZING AGENT- 95% alcohol or a mixture of alcohol and acetone- is briefly added. these chemicals quickly remove the dye-iodine complex from Gram-negative, but not gram positive bacteria. 4. a COUNTERSTAIN is then applied to give a different color to the now colorless gram negative bacteria. for this purpose, the red dye SAFRANIN is used. this dye enters gram positive cells as well, but because they are already purple, it makes little difference to their color.

Question 79

Acid-fast stain

Answer 79

used to detect a small group of organisms that do not readily take up dyes. among these are members of the genus MYCOBACTERIUM, including a species that causes tuberculosis and one that causes Hansen's disease (leprosy). the cell wall of these bacteria contain high concentrations of mycolic acid, a waxy fatty acid that prevents uptake of dyes such as those used in gram staining.

Question 80

what are the steps in acid fast staining?

Answer 80

the primary stain is carbolfuchsin, a red dye. in the classic procedure, teh dye flooded smear is heated, which facilitates staning. this does not need heat, but instead uses a concentrated solution of dye for a longer period of time. the slide is then rinsed briefly to remove excess dye before being flooded with acid alcohol, a strong decolorizing agent. this agent removes the carolfuchsin from tissue cells and most bacteria; those few species that retain the dye are called acid-fast. methylene blue is then used as a counterstain. as a result of the staining procedure, acid fast organisms are bright reddish pink making them easy to distinguish from the blue non acid fast cells.

Question 81

capsule stain

Answer 81

a capsule is a gel like layer that surrounds certain microbes. this layer has a protective function and often increases an organisms pathogenicity. capsules stain poorly so capsule stains often use negative staining to make them visible. in one common method, kinda ink is added to a suspension of cells to make a wet mount. the fine particles of ink darken the background, allowing the capsule to stand out as a clear area surrounding a cell.

Question 82

endospore stain

Answer 82

Members of certain genera, including Bacillus and Clostridium form a special type of resistant, dormant cell called an endospore. These structures do not stain with the gram stain, but they canb often be seen as clear, smooth objects within stained cells. To make endospores easier to see, an endospore stain is used. this multistep procedure often uses malachite green as a primary stain, with gentle heating to facilitate uptake of the dye by endospores. the smear is then rinsed with water, which removes the dye from everything but the endospores. the smear is then counterstained, most often with the red dye safranin. using this method the endospores will be green while all other cells will be pink.

Question 83

Flagella stain

Answer 83

Flagella are appendages that proved the most common mechanism of motility for prokaryotic cells, but they are ordinarily too thin to be seen with the light microscope. the flagella stain uses a substance that allows the staining agent to adhere to and coat the thin flagella making them visible, but those that do can have them in different arrangements around a cell, so the presence and distribution of these appendages can be used as identifying features.

Question 84

Fluorescent dyes

Answer 84

some fluorescent dyes bind to compounds found in all cells wheras other bind only to certain components. as an example acridine orange binds DNA, making it useful for determining the total number of microbes in a sample. in contrast, calcofluor white binds to a cell wall component of fungi and certain bacteria, causing those organisms to fluoresce bright blue. the fluorescent dyes auramine and rhodamine bind to the mycolic acid in teh cell walls of Mycobacterium species, making the dyes useful in a staining procedure similar to the acid fast stain. other fluorescent dyes are changed by cellular process, allowing microbiologists to distinguish between living and dead cells.

Question 85

Immunofluorescence

Answer 85

a technique used to tag specific proteins with a fluorescent compound. by tagging a protein unique to a given microbe, immunofluorescence can be used to detect that organism. immunofluorescence uses an antibody to deliver the fluorescent tag.

Question 86

what are the 2 most common shapes of bacteria?

Answer 86

Coccus- spherical | Rod- cylindrical (a rod shaped bacterium is sometimes called a BACILLUS.

Question 87

What is coccobacillus?

Answer 87

a rod shaped bacterium so short that it can easily be mistaken for a coccus

Question 88

Vibrio

Answer 88

a short curved rod

Question 89

Spirillum

Answer 89

curved rod long enough to form spirals.

Question 90

Spirochete

Answer 90

a long, helical cell with a flexible cell wall and a unique mechanism of motility

Question 91

pleomorphic

Answer 91

bacteria that characteristically vary in their shape.

Question 92

Groupings

Answer 92

most prokaryotes divide by binary fission, a process in which one cell divides into 2. cells often stick to each other following division, forming characterstic groupings.

Question 93

Diplococci

Answer 93

cells that divide in one plane can form chains of varying length. Cocci that typically occur in pairs.