Quiz Questions

Question 1

If 4mL of a bacterial sample is added to 94 mL of diluent, the dilution of this suspension is:

Answer 1

(4/100)=4x10^-2

Question 2

Starting from an unknown sample, it is important to prepare multiple plates from multiple dilutions.
True or False?

Answer 2

True.

Question 3

A 10-7 dilution was prepared from a bacterial sample and 1 ml was spread on an agar plate. If you counted 72 colonies on this plate, then the original number of CFU/ml would be:

Answer 3

7.2x10^8

Question 4

In the standard plate count, the purpose of using serial dilutions is: [3]

Answer 4

• To reduce the cell population by a known amount
• To obtain plates that can be counted
• To generate isolated colonies

Question 5

CFU’s from pour plates appear:

Answer 5

On the surface and in the agar

Question 6

What would you predict as the outcome of a Gram-stained slide that has been incubated too long by ethanol during the Gram stain procedure? Assume that the counter stain has not be used.

Answer 6

Both Gram positive and Gram negative cells would not be stained (clear).

Question 7

When performing a restriction enzyme digest, what other components would be added to the tube? [4]

Answer 7

• Buffer
• Water
• DNA
• Enzyme

Question 8

In DNA electrophoresis, a 0.7% agar gel percentage in a gel of 70 ml volume is made by:

Answer 8

0.49 grams agarose + 70mL buffer

Question 9

Which component allows one to visualize the expected migration of the DNA bands during electrophoresis?

Answer 9

Bromophenol blue & xylene cyanol

Question 10

You have loaded your DNA sample into the well of an agarose gel, and apply the electric field. In which direction do you expect the DNA to migrate, and why?

Answer 10

Towards the positive electrode because the DNA is negatively charged

Question 11

You have loaded a sample of undigested plasmid DNA into the well of an agarose gel. Even though you were careful during the isolation protocol, you know that some DNA will be cut. This may result from shear forces that act on DNA (and DNA is a relatively fragile molecule).

Starting from the top of the gel where the wells are towards the bottom of the gel), what is the order of DNA bands you expect to see after running the DNA in the electric field?

Answer 11

Open circle, linear, supercoiled

Question 12

Both the standard plate count method and optical density measure the exact number of cells in a sample.
True or False?

Answer 12

False.

A standard curve is needed to correlate standard plate counts to optical density.

Question 13

The time required for a tenfold reduction of the viability of a microbial population at a given temperature is called the […] time.

Answer 13

Decimal reduction

Question 14

What will cause the decimal reduction time (D) value to increase?

Answer 14

Decrease of temperature

Question 15

The process by which macromolecules lose their structure and ability to function is called:

Answer 15

Denaturation

Question 16

What do high concentrations of salt and sugar have in common as preservatives?

Answer 16

• They reduce the available water in the environment.
• They cause the bacterial cell to dehydrate.

Question 17

The pressure inside the autoclave kills the microbes.
True or False?

Answer 17

False.
The high temperature in the autoclave kills the microorganisms.

Question 18

The high temperature in the autoclave kills the microorganisms.
True or False?

Answer 18

True.

Question 19

Large volumes of liquid would take longer to reach sterilization temperatures in an autoclave.
True or False?

Answer 19

True.

Question 20

Large volumes of liquid would take less time to reach sterilization temperatures in an autoclave.
True or False?

Answer 20

False.
Large volumes of liquid would take longer to reach sterilization temperatures.

Question 21

Which method would be the most common method to process milk after it has been collected from the cow?

Answer 21

Pasteurization

This method would kill 90% of microbes in milk.

Question 22

Which method would kill 90% of the mirobes present in milk?

Answer 22

Pasteurization

This is the most common method to process milk after it has been collected from the cow.

Question 23

In practice, sterility is difficult to achieve.
True or False?

Answer 23

True.

Question 24

In practice, sterility is easy to achieve.
True or False?

Answer 24

False.
In practice, sterility is difficult to achieve.

Question 25

In general, vegetative cells are more heat resistant than bacterial endospores.
True or False?

Answer 25

False.
In general, vegetative cells are less heat resistant than bacterial endospores.

Question 26

In general, vegetative cells are less heat resistant than bacterial endospores.
True or False?

Answer 26

True.

Question 27

Pasteurization is synonymous with sterilization; the only difference is that the term pasteurization is used with heat sensitive foods.
True or False?

Answer 27

False.

Question 28

Radiation would be a decontamination measure suitable for foods particularly susceptible to microbial contamination, but cannot be pasteurized.
True or False?

Answer 28

True.