Lecture 5

Question 1

What does a pH scale indicate?

Answer 1

It expresses the hydrogen ion concentration of aqueous solutions.

Question 2

A pH of a solution is given what logarithm and what unit of measure?

Answer 2

It’s given a negative logarithm of hydrogen ion concentration expressed in moles/litre.

Question 3

Give an example of a basic pH level, an acidic pH level and a neutral.

Answer 3

Basic= 10-11
Acidi=10-2
Neutral=10-7

Question 4

What is the difference of one pH unit in hydrogen ions.

Answer 4

10 times

Question 5

How do you adjust the pH level of a culture medium in order to make the pH favourable for microbial growth. Explain the procedure for both mediums that are too acidic or too basic.

Answer 5

A culture medium that is too acidic= adding an alkaline substance such as NaOH (sodium hydroxyde).
A culture medium that is too basic= adding an acidic substance such as HCl (hydrogen chloride).

Question 6

What type of substance can be added to a medium in order to keep the pH level constant during growth.

Answer 6

A buffer.

Question 7

What is the most common method of sterilization and in what device is this achieved?

Answer 7

Steam at 121 degrees celsius. Autoclave.

Question 8

Define inoculate.

Answer 8

To add microorganisms to a medium.

Question 9

Define contamination.

Answer 9

Introduction undesired microorganism into a culture or other material.

Question 10

Define aseptic technique.

Answer 10

Reducing the chances of contamination.

Question 11

Enumerate the techniques to use while isolating microorganisms.

Answer 11

Streak plates
Pour plates
Inhibition or killing undesired microorganisms
Dilution method
Single cell isolation

Question 12

Explain the procedure of streak plate

Answer 12

A steril loop or needle is used to lightly streak the surface of an agar plate. The pattern of streaking is important (first streak lines up, second streak lines across the top, third streaks downwards and then a zigzag in the middle). The plate will then be incubated in order to multiply colonies.

Question 13

True or false. A colony can be seen to the naked eye.

Answer 13

True

Question 14

True of false. A pure culture can’t be obtain by a streak plate method.

Answer 14

False. You can obtain a pure culture by this method.

Question 15

Explain the preparation of a pour plate method.

Answer 15

A pour plate is a dilution of a sample of the mixed culture and adding a small volume to the dilution to melted agar. The mix is then added to a Petri plate to solidify then incubated.

Question 16

Define the results of a pour plate method.

Answer 16

If dilution was appropriate, well separated colonies will be appreciated.

Question 17

What two types of colonies does the pour plate method provide?

Answer 17

A subsurface colony (within the Agar).

A surface colony

Question 18

True or false, the same species colonies will have similar appearances from the pour plate method. Elaborate.

Answer 18

False, same species colonies may have different appearances.

Question 19

Elaborate on the method of inhibition or killing of the undesired microorganism.

Answer 19

The addition of a chemical to the medium, which will stump the growth or kill unwanted microbes while permitting the wanted species to multiply.

Question 20

Give an example of a product used to facilitate the killing of unwanted microorganisms this method.

Answer 20

Basic dyes such as Crystal Violet or brilliant green will inhibit the growth or kill Gram-positive bacterial and permit the isolation Gram-negative bacteria.

Question 21

Explain the dilution method.

Answer 21

The dilution method is used to isolate only the most predominate bacteria in the medium.

Question 22

What liquid is considered a suitable diluent?

Answer 22

Water.

Question 23

Name 3 acceptable ways of representing a 1 in 10 dilution.

Answer 23

1:10, 1/10, 10-1

Question 24

Calculate the dilution made when 0.2 mL of 10-2 dilution is added to 4.8mL of diluent with the formula D2=(V1xD1)/V2

Answer 24

D2=(0.2x 10-2)/5 (.2+4.8) 5
D2=(2/100 x 1/100) /5
D2=(0.2 x 0.01) /5
D2=0.002 / 5
D2=0.0004
D2= 4/10000
D2=1/1250

Question 25

Describe the device used to isolate a single cell from a mixed culture.

Answer 25

A micromaniulateur.