Unit 2 Lab Exam

Question 1

What does sterile mean

Answer 1

lacking ALL life forms

Question 2

Define a pure culture

Answer 2

a growth of microorganisms that contain only one specific kind (strain) of microbe

Question 3

What is the most common way to obtain pure cultures

Answer 3

streaking a culture of microbes for single colonies on a solid medium (agar plate)

Question 4

How much should we turn the bunsen burner for gas flow

Answer 4

1-half of a turn

Question 5

When should we take the wire out of the flame for sterlization

Answer 5

when it turns orange

Question 6

How long should we let the flamed wire cool before use

Answer 6

10-15 seconds–do not wave it around

Question 7

When re sterilizing the wire which direction should we move

Answer 7

towards the tip so that the inoculum doesn’t spatter and create aerosol of viable cells

Question 8

Do we hold the tube containing the inoculum source and the tube with the recipient medium in the same or different hands for a tube to tube transfer

Answer 8

same

Question 9

How should the plugs or caps be removed for tube to tube transfer

Answer 9

with the last two fingers of the hand holding the needle or loop, leaving the thumb and index finger free to hold and manipulate the loop with the middle finger as a guide

Question 10

With a plate to tube transfer should both be handled at the same time

Answer 10

no

Question 11

For a plate to tube transfer where do we want to place the inoculum in the tube? How do we mix it?

Answer 11

rub the wire on the moistened side of the tube just above fluid level and slant it to wash the inoculum down; do not rattle the wire against the sides of the tubes to shake it into broth

Question 12

What is the streaking plate method used for

Answer 12

mechanically diluting a concentrated sample of microorganisms to a small, scattered population of cells over the surface of the solid medium

Question 13

What is the primary purpose of plating

Answer 13

obtain well-isolated colonies on a large part of the plate surface

Question 14

What must be done to the wire when streaking a plate

Answer 14

re sterilize the loop with the flame between each streak

Question 15

How big should our first phase of the streak be

Answer 15

1/4th of the plate

Question 16

How big should our second phase of the streak be

Answer 16

1/2 of the plate

Question 17

________ _________ are essential in pure culture techniques

Answer 17

isolated colonies

Question 18

What does colony formation result from

Answer 18

growth and replication of a cell that can use the medium as a source of nutrients and that can tolerate the physical conditions present

Question 19

After streaking a plate, the cell should multiply and result in

Answer 19

resulting, during incubation, a colony of identical cells

Question 20

Define colony

Answer 20

visible (to the naked eye) mass of millions of cells that arose from a common source

Question 21

What do we use when we consider the common origin for the cells of a colony

Answer 21

CFU–colony forming unit

Question 22

Define a spore

Answer 22

dormant type of cell whose main advantage is being able to withstand harsh environmental conditions

Question 23

When will a spore become a vegetative cell again

Answer 23

when growth conditions return

Question 24

Spores qualify as colony forming units T/F

Answer 24

True

Question 25

What type of growth is the first streaking of a streak plate

Answer 25

confluent growth

Question 26

What are the three reasons that we should treat all cultures as pathogenic

Answer 26

1. cultures may have been contaminated
2. they may contain unknown environmental microbes
3. microbes may have acquired virulence by mutation or natural transformation

Question 27

What is Nutrient broth medium for

Answer 27

organisms that are not nutritionally fastidious

Question 28

Glucose is added to NB for what

Answer 28

to allow fermentation under the low oxygen conditions by incubating the tubes in non shaking incubator

Question 29

What is the purpose of sterlizing between streaks

Answer 29

to ensure that we will eventually dilute the culture to have isolated colonies in the last streaking quadrant

Question 30

Streaking a plate will check ______ among colonies

Answer 30

uniformity

Question 31

Cloudiness =

Answer 31

turbidity

Question 32

Can you tell if you aseptic technique in the tube transfers are only the desired microbes

Answer 32

no, we can’t be certain because it could have been contaminated during the incovulation procedure