Microbiology worksheet Exercise 8 Questions 1. Define a culture medium. A culture media are agar gelatinous or liquid mediumnutritive substances such as microorganisms, animal cells, plant cells,...

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Microbiology worksheet

Exercise 8

Questions

1. Define a culture medium.

A culture media are agar gelatinous or liquid mediumnutritive substances such as microorganisms, animal cells, plant cells, ortissues and are cultivated for scientific purposes.

The American Heritage® Dictionary of the English Language,Fourth Edition copyright ©2000 by Houghton Mifflin Company. Updated in 2009.Published by Houghton Mifflin Company.

2. Discuss some of the physical and chemical factorsinvolved in the

composition, and in the preparation, of a culture medium.

Nutrient ingredients:

___________________________________________________________

___________

pH and buffering:

___________________________________________________________

___________

Heat (to reconstitute):

___________________________________________________________

___________

Heat (to sterilize):

heating in an autoclave at 121°C for 15 min. kills all living organisms,including spores for the media

glassware heated at 160 °C for 2 hours

Other:

___________________________________________________________

____________

3. At what temperature does agar solidify?

________________________________________________________________

_____________

Page 1 of 5

From Laboratory Manual & Workbook in MicrobiologyApplications to Patient Care (9th ed.). By

Josephine A. Morello, Helen Eckel Mizer, and Paul A. GranatoCopyright © 2006 The McGraw-

Hill Companies, Inc. Reprinted with permission of TheMcGraw-Hill Companies, Inc.

BIO2071_Microbiology Laboratory

At what temperature does agar melt?

________________________________________________________________

_____________

4. What would happen to plates poured with agar that is toohot?

________________________________________________________________

_____________

Could they be used?

________________________________________________________________

_____________

5. What would happen to plates poured with agar that is toocool?

________________________________________________________________

_____________

Could they be used?

________________________________________________________________

_____________

6. Why are culture media sterilized before use?

7. Discuss the relative value of broth and agar media inisolating bacteria from

mixed cultures.

8. Are nutrient broths and agars, as you have prepared them,suitable for

supporting growth of all microorganisms pathogenic forhumans? Explain your

answer.

Page 2 of 5

From Laboratory Manual & Workbook in MicrobiologyApplications to Patient Care (9th ed.). By

Josephine A. Morello, Helen Eckel Mizer, and Paul A. GranatoCopyright © 2006 The McGraw-

Hill Companies, Inc. Reprinted with permission of TheMcGraw-Hill Companies, Inc.

BIO2071_Microbiology Laboratory

Exercise 9

Questions

1. When an agar plate is inoculated, why is the loopsterilized after the initial

inoculum is put on?

2. Distinguish between a pure culture and a mixed culture.

3. Define a bacterial colony. List four characteristics bywhich bacterial

colonies may be distinguished.

4. Why should a Petri dish not be left open for any extendedperiod?

5. Why does the streaking method you used to inoculate yourplates result in

isolated colonies?

6. Why is it necessary to isolate individual colonies from amixed growth?

7. Why was a blood agar, rather than a nutrient agar, plateused for the

culture from your mouth?

8. Are the large numbers of microorganisms found in themouth cause for

concern? Explain.

9. How do microorganisms find their way into the mouth?

Exercise 10

Questions

1. Discuss the relative convenience of pour- andstreak-plate techniques in

culturing clinical specimens?

2. Why are plate cultures incubated in the invertedpositions?

3. How do you decide which colonies should be picked from aplate culture

of a mixed flora?

4. Why is it necessary to make pure subcultures of organismsgrown from

clinical specimens?

5. How can you determine whether a culture or subculture ispure?

6. What kinds of clinical specimens may yield a mixed florain bacterial

cultures?

Page 3 of 5

From Laboratory Manual & Workbook in MicrobiologyApplications to Patient Care (9th ed.). By

Josephine A. Morello, Helen Eckel Mizer, and Paul A. GranatoCopyright © 2006 The McGraw-

Hill Companies, Inc. Reprinted with permission of TheMcGraw-Hill Companies, Inc.

BIO2071_Microbiology Laboratory

7. When more than one colony type appears in pure culture,what are the

most likely sources of extraneous contamination?

Exercise 16

Questions

1. Define a differential medium and discuss its purpose.

2. Define a selective medium and describe its uses.

3. Why is MacConkey agar selective as well as differential?

4. Why is blood agar useful as a primary isolation medium?

5. How can one distinguish E. coli from P. aerugionosa on

Nutrient agar?

___________________________________________________________

____________

Blood agar?

___________________________________________________________

____________

MAC agar?

___________________________________________________________

____________

6. What is the major difference between ModifiedThayer-Martin (MTM) and

chocolate agar? When would you use MTM rather than chocolateagar?

7. If you wanted to isolate S. aureus from a pus specimencontaining a mixed

flora, what medium would you choose to get results mostrapidly? Why?

8. What is the value of making a Gram stain directly from aclinical

specimen?

9. Why is aseptic technique important in the laboratory? Inpatient care?

Page 4 of 5

From Laboratory Manual & Workbook in MicrobiologyApplications to Patient Care (9th ed.). By

Josephine A. Morello, Helen Eckel Mizer, and Paul A. GranatoCopyright © 2006 The McGraw-

Hill Companies, Inc. Reprinted with permission of TheMcGraw-Hill Companies, Inc.

BIO2071_Microbiology Laboratory

Exercise 17.2 and 17.3

Questions

1. What is the color of phenol red at an acid pH?

2. What is the function of a Durham tube?

3. Why is iodine used to detect starch hydrolysis?

4. Name one indole-positive organism?

5. How is indole produced in SIM medium? How is it detected?

6. How is hydrogen sulfide demonstrated in this medium?

7. Name two methods of determining bacterial motility.

8. Why is it essential to have pure cultures for biochemicaltests?

9. Could a pH-sensitive color indicator be used to revealthe presence of a

contaminant in a fluid that should be sterile? Explain.

Answered Same DayDec 20, 2021

Solution

Robert answered on Dec 20 2021
3 Votes
Microbiology worksheet
Exercise 8
Questions
1. Define a culture medium.
A culture media are agar gelatinous or liquid medium nutritive substances such as
microorganisms, animal cells, plant cells, or tissues and are cultivated for scientific purposes.
.
2. Discuss some of the physical and chemical factors involved in the
Composition, and in the preparation, of a culture medium.

Nutrient ingredients:

Ans-Macronutrient likenitrogen,phosphorus,calcium,potassium ,Micronutrients like
Iron,molebdenum,manganese,zinc,boron And some vitamins and Ca
on.

pH
Ans-Ph is 7.4 approx.if the ph gives pink color that means it is basic if it gives yellow than acidic
pH and buffering:
Heat (to reconstitute):
Ans-culture media have to be boiled if it contains agar and for reconstitution distilled water is
used.
Heat (to sterilize):
heating in an autoclave at 121°C for 15 min. kills all living organisms, including spores for the
media
glassware heated at 160 °C for 2 hours
Other:
Ans-Flaming in Bunsen flame.
3. At what temperature does agar solidify?
Ans-32-40 degree
At what temperature does agar melt?
Ans-85 degree approx...
4. What would happen to plates poured with agar that is too hot?
Ans-if the agar is too hot it will kill the bacteria and bu
les will come at the time of pouring.
Could they be used?
Ans-no, if used gives inappropriate results
5. What would happen to plates poured with agar that is too cool?
Ans-It cannot be poured and if somehow poured than streaking will be difficult.
Could they be used?
No
6. Why are culture media sterilized before use?
Ans-To reduce the risk of contamination and growth of undesired microorganisms.
7. Are nutrient
oths and agars, as you have prepared them, suitable for
supporting growth of all microorganisms pathogenic for humans? Explain your
answer.
Ans-No, because some microorganisms cannot grow on nutrient
oths and agar.
Exercise 9
Questions
1. When an agar plate is inoculated, why is the loop sterilized after the initial
inoculum is put on?
Ans-To decrease the risk of contamination.
2. Distinguish between a pure culture and a mixed culture.
Ans-A pure culture is a type of culture in which only one type of colonies are found while mixed
culture in which different types of colonies are found.
3. Define a bacterial colony. List four characteristics by which bacterial
colonies may be distinguished.
ANs-A bacteria colony is defined as a group of bacteria that grow in the solid media or surface.
There are four characteristics of bacteria by which they are distinguished are cocci, rods, vi
io
and spiral
4. Why should a Petri dish not be left open for any extended period?
Ans - A petri dish is a type of container used to grow the cultures. One cannot open a petridish for
a long time to decrease the chance of contamination.
5. Why does the streaking method you used to inoculate your plates result in
isolated colonies?
Ans-Streaking method is used to inoculate...
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