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Straigherline Selective Media and Agar Lab with Answers
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Straigherline Selective Media and Agar Lab with completed answers, pictures and tables
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Lab 4 Selective Media & Agar BIO250L”Student Name: XXXX
Access Code (located on the underside of the lid of your lab kit): XXXX
“Pre-Lab Questions”
1. What is the difference between chemically defined and chemically complex media? Give either a
clinical or environmental research example for which each media type would be the most
appropriate choice for culturing microorganisms.
Chemically defined:is all known compositions
Chemically complex: .is unknown and can vary from batch to batch
2. Why is differential media typically inoculated with isolated colonies that have been previously
cultured on general growth media?
Differential media typically is inoculated with isolated colonies that have been previously
cultured on general growth media because it allows the growth of certain bacteria to
form. These organisms can be differentiated from biochemical reactions from different
groups or species.
3. Use a textbook or a reputable internet source (such as www.cdc.gov) to research and describe a
scenario in a lab or clinical setting in which a selective and/or differential test would be
necessary.
Selective media allows organisms to grow and inhabit the growth of another organism
and differential test.
“EXPERIMENT 1: Bioprospecting for Starch Degrading Bacteria
Data Tables
Table 3: Starch Agar and Gram Iodine Results
Growth on Starch Clear area around Do these bacteria
Sample
Agar? (Yes or No) colonies? contain amylase?
yes yes yes
A
yes yes yes
B
yes yes yes
C
yes yes yes
D
Post-Lab Questions
1. Why is cow manure used as a potential source of starch-degrading bacteria? (If you are not
familiar with the process of digestion in cows, use a reputable internet source to inform your
answer.)
, Lab 4 Selective Media & Agar BIO250L”
Cow manure has a potential source of starch-degrading bacteria, because it contains
amylase, which is an enzyme that can break down carbohydrate molecules.
2. What are some other potential sources of starch-degrading bacteria?
Some potential sources of starch degrading bacteria are potentially found in food, soil,
paper, textiles, and fermentation.
3. What component makes starch agar selective for starch-degrading bacteria?
The components that make starch agar selective for starch-degrading bacteria is that
their ability to distinguish if it can produce amylase or not. Sugar and amylase are the
components and nutrients that help/allow bacteria to grow.
4. Why were each of the following steps performed in this experiment?
a. Serial dilution:
Serial dilution is a step that is used to reduce concentration of microorganisms
and to obtain the number of cells on the media.
b. Growth on the nutrient agar plates:
Growth on the nutrient agar plates is a step used for purification and isolating the
bacteria so that the bacteria can grow, to be identified and tested.
c. Streak on the starch agar plates:
Streak on the starch agar plates is the last step used to isolate the sample and
the technique helps identify on a new medium.
Insert a photo of your plates. Include your name and access code handwritten in the background of
your photo.
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