Sign In
Not register? Register Now!
Essay Available:
3 pages/≈825 words
3 Sources
Life Sciences
Lab Report
English (U.S.)
MS Word
Total cost:
$ 11.88

Unknown Identification Laboratory Report Assignment (Lab Report Sample)


Unknown identification:
Students will also be given a bacterial culture to identify. Most of these will be organisms we have used
in exercises. ALL students will perform 5 tests in total: a Gram stain, fermentation tests (fermentation
tests for glucose, sucrose, and lactose are considered a single test), and then 3 other tests (enzymatic or
selective/differential media) on the unknown sample (these are selected by the student, must represent
logical/critical thinking for which tests are to be performed, and MUST be approved by Ms. Williams
prior to being performed). A handout titled “Ms. Williams’ Unknown Record sheet” MUST be used when
performing and recording data for your unknown tests. ALL test results MUST be shown to Ms.
Williams. A final report for the unknown identification must be turned in as a LAB REPORT by the date
stated in the class schedule. Unknowns are graded in two parts:
(i) 50 points for technique performance. For each test you perform incorrectly 5 points will be
deducted from the 50 points (example: you have to perform the gram stain 2 times to get it
correct = 5 points lost for the first incorrect result; have to perform the gram stain three times
= 10 points lost for the first and second incorrect results). This section is designed to assess
your ability to perform the techniques you have learned in the course.
(ii) 50 points for the laboratory report. Follow instructions below that give specific requirements for
each section (the bold blue percentages shown after the section title represent how much that
section is worth of the grade for the lab report):
 INTRODUCTION (15%): The introduction will only include a description of the tests performed:
the principle (biology) of the test, and how to interpret ALL possible results for that test. For example,
with the gram stain, you would discuss that the gram stain identifies the differences between two cell
wall types, the structures of the two cell wall types, how each cell wall type is detected/identified in
the gram stain, and how the gram stain is also used for observing cell morphology. Do NOT include
any methodology of the tests in the introduction. You CANNOT state what your organism is or its
importance in the introduction. You cannot “ramble” on about how identifying organisms is important,
only discuss the tests you performed as described above. This section must be between half to one and
a half pages/sides long. This is to allow you to discuss each of the tests you performed in the required
 OBJECTIVE (5%): You will have a single objective (to identify the unknown organism).
 HYPOTHESIS (10%): You will have a single, broad hypothesis. Hypotheses are written before you
start any work, so you cannot state what tests you will use, as you do not know that until you have the
results of the first tests. You cannot state what organism will be identified at the end either, as you
have no way of knowing this information before you start.
 MATERIALS/PROCEDURE (5%): The materials will be a paragraph list for all tests. The
procedure will be a 3-5 line summary of the chronological order you performed the tests in and which
tests required repeating. If you changed any parts of the procedure compared to the method(s) in the
laboratory manual for any of the tests, then you MUST give detailed information of how it was
changed. If you had to repeat any tests, then list that here.
 RESULTS (15%): The results section MUST be a table of ALL the results. There will be no images 
Required Texts (BOTH lab books are required and are available in the Clarkston campus
1. Mcallister, Carl F., 2011. Manual for Microbiology Laboratory 3rd ed., (this is a GPC published
laboratory manual and thus no ISBN)
2. Leboffe & Pierce, 2011. Photographic Atlas for the Microbiology Laboratory, 4th edition. Please use these two books as extra two sources, making total of five sources.
This paper have big portion of my grade 
I suppose to be in my nursing programme this month and without this class I can't . And very difficult to admission to nursing school

Student’s Name:
Instructor’s Name:
Course Number:
The Gram Stain test: This is a very important preliminary test used in initial classification as well as characterization of bacteria. It is used to differentiate bacteria based on staining differences in biochemical and physical characteristics of bacterial cell walls. The Gram Stain test therefore groups bacteria into two major categories: Gram-positive and Gram-negative bacteria. Not only is the test important in distinguishing between the two classes of bacteria, but also helpful in staining the bacteria for clear observation of their morphology under a light microscope. Gram-positive bacteria are identified by the purple color retention after the staining procedure while the Gram-negative bacteria give pink coloration on their cell walls. The differences in color retention are attributed to difference in physical and chemical composition in their cell walls. For example, the Gram-positive have a relatively thick cell wall composed of 90% peptidoglycan complex and teichoic acid cross-links. On the contrary, Gram-negative bacteria have thin cell walls composed of only 10% peptidoglycan complex and high lipid content. The thick cell walls in Gram-positive bacteria make them retain the purple color of crystal violet dye, even after being treated with ethanol. However, the crystal violet dye is quickly decolorized by ethanol, and they only retain the color of the second dye, Safranin. Based on the morphological characteristics of bacteria, the Gram stain test can identify different bacteria based on their sizes and shapes. Bacteria vary in size ranging from 0.5 to 10 microns. As for the shapes, they can be rod-shaped (or bacillus); helical (or spirilum); curved (or comma-shaped); and spherical (or coccus).
Sugar Fermentation Test: some bacteria are known to ferment carbohydrates, especially the simple sugars such as glucose, lactose, xylose, maltose, and sucrose. Each category of bacteria can only ferment some, and not all, of the sugars. As a result, this test is used separately and differentially to identify bacteria that are capable of fermenting different sugars. Bacteria that ferment a specific sugar can be identified by noting color changes when the bacteria are put into the sugar-phenol red broth. Positive results are noted when the phenol red broth changes color from red to yellow, indicating the presence of acidic end products as a result of sugar fermentation. On the contrary, negative changes are detected when there is no color change, indicating that the organism cannot ferment the sugar in question.
The Catalase test: Certain groups of bacteria are known to produce the enzyme catalase due to their use of oxygen in respiration. The enzyme catalase is meant to protect these classes of bacteria from harmful and destructive oxygen radicals and metabolites released during respiration. A classic example of a metabolite released during oxygen respiration is hydrogen peroxidase, which is bactericidal. To prevent themselves from such bactericidal metabolites, these bacteria produce catalase which breaks down hydrogen peroxide to water and oxygen molecules. Catalase-positive bacterial isolates will give effervescence immediately hydrogen peroxide is added to the bacterial culture. On the other hand, catalase-negative isolates do not give any effervescence.
The Urease test: Some bacteria possess the ability to breakdown urea, the main product in amino acid decarboxylation, to its constituent products – ammonia and carbon dioxide gas. For these bacteria, this is an indication that they possess the enzyme urease. On urea agar medium, urease-positive bacteria will give a strong reaction which is shown by an intense color change from yellow to bright pink. Contr...
Get the Whole Paper!
Not exactly what you need?
Do you need a custom essay? Order right now:

Other Topics:

  • Unknown Identification Laboratory Report Assignment
    Description: Unknown Identification Laboratory: The Gram Stain test therefore groups bacteria into two major categories: Gram-positive and Gram-negative bacteria...
    3 pages/≈825 words | 3 Sources | MLA | Life Sciences | Lab Report |
Need a Plagiarism Free Essay?
Submit your instructions!