The primary objective of this report is to design and perform an experiment with
ID: 96157 • Letter: T
Question
The primary objective of this report is to design and perform an experiment with yeast metabolism. This experiment can provide evidence on metabolic pathways, enzymes in the microbe, and could be adapted to a differential test. The last experiment focused on technique, this experiment has a large focus on experimental design. The secondary objective is to demonstrate lab report writing skills, this time with a more complex experiment and experiment options. The latter will be done using a standard manuscript format, although scientific writing is a universal skill for any format (e.g. charts, lab notes, memoranda).
CONTENTS
I. OVERVIEW II. INSTRUCTIONS III. SPECIFIC LAB REPORT & SUBMISSION INSTRUCTIONS IV. EXAMPLE OUTLINE OF MATERIALS AND METHODS V. APPROXIMATE GRADING VI. GENERAL LAB REPORT INSTRUCTIONS VII. EXAMPLE STUDENT LAB REPORT
I. OVERVIEW
Yeast metabolism experiments are a fairly common lab in Microbiology, and can be done with safe household items. Although items are generally regarded as safe, it is important to properly sanitize or disinfect equipment and surfaces after the experiment. Do not allow children or others to come into contact with aspects of the experiment, and never ingest any product of the experiment. Contact the instructor if there is a safety concern or any other reason an alternative lab is needed.
This experiment is to grow baker’s yeast in at least two different conditions (e.g. one variable and one control) and measure the difference by gas formation. There are several options of experimental aspects to vary in this experiment, and you can also just follow the example protocol. The example protocol below used a regular soda (with fructose) and diet soda. These were incubated for the same period at the same temperature, and measured by balloon size. The variable here was the presence of fructose (although pH varied too, but that was discussed in the conclusions of the report). Sugar type, temperature, and starting pH are all good examples of experimental variables. There are several examples on the internet if you need more examples, and you are required to have a minimum of two references in your report. You will need to take pictures of the observations and methods, and taking notes may be useful for writing the report. The grade of this lab is NOT dependent on expected results. However, it is affected by experimental setup, rationalizing methods, and discussing your results.
II. INSTRUCTIONS
Read the example outline, research the internet, and plan out your experiment. No problem in saving time or money, look around the house for items and decide if there is a more convenient option to get other materials like a local market. There are also example items listed at the end of the example outline. You will need baker’s yeast, other item can vary. You will need to reference at least two sources in your report, and this could be from any internet research you used for preparation. You will also need to discuss two variables that you did not use in the report, and using a second variable with proper controls will add points.
Plan out your methods. You will need baker’s yeast and will have measure the amount used. Examples are using one individual packet for each condition, using a measuring spoon, and using the same serving spoon to measure each amount. Here are more items to consider:
Container and liquid. Soda bottle is the classic example. Any size works but must be the same size unless that is your variable. Tall glasses have been used in the past. Decide the sugar source. The example used fructose and no sugar (purchased as such). If soda is used, let it sit out overnight to remove carbonation. Could also use water with table sugar (sucrose), or have a variable like mashed rice (mostly carbohydrate). Overall, if this involves your variable have two conditions to compare, and if it does not then make sure these are the same (e.g. using a variable temperature).
Bubble measurement. Balloons are the classic example. If there is any doubt, make sure it fits over the container. Yes, condoms have been used in the past. A ruler can help measure size, or even something standard like a dollar bill. An alternative is measuring bubble height, but make sure the glass/bottle is narrow or the soda bottle has the label removed.
Heat source and temperature measurement. Unless it is your variable, temperature should be the same for all conditions. This should also change to the same amount. The example used bowls that are the same size, filled with water at the same starting temperature. Even if the temperature dropped over time, it would likely be the same drop for both conditions. The optimal growth temperature is around 37°C, but other temperatures can be used. Room temperature will take a long period. If you do not have a thermometer, an alternative is using hot tap water. Adjust the tap water until you feel a slight burn (don’t hurt yourself, use a lower temperature if needed). This occurs at 60°C. Fill the bowl(s) and place your containers. Even though you started at a high temperature, it will drop over the incubation period and should cause a faster reaction than at room temperature. Or use half the maximum tap water temperature and half room temperature tap water.
pH measurement. Not everyone gets pH strips, and if it is not your variable then these are optional. If you start with the same liquid, it should be the same pH. The example used a regular and diet soda. You could search on the internet to find the pH difference at the start. Even if you cannot measure pH, it should be discussed in the lab report (internet resource, expected changes, etc). If you are changing your pH, consider items like lemon juice, vinegar, or baking soda.
Execute your experiment. Do not forget to make observations at the start. Depending on your conditions, time can vary before seeing results. The example used 30 minutes (after 5 minutes at room temperature to let the yeast mix and start metabolism). If the whole incubation was done at room temperature, this could take hours. If you do not see results, or the results are the same for both conditions, this is not a problem. However, the results, interpretation, and alternatives must be discussed in your report.
Finish and write report. When your last observations are made, materials can be discarded and other items can be cleaned. Properly disinfect any working surfaces, and wash/sanitize any containers and utensils. A small amount of bleach is recommended, but not needed if you have other preferred methods.
III. SPECIFIC LAB REPORT & SUBMISSION INSTRUCTIONS
General lab report instructions for a manuscript format are below in another section. If you are not familiar with this standard format, read those instructions first. These contain the second and third most common mistakes, which are not citing sources and not using paragraph format like listing items or using bullet points.
Details remain important in this experiment, specifically on experimental setup, and the observations by association. Having expected results is not a grading criterion for this activity, but discussing any problems or other alternatives is. Specific to this report, you must include at least two references, and discuss two possible variables that you did experiment with. Below are other considerations specific to this report:
Introduction-
What was the purpose of this experiment (i.e. what objective do you accomplish)? What are potential variables you can use in yeast growth experiments? What variable did you choose?
What species is in baker’s yeast? What is the optimal growth temperature? Optimal pH? What metabolic pathways can this yeast use, and the chemical end products?
Briefly preview (summarize) what was done in the experiment and the end results.
Materials & Methods-
What materials did you use (sentences, no listing!)? What brands (as applicable)? Was there any preparation, such as letting the carbonation out of the soda? If you used soda, table sugar, rice, milk, or something else, what type of sugar does it contain and how much?
Describe your methods as you did them. Do not personalize (I, my, we) and cover beginning to end (preparation, execution, and analysis of results). Specifically mention the measurement of beginning yeast, temperature, pH, and incubation periods.
Results-
Describe observations at the beginning of the experiment. If you used a balloon, how big was it in the beginning? Where there any bubbles already formed? Was the yeast mixed, all at top or bottom?
Describe all the changes in from the beginning of the experiment to the end. What was the size of the balloon, or measurement of bubble height? Anything else measured such as pH?
Was there any color change in the solution? Did the yeast move from top to bottom or other?
Focus only on observations, conclusions and interpretations belong in the next section.
Discussion-
What conclusions can you make from this experiment? What was your variable and what was your control, and were the observations different in the end?
How did your results lead to your conclusion? What does this suggest, specifically about yeast metabolism?
Was there anything unexpected in the results? Were there other parameters that could have been measured or measure better (e.g. pH strips or a thermometer)? Could any other difference between the control and variable condition have affected your results (e.g. in the example, fructose was the variable but pH also changed)?
What other variables did you not test for, but could have? Discuss a minimum of two.
References (Bibliography)
1) Reference each source you used in APA format. Then cite the references you used in the text of report, generally at the end of the sentence it applies to. There is a minimum of two references for this report. Refer to “General Lab Report Instructions” for information/links on APA citations.
Figures & Legends
1) Post each picture you took here, after the references. Refer to each figure in the appropriate section of your paper (such as the Results) by number based on when you discussed these (i.e. Picture 1, Picture 2, etc.). Write a short description below it (legend), usually 1 or two sentences.
Activity submission: Save the report as one file (pictures embedded) and upload it to the submission folder on the course website (preferably Word file, .doc .docx .rtf .pdf). You are always welcome to email a backup copy to the instructor. Typical submission is about 3 pages single spaced (excluding figures).
IV. EXAMPLE OUTLINE OF MATERIALS AND METHODS
The following is an example from a past student written as an outline, not a lab report. There are notes from the instructor at the end.
Materials:
One 20oz bottle of 7up, one 20oz bottle of Diet 7up
Two ¼ oz Dry yeast packets measuring spoons
2 latex balloons Thermometer
4 pH test strips
2 large bowl’s filled with water, heated to 90* F to use as a water bath.
Method:
Step one: Open 7up/Sprite bottle, and Diet 7up/ Diet Sprite and allow setting out overnight, with the caps partially off. The reasoning behind this is to let carbonation escape. Take a pH reading right before experiment, and record it.
Step two: In the morning, take off cap of soda bottle, hold bottle over kitchen sink, to prevent spilling, and add 2 tablespoons of baker’s yeast to each soda bottle and top with balloon, and let yeast incubate in bottle for two minutes.
Step 2, adding baker’s yeast. Step 2, five minutes of incubation.
Step three: Place soda bottles, with balloons still attached, in the 90* water bath. Let the soda bottles sit, for 15-20 minutes, and then swirl. During this procedure, be looking to see if bubbles appear, or if the balloons are getting largeren minutes in 90* water bath.
Thirty minutes in 90* water bath.
Student Notes
In the beginning of the pH lab, the sodas were slightly different, the regular soda having a slightly more acidic base to it, than the diet soda. With the addition of the baker’s yeast, the regular soda began to form bubbles, and the balloon enlarged much quicker than the diet soda.
At the end of the lab, the pH level was more of a neutral base on both the diet and regular soda. With the regular one being closer to an alkaline base.
Notes from the Instructor
-You will be submitting a manuscript-style lab report, not anything similar to this presentation -The pH ended up being a second variable, with no control. This happens, but it has to be discussed in the lab report as potentially affecting the results.
-Student used 90°F (about 32°C), which is fine but did not really cover if the temperature changed over time.
-Over time I have asked where students get their materials. Here are examples with costs:
Wal-Mart: 3 pack of baker’s yeast, .98. Package of balloons, .97. Two bottles of soda, 1.59 each. 5 pack of pH testing strips, found in the pet department (fish supply) 4.97. This is where I chose to purchase my testing materials. Finding the pH strips in the pet department was much more affordable than in the swimming section. They were 11.97 in the swimming section.
Target: 3 pack of baker’s yeast, 1.15. Package of balloons, 1.25. Two bottles of soda, 1.49 each. 7 pack of pH testing strips, found in pool department 11.49
Aldi: 3 pack of baker’s yeast, .49. Did not have balloons, did not have 20oz bottles, but did have 2-liters for 1.19. Had pool pH strips for 10.99 (but I believe this is only a seasonal item there).
Dillon’s: 3 pack baker’s yeast, 1.15. Package of balloons, 2.35. Two bottles of soda, 1.79 each, and I was not able to find pH testing strips
VI. GENERAL LAB REPORT INSTRUCTIONS
Lab reports are divided into sections. Each section has a heading and provides clarity to the report, and serves a purpose (avoid the wrong information in the wrong section!). Reports in this course all contain the sections (described below):
-Title/Byline
-Introduction
-Materials and Methods
-Results
-Discussion
-References
-Figures, Tables, and Legends
Lab reports are written in paragraph form. With the exception of the References Section, any pictures, charts, tables, and lists go in the last section. Anything in the last section is referenced and described in the paragraph text of the previous sections.
Length and word count ranges are only suggestive (no direct grade impact). Shorter papers often have missing information and longer papers tend to be unfocused.
Materials and Methods/Results sections are written in past tense (what happened, not a procedure for someone else).
A very fundamental aspect in science and this course is knowing the difference between observations (results) and interpretations (conclusions). An observation is a measurement, detection (when equipment is used), or something you see. An interpretation is what the observation implies, common knowledge conclusions, or what you think it suggests. The lab workbook is full of examples. Keep in mind interpretations are not 100% correct, and there is always some possibility of error (students often forget this on common experiments, e.g. Gram stains).
Your grade is considered your primary feedback. Grades are usually posted within two weeks of the due date. If you desire specific feedback on what impacted the grade, email the request to the instructor and generally the three aspects that impacted your grade the most will be returned. You are always welcome to ask for more feedback after. You can always ask for feedback on a draft before submission. Generally give a few days for comments (start early, don’t wait until the deadline is near).
Reports can always be resubmitted up to the deadline. Emailing copies to the instructor before the deadline is encouraged. If your grade is a zero because it did not submit correctly, the instructor will grade the emailed copy upon request (and no penalties applied if original email was received before deadline). Please note that emailed copies are not automatically graded.
The following is more information on items for each section:
Title Section
-Title (come up with something relevant)
-Byline (your name, course section)
Introduction
Basic Introduction (1 paragraph)
What is the scientific objective of the experiment? What is the concept, or how do you plan on primarily achieving this objective? How does this relate to other applications, theories, the environment, diseases, industrial/lab/medical aspects, etc?
Background (1-3 paragraphs)
State any relevant microbiology background details, such as some information about a microbe genus possibly involved. Then, provide information on how the experiment aspects work (not how to do it, but what is actually happening during the experiment). Don’t forget details of aspects later in the report (e.g. if you measure pH, mention here how pH could affect growth). [In a simple experiment, this can be short. In complex experiments, touch as each aspect.]
Summarization overview (1 paragraph)
This is a summary of the next three sections. At a minimum, give a couple sentence summary of the discussion including your main interpretation. Also, include any introduction, theory, or background details that didn’t quite fit in before.
Materials and Methods
Materials (1 paragraph)
Describe the materials you used in this lab, and brands, sizes, and when it came from.
Methods (1 paragraph for each individual method, analysis method can be a separate paragraph) Be comprehensive, start at the beginning and continue until the lab activity was complete. Remember to right in past tense, or how it was done (not instructions for how to do it). Do not write “how to” do it, but give enough detail that a classmate could repeat what you did based on your account. Finally, end each method with how the experiment was analyzed (i.e. how results were observed, compared).
Results
Describe all beginning and end states, and any changes in between. (1 paragraph per experiment) Note all observations and any measurements taken during the experiment (including no change). Make statements regarding the consistency of observations (e.g. approximately half of the colonies appeared golden, and these were not isolated from the red colonies). Remember that a result is a measurement or observations (e.g. you do not see lysis of red blood cells, you see discoloration in the plate). Do not forget any of the positive or negative control results, or results of any comparisons (including expected results from the book, or from another external source).
Discussion
1) Interpretation of the results (1 paragraph or 1 paragraph per method)
Give a summary/recap of each result and state what you believe it indicates (e.g. The purple color of the cells suggest these cells are Gram-positive.). Then state why this is the likely conclusion (e.g. The purple Gram stain did not appear to wash out after alcohol was applied). Remember that every
interpretation/conclusion can have some degree of error. Never say “prove”, but instead use words like suggest, indicates, etc. 2) Conclusion (1-2 paragraphs)
Summarize the conclusion(s). Start with the conclusion you are most confident with, and move to less confident conclusions. This is often going from less to more specific (e.g. The Gram-stain results suggest we isolated Gram-positive bacteria. Based the shape, these bacteria appear to be the Staphylococcus genus. Based on where they were sampled from, the bacteria are likely Staphylococcus aureus.). In the same or a new paragraph, state how much scientific confidence there is in the interpretations (e.g. Both the positive and negative Gram stain controls were purple and red cells as expected, which suggests the unknown sample was indeed Gram positive. The shape and arrangement of cells were more difficult to observe, and it is possible that another genus was present.).
3) Summary of conclusion and limitations (1-2 paragraphs)
Recap the conclusions, what could not be strongly concluded, and add any limitations, while associating the conclusions with the objectives of the experiment (e.g. The objective of this experiment was to identify the genus of a skin sample. The results strongly indicated the bacteria were Gram-positive, but this simplistic method was not able to determine the genus with high confidence based on equipment used.). State an alternative conclusion, and compare these results to expected results of the alternative (e.g. The cells could have also been Streptococcus, which are Gram-positive and spherical too). State further tests that could provide more evidence, and how (e.g. The experiment could be repeated with a higher powered microscope to see the arrangement detail, or a biochemical method such as streaking the sample on an MSA agar plate and comparing growth/agar color would help differentiate these alternatives.). Finally, state any issues or concerns with the experiments and how it may have impacted the results (e.g. After the triple streak method, the colonies were not completely isolated for sampling. This could have lead to a mixture of cells, however the colonies appeared to have the same morphology characteristics and the cells after the Gram stain were consistent across the microscope slide.).
References
List out a bibliography of all resources used. The APA format is required, but any other format that has the same information will not lose points (i.e. use any format you want, but if something is missing the APA requirement will be referred to for why the reference is incorrect). Be sure that all citations and cited in the text. At a minimum, you will generally need to cite the lab manual and text. It is alright to reference a book and cite different chapters and sections separately in this course. Choose good external resources, and do not directly use anonymous resources (see Wikipedia Policy in First Day Handout).
APA examples can be found all over the internet, including:http://www.liu.edu/CWIS/CWP/library/workshop/citapa.htm
Citation in the Text:
During the turbulent 1960s, science fiction programs on television reflected the public's attitudes toward the older generation (Hodges, 2000).
Bibliography Listing for a Book Article or Chapter:
James, N. E. (1988). Two sides of paradise: The Eden myth according to Kirk and Spock. In D. Palumbo (Ed.), Spectrum of the fantastic (pp. 219-223). Westport, CT: Greenwood.
Another link for a brief and basics of APA format: http://flash1r.apa.org/apastyle/basics/index.htm
Additional links on citations:
http://www.mhhe.com/biosci/genbio/maderinquiry/writing.htmlhttp://www.csub.edu/chemistry/331/laboutline.html
Figure, Table, and Legend
In this section, place all figures, tables, etc. in the order the item is referred to in the report. Remember that any item in this section must be mentioned in one of the previous sections of the lab report. These items are intended as aids, and do not replace descriptions in the report (i.e. a picture of a result does still needs to be described in the Results section). Each item must have a title (Words, numbers, or letters) and a legend (e.g. Figure 2: Isolated colonies on the agar plate after incubation period).
I. The following is a list of general lab manuscript considerations:
Write information in a concise, organized, and easy to read manner. The report should “flow”.
Do not personalize (e.g. I, my, mine, we, us, you, your).
Do not use contractions (e.g. Don’t, can’t).
Do not give possession to materials (e.g. yeast’s, bacteria’s, plate’s).
Declare all abbreviations.
(e.g. Gram-positive (Gram+) bacteria can contain toxins. Not all Gram+ bacteria have toxins.)
Repetition is encouraged, but make sure each aspect is repeated appropriately. Example:
Introduction: Gram staining is a differential stain.
Materials and Methods: Gram staining was finished by adding crystal-violet and iodine.
Results: Gram staining of a sample from the colony resulted in a purple color.
Discussion: Gram staining the unknown bacteria suggested it was Gram-positive because it appeared to retain the purple color.
The introduction should introduce the rest of the paper (i.e. overall project, microorganisms possibly involved, and each experiment should be covered with background information and purpose).
Avoid quoting other sources when it is something you can paraphrase. Remember, this is an evaluation of your knowledge.
Any other subheadings (beyond main headings like Introduction, Materials & Methods, Results, Discussion, References) should come at the beginning of the paragraph; never bold and underline something inside a paragraph (with the exception of using italics or underlining the genus and species of a microorganism).
Proper names are capitalized, including brand names. Sometimes a dye or a test is capitalized to because it is named after a proper noun. (e.g. Identification is made by a Gram stain, first invented by Hans Gram. We use mannitol salt agar to differentiate bacteria that can tolerate a high salt environment. If you are unsure about capitalization, at least be consistent (your book gets confused too).
Provide alternative conclusions in your discussion. These can be based on a tests with unclear results, tests that you were not able to perform, or additional tests that could have confirmed conclusions.
Conclusions are usually not absolute. Apply words such as suggests, probably, most likely…
Italicize the genus and species of a microorganism. (e.g.Escherichia coli)
The genus of a microorganism is abbreviated by the first letter every time it is mentioned after the first time. (e.g. E. coli). The genus and species are always italicized (underline if italics are not an option).
Book and periodical citations hold more credit than general websites. If you find the book online, cite it the same as if you had it physically. Avoid using anonymous sources such asWikipedia.org.
Use past tense when describing what you did in the lab and present tense when making statements of facts and chemical properties.
Write the report to the audience of your peers in terms of level.
Introduction, Materials and Methods, and Discussion sections will always have citations. Results section will sometimes have citations.
VII. EXAMPLE STUDENT LAB REPORT
The following is a past example of a lab report. They had different instructions and many mistakes, but may serve as examples for you. If you can identify the mistakes, then you are on the right track. Some parts have been omitted, such as references and figures.
Introduction
The purpose of this experiment was to determine the causative agent of bacterial contamination of a plastic bottle filled with drinking water, belonging to a college student. Upon drinking the contaminated water the student presented with gastrointestinal problems and was treated with antibiotics. After treatment with antibiotics that work on Gram positive and Gramnegative bacteria, the student recovered and symptoms disappeared. Based upon the symptoms the student presented with, it is suspected that the culprit of contamination and illness is Escherichia coli.
The experiment began with a 10mL sample of cloudy water obtained from the plastic bottle. The sample was inoculated on a nutrient agar plate, incubated, heatfixed, and Gram stained. The size, shape, color, and morphology of the microorganisms were then studied for determination of bacterial contamination.
A microbial culture can be a mixed culture or pure culture. A mixed culture is a microbial culture consisting of two or more different types of species. A pure culture consists of only one type of species. When dealing with a mixed culture, it is important to isolate the individual species so that proper identification can be made. A common technique used for isolating species in a mixed culture is the streak plate method. “In the streak plate method of isolation, a bacterial sample is streaked over the surface of a plated agar medium” (Leboffe & Pierce, 2008). Cells that have been isolated grow into colonies consisting only of the original cell type.
Basic stains are used to help identify bacterial species. A basic stain causes the bacterial cells to become colored. Prior to staining, the bacteria are prepared into a bacterial smear and heatfixed. Heatfixing kills the bacteria, allowing them to stick to the slide, and coagulates cytoplasmic proteins to make them more visible (Leboffe & Pierce, 2008). Staining the cells with colored dye make them more visible under the microscope.
Gram stain is a differential stain. A differential stain allows a microbiologist to detect differences between organisms or differences between parts of the same organism. In a gram stain, the primary stain crystal violet, is applied to the cells. Iodine is then added to enhance the crystal violet staining. Decolorization then follows. Applying alcohol or acetone causes decolorization. Gramnegative cells become decolorized, whereas Grampositive cells do not. Grampositive cells remain crystal violet.
Materials and Methods
Equipment used: one 10mL sample of cloudy water, one sterile inoculating loop, one nutrient agar plate, one Bunsen burner, one clean glass microscope slide, Gram stain crystal violet, Gram stain safranin, Gram stain iodine, 95% ethanol, bibulous paper, squirt bottle with distilled water, slide holder, disposable gloves, staining tray, staining screen, one compound microscope with oil objective lens, immersion oil, lens paper
To isolate the species in the mixed culture, a sample was aseptically obtained from the mixed culture with a sterile loop. To aseptically obtain the sample the tube containing the 10mL sample of cloudy water was held at an angle to minimize the chance of airborne microbial contamination. The inoculating loop was then carefully dipped into the tube and a sample was obtained from the cloudy water. The lid of the sterile agar plate was then lifted and used to shield the agar plate from airborne contamination. The quadrant streak method was used to transfer the sample from the inoculating loop to the agar plate. Beginning in one quadrant of the agar plate, using the inoculating loop, the mixed culture was streaked back and forth. Light pressure, and the side of the end of the loop were used to reduce the chances of cutting the agar. The loop was removed from the agar plate and the lid replaced onto the agar plate. The loop, from base to tip, was then sterilized by passing it through the flame of a Bunsen burner. The agar plate was rotated 90 degrees. Using the sterile loop, the agar plate was again streaked, beginning at one end of the first streak pattern, in a back and forth fashion. This procedure was repeated twice more until there were four streaks on the agar plate. After each streak the loop was sterilized and the agar plate rotated 90 degrees. The plate was labeled with the date, time, and sample inoculated. The plate was then inverted and incubated at 25 C for 48 hours.
A small drop of distilled water was placed on a clean slide using a sterile inoculating loop. A sample of bacteria was aseptically obtained from the agar plate using an inoculating loop. The inoculating loop was sterilized by flaming it using the Bunsen burner. The lid of the agar plate was lifted and used to prevent airborne contamination. The loop was touched to an uninoculated portion of the agar plate to cool. After cooling, a small amount of bacterial growth was obtained by gently touching a colony with the wire tip of the loop. The loop was carefully removed from the plate and the lid was replaced. Using the loop, the bacteria were then added to the slide and mixed with the water on the slide. The loop was then flamed. The smear was allowed to air dry. To heatfix the preparation, a slide holder was used to pass the smear through the upper part of a Bunsen burner flame two times. The slide was then allowed to cool.
Wearing gloves, and holding the slide over the staining tray, the smear was covered with Crystal Violet stain for one minute. Grasping the slide with a slide holder, the slide was gently rinsed with distilled water. The smear was then covered with Iodine stain for one minute. The slide was then gently rinsed with distilled water. The smear was then decolorized by applying 95% ethanol to the slide until the runoff was clear. The slide was then gently rinsed with distilled water. The smear was then counterstained with Safranin stain for one minute. The slide was then gently rinsed with distilled water. The slide was then gently blotted dry with bibulous paper. The slide was then observed under oil immersion on a compound microscope with oil objective lens.
Results
Nothing was visible on the Nutrient Agar plate immediately after streaking. After incubation at 25 C for 48 hours, one distinct bacterial colony was observed on the nutrient agar plate. The characteristics and morphology of the cultured microbes were as follows: Shape – circular, Type – bacteria, Margin – entire, Elevation raised, Texture mucoid, Pigment production – opaque.
After applying a sample of the bacteria onto a slide plate and performing a Gram stain the sample of bacteria were observed under a compound microscope with an oil objective lens. The bacteria on the slide appeared reddishpink in color and were rodshaped. The shape of the bacteria on the slide was consistent with the shape of the bacteria on the nutrient agar plate. Discussion
The fact that only one distinct bacterial colony appeared on the nutrient agar plate, suggests that the water in the bottle was contaminated with only one type of bacterium. After Gram staining the bacteria, the resulting reddishpink appearance of the bacteria indicates that the bacteria are Gram negative.
It is suspected that the causative agent of contamination is Escherichia coli. The findings of the lab tests are consistent with this assumption. E. coli is a Gram negative, rodshaped bacterium. There are many different strains of E. coli, most of which are harmless. One stain, of E. coli O157:H7, is pathogenic and can cause gastrointestinal infection in humans.
A fermentation test could be used to confirm or deny these suggestions. E. coli ferments the carbohydrate sorbitol (Tortua, Funk, Case, 2010). Pathogenic E. coli O157:H7, however, does not ferment sorbitol.
[Reference List Omitted]
Explanation / Answer
Yeast carbon metabolism at two different conditions: a comparitive study
Introduction: Yeast are chemo-organotrophs and they use organic compounds as their source of energy. Yeast can utilise monosaccharides like glucose and fructose or disaccharides like sucrose and galactose. The experiment was designed to study the yeast carbon metabolism at two different conditions.
Materials and methods: An observational cross sectional study is desiged to observe the amount of gas produced by yeast in media containing regular soda with fructose and diet soda. Temperature, period of incubation and pH is maintained constant between the two media.
Results: The growth of yeast cells can be compared in two media with the help of amount of gas produced.
Conclusion: The growth of yeast is more in the media contain regular soda with fructose. The results of the study indicates that hexose sugars are needed for yeast metabolism.
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