Week 4 Lab
Posted by drstocksblog on September 20, 2009
Exercise 5 — Organisms in the Environment.
This exercise is pretty straight forward:
You will sample two environments — your body and any non-body environment. For each:
- Swab the environment with a sterile swab; if the environmental surface is dry, moisten the swab with sterile water.
- Zig-zag the swab over the surface of a trypticase soy agar plate. [Don't forget to label the plate!]
- Then swish the swab in a tube of sterile broth. [NOTE: broth is just a liquid medium.]
- What do you do with the swab?????
- Place the plate in the appropriate bin for incubation:
- 37 degrees C for the body
- 25 degrees C for room temperature
- Place both tubes of broth in a test tube rack which will be incubated at 37 degrees C.
Exercise 6 — Hand Washing Experiment
About the Scientific Method:
- All scientific investigations start out with observations. These may include observations in nature or information from sources such as advertising claims and scientific reports and papers in refereed scientific journals.
- Do some background reading before you come to lab!!!!
- Such observations lead to questions that may be answered by good experimental design. They lead first to objectives of the investigation overall. For example, in this exercise your objective clearly is to determine the effectiveness of some method [you fill in the method] of hand cleansing.
- From this comes your hypothesis. The hypothesis is based on observations. It is a statement of the expected results of your experiment. [It is not a question.] It should be stated in a way that it can be affirmed or denied by the experiment you are designing.
- Your experimental design should follow from your hypothesis.
- It should clearly test the hypothesis. And must contain a control as well as one or more experimental variables.
- For example an unwashed hand would be a control for most of your experiments.
- If you were testing the effectiveness of water temperature you would have cold and hot water washing as your experimental variables.
- Your experiment must be replicated to insure that your results are dependable.
- In this case each member of your group conduct exactly the same experiment. That way each person is replicating the experiment.
- Your experimental results must be quantified in some way so that you can calculate a mean (average) of the replicated results!
- The easiest way to do this is to use a scale of your design which will assign a numerical score (say 0 to 3) to the amount of growth on the agar plate.
- Your results will be “published” in a PowerPoint report!
Practicalities:
- Work in groups. Four members is ideal. Three is too few to get good replication and 5 is really too many.
- Five will be allowed only with approval of your lab instructor and only when there is no other way to formulate groups.
- Each person gets one plate of agar.
- Test methods by lightly pressing a finger on the surface of the agar.
- You can easily divide a plate into 4 sections: one a control and one for each variation on a method. [For example, time would be 1 minutes, 5 minutes, 10 minutes, 15 minutes.]
- Remember that each person does exactly the same thing.
- Don’t overlap variables. For example: washing both hands with cold water, testing, then washing with hot water and testing is examining the effect of double washing not the differences between the two!
- You can remedy this by using different fingers for different treatments OR by recontaminating your hands between treatments.
- All plates will be incubated at 37 degrees C for approximately 48 hours.
- Results will be collected and pictures taken of plates during the return lab.
- Note the computer int he lab has a digital camera attached or you can use your own cameras.
- Completed reports will be in one week — the date depending upon the date of Exam 1 to avoid having the exam and the reports due on the same day.
- Reports will include PowerPoint with narration and a written abstract. [Instructions on Vancko Hall.]
