Biology Projects

DNA Extraction Lab #2-Introducing a Variable

DNA Extraction Lab

You will need to refer to the DNA Extraction lab that is the project listed before this one. The first lab serves as the basis for making comparisons, so you should have completed the activity exactly as described. If you need to make any changes (for example using a DNA source other than split peas), make sure you note these in the Procedure section of your Lab Report. This second time you do the experiment, you will be changing one thing. This is called introducing a variable (a variable is a factor that changes in an experiment).

The variable you choose is up to you. You might try one of the following:

  1. using a different DNA source than in your first experiment
  2. using a different enzyme (for example if you used meat tenderizer the first time, use pineapple juice the second time)
  3. using hot water instead of cold water
  4. eliminating the salt.

    Make sure you only change one thing in your second experiment. This is so that whatever differences you notice, you can be sure they occurred because of the change you made in your experiment design.

    Go to The Scientific Method (Writing a Lab Report—Introduction).

    To write your Lab Report, follow the instructions and format . Here are some tips and guidelines to help you:

    Activity Name: Kitchen Lab—DNA Extraction

    Purpose:
    This will vary depending upon what you have decided to use as your variable. For example, if you have chosen to use two different food types (for example split peas and broccoli) your purpose might be 'to determine if broccoli is a better food than split peas for the extraction of DNA.'

    Hypothesis:
    Using the previous example, your hypothesis might be 'Different food types will yield different amounts of DNA.'

    Procedure:
    You can 'cut and paste' the instructions given in this lesson, or rewrite them under the 'Procedure' subheading. You will need to change some parts of the instructions because you are going to be introducing a variable—you are modifying the original experiment. Using the above example, your instructions might say 'blend 125 ml broccoli' in place of split peas.

    Observations:

      • Briefly describe the appearance of your mixture at each stage (before and after adding each ingredient) and note any differences between the control mixture (original experiment) and the mixture you created according to the variable you are testing. You might choose to display your observations in a chart or table form, or as notes.

      • Once you have extracted DNA, make a comparison between the amounts you got from each of your samples. This will probably be qualitative—which sample looks as if it has more? You are not required to weigh each amount.

      • Finally, read ahead to the Lab Report Conclusion section below, and note that you are asked to think about how you interpreted your results. For example, if your experiment did not yield any visible DNA, what might have happened?

    Questions:

    1. Briefly describe all of the effects of the change you made to the original experiment. For example, were you able to extract more DNA? Was there a visible reaction when you added an ingredient that did not occur before?

    2. Why do you have to add an enzyme in this experiment? What do you think would happen if you skipped this step?

    3. Give two possible sources of error in this activity—what might have affected your success at extracting DNA?

    4. Give one way that you think you could improve upon this experiment.

    Conclusion:
    Answer the following

    1. If you were going to do this experiment again, how would you change the experiment this time?
    2. What else would you like to find out?

    Upload your lab to project submissions or submit a hard copy to your instructor.