[ 10 pts. Anderson takes his high school science class on a field trip to a biology lab that studies an enzyme that catalyzes conversion of hydrogen...
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# 37. [ 10 pts.] Mr. Anderson takes his high school science class on a field trip to a biology lab that studies an

enzyme that catalyzes conversion of hydrogen peroxide into water and oxygen gas. A graduate student in the lab currently is investigating the cellular location of this enzyme in a newly discovered plant species. The grad student first shows the students how to prepare plant cell fractions by homogenization and differential centrifugation. After preparing three fractions to test, she explains the enzyme assay. First, 1 ml of buffer solution containing a detergent is added to a series of test tubes. Next, 0.4 ml of a particular cell fraction is added to each test tube. Finally, 0.1 ml of concentrated hydrogen peroxide is added to each test tube. If the enzyme that acts on hydrogen peroxide is present in a cell fraction, it converts the hydrogen peroxide to water and oxygen gas. The oxygen gas causes the detergent to foam. The height of the foam in the tube after 15 minutes of reaction time is proportional to the amount of the enzyme present. The grad student lets the visiting students perform the assay. They prepare two replicates of each experimental condition. The students' data are recorded below. Test Tube # Cell Fraction Tested Height of Foam (in mm) Average Replicate A Replicate B Height 1 Complete Cell Homogenate 70 94 82 mm 2 No Homogenate (buffer only) 0.1 0.0 0.05 mm 3 Pellet 1 from 2000 x g centrifugation 0. 2 0.5 0.35 mm 4 Pellet 2 from 20000 x g centrifugation 60 86 73 mm 5 Supernatant from 20000 x g centrifugation 10 13 11.5 mm A. What is the independent variable in the experiment? (1 pt.) B. What is the dependent variable in the experiment? (1 pt.) C. Which test tube is included as a negative control? Explain what makes it a negative control and its purpose in the experiment. (2 pts.) D. Which test tube is included as a positive control? Explain what makes it a positive control and its purpose in the experiment. (2 pts.)

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