BISC110/S13: Series 3 Lab 10 Hill Reaction Variables

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Wellesley College

BISC110/112- Introduction to Cell Biology- Spring 2013

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Lab 10 Investigation of Variables Affecting Photosynthetic Rate

In this lab, you and your partner(s) will explore, in a self-designed, controlled experiment, one factor that may affect the rate of photosynthesis as measured by the Hill reaction.


Make table(s) and flow charts in your lab notebook for the data you will obtain from your self-designed and instructor approved experiment. Be sure you have adequate controls and replicate reactions and that all of the final volumes in your reactions are the same. Calculate how to make any dilutions and know final concentration of any crucial material in the reaction before you come to lab. Set up a table in which you can keep track of the times vs. the absorbance for each reaction.

When you and your partner(s) have collected all of your data, plot the A580 data (y-axis) versus time in seconds (x-axis) for the different treatments (you can plot several or all data sets on one graph or plot each treatment on a separate graphs). When making these graphs, do not include points where substrate is limiting. Add regression lines to each of your plots. Include the regression equations. The slopes represent the Hill reaction rate, which in this artificial system is the electron transport rate of photosystem II in photosynthesis. Plot the rates (y-axis) against your variable (x-axis) as directed by your instructor. Discuss your graphs with your partners to determine how your data answers your experimental question. Does the data support your hypothesis? If not, should you rethink your hypothesis or consider confounding variables that you didn't account for in your experiment? Show your graphs to your instructor and discuss your findings with her/him before you leave lab.

Laboratory Cleanup

  1. Clean all glassware with water, centrifuge tubes with ethanol and place pipettes in the wash bucket at the end of your bench.
  2. Dispose of any hazardous waste (reactions containing DCMU) in the container in the hood.
  3. Other assay reactions can be discarded in the sink.
  4. Place test tubes in the glass disposal container.
  5. Return the color filters to the instructor’s bench.


  1. A partial paper (title and results with figures) based on your experiment today is due on the date designated in the Calendar or by your lab instructor. This assignment must be done individually. Refer to the Guidelines for science writing information found in the Resources section of the Wiki.

After you complete your partial paper, please answer the following self assessment questions and include them at the very end of your partial paper word document.
a. What did you learn?
b. What did you wish you knew before you started?
c. What challenges did you face? Do you feel like you were able to work through those challenges? How?