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Revision as of 21:34, 26 December 2012
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.
- Clean all glassware with water, centrifuge tubes with ethanol and place pipettes in the wash bucket at the end of your bench.
- Dispose of any hazardous waste (reactions containing DCMU) in the container in the hood.
- Other assay reactions can be discarded in the sink.
- Place test tubes in the glass disposal container.
- Return the color filters to the instructor’s bench.
- A partial scientific paper on your experiment today is due on the date designated in the Calendar or by your lab instructor. This assignment must be done individually. It is important that you discuss your results in terms of how the factor that you chose to investigate affects the electron transport rate and the coupling of electron transport with the photophosphorylation of ADP and/or the role of the H+ gradient in photosynthesis. Refer to the Guidelines for science writing information found in the Resources section of the Wiki.
- During next week's lab, you will participate in a writing workshop focusing on the photosynthesis paper. INDIVIDUALLY, prepare an outline of your introduction and results sections. Bring hard copies to class so they can be exchanged in peer review. The outlines of the introduction and results sections should contain citations. A Word document list of references relating to each variable is available on your section's Sakai site, instead of the pdf files. You should search for these articles using the Wellesley College Library Research Guides or a reference database such as PubMed or Google Scholar. You are encouraged to search for additional articles that may be useful outside of those on this list. AS A GROUP OF FOUR, prepare a few PowerPoint slides that display your figures and captions. Please include (a) a representative trial from each condition graphed against time and (b) mean rates of electron transport vs. your variable. Provide your instructor with an electronic version of this PowerPoint before lab. Be prepared to describe your results informally to the class for a group peer review.
- Please come to the workshop with any questions you might have about this final paper.