Productivity Lab
Analyzing DO Using Lab Pros (2008-09)
1. Read and discuss background information – gross productivity, primary productivity, net productivity, dissolved oxygen, carbon fixation, dissolved oxygen saturation,
2. Write the problem question and hypothesis in your lab notebook.
3. Read the procedure, and write the procedure in you lab notebook.
-Include independent variable, dependent variable, controlled variables
4. Set up the lab, recording any changes from the prescribed procedure.
-Important notes: very carefully pour the algae/water solution into the small beakers;
- Be sure to slowly but continuously move the DO probe when taking readings.
- Record the average DO reading for 10 seconds AFTER the probe has stabilized.
- Be sure to rinse probe with distilled water between each use.
5. Create data table in your notebooks for raw data, and record the data. (dissolved oxygen) (Columns in data table: # of screens, % light, DO)
6. Record class averages in the same data tables in your lab notebooks.
7. Calculate the respiration rate. Put the below chart in your notebook. You must show the dimensional-analysis setup for your calculations.
Bottle
/ ppm DO / mg O2/literInitial DO
Dark Bottle DO
DO used due to respiration
(initial – dark)
8. Create calculation data table in your notebook. (the chart below is a beginning point for your data table). You must show the dimensional-analysis setup for your calculations.
Bottle
/ ppm DO / mg O2/liter / ml O2/liter / mg C fixed per liter / Gross productivity(mg fixed C/L) / Net Productivity
(mg fixed C/L) / Class average – net productivity
(mg fixed C/L)
Initial
100% light
65% light
Continue table for all bottles in your notebook
Calculations: Formulas – use for stochiometry
ppm DO/24 hrs = mgDO / L / 24 hrs
(mgDO /L) (.698 ml DO/ mg D) = ml DO / L
(ml DO / L) (.536 mg C/ ml DO) = mg carbon fixed / L
gross productivity = (net productivity in mg C/Liter/24 hrs) +
|(respiration rate in net productivity in mg C/Liter/24 hrs)|
note that dark bottle will be a negative number- use absolute value
net productivity = (experimental light bottle) – (initial level of carbon)
Example Calculation: make a table AND show all dimensional-analysis setups.
Initial = 9.7 mg DO/L
Dark = 1.8 mg DO/L
100% light = 10.50 mg DO/L
65% light = 4.1 mg DO/L
Calculate for above example:
Respiration rate:
in DO / Liter = (dark bottle) – (initial); then convert to mg C/ml/23 hrs
Net productivity and gross productivity at 100% light
Net productivity and gross productivity at 65% light
Graph: Graph the primary net productivity. % light is the x-axis, productivity is the dependent variable on the Y-axis.
Analysis : Answer in lab notebook or process and staple into notebook
1. Discuss the differences between gross and net productivity, relating BOTH cellular respiration and photosynthesis to these concepts.
2. Contrast class average with your results, and discuss similarities and differences.
3. Discuss the reason for using oxygen production as a way of calculating the assimilation (fixing) of carbon.
4. How do you think your results would differ if you used a sample of lake water for the experiment rather than the Chlorella culture? Explain why.
5. It is found that the gross productivity of two lakes at a given depth is the same, but the net productivity at the same depth is different. Explain this.
6. What factors in a lake affect the net and gross productivity? Name several.
7. Net productivity at a given depth in Lake Cayuga is determined to be greater on the day before a rainstorm as contrasted to the productivity a day following a very heavy rainstorm. How might this be explained?