Name___________________________________

This exercise uses a vat culture of Chlamydomonas (a motile photosynthetic alga) to assess the effect of photon flux on photosynthesis. The culture of algae was donated by Dr. Adams. The medium contains 2.7 grams of salts per liter (2.7 PPT). The classroom is at about 300 feet above sea level. The algae have been growing without acetate and are photosynthetically active. They have been in continuous light until about one hour prior to the lab exercise and the culture has been stirred/shaken to avoid any settling.

Calibrate the oxygen electrode. With the electrode in the calibration chamber (on the side), turn the instrument on. Wait for a few minutes for the readings to stabilize (may take a few minutes). Use two fingers to depress and release the up and down arrow keys simultaneously. Then enter our altitude in hundreds of feet by using the up and down arrows. Press ENTER twice. Then enter the salinity of our medium in PPT, again by using the up and down arrows. Press ENTER. Now you can measure O2 levels in mg/L (use the MODE key if necessary...we don't want % air saturation!).

Pour out about 300 mL of the stock culture into the large beaker and put the beaker on the stirring plate. Be sure the stir-bar is stirring and not "jumping around." Remove the oxygen electrode from the calibration chamber and carefully lower the electrode into the beaker. Be sure that the stir-bar does not strike the electrode. You want to measure the oxygen level in a rapidly moving stream as the electrode uses up the oxygen inside the electrode as it measures it! Allow the reading to stabilize before recording it.

Initial level of oxygen __________ mg/L. (should be less than 10! If more than 80, press MODE!)

Rinse the electrode thoroughly with a stream of distilled water into the waste beaker. When you are SURE it is rinsed on every surface, return the electrode to the calibration chamber.

Now pour from your beaker of culture into the graduated cylinder, and measure out 25 mL into each of 10 cups. Place the cups in a drawer. Then position the cups at various distances from the lamp. Use the photon flux meter to determine the flux at each position. Be sure to hold the white sensor directly toward the lamp and at the level of the cup! You want to stagger the start of your cups by about 2 minutes.

At the end of the target time of __________ minutes, drop the tiny stir-bar into the cup, place the cup on the stirrer and measure its oxygen level...be sure to allow stabilization time. Rinse the electrode thoroughly, and move to the next cup. Discard the culture...DO NOT RETURN IT TO THE LARGE FLASK! Go on to the next cup.

Distance from Lamp	Photon Flux	Start Time	End Time	Elapsed Time*	Final Oxygen Level	Oxygen Produced*	Oxygen Production Rate*

At least two graphs come to mind. Maybe the leaf project will lead you through one of them. The other one might be to deal with distance on one axis. Think about how you can use a linear curve-fit through at least some of the points. How does y = mx + b assist you in finding the rate of dark respiration and the light compensation point? Make sure your software provides three significant figures (use scientific notation if needed!).

Go back to the Course Schedule.