The Interdisciplinary Laboratory

 Pre-Lab Assignment for Experiment #6:
Investigation of Photosynthetic Electron Transport

While the following calculations are mathematically simple, these exercises will give you practice on the manipulations of volumes and concentrations prior to the laboratory. Report the values with the correct number of significant figures.
 
 

As described in the procedure for Experiment 6, a student places 200.0-µL of a freshly-prepared chloroplast solution into a 10.000-mL volume of a mixture of 80% acetone-20% water (% by volume). After filtering this solution through #1 filter paper, she places a quartz cuvette containing 3.500 mL of the filtered chloroplast solution into the spectrophotometer. An absorption spectrum is recorded, and the absorbances at 663.0, 652.0, and 645.0-nm are determined as noted below.
 
 

1. What is the concentration of chlorophyll in units of µg Chl per ml of solution?  What is the uncertainty in the concentration if the uncertainty in each absorbance reading is +/- 0.0005?
2. What is the volume of this chloroplast stock solution that is needed to make a sample with a total volume of 3.500 mL and a concentration of chlorophyll equal to 10.00-µg/mL?
3. What volume of buffer solution should be added to the volume of chloroplasts in (b) to make a sample with a total volume of 3.500 mL?
4. Now the student makes a solution which consists of chloroplasts, buffer solution, and the electron acceptor DCIP. She uses the same amount of chloroplasts as determined in (b). How much of a 22.50 mM DCIP stock solution should she use to give a final concentration of 12.50 µM?
5. How much buffer solution should be added to the chloroplasts and DCIP in (d) to make the total volume of the sample 3.500-mL?
6. The student plans to examine the inhibitory activity of four quinones whose stock solutions have concentrations of (i) 16.50 mM, (ii) 10.25 mM, (iii) 8.75 mM, and (iv) 3.40 mM. What volume of each quinone solution should be added to separate chloroplast samples so that the final concentration of each quinone in the cuvette is always 100.0 µM?
7. After having read throught the laboratory manual for this experiment, what remaining questions do you have on either the background for the experiment or the experimental procedures?