Spring.wmf (18300 bytes) Plant Physiology (Biology 327)  - Dr. Stephen G. Saupe;  College of St. Benedict/ St. John's University;  Biology Department; Collegeville, MN  56321; (320) 363 - 2782; (320) 363 - 3202, fax;    ssaupe@csbsju.edu

Lab #1:  Measuring Photosynthesis With a Qubit CO2 Gas Analyzer


  1. to learn how to measure photosynthesis with a gas analyzer
  2. to learn how to measure chlorophyll concentration in leaves

    In today's lab we will follow the procedures given by Dr. Diane Robertson in Part I of her Intermediate Lab 1.  We will compare the rate of photosynthesis in a C3 (bean) and C4 (maize) plant.  We will express the results on the basis of fresh weight and per unit chlorophyll.

  1. Follow the procedures in Part I.  Record your data in Table 1.
  2. Measure the chlorophyll concentrations of the leaf samples:
  • Prepare 3 leaf disks using a cork borer or hole punch
  • Weigh the disks (record data in table 2)
  • Put the disks in a mortar and add a small amount of buffered 80% acetone
  • Grind the disks thoroughly with a pestle
  • Transfer the grindate to a centrifuge tube.  Rinse the mortar with a small amount of fresh 80% acetone.  Repeat until green color is gone.  Stopper and spin at the highest setting for 5 minutes
  • Pour the supernatant into a graduate cylinder.  Add fresh 80% acetone to yield a final volume of 10 mL
  • Record the absorbance at 645 and 663 in Table 2.  Use Licthenthaler's and Welburn's equations to calculate chlorophyll concentrations.
  • Complete Table 2.
  1. Complete the calculations in Table 1.  


Table 1.  IRGA results 
Species Corn Bean
Air temperature (C)    
flow rate (mL min-1)    
flow rate (L sec-1)    
Leaf area (cm2)  Note:  Area equals 9 cm2 if leaf fills the entire chamber.  For smaller lvs, calculate the area using the tracing technique)    
Leaf area (m2)    
LED (μm m-2 sec-1)    
Light - reference (baseline) CO2 (ppm)    
Light - analysis CO2 (ppm)    
Light - Δ CO2    
Dark - reference (baseline) CO2 (ppm)    
Dark - analysis CO2 (ppm)    
Dark - Δ CO2    
Photosynthesis rate (μmol CO2 m-2 sec-1)    
Photosynthesis rate (μmol CO2 mg chl-1 sec-1)    
Respiration rate (μmol CO2 m-2 sec-1)    
Respiration rate (μmol CO2 mg chl-1 sec-1)    


Table 2.  Chlorophyll Data
sample # 1 2 3 Mean 1 2 3 Mean
tissue fresh weight (g)                
final volume (mL)                
Chl a (μg mL-1) in solution                
Chl b (μg mL-1) in solution                
Ttl Chl (μg mL-1) in solution                
Chl a (μg) in leaf disks                
Chl b (μg) in leaf disks                
Ttl Chl (μg) in leaf disks                
Chl a (μg  g fw-1)                
Chl b (μg  g fw-1)                
Ttl Chl (μg  g fw-1)                

Postlab Assignment:

  1. Prepare an abstract of this lab.  Be sure to discuss if the rates you observed were expected and compare and contrast the rate in the two species.
  2. Append to your lab
  • copy of Table 1
  • copy of Table 2
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Last updated:  01/07/2009     � Copyright  by SG Saupe