Photosynthesis

Photosynthesis Overview

• Photosynthesis is a biochemical process that converts light energy into chemical energy.
• Cooperation of light reactions and dark (light-independent reactions).
• Major components involved:
  • Light
  • Water (H₂O)
  • Carbon Dioxide (CO₂)
  • Chloroplasts (where photosynthesis occurs)
  • NADP⁺ and ADP + Pi involved in light reactions.
• Calvin Cycle produces sugars (CH₂O).

Gas Exchange Measurements

• Photosynthesis Equation:
  $ext{H}<em>2 ext{O} + ext{CO}</em>2 <br /> ightarrow ( ext{CH}<em>2 ext{O})</em>n + ext{O}_2$

Rate of Photosynthesis Measurement

• Rate of photosynthesis (A) denoted as CO₂ assimilation.

• Described using Fick’s Diffusion Law:
  $A = (C<em>a - C</em>i) imes g_{CO2}$
  Where:

  • $C_a$ = concentration of CO₂ in air
  • $C_i$ = concentration of CO₂ inside the leaf
  • $g$ = leaf conductance to CO₂ = $rac{1}{ ext{resistance}}$

• Alternative Form:
  A = rac{(Ca - Ci)}{r{CO2}} where $r</em>{CO2} = r<em>{bl} + r</em>{st}$

Gas Exchange Systems

• Closed vs. Open Systems for CO₂ assimilation.
• Infrared Gas Analyzer (IRGA): measures CO₂ (and H₂O) in the air stream using IR absorption.
• Cuvette (Leaf Chamber):
  • Controls the environment of the leaf
  • Reduces boundary layer via air movement (fan)

Data Collection

• Raw Data Required:
  • Reference and sample CO₂ concentrations
  • Flow rate of air
  • Leaf and air temperatures
  • Humidity of air streams
  • Leaf area (one-sided) measured or calculated

Data Derived from Measurements

• Calculate:
  • Photosynthesis (net CO₂ uptake)
  • Internal CO₂ concentration
  • Stomatal resistance/conductance

Chlorophyll Fluorescence

• Indicator of photosynthetic energy conversion.
• Useful for understanding photosystem II photochemistry.

Key Measurements:

• Fm: maximal fluorescence
• Fo: minimal fluorescence
• Fv: variable fluorescence
• Quantum efficiency calculated as $rac{Fv}{Fm}$

Objectives of Lab

1. Assemble and calibrate Qubit gas exchange system.
2. Measure light-saturated photosynthesis and calculate related parameters.
3. Generate photosynthesis-light response curve.
4. Measure Fv/Fm using a chlorophyll fluorometer.
5. Analyze data and submit lab report.

Procedures Overview

1. Familiarize with the Qubit Plant Photosynthesis System.
2. Calibrate Qubit IRGA (zeroing out CO₂).
3. Prepare and record Light Response Curve:
   • Place leaf in cuvette at high light intensity.
   • Systematically reduce light and record data until darkness.
   • Calculate and graph net photosynthesis rates.
4. Measure Fv/Fm on a nearby leaf.

CO₂ Exchange Rate Calculations

1. Calculate CO₂ concentration difference:
   $A_{CO2} = ext{Reference} - ext{Sample}$
2. Convert ppm to $ext{μmol CO}_2/ ext{L}$.
3. Multiply by flow rate (L/s) to get CO₂ exchange rate per second.
4. Express exchange rate per leaf area(m²).

Lab Report Requirements

• Short lab report (1-2 pages) including:
  • Photosynthesis Light Response Curve graph
  • Table with:
  • Light-saturated rate of photosynthesis
  • Light-saturation point
  • Light compensation point
  • Dark respiration rate
  • Quantum Efficiency
• Submit to Canvas; no late reports accepted; raw data not required in report.