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PH1LP Photosynthesis Teaching Package

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The PH1LP Photosynthesis Teaching Package may be used to measure photosynthesis in attached or detached leaves maintained in a sealed leaf chamber. O2 is produced by the light reactions of photosynthesis causing an accumulation of O2 in the chamber, which is measured by a gas phase O2 sensor. The rate at which O2 concentration in the chamber increases provides a measurement of the rate of photosynthesis. This package has been designed for teaching purposes only.  For research in plant photosynthesis try our Q-Box CO650 Plant CO2 Analysis Package.

The PH1LP Photosynthesis Teaching Package includes everything you require to conduct numerous experiments investigating photosynthetic physiology in a teaching laboratory. You supply only the computer and the plant! Equipment specifications and experimental designs are fully documented in an Instructor’s Manual. A separate Student’s Manual guides undergraduates through experimental protocols and data handling. Minimal set-up time is required and experiments are easy to perform.

The PH1LP Package Includes:

Photosynthesis requires both light and CO2. In the PH1LP Photosynthesis Package, light is provided by a halogen light source (A111), the intensity of which, may be varied by a sliding dimmer control (A112) . The amount of light passing through the leaf is measured by a photosensor (S141) placed beneath the transparent leaf chamber. CO2 is supplied from a gas bag (G121), which the user inflates with exhaled breath, the breath providing sufficient CO2 (usually about 3%) to saturate photosynthesis. The concentration of CO2 in the chamber declines as it is fixed in photosynthesis, and its rate of fixation is directly related to the rate of O2 production. Eventually, the CO2 concentration declines to a level that will not support net fixation, and O2 production ceases as a consequence. At this point (the CO2 compensation point) the O2 concentration in the chamber remains stable unless processes are activated that inhibit photosynthesis or stimulate respiratory O2 consumption.

The photosynthesis package is best used to measure photosynthetic O2 production under CO2-saturated conditions, and the experiments described in the manuals reflect its capability under these optimal conditions. However, there is great scope for measuring the effects on photosynthesis of other environmental parameters such as light quantity and quality. In addition, plants may be pre-treated in various ways that affect their photosynthetic rate and the effects of these treatments may be measured under conditions of both CO2 and light saturation.

The photosynthesis package may also be used to measure leaf respiration. If the flux of light to the leaf chamber is maintained below the light compensation point, respiratory O2 consumption will exceed photosynthetic O2 evolution, and the O2 concentration in the chamber will decline. The O2 sensor is able to measure this decline in O2 concentration, and the rate of decline provides a measurement of leaf “dark respiration”.

Applications

The Photosynthesis Package is suitable for use in both entry-level undergraduate courses and in research-based upper level courses. The Instructor’s Manual provides step-by-step protocols for each experiment. It includes suggested variations to make experiments more or less challenging.

Experiments Include:

  • Photosynthetic rate
  • Light compensation point
  • Light saturation point
  • Photochemical efficiency
  • Wavelength dependence of photosynthesis
  • Temperature effects on photosynthesis
  • Photoinhibition
  • CO2 limitation of photosynthesis
  • Comparison of sun and shade plants
  • Comparison of C3 and C4 species

A leaf is enclosed in a transparent chamber incorporating a sensor that measures photosynthetic O2 evolution. Calibration of the O2 sensor requires only that its output be adjusted to read atmospheric O2 level (20.9%). The student fills a gas bag with exhaled air (approximately 17% O2 and 3% CO2) which is then pumped through the chamber. The chamber is then sealed and the leaf illuminated with a halogen light source. Chamber O2 concentration increases as photosynthesis progresses.

Light level may be varied using a voltage regulator control. The light level used in the experiment is monitored by a light sensor situated beneath the leaf chamber. Light sensor output is given in µmol quanta/m2/s and no calibration is required. Analog outputs from both the O2 sensor and the light sensor are converted to digital signals by a LabPro Interface. They are recorded and displayed to the screen using Logger Pro data-acquisition software. The software is also used for subsequent data analysis.

In the following graph, the derivative of O2 concentration against time has been calculated to produce a data set representing photosynthetic rate (%O2 increase per minute). This derivative has been plotted against irradiance to generate a photosynthetic light response curve.

Dr. Steven Spilatro of Marietta College, Marietta, Ohio, has put together a great Photosynthesis Investigation Study Guide. It is definitely worth a look!

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