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Doug Herman, Biology Teacher , East High School, Sioux City, IA. 51106

I have been trying for some time to locate usable interfacing equipment for measuring some of the variables that indicate to students that photosynthesis is taking place in plants. Biology teachers all familiar with the classic tests for starch and sugar in the leaves of geraniums left in the light and dark for 24 hours.

These labs were designed using Vernier probes and software to measure variables in photosynthesis such as temperature, light, oxygen pressure, and pH. Although this set-up was done using a PC, the Mac environment should work nicely as well. I am in the process of working and designing some ways to use the newer TI82/85 and CBL technology from Texas Instruments to gather this same data.
The TI82/85 and CBL should give the biology teacher more hardware and some flexibility in the laboratory that computers might not offer. Any biology teacher who has successfully used this technology might consider sharing your ideas with those of us just getting started.


Vernier Probes for pH, temperature, pressure and light.
PC or Mac with game ports or open serial ports
Serial Box Interface & Data Logger Software(Vernier) or
Software for each probe for PC or Mac
NOTE: 1. Probes can also be used with ULI interfaces from Vernier and their other newer MPLI unit. These are not yet in our lab.
    1. The Vernier probes can now be interfaced through the new
      CBL technology from Texas Instruments.
250ml flask and 1-2 hole rubber stopper
Elodea plants
0.25% Sodium Bicarbonate dissolved in pond water
150watt lamp
1000ml of beaker of water
meter stick


Elodea plants are placed in 200ml of aquarium water with 0.25% Sodium bicarbonate dissolved in it. Mix the sodium bicarbonate in the aquarium water so the resulting solution is 25%. Place a healthy sprig of Elodea in the flask with the pH probe and temp. probe cords fit through the stopper. The rubber stopper will need to be slit in order to accomodate the cords of the probes. Follow the software directions for probe calibration and taking readings. The stopper of the flask will need to be sealed to prevent gas loss and a 150 watt bulb is used to illuminate the plant. Students can study the variable of light intensity in the experiment by adjusting the distance the plant is from the light. During several minutes of readings data is collected on pH and temperature in the flask. I have had students use color light filters in front of the flask to show how wavelength of light

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