The Affect of Light Frequency on Photosynthesis


Meaghan Cusack, Lindsey Book, Jesse Clarke


University of Colorado, Boulder - Fall 2006


We tested to see if different wavelengths of light had an affect on  a plants rate of photosynthesis.  Plants use light to carry out the  light dependant reaction in the first stage of photosynthesis.   Blue light has a shorter wavelength, which gives it more energy,  than red light.  Because of this, we predicted that blue light  would increase the rate of carbon dioxide consumption, in other  words, increase the rate of photosynthesis.

We used the juniper sprig in our experiment.  We put the sprig in a  gas chamber and let the chamber air out.  Then we put in a CO2  sensor, and turned on the lights with the blue cellophane covering  it, shining on the plant.  We took calculations for ten minutes.   Then we put it in the dark in between, as a buffer.  We then used  the same procedure, using red light.  We again measured it for ten  minutes, and used the same plant.  In the second trial, we used a  different plant section of the juniper sprig.  We used red first  this time, followed by the blue light, getting rid of any bias that  we might have created.  In this trial the same procedure was gain  used.

Our results showed that the rate of photosynthesis was greater  under the blue light.  The average rate of photosynthesis was 66.52  ppm/min/g for blue and 35.215 ppm/min/g for red.Our t test resulted in a p value of .0008.  this number was less than the value .05, which leads us to conclude that our data  was in fact significantly different.  The blue light was significantly making the rate of photosynthesis faster.


Our results were consistent with our hypothesis.  We predicted that  the blue light would be more affective because of its greater  energy.  This proved to be affective on plant photosynthesis.  Some  potential problems could have come up during our experiment.  We  only ran the experiment two times.  To make it more accurate, we  might want to try doing the experiment four or five times.  It  would make our data a better model.  Another problem that might  have come up was the preciseness of the carbon dioxide sensor.  The  one that we used during our experiment was old, and had tape around  it.  It would help if we used a different monitor, and possibly  tried the experiment on several monitors.  The CABLE website showed  that other students had in fact performed an experiment somewhat  like ours.  The results were practically the same, again showing  blue light as more effective.

From the results of our experiment, many extensions may be tried.   One

example could be that we could try this experiment using a C4, and  CAM plants.  This would help us see if the blue light was absorbed  better only because it was a C3 plant, or if this is true of all  types.