UV Radiation and Plants

A Paper by Ethan Stricker-Chapman

Español (Spanish)

Introduction
Ultra-violet radiation is the light that is beyond violet in the spectrum, hence the name. It has been shown in numerous experiments that UV light is a major risk factor in life. And with the growing hole in the ozone, there are even more warning signs than before.

A number of deformed frogs were found in northern Minnesota. Through experiments, it was shown that these deformities, which included loss of limbs and an abundance of limbs, are probable attributed to UV radiation.

UV light has been divided into 3 main groups: UV-A(320-400nm), UV-B(280-320nm), and UV-C(<280nm). UV-C is absorbed by the ozone, and UV-A does not pose a biological threat, do UV-B is all we have to worry about.

Materials
In order to photosynthesize, plants need three things: water, chlorophyll, and sunlight. Whether plants can photosynthesize with UV light is unknown, but I think they can't.

Procedure
To test this, I set up two relatively equal portions of rock cress (Lepidium Sativum), about 100 speeds in each plastic pot. The control was exposed only to sunlight, while the test pot was exposed to both sunlight and a UV black light from a distance of 4 inches.

The black light was a Sylvania F15T8 bulb, with 15 watts, and 18-inch MOL, and 7500 hours of life. The wavelength is 356 nm, in the UV-A range, however, since UV-B is more harmful than UV-A, the results should provide a sound basis for extrapolation.

The experiment lasted from March 21 to April 12, 1998. It took place in southeastern Minnesota (Crystal), with eastern exposure. The light was propped up on two wooden blocks, each an inch thick. The cress sprouted on March 28. There was no visible difference at the time of sprouting, because I delayed the use of the black light until the plants had sprouted. In the beginning, I had the black light on 24 hours a day, but on March 30, I decided to turn it on at sunrise and turn it off at sunset, in order to more effectively model the real conditions. Earlier, I had tried the same experiment with beans, but the growth was more controllable with rock cress, so I decided to switch. Also, on March 30, I decided to take one of the lights out, because there was far too much UV light and far too little sunlight. After only about a day, the UV light was producing visible effects, such as slower growth and difference in color. Most of the UV plants had died by the end of two weeks, and remain dead (see leaves). An interesting thing was that the blocks had stopped the UV light from reaching some of the plants, and those plants all survived. At the end of my experiment, I also looked at a control and a UV leaf. The control's leaf was 0.8 cm at its longest, and the UV's was 1.4 cm (see growth record).

Results and Conclusions
It seems as though the only ones left alive were ones that had bigger leaves and were darker green than even the control. So, they either could have survived due to their ability to receive more sunlight for photosynthesis, could have changed by the UV radiation, or both. This subject, however, would require further study.

Given the results of my experiment, I feel I can safely say that if you were a rock cress in southeastern Minnesota in March with a steady dose of UV light, you'd probably be dead.

Bibliography
Allen S. Lefohn, 1992, Surface level ozone exposures...

American Society for Photobiology, Light and Life, http://www.kumc.edu/ASP/ASP_Home/asp_bro2.html

Annika Nilsson, 1996, UV reflections: life under a...

Effects of ozone depletion on...
http://www.greenpeace.org/home/gopher/campaigns/air/1992/ozholb4.txt

Greg Bodeker, UV radiation
http://www.miwa.cri.nz/lauder/uvinfo.htm

I. Asimov, 1989, How did we find out about...

J.W. Hart, 1988, Light and plant growth

Pedro J. Aphalo, The electro-magnetic spectrum
http://cc.joensuu.fi/~aphalo/mrainbow.html

R. Walden, 1989, Genetic transformations in plants

Return to List of Middle School Reports

Frogs Home