The Effects of Over Exposure to Ultraviolet Radiation on the Growth of 
Plants and Bacteria

Chaffin, Mildred C. Hyde Park Career Acad.HS.


Students should be able to explain the deleterious effects of
ultraviolet radiation on the growth and development of plants and
bacteria. Also students should be able to describe the effect of
ozone on ultraviolet radiation.

Materials: String bean and mustard green seeds, ultraviolet lamp, glass apparatus, potting soil, water trays, pots for the plants, glass plate, slide projector, autoclave, fluorescent poster board and chalk, slides, E.Coli bacteria, nutrient media, petri dishes, petri dishes with nutrient agar, incubator, bunsen burner, test tube racks, NaCl, cardboard box, ring stand Strategy: Two experiments were performed to demonstrate the effect of ultraviolet radiation on plants and bacteria. Another experiment was performed to further demonstrate how glass filters ultraviolet radiation. The glass was used to mimic the effects of ozone on ultraviolet radiation. Experiment 1: 1. String bean and mustard green seeds were germinated on cotton in petri dishes for 3 days. During that time, the seeds were given a few drops of water daily. 2. On day 4, the germinated seedlings were transferred to the pots containing potting soil. Each seed type had two test groups and one control group. Eight plants were used in each group.The two test groups differed in that one was shielded by glass when exposed to ultraviolet radiation (u.v.r.) -labeled (SE)- but the other was not shielded when exposed to u.v.r. and it was labeled (U.S.E.). 3. From day 5 to day 10 the test groups were exposed to (u.v.r) for 2 hours daily. Experiment 2: 1. Expose a fluorescent surface to a dark room. 2. Expose the fluorescent surface to u.v.r. but this time place a glass plate in front of the u.v.r. lamp. Experiment 3: 1. Grow E.Coli cells in nutrient media for 24 hours. 2. Take out 1 mL of the E.Coli cells to use as the control group. Do not expose this group to u.v.r.. 3. Expose the remainder of the cells to ultraviolet light. 4. At 5, 20, and 60 seconds take out .1 mL of E.Coli cells Place each group of cells in separate test tubes and label each one. 5. Dilute each group of cells to 10-6 concentration and plate out .1 mL of cells on nutrient agar then incubate for 24 hrs. Conclusion: Experiments have shown that ultraviolet radiation damages and kills the cells of living organisms. The experiments performed in this project alone demonstrate this. We see examples of its deleterious effects not only in plants and bacteria but in human beings as well. Skin cancer is an example of this. It is caused by ultraviolet radiation being absorbed by our skin cells.There are, however, protective mechanisms in our bodies and in our environment that function to minimize or prevent the deleterious effects caused by over exposure of living organisms to ultraviolet radiation. Pigment, present in the skin of most human beings, and ozone, present in the stratosphere, both serve to absorb ultraviolet radiation. References: Regan, James and Parrish, John The Science of Photomedicine.
Plenum Press, New York Medical School.

Biswas, Asit The Ozone Layer Plenum Press.

Giese, Arthur Living With Our Sun's Ultraviolet Rays. Plenum Press: New York Ellis, Carlton and Wells, Alfred The Chemical Action of Ultraviolet Rays.
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