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

Chaffin, Mildred C.                          Hyde Park Career Acad.HS.
7354 S. King Dr.                             947-7180   
Chicago, Il 60619 

Objective: 

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 u.v.r.in 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.