Pesticides

Gutter, Nadine                         Robeson High School
                                       723-1700
                          

Objectives
1. The student will understand the definition of a pesticide. 
2. They will recognize why pesticides are used.  
3. The student will understand why certain pesticides are no longer 
   used. 
4. The student will be able to make a judgement about the use of 
   pesticides. 
5. The student will understand the nature of an enzyme. 

Materials
a variety of fresh fruits and vegetables      
petri dishes 
water
vegetable oil
florence flask
a variety of pesticide containers
naphthalene
data sheets
damaged fruits/vegetables/leaves
labels
graduated cylinders
two small stuffed animals exactly alike
sewing needle
thread
black tape
two small plants exactly alike
wood splints, cotton balls, paper, cotton cloth

Recommended Strategy
Preplanning
1. Display the fresh fruits and vegetables and the pesticide containers 
   on the demonstration table. 
2. Pour about 20 mL of the vegetable oil into a florence flask and label 
   it "human body fat". 
3. Pour about 20 mL of the water into a florence flask and label the 
   flask H20. 
4. Place a small amount of the naphthalene crystals into a petri dish 
   and label the dish "DDT"".  
5. Prepare the two small stuffed animals by labeling them as baby #1 
   and baby #2. Tape or sew back the ears, arm, eyes, nose, etc. of #2. 
6. Prepare the two plants by labeling them as plant #1 and 
   plant #2. Remove the leaves from plant #2. 

Introduction
Begin the demonstration by having the students observe the damaged 
vegetables/fruits/leaves. Get some oral responses to the question, 
"what happened to this produce?" Have students circle demo table to 
observe the fruit/vegetable display. Ask students if they can get the 
same or better quality items near where they live. Relate quality and 
quantity of produce to pesticide use by farmers. At this time you 
should point out the different types of pesticides that were brought in 
the containers on the demo table. Briefly discuss pesticide use in 
relation to limited resources and growing world populations. Tell 
students that chemists are constantly working to produce pesticides 
that do not have negative effects on the environment. 

Procedure
1. Discuss the pesticide classes chlorinated hydrocarbons, defoliants
and organophosphates in this order. The student should record the 
class, name, helpful and harmful effects of a particular pesticide on 
his data sheet.
2. Demonstrate the actions and effect of the pesticides by simulation. 
Below are some simulations which show actions and effect of some 
pesticides. Students should do each simulation before the action or 
effect of the pesticide is covered in the discussion. 

action/effect                          simulation
a)how DDT builds up in the bodies      drop a few of the naphthalene 
  of aquatic animals and plants        crystals into a florence flask
  mammals eat                          filled with 20 mL of water
b)how DDT builds up in toxic           drop a few of the naphthalene 
  amounts in the fatty tissues of      crystals into a florence flask
  mammals                              filled with 20 mL of vegetable oil
c)to show the effect of defoliants     use plant #1 and plant #2
  on forest                            use cotton and cotton cloth
d)to show defoliant effect after a     use wood splints and paper
  second application                   (losses to industry)
e)to show birth defects caused by      use baby #1 and baby #2
  defoliants
f)to show how organophosphates         have students contract and
  inhibit the enzyme                   relax their arm muscles:then 
  acetylcholinesterase                 have them continuously 
                                       contract the arm muscle 5
                                       or 6 more times
3. At the end of the demo ask students the following questions:
On the basis of the data collected,decide if:
a) pesticides should be continued to be used
b) pesticide use should be banned
c) chemist should continue working to develope pesticides that do not 
   produce negative effects on the environment. Give reasons for your 
   answer. 

References
Medeiros, Robert W. Chemistry, A Modern Perspective. D. Van Nostrand  Company:
New York, London, Cincinnati, Toronto, Melbourne, 1973. pp. 300-314. 
Jarvis, Bruce and Paul Mazzocchi. Form and Function. Harper and Row:
New York, Hagerstown, San Francisco, London, 1978. pp. 12-60. 
Stryer, Lubert. Biochemistry. W. H. Freeman and Company:  San Francisco,
California, 1981. pp880-893. 
Cram, Donald and Jane. The Essence of Organic Chemistry. Addison-Wesley
Publishing Company:  Menlo Park, California, 1978. p. 139.