Supported by:
Ozone Testing with Milkweed
Indiana Indicators Addressed
6.3.16 Explain that human activities, such as reducing the amount of forest cover,
increasing the amount and variety of chemicals released into the atmosphere,
and farming intensively, have changed the capacity of the environment to support
some life forms.
6.3.13 Identify, explain, and discuss some effects human activities, such as the creation
of pollution, have on weather and the atmosphere.
7.4.14 Explain that the environment may contain dangerous levels of substances that
are harmful to human beings. Understand, therefore, that the good health of
individuals requires monitoring the soil, air, and water as well as taking steps to
keep them safe.
Introduction
We need air!
Air is a mixture of many gasses, some good and some bad. Air is essential for most life
on Earth. Plants take in carbon dioxide from the air to help them grow and return
oxygen back into the air. Humans and other animals use this oxygen and breathe out
carbon dioxide. Plants and animals can benefit each other as long as a balance is
maintained.
Not all air is good air.
There are also some harmful substances in the air. Some of these materials are created
naturally while others are manmade. Volcanoes and forest fires often produce many
harmful materials such as soot, ash, and carbon monoxide. Society uses a lot of energy
to heat their homes, to generate electricity, and to travel from one place to another.
Most of this energy comes from the burning of fossil fuels such as coal, oil and gas.
However, this combustion also adds many harmful pollutants to the air, such as ozone,
nitrogen oxides, and volatile organics.
A good mixture – better than the sum of its parts
There are not many who would enjoy eating a stick of butter or a raw egg. How would
you like to eat a cup of flour or a cup of sugar? Unless you are trying to impress
someone, then chances are that eating any of these ingredients individually does not
sound appealing. However, if you mix them in the right proportions and cook them just
right, lots of people would love to eat these cookies! The point is that sometimes a
mixture is better than the individual parts.
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A bad mixture – worse than the sum of its parts
It is also true that the mixture could be worse than the individual parts. This is definitely
the case when it comes to air pollution. One important example is smog. The origin of
the word “smog“ is a combination of smoke and fog, which was common in industrial
areas like London, England. However, an even more destructive mixture is
photochemical smog. This is created when chemicals from vehicle exhaust or industrial
smokestacks combine with sunlight. More specifically, sunlight shining on nitrogen
oxides produces ozone and nitrogen dioxide. Nitrogen dioxide is the main producer of
acid rain. Let’s take a closer look at ozone.
Good ozone versus bad ozone
Ozone is a high energy molecule. There is a blanket of ozone in the upper atmosphere
which helps protect us by absorbing much of the sun’s harmful ultraviolet light. So the
ozone in the upper atmosphere is good. However, ozone in the lower atmosphere is
bad. It reacts with and damages almost everything it contacts, living and nonliving. It
causes rubber and plastic to deteriorate rapidly. It is especially damaging to soft tissues
of living organisms, such as eyes, nose, throat and lungs.
Health effects of ozone.
Ozone is an invisible gas, but because it is so reactive people often feel its effects
directly. People exposed to ozone for a short time may experience these types of
symptoms: stinging and watery eyes, scratchy and sore throat, coughing, pneumonia or
even a headache. Long-term exposure of years produces more serious effects such as
damage to the brain, liver, kidney, heart and possibly lung cancer.
Solutions to the ozone problem.
For good health it is best to minimize your exposure to ozone. Because there is more
sunlight in the summer, ozone risk tends to be higher in the summer. Most news outlets
report something called the A.Q.I. (Air Quality Index) to the public each day. The higher
the A.Q.I. number the worse the air quality is. Staying inside to avoid ozone exposure is
one solution, but it is not the best long-term solution. It would be better to reduce the
amount of ozone being produced in the first place. One way to do this is to reduce the
amount of energy being used. For example, turn off lights and appliances when they are
not needed, or choose not to use a car when you can walk or ride a bike instead.
Testing for ozone.
How do you test for ozone? You could simply take some deep breaths: the more it
stings, the more ozone there is. A safer way is to use special strips of detection paper.
Special electronic meters can be used to detect the levels of ozone, too. There are
natural ways that you can use that won’t hurt your nose.
Scientists often use milkweed plants to observe the levels of ozone in the area. This is
what we will do in this activity.
Note: This article is based upon work supported by the National Science Foundation under
Grant DGE-0231863. Any opinions, findings, and conclusions or recommendations expressed in
this material are those of the author(s) and do not necessarily reflect the views of the National
Science Foundation.
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The following is an adaptation from a lesson plan from Environmental Education
for Kids on Wisconsin’s Department of Natural Resources website.
http://www.dnr.state.wi.us/org/caer/ce/eek/teacher/milkweed.htm
Milkweed and Air Pollution
Applicable Standards:
6.3.13 Identify, explain, and discuss some effects human activities, such as the
creation of pollution, have on weather and the atmosphere.
6.3.16 xplain that human activities, such as reducing the amount of forest cover,
increasing the amount and variety of chemicals released into the
atmosphere, and farming intensively, have changed the capacity of the
environment to support some life forms.
7.4.14 Explain that the environment may contain dangerous levels of substances
that are harmful to human beings. Understand, therefore, that the good
health of individuals requires monitoring the soil, air, and water as well as
taking steps to keep them safe.
Objectives:
Students will observe signs of ozone damage on milkweed and determine the
severity of ozone damage to individual areas based upon the degree of damage
on the milkweed leaves.
Required Materials:
- Milkweed plants growing in different areas, preferably between late August
to early October
- Attached worksheet
- Paper for drawing a map
Lesson Introduction:
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Common milkweed (Asclepias syriaca) is a plant that has leaves which are
sensitive to ozone pollution. Common milkweed is found in old fields, roadsides,
waste places, and other areas which receive moderate to high levels of sun.
Milkweeds bloom from late May to August and have rose-pink groups of flowers
often arranged in a ball-like shape. Milkweeds are named due to the milky sap
that occurs when leaves and stems are broken. This sap is toxic and should not
be ingested. Milkweeds are an important host to monarch butterflies, because
monarch caterpillars can consume the sap with no ill effects. Instead, the
monarch itself becomes poisonous to most predators.
Ozone is a gas composed of three oxygen atoms. Motor vehicle exhaust and
industrial emissions, gasoline vapors, and chemical solvents are some of the
major sources of ozone. Sunlight and hot weather cause ground-level ozone to
form in harmful concentrations in the air.
Ozone injury on milkweed can be seen on the leaves. This injury is unique and is
easy to identify. An injured leaf will have sharply defined, small dot-like lesions,
called stipples, on the upper surface of the leaves. These markings appear only
on the top of the leaf and are black to dark purple. If the ozone effects are severe
you’ll see a large dark area on the upper leaf surface as the markings blend
together.
Ozone injury can look different on leaves of different ages. Minor ozone injury on
young leaves can be found on the tip of the leaf. It is found in the center of fully
grown leaves and at the base of older leaves. Leaves that are exposed to lots of
ozone may show injury symptoms all over the upper leaf surface.
Procedure:
1. Discussion.
Provide students with the background information included in the lesson
introduction, either in written form or through discussion. Make sure they take
notes and understand that they will be writing a report later. Be sure to also
discuss the study area (see next step). Have the students devise hypotheses
concerning leaf damage. (For example, in which areas will more leaf damage?)
2. Select a Study Area.
Select a study area in late August or September. Remote unmowed areas in
parks or prairies are ideal sites. Areas with lots of variation are preferred. At
least 20 milkweed stems should be present.
3. Have students select milkweed plants.
a. Have students choose 10 stems at random for the study. Plants with 10
or more leaves are preferred. Have students avoid plants that are
diseased or have insect chewing marks on them.
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b. Have students draw a map showing the location of the study area.
Show features near the site like roads, trails, signs and buildings that
would allow another person to easily find the site.
c. Have students use the attached chart below to record their findings.
4. Have students check the leaves for ozone damage.
a. Students should select their first milkweed stem and measure and
record the height of the stem from the base to the top. Record this on the
chart.
b. Students should count and record the number of leaves showing ozone
injury on the plant (see the picture to identify leaf injury). Have them
evaluate only mature leaves that measure over 2 inches in length.
c. Have students estimate the percentage of leaf area injured using the
following code:
Codes for % of leaf area injured
0 = no visible signs of injury
1 = very light to some (1-15%)
2 = moderate to moderately heavy (16-50%)
3 = heavy (more than 50%)
d. Have students count and record the number of leaves showing ozone
injury on the plant.
e. They should also record the total number of leaves on the plant.
Students should then determine the percentage of injured leaves per plant
using the guide above. Have them check all 10 plants.
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Plant
Number
Plant
Height
Total #
Leaves
# Injured
Leaves
1
2
3
4
5
6
7
8
9
10
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% Injured
Leaves on
Plant
% Leaf
Area
Injured
Closure
Have students summarize and compare their data in class, reminding them to
continue to take notes for their final report. Engage a discussion concerning
what the results say and what that means for the “real world.” Sample discussion
questions may include the following:
1. What level of injury did you find?
2. If you found no ozone injury, what might this mean? How can you verify your
results?
3. What is a bioindicator? How can using milkweed and other plants as
bioindicators help us keep the air clean?
4. What are the advantages or disadvantages to using biomonitoring projects?
5. What do the results indicate about local air pollution? Where is the air worst?
Where is it best? Why?
6. What consequences will air pollution have for humans? For monarch
butterflies? For ecosystems in general?
Assessment
Students will construct a report including their hypothesis, results, a discussion
(i.e. what the results mean – include material from the discussion), and their data
sheet. When grading, emphasis should be placed on the discussion to assess
understanding of pollution and its consequences.
Extension
Ozone meters and ozone measuring “eco-badges” are available to quantitatively
measure ozone levels. These can be used to compare with the milkweed results
and discuss the advantages and disadvantages of bioindicators vs. technology.
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The following is supplemental information on the topic of milkweed and
monarch butterflies. It can be accessed online at:
http://www.dnr.state.wi.us/org/caer/ce/eek/veg/plants/milkweed.htm
Signs of Summer - Monarchs and Milkweed
Q: Where does the milkweed plant get its name?
A: It leaks a thick, white sap when cut or broken that makes it look like it’s
leaking milk.
Common Milkweed - The Facts:
Height: grows from 2-6 feet high. It usually has a single, simple stem.
Leaves: are opposite, oval-shaped and 2-10 inches tall. The top surface of
the leaf is smooth, but the bottom surface is hairy.
Flowers: bloom from late June to August, pink to lavender in color, and are
found in bunches. The main flower is actually a bunch of little flowers on the
same stalk.
Fruit: in the fall, flowers develop into seed pods. The pods have a warty
outer skin filled with downy fluff that will carry the seeds on the wind like a
parachute.
A sure sign of summer in Wisconsin is when the common milkweed (Asclepias
syriaca) is in bloom. You’ll find this plant in fields, meadows, and along
roadsides. If you find milkweed, you’re also likely to find monarch
butterflies. Monarchs need milkweed to survive. The butterfly lays its eggs
on milkweed plants. The growing larvae (caterpillars) eat milkweed leaves.
These leaves contain toxins- poisonous chemicals. These toxins don’t hurt
the caterpillar, but they do make the caterpillar poisonous to most
predators. Because it eats milkweed leaves as a caterpillar, the monarch
butterfly is also poisonous. The survival of the monarch butterfly depends
on this self-defense system provided by the milkweed.
Did you know that...
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Sap from milkweed was used by pioneers as a cure for warts?
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The airborne fluffy parachute of the seed was used by Native
Americans to insulate moccasins?
The dried empty seed pods were used as Christmas tree decorations
by early pioneers?
The boys and girls from Wisconsin schools collected 283,000 bags of
milkweed fluff for use in military life jackets during World War II?
It is used as an indicator of ground-level ozone air pollution? Find out
how to conduct a milkweed check-up to check for signs of pollution
You can attract butterflies to your yard by planting a butterfly
garden.
Classic Ozone Injury on Milkweed
Ozone damaged leaf
Check out this leaf. It has all the signs of classic ozone injury. Check for:
 stipples (black dots), only found
between the veins, not on them
 stipples are only found on the
upper leaf surface
 stipples have distinct, sharp
edges
 no haloes or discoloration around
the stipple
 black or very dark in color;
colors are not variable
 stipple is scattered over the leaf surface not clustered in groups or in
obvious shapes, such as circles
For more types of leave damage on milkweed, refer to the following link:
http://www.dnr.state.wi.us/org/caer/ce/eek/earth/field/milkweed/slideshowindex.htm
Good site for smog: http://www.epa.gov/airnow/health/smog1.html#1
Good background for ozone: http://www.dnr.state.wi.us/org/caer/ce/eek/earth/air/ozone.htm
Ozone Lesson: http://www.tnrcc.state.tx.us/air/monops/lessons/ozonelesson.html
Good temperature inversion lesson:
http://www.tnrcc.state.tx.us/air/monops/lessons/templesson.html
Good site for investigating monarch butterfly migration patterns:
http://www.learner.org/jnorth/fall2000/monarch/Update100400.html
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