Activity: Pollution and Plants
Objective: To examine the effects of oil, salt, and acid pollution on plant germination and
growth.
Grade level: 6th
Format: Lab experiment
Materials: Per student or group – 2 plastic petri dishes with lids (clear plastic cups work just as
well), potting soil, 20 fast germinating seeds (grass or radish), metric ruler, small (50 mL)
beaker, masking tape, pen or marker, 10 mL of day-old tap water, 10 mL of pollutant (oil,
salt, or acid). Letting the tap water stand uncovered for 24-48 hours allows the chlorine
to dissipate. Prepare each pollutant solution by mixing 5 mL of the pollutant with 100
mL of water (use vinegar for acid, cooking oil for oil). I used 1 tsp of salt per 100 mL of
water for the salt solution.
Description: My teacher facilitator and I used this lab experiment to introduce students to
scientific inquiry. During the lab, students form a hypothesis about the effects of
pollution on plant growth, control variables during testing of the hypothesis, interpret and
present data, and determine if results are consistent with the hypothesis.
Lab procedure: Students plant seeds in two containers – a control group watered
with tap water, and an experimental group watered with either oil, salt, or acid solution
(for detailed procedure see attached student handout). Planting seeds takes about 15-20
min. For the next week to 10 days, students observed the seeds, recording both the
number of seeds that germinated and the condition of the seedlings (color, size,
presence/absence of leaves, etc.) in a data table. After data collection was complete, I
had students make pie graphs of the percentage of seeds that germinated in the control
versus the contaminated group. We discussed the results of the experiment and students
evaluated their hypotheses based on these results.
Words of wisdom: Trying to get a class of 6th graders to follow written directions
is like trying to herd bees. I simply put the lab directions on the overhead and went over
them verbally, but in retrospect, I think I should have demonstrated or broken the
procedure down into smaller steps. Additionally, make sure the students only plant 10
seeds (or at least they count the number of seeds they plant)! Finally, for reasons still
unknown, nearly all of the grass seeds in the acid solution germinated and grew as well as
the control seeds (I used white vinegar as the acid “pollutant” – maybe another type of
vinegar would work better?).
Modifications: We didn’t spend a lot of time discussing methodology and sources of error in
the experiment, which is something that could have easily been done. As an extension to
the experiment, students could explore the effects of different pollutants (detergent,
chemicals, etc.), or the effects of pollution on different types of seeds.
Resources: This activity was adapted from “How does that garden grow?” in Science Explorer:
Environmental Science (Teacher’s Edition), Prentice Hall, Needham, MA: p. 148E.
Your name and Fellow year: Heather Petcovic, 2000-2001
School or outreach event where activity was used: Gregory Heights Middle School, Portland
Name: _____________________________ Date: ________ Period: _______
POLLUTION AND PLANTS
Mike’s Summer Job (A True Story)
My friend Mike spent last summer working for an environmental science
laboratory in Corvallis. In the area around Corvallis, there are a lot of paper mills.
Making paper produces a waste chemical called PCP (pentachloraphenol). While
scientists know that PCP can be toxic, they weren’t sure how much of the chemical (the
concentration) could cause damage to plants and animals. So they hired Mike’s lab to
find out.
Mike’s job was to study the effects of PCP (and a bunch of other nasty
chemicals) on the growth of different types of plants. First, Mike carefully prepared soils
contaminated with different concentrations of PCP. He then planted thousands of
radish, grass, and wheat seeds in the contaminated soils. He also planted seeds in
uncontaminated soils so he could compare how the plants in the two groups grew. For
many weeks he monitored the plant growth and weighed and measured the seedlings.
At the end of the experiment he found that as little as 20 parts per million (ppm,
or less than 0.0005%) of PCP could cause seedling to be brown and shriveled, and
many seeds didn’t grow at all. This information will be used by the state and U.S.
Environmental Protection Agencies to regulate how much PCP paper mills can produce
as waste in the future.
Lab Procedure:
1. As a group, choose one pollutant to investigate: oil, acid, or salt.
2. On a piece of masking tape, write your table group’s first names, the period, and the
name of the pollutant. On a second piece of tape, write your names, the period, and
the word “Control.” Tape each label to one of the containers.
3. Fill each container loosely with soil. Do not pack down the soil!
4. Pour 10 mL of tap water into the control container. Pour 10 mL of polluted water into
the pollutant container.
5. Lightly scatter 10 seeds on the top of the soil in each container. Do not push the
seeds down into the soil!
6. Cover each container and tape down the lid. Put containers in the tray on your
table.
7. Observe your seeds every day without removing the lid. Record your observations
in the data table.
A. Pre-lab questions (please answer in complete sentences)
1. Write a question that we will try to answer in this activity:
2. Which pollutant has your group chosen to investigate?
3. Write a hypothesis about how you think the pollutant will affect plant growth:
4. List the variables that affect the lab:
5. What is the manipulated variable in this lab? (Think about why we have 2 containers
and one is labeled “control.”)
6. List observations you could make of the seeds during the experiment:
B. Data Collection
DATE
NUMBER OF
GERMINATED SEEDS
CONTROL
POLLUTED
PLANT OBSERVATIONS
CONTROL
C. Follow-up questions
1. How many total seeds germinated in each dish?
2. Did the seedlings grown in each dish look different? If so, how?
3.
Did your results support your hypothesis? Explain.
POLLUTED