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Inquiry Lab • Scientific Method
Chapter 15
Acid Rain and Seeds
Directions: Read the entire lab before doing the procedure and answering the questions.
Problem
How does acid precipitation affect the germination of seeds?
Background
Seed Germination
Every plant seed contains a tiny plant embryo and a food supply to nourish that
embryo when it begins to grow. The embryo and the food supply are enclosed in
a tough protective coat, which keeps the contents of the seed from drying out or
being eaten. The embryo can survive within the seed for weeks, months, or even
years. This period is called dormancy. Factors such as temperature and moisture
determine when the embryo within the seed will start to grow again, or
germinate. Before a seed can germinate, it must absorb water. The absorbed
water causes the food-storing tissues to swell and crack the seed coat. The root is
the first part of the plant to emerge from the seed.
Acid Deposition
All rain is mildly acidic because atmospheric carbon dioxide forms a weak acid
(specifically, carbonic acid [H2CO3]) when it dissolves in water vapor. When
other particles get into the atmosphere, some of them, such as sulfuric acid, can
react with water vapor to produce strong acids that cause environmental damage.
If strong acids form, causing the pH of rainwater to fall below 5.0, the rain is
usually classified as acid rain. In this lab, you will determine whether the pH of
the water that a seed absorbs can affect germination, stimulating the effect of acid
rain on seed growth.
Materials
• vinegar solutions (5)
• pH paper (5 pieces)
• pH color chart
• dropper
• jar containing distilled water
• marking pen
• dried beans (50)
• paper towels (5)
• resealable plastic sandwich bags (5)
• hand lens or magnifying glass
• graph paper
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Safety
Wear goggles and a lab apron when you handle the vinegar solutions. Rinse off
any solution that spills on your skin or clothing. Wash your hands thoroughly
with soap and warm water before leaving the lab.
Procedure
Step 1
Put on your safety goggles and lab apron.
Step 2
Your teacher has prepared 5 solutions of vinegar and water, which are
labeled A, B, C, D, and E. Each solution in the series is 8 times more
concentrated than the next solution. Solution A is the most
concentrated and is 8 times more concentrated than Solution B.
Solution B is 8 times more concentrated than Solution C, and so on.
Solution E is the least concentrated.
Step 3
Use the dropper to place 1 drop of Solution A on a piece of pH paper.
Step 4
Compare the color of the wet pH paper with the pH color chart. Note
the pH of the color on the chart that most closely matches the paper.
Record the pH of Solution A in the Data Table.
Step 5
Flush out the dropper in the jar of distilled water.
Step 6
Repeat Steps 3 –5 with the remaining vinegar solutions B through E.
Step 7
Make a hypothesis that will explain how changing the pH of a solution
will affect the percentage of seeds that germinate. Record your
hypothesis in Question 1, as an “If . . ., then . . .” statement: “If the pH
of the solution . . . , then the percentage of seeds that germinate . . .”
Step 8
Place a paper towel on the table and put 10 bean seeds on the towel.
Step 9
Wrap the seeds carefully in the paper towel to make a neat package.
Step 10 Fill the dropper with Solution A and soak the paper towel package
with Solution A. Repeat until the paper towel package is fully
saturated—evenly wet, but not dripping—with Solution A.
Step 11 Carefully place the wet package in a resealable plastic bag. Seal the
bag, making sure there is air in the bag. With a marking pen, label the
bag "A" and include your group name.
Step 12 Repeat Steps 8–11 with the remaining paper towels, bean seeds, and
vinegar solutions. Be sure to flush out the dropper between solutions.
When you finish, you should have 5 plastic bags, labeled A through E
with your group name, each containing a wet paper towel package.
Step 13 Store your plastic bags for 3 days in a warm location without direct
sunlight.
Step 14 Follow your teacher's instructions for cleanup and disposal of
materials. Wash your hands thoroughly.
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Step 15 After 3 days, collect your plastic bags. Remove the paper towel
package from Bag A. Carefully unwrap the bean seeds and examine
them with a hand lens. Record in the Data Table the number of seeds
that have germinated in Bag A. A seed has germinated if the seed coat
has cracked and a tiny root has emerged.
Step 16 Repeat Step 15 for Bags B through E.
Step 17 Follow your teacher's instructions for cleanup and disposal of
materials. Wash your hands thoroughly before leaving the lab.
Observe and Collect Data
1. Write a hypothesis that will explain how changing the pH of a solution
affects the percentage of seeds that germinate. Your hypothesis should be an
“If . . ., then . . .” statement.
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2. Fill in the first two columns of the table with the data you collect.
Data Table
Solution
pH of Solution
Number of Seeds
Germinated After 3 Days
Percentage of
Seeds Germinated
A
B
C
D
E
3. Use your data to calculate the percentage of seeds that germinated at each
pH level. Record the percentages in the last column of the data table.
Analyze and Conclude
4. Graph On a separate sheet of graph paper or using graphing software, make a
bar graph to show the effect of pH on seed germination. Plot pH on the x-axis
and the percentage of seeds germinated on the y-axis.
5. Interpreting Graphs Does your graph support the hypothesis you made?
Why or why not?
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6. Review What is the relationship between pH and acidity?
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7. Control Variables What was the independent variable in this lab? What
was the dependent variable?
Independent Variable:
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Dependent Variable:
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8. Use Models What do the 5 vinegar solutions represent?
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9. Evaluate Identify at least one way that this lab was not a perfect model for
demonstrating the effect of acid rain on the germination of seeds.
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10. Analyze Data Based on your data, what pH for rainfall would be optimal
for producing the most plants in an area? How does this pH compare to the
average pH of normal rainfall?
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11. Extension Explain why acid rain could harm animals as well as plants.
Which types of animals do you think would be most at risk from acid rain?
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