THE EFFECTS OF
ACID RAIN ON YEAST
Introduction
Chemicals such as sulfur dioxide and hydrogen chloride often find their
way into the atmosphere as by-products of human activity. When these
substances mix with water vapor, they become acid precipitation (acid
rain). This type of pollution can cause serious damage to organisms in
ecosystems. One kind of ecosystem resident, the single-celled fungus
known as yeast, is especially vulnerable. Yeast cells can be seen only
under a microscope (Figure 1). They can be found in most parts of the
ecosystem, from the surfaces of leaves to deep in the soil. When acid
rain enters the environment, the ability of yeast to grow can be affected.
In this activity, you will conduct an experiment that tests the effects of
acid rain on yeast growth.
Figure 1
Figure 1
Walker/Wood, (JNEOF), Vol. 3 Fig 1(6-6-1)
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THE EFFECTS OF ACID RAIN ON YEAST
Time Needed
50 minutes on day 1
30 minutes on day 2
What You Need
F goggles
F apron
F 75 milliliters (ml) of warm water
F two 250-ml beakers
F 25 ml .01 M HCl
F package of dried baker’s yeast
F glass stirring rod
F labeling tape and pen
F 1 teaspoon of sugar
F 2 sterile petri dishes with lids
F graduated cylinder
F shoe box with lid
F measuring spoon
F paper towels
F pH strips
F science notebook
Safety Precautions
Wear safety goggles and an apron when working with acid.
Please review and follow the safety guidelines.
What You Do: Day 1
1. Put on your goggles and apron.
2. Label a 250-ml beaker as “acid.” This is your experimental beaker.
3. Label the second 250-ml beaker as “normal.” This is your control
(Figure 2).
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THE EFFECTS OF ACID RAIN ON YEAST
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Figure 2
4.
5.
6.
7.
8.
9.
10.
Label one petri dish and lid as “acid.”
Label the second petri dish and lid as “normal.” Set both petri
dishes to the side for later.
To the beaker marked “acid,” add the following:
25 ml of warm water
25 ml of .01 M HCl
1/2 teaspoon of sugar
1/2 teaspoon of dried baker’s yeast
Mix the ingredients using the glass rod. Test the pH of the solution
and record it in the second column of the data table. Cover the
beaker with a paper towel and allow it to sit for 20 minutes. Rinse
the glass rod and graduated cylinder.
To the beaker marked “normal,” add the following:
50 ml of warm water
1/2 teaspoon of sugar
1/2 teaspoon of dried baker’s yeast
Mix the ingredients using the glass rod. Test the pH of the solution
and record it in the second column of the data table. Cover the
beaker with a paper towel and allow it to sit for 20 minutes.
As you wait, turn the shoe box upside down so that the lid becomes
a tray and the bottom becomes a cover. Remove the cover.
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THE EFFECTS OF ACID RAIN ON YEAST
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11.
12.
Place the two petri dish lids on the shoe box lid.
Following the 20-minute wait, prepare the petri dishes as follows:
Half-fill the petri dish labeled “acid” with acid solution. Replace the
lid on the petri dish.
Half-fill the petri dish labeled “normal” with normal solution.
Replace the lid on the petri dish.
13. Cover the petri dishes with the top half of the box and allow them
to sit undisturbed until day 2.
What You Do: Day 2
1.
2.
3.
Put on your goggles and apron.
Remove the cover from the tray.
The growth of yeast in a solution will make it cloudy. Compare the
clarity of the solutions in the two petri dishes. Rate the clarity of
each solution using a scale of 1 to 5, with 5 as very cloudy and 1 as
clear. Record your findings on the data table.
Data Table
Petri dish
pH
Clarity
Acid
1 2 3 4 5
Normal
1 2 3 4 5
Observations
1. In which petri dish was the solution the cloudiest? Why do
you think this was so?
2. Why do you think that sugar was mixed in both beakers?
3. Why do you think the petri dishes were placed inside the
shoe box?
4. How do you think your results would have been different if
a lower concentration of HCl had been used?
5. Based on this experiment, do you think that acid rain is
harmful to yeast?
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SAFETY PRECAUTIONS
Review Before Starting Any Experiment
GENERAL
• Always obtain your teacher’s permission for experiments performed
at school, and your parent’s permission for experiments performed
at home, before attempting any experiment.
• Read all instructions for an experiment before starting the
experiment, and follow the directions exactly as they appear in
this volume.
• If an experiment requires adult supervision, do not perform the
experiment unless you have an adult supervising you the entire
time you are performing the experiment.
• Wash your hands before the start of and after each experiment
you perform.
• Keep your work area clean.
• Never eat or drink while performing an experiment. Never taste a
substance used in an experiment unless you are told that it is safe
to do so.
• Be aware of the location of safety equipment you may need in an
emergency, such as running water, an eyewash if you are at school,
and a fire extinguisher.
• If you are going outside, make sure you have permission to go
from your teacher and parent. Take a buddy with you, and dress
appropriately for the weather. Make sure you or someone who
accompanies you is familiar with the area, and bring along a firstaid kit in case of emergency.
• Never look directly into the Sun.
CHEMICAL SAFETY
• Always wear goggles when working with chemicals, such as acids
and bases, and near heat sources like flames. If at all possible,
avoid wearing contact lenses when working with chemicals.
• If any substance gets into your eyes, notify an adult (e.g., your
teacher or parent) immediately, and flush your eyes with running
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SAFETY PRECAUTIONS
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water for at least 15 minutes. Do not mix chemicals unless you are
told to do so by a teacher or parent.
• Never touch, taste, or smell chemicals unless instructed to do so.
• Keep chemicals in closed containers when they are not in use.
• Dispose of all chemicals properly. Do not pour any chemicals or
solids down the drain unless instructed to do so.
• Use safety gloves and a plastic apron when handling chemicals. If
any chemicals spill on your skin, rinse the affected area with
running water for at least 10 minutes, and notify your teacher or
parent immediately.
• Take precautions to avoid spilling chemicals. If a chemical spills on
any surface, notify your teacher or parent immediately to assist
with clean-up.
• Exercise caution when using sharp instruments such as knives or
scissors. Always cut away from yourself, not toward yourself. If you
cut yourself, notify your teacher or parent immediately.
GLASSWARE
• Clean glassware when you are finished with the experiment.
• Be careful when using glassware. If a piece of glassware breaks,
have an adult assist you in clean-up to avoid injuries from broken
glass. Never use broken or damaged glassware.
FIRE SAFETY
• Do not heat glassware that is not completely dry. Do not pick up
hot glassware without heat-resistant gloves or tongs.
• When heating glassware, keep it away from yourself and from
others.
• Do not heat anything unless instructed to do so by a teacher or
parent.
• Do not heat substances in a closed container.
• After an experiment, make sure that all heating sources are off
and that all flames have been put out.
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SAFETY PRECAUTIONS
• Do not reach across such heating sources as flames.
• If you have long hair, tie it back, out of the way. Do not wear
clothing with loose sleeves, scarves, bows, ties, or anything else
that may hang into a fire. Do not wear long earrings.
ELECTRICAL SAFETY
• Do not touch electrical equipment when your hands are wet.
• Do not plug several electrical devices into one outlet or use an
extension cord.
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