Theme: The Air We Breathe
Learning and Teaching Activities
Effect of acid rain on plants
Teaching Tips
This is an investigative approach to let students master the biological concept. However, the
success of this experiment may be greatly affected by the type of plant used and the control
of experimental conditions and the level of sulphur dioxide generated by the chemical means.
So prepare well and guide the students to understand that when an expected result is not
obtained, there must be something wrong. Trouble-shooting is very important in training for
logical thinking, care in observation and communication skill. When the environmental
conditions cannot be standardized, an experimental result may not be obvious and nor
reproducible. Depending on the plant chosen for investigation, the incubation period lasts
from 2 days to 1 week.
Objective: To simulate the effect of acid rain on plant germination or to examine the effect of
acidic solution on plant germination.
Introduction
Acid rain is rain that is polluted by acidic gases in the atmosphere. It is more acidic than
normal rain, which has a pH of about 5.6. Acid rain contains appreciable quantities of
sulphuric acid, probably due to industrial release of sulphur dioxide and sometimes coal
burning into the air. When acid rain falls in an area, hydrogen ions from the acid tend to
displace nutrient cations out of the soil particles. This will lead to acidic soil. According to
the electrochemical series, hydrogen ions will replace the bound ions in soil particles. Thus it
favours leaching of mineral ions, and consequently decreases soil fertility. Acid rain is
harmful to people, animals, forest and crops, water and buildings and structures.
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Acidic soil also favors the growth of certain mosses but may kill the symbiotic fungi, which
are beneficial to the roots of trees. In a biological sense, acid rain will accelerate
eutrophication due to the loss of nutrients into water bodies and leads to major changes into
the character and abundance of species. Moreover, as plants are producers in the food chain,
its affected growth will have negative effect on primary consumers, secondary consumers, etc.
and cause imbalance of the food chain and food web.
Figure 1. A simplified diagram of different trophic levels for the ecosystem.
Form a group of 4 – 6 students and use the following materials to perform the experiment.
Students are required to follow the experiment for 1-2 weeks and record the observations.
Answer the questions and hand in the report after the experiment finished.
Materials
 Sodium bisulphate (IV) in distilled water (0, 0.2, 0.6, 1.0 and 2.0g/10 mL distilled water)
 Dilute Sodium Chlorate (I) Solution
 10 Sterilized Petri Dish
 100 wheat grains, Chinese white cabbage seeds, corn grains, rice grains (unpolished)
 5 Clear Polytene Bags with sealing edge
 20 Sterilized Filter Paper
 Rubber Bands
 10 ml measuring cylinder
Safety measures
- Keep aware when performing an experiment
— Study the laboratory manual beforehand.
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— Obey instructions and follow instructions step by step.
— Do not play or disturb others.
— If there is an accident, leave immediately. When safe, report the accident and ask for help.
— When acid solution is handled, be careful and do not spill.
— Make sure that the bags are sealed tightly to avoid the emission of acidic gasses.
— Perform the experiment in a well-ventilated area.
Procedures
1. Sulphur dioxide is produced by dissolving sodium bisulphate (IV) in distilled water.
Prepare a series of different concentrations (0, 0.2, 0.6, 1.0 and 2.0g/10 mL distilled
water).
2. Prepare a moist chamber by soaking two pieces of filter paper in 5mL of the solution
using measuring cylinder and place the filter paper in the sterilized petri dish.
3. Surface-sterilize grass seeds/ grains with diluted sodium chlorate (I) solution (or chlorxo :
water, 1:99; v/v) for 30 sec.
4. Dry the sterilized seeds with a new filter paper.
5. Spread 20 seeds or grains onto the sterilized moist chamber.
6. Cover the plant with two pieces of filter paper that previously soaked with the solution.
7. Put the moist chambers inside separate clear polytene bag sealed with a rubber band.
8. Incubate at room temperature for 3-one week.
9. Count the number of seeds or grains germinated. Record any change in the morphology
of the seeds/ grains/ seedlings, such as colour, shoot or root lengths.
10. (Optional) Repeat Step 1-9 by replacing wheat with Chinese white cabbage or other
plants.
In addition, to simulate the effect of acid rain, two petri dishes are required. One plate serves
as the solution to generate sulphur dioxide which is volatile. The other plate is the moist
chamber for seeds/grains to germinate. Both plates have to be put side by side in a plastic
sealing bag. As the gas needs to fill up the void volume in the sealing bag, the effective
concentration will have to be higher than the acidic solution to cause the same harmful effect
and takes longer to effect the damage (e.g. in terms of 1-2 weeks).
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Seed Germination on moist chamber
0g/10ml
0.2g/10ml
0.6g/10ml
1.0g/10ml
2.0g/10ml
Observation
Discussion
1. Tabulate the final results for the number of seeds germinated for different sulphur dioxide
concentrations. Describe the seed morphologies.
(Hint: Any leaf observed? Length of shoot and root? Strength? Colour?)
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Conc. (g/10 mL) No. of seeds germinated
Descriptions
0.0
0.13
0.25
0.50
1.00
2. From the results, how does the concentration of sulphur dioxide affect the growth of grass
seeds?
3. Grass seeds in this experiment serve as a producer in the food chain. What will be the
consequences of acid rain on the ecosystem?
D
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Suggested Answers (Accept alternative and correct answers)
1. Tabulate the results for the number of wheat grains germinated for different sulphur
dioxide concentrations. Describe the seed morphologies.
(Hint: Any leaf observed? Length of shoot and root? Strength? Colour change?)
Most wheat grains can tolerate the acidic solutions tested but growth is inhibited. When
other plants are tested, e.g. Brassica (Chinese white cabbage), there might be total inhibition
on germination at the highest dose tested. I.e. different plants have different sensitivities.
Conc.
No. of wheat
(g/10mL)
germinated
0.0
19
0.13
19
0.25
20
0.50
20
1.00
19
Descriptions
Strongest, thickest and long shoot and root; presence of
root hair and branching; 4-5 small green leaves per grain
Strong, thick and long shoot and root; presence of root
hair; 4-5 small green leaves per grain
Strong and long shoot and root; 4-5 small green leaves
per grain
Shorter, thinner shoot and root; 2-3 small green leaves
per grain; few yellow leaves present
Shortest, weakest shoot and root; 2-3 small leaves per
grain; most leaves are yellow
2. From the results, how does the concentration of sulphur dioxide affect the growth of grass
seeds?
Increasing sulfur dioxide content will decrease the strength of the root and shoot of the
germinated seed.
The quality of germinated seeds decreases, in terms of:
 Length and strength of roots and shoots (strong and thick at low conc., weak and thin
at high conc.);
 Colour of the leaves (green at low conc., but yellow at high conc.)
3. Grass seeds in this experiment serve as a producer in the food chain. What will be the
consequences of acid rain on the ecosystem?
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Acid rain will lead to a decreased no. of producers, which will cause the imbalance
nutrient supply in the food chain.
Consequently, there will be decrease in the no. of primary, secondary and tertiary
consumers and affect the whole food web.
Extinction of species may be resulted in worse case and lead to decrease in biodiversity.
The release of toxic chemicals (e.g. aluminum ion) may be resulted and being
bioaccumulated.
Any appropriate answers.
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