Ocean Acidification_Teacher Answer Keys

Check one:
This survey is both a pre- and post- survey. Put a check mark at the top of this paper next to the survey you are doing
(pre- or post- survey). Please answer each question to the best of your ability. Circle the most correct answer.
1. The average concentration of carbon dioxide (CO2) in the atmosphere has _______________in recent years.
a. increased
b. decreased
c. remained constant
2. When carbon dioxide dissolves in water, it forms a(n) ________________.
a. base
b. acid
c. precipitate
d. metalloid
3. When carbon dioxide dissolves in water, the pH ____________________.
a. increases
b. decreases
c. stays the same
4. Bread dough rises because yeast in the dough produces _______________.
a. hydrogen (H2)
b. carbon dioxide (CO2)
c. oxygen (O2)
d. nitrogen (N2)
5. Increasing carbon dioxide (CO2) in the ocean results in _____________.
a. higher salinity
b. lower salinity
c. benefits for reef-building corals
d. problems for reef-building corals
6. The pH scale ranges from 0 to 14 and is a measure of how acidic or basic a substance is. Pure water is
___________with a pH of 7. Solutions with a pH less than 7 are ___________ while solutions with a pH greater
than 7 are ____________.
a. neutral / basic / acidic
b. acidic / basic / neutral
c. basic / neutral / acidic
d. neutral / acidic / basic
e. acidic / neutral / basic
7. If the pH of a solution changes from 2 to 3, there is a ___________change in acidity.
a. 1 x
b. 2 x
c. 10x
d. 20x
8. The salmon fishing industry is a multibillion dollar business that supplies food for a large population of the
world. How could ocean acidification affect this industry?
a. It would not have any impact on the industry
b. It would increase fishing stocks
c. It would decrease fishing stocks
9. Please share your opinion and circle how you feel about the following statement (question not scored):
Higher levels of carbon dioxide emissions have a negative effect on the ocean environment.
Strongly Disagree
For information only, do not grade question 9.
Strongly Agree
Lesson 1a: Honolulu Declaration
1. What did scientists in Florida declare as “the largest and most significant threat that oceans face today”?
Scientists declared ocean acidification as the largest and most significant threat.
2. In your own words, what does the “Honolulu Declaration on Ocean Acidification and Reef Management” hope
to accomplish?
The Declaration hopes to prevent further ocean acidification and to protect coral reefs.
3. The two major strategies supported by the declaration are:
a. Reducing the amount of fossil fuels we use.
b. Creating healthier coral reef ecosystems so that they are better able to resist climate change.
4. What are two actions you could take to help support these strategies?
Students could support these strategies by limiting their own fossil fuel emissions. Some ways to do this are
to drive less and walk or ride a bike more, buy local food to reduce “plate mileage”, not use air conditioning,
turn off the lights when you leave a room, etc.
Students could help create healthier coral reefs by supporting the development of marine reserves, not
allowing pollutants to enter the ocean, not touching corals, etc.
5. If coral reefs in Hawai‘i are unable to survive due to ocean acidification, what effects would this have on your
life? List three examples.
Coral reefs provide humans many benefits. For example, reefs are good for the economy and provide jobs
because they support ecotourism. Reefs are the rain forests of the ocean and support a wide variety of
marine life, some of which is eaten as food. Reefs also help protect the land from the impacts of waves and
storms. Coral reefs are also a source of compounds used in medicines. If coral reefs disappear, our economy
may weaken, there may be less seafood to eat, there will be fewer marine creatures to observe, and coastal
erosion might increase.
Lesson 1b: The Dangers of Ocean Acidification
1. Why was Mauna Loa chosen as a location to measure CO2 concentrations in the atmosphere?
Mauna Loa is a remote location that is far away from major sources of carbon dioxide, which could affect the
measurements of carbon dioxide levels. Though Mauna Loa is an active volcano, the measurements are made
at a high enough altitude so that contamination from the volcano is negligible. In addition, Mauna Loa is
relatively easy to access compared to other isolated locations like Antarctica.
2. Why are carbon dioxide levels in the atmosphere increasing?
Carbon dioxide levels are increasing mainly due to human activities, such as the burning of fossil fuels (i.e.,
coal, oil, and natural gas) and the production of iron, steel, and cement.
3. How does carbon dioxide cause the pH of the ocean to decrease?
When carbon dioxide dissolves in water, it forms carbonic acid (H2CO3). Acids lower pH. Thus, as more
carbonic acid forms, the pH of the ocean decreases.
Additional information: Carbonic acid rapidly dissociates into hydrogen ions (H+) and bicarbonate ions (HCO3-).
Since pH is a measure of the H+ concentration, the increase in H+ in solution lowers the pH of the water.
4. What types of organisms are directly threatened by ocean acidification? Why?
Organisms that make skeletons or shells out of calcium carbonate, including corals, mollusks and calcifying
plankton, are threatened by ocean acidification. Calcium carbonate is a basic compound. As the ocean
acidifies, calcium carbonate dissolves, and there are fewer carbonate ions available for organisms to build
their shells. Therefore, organisms that make calcium carbonate shells will have a hard time growing as ocean
pH decreases.
Additional information: It might seem reasonable to think that if you add carbon to the ocean (in the form of
CO2), other carbon containing compounds such as carbonate ions would also increase. However, this is not
the case. When carbon dioxide dissolves in water, hydrogen ions (H+) form. These hydrogen ions tend to
combine with carbonate ions (CO32-) to form bicarbonate ions (HCO3-). Thus, as the ocean becomes more
acidic, there are more bicarbonate ions, and fewer carbonate ions in the water.
5. Are cold water or warm water ecosystems more susceptible to ocean acidification? Why?
Cold water ecosystems are more susceptible to ocean acidification because CO2 is absorbed more readily in
colder water.
6. What is one type of experiment the author suggests that scientists could perform to gain a better understanding
of the threat that ocean acidification poses to marine environments?
The author suggests a variety of experiments, including: elevating carbon dioxide levels in a patch of ocean
over a long period of time; studying marine organisms in environments that naturally have a low pH; and
examining the geologic record of times when carbon dioxide concentrations were naturally much higher than
they are today.
7. If the geologic record shows that CO2 levels have been higher in the past than they are today, why are current
changes in CO2 levels such a concern?
CO2 levels today are changing at a much faster rate than at any time in the past, so marine organisms will
have little time to adapt to these changes.
Lesson 2: Yeast Experiment
1. Make a prediction! After the yeast is activated, what will happen to the pH and CO2 levels over time? Record
your hypothesis here:
The yeast will create carbon dioxide, so carbon dioxide levels are predicted to increase over time. Since
carbonic acid is formed when CO2 dissolves in water, the pH would be expected to decrease over time.
2. Record the readings from your sensor in the following table. Record a reading every 3 minutes. The value may
be jumping around on the LabQuest Handheld, so watch it for 5 seconds, and record the highest value it gives
you. You will be recording pH OR CO2 concentration. After the experiment, get the data for the other
measurement from the other members of your group. Record any observations for each time period.
Measurements will vary. The initial CO2 concentration is typically ~300-600 ppm. Outside air has a CO2
concentration of ~380 ppm, but indoor CO2 values can be much higher and may even exceed 1000 ppm if the
ventilation is poor. The pH of the water should be between 6 and 8. Distilled water has a pH of 7, but tap
water often contains harmless, dissolved minerals that can affect its pH.
The changes in CO2 concentration and pH will vary among groups. Some yeast may react more quickly than
others, as evidenced by rapid foaming. The amount of swirling of the yeast/sugar solution affects this rate.
A few minutes after the start of the experiment, students should observe the yeast foaming, and bubbles of
carbon dioxide should be seen entering the water sample being measured by the pH group. Generally, CO2
will increase slowly for the first several readings, and then will rapidly begin increasing.
For the pH group, it is very important that students allow sufficient time for their pH meter to equilibrate
before starting the experiment. If the meter is not equilibrated, students may actually observe an increase in
the pH value (meaning the water is becoming more basic). If the meter is equilibrated properly, the pH value
should decrease by about 1 pH unit over the course of the experiment. Remember that pH is measured on a
logarithmic scale, so a decrease of just 1 pH unit represents a 10-fold change in hydrogen ion concentration
(i.e., becomes 10 times more acidic). The following table shows sample data and observations (answers will
Time (minutes)
CO2 (ppm)
Bubbles are coming out of the tube into the water.
A bubble comes out of the tube about every second. The yeast is
starting to foam.
Foam is about ½ way to the top.
CO2 is starting to get really high!
3. What gas is the yeast producing?
Carbon dioxide (CO2)
Before starting this experiment, we waited 5 minutes until pH reached
an equilibrium value.
Foam is about ¾ of the way to the top.
Foam is just below the red line. Stopped the experiment.
4. Create a graph of the change in pH or CO2 concentration (depending on which data you collected) over time
using the grid below. Label your axes, and include units. Time (in minutes) will be on the x-axis.
Below are sample graphs of the CO2 and pH data. Student graphs should show similar trends. In order to
make the change in pH evident in a graph of the pH data, make sure students scale the y-axis appropriately.
The scale should not run from 0–14; it should just cover the range of pH observed in the experiment (see
example below).
Carbon Dioxide
C02 (ppm)
Time (minutes)
Time (minutes)
5. What does your graph show? Did the CO2 concentration increase or decrease? What about the pH?
Carbon dioxide increased, and pH decreased.
6. What is the relationship between CO2 and pH? Explain.
Carbon dioxide dissolves in the water and causes carbonic acid to form. This decreases the pH of the water.
7. The following graphs show changes in the levels of atmospheric and oceanic carbon dioxide over the past 20
years, as well as a corresponding change in ocean pH. The x-axis measures time in years, from October 1988
until December 2007. The y-axis of the top graph measures CO2 concentration. This top graph shows how the
CO2 concentration in both the atmosphere (red line) and ocean (blue line) change with time. The actual data
collected are shown with dots, and each line is the "best fit" to the data. The y-axis of the bottom graph
measures pH of the ocean. Use the graphs to answer the following questions.
a. How much carbon dioxide was in the atmosphere in 1988? 350 ppm
2007? ~380 ppm
b. How much carbon dioxide was in the ocean in 1988?
330 ppm
2007? ~350-380 ppm
c. What was the pH of the ocean in 1988?
2007? ~8.06-8.11
The pH and CO2 readings vary throughout the year because they are affected by the northern hemisphere
growing season. In the spring and summer, plants grow and take in CO2 for photosynthesis, so there is less
CO2 in the atmosphere. In the winter, plants lose their leaves, which decompose and release CO2 into the
Data from the Hawai‘i Ocean Time Series (HOT) and the Mauna Loa Observatory.
8. How do the data in these graphs compare to the data you collected?
These graphs show that as the CO2 concentration in the atmosphere increases, the CO2 concentration in the
ocean also increases. Scientists have also seen that with this increase in CO2, there is a subsequent decrease
in the ocean's pH. These results should be very similar to what the students found – as CO2 was generated by
the yeast, the pH of the water decreased.
9. According to these data and the data you collected, how will increasing atmospheric CO2 affect marine
Since CO2 increases the acidity of the water, increasing CO2 will cause marine organisms that have calcium
carbonate shells to have difficulty growing. Some of the organisms affected are corals and calcifying
plankton. Lots of organisms depend on coral reefs for shelter and plankton for food, so the effects of ocean
acidification on marine ecosystems could be devastating.