Lab 7: Ocean Acidification

The lab activity described here was developed by Candace Dunlap of TERC for the EarthLabs project.

Summary and Learning Objectives

Oceans are absorbing about a third of of carbon dioxide emitted from burning fossil fuels. In Part A, students learn about the pH and ocean carbonate chemistry of ocean acidification and examine time series evidence that our oceans are becoming more acidic. In Part B, students learn about the effect of ocean acidification on shell-building organisms such as oysters, lobsters and sea urchins. They use the Virtual Urchin lab, developed by Stanford University, to investigate the effects of a more acidic ocean pH on the ability of sea urchins to form their carbonate internal skeleton

After completing this investigation, students will be able to:

Explain what ocean acidification is and why it is happening;
Describe ways in which individual species and marine ecosystems may respond to ocean acidification; and
Describe how ocean acidification may impact the ability of oceans to store carbon in deep sea sediments.

Open the Student Lab »

Overview and Teaching Materials

Detailed overview of what students will do in each lab activity, how long it will take, and what materials are required to complete the lab.

In Part A: Students analyze time series graphs to search for relationships and trends in atmospheric CO₂, dissolved seawater CO₂ and changes in ocean pH. They are introduced to a chemical understanding of pH. Students then carry out a class experiment on the effects of increased amounts of CO₂ on pH of water.

Time estimate: 1 to 2 50-minute class periods

In Part B: Students review and analyze the results of research compiled by the Woods Hole Oceanographic Institute on the effect of ocean acidification on a variety of marine organisms. They then read research on the importance of echinoderms in the carbon sink and carry out a Virtual Lab on the effect of increasing acidic sea water on sea urchin larvae.

Time estimate: 1 to 2 50-minute class periods

Materials needed: NOTE: See the Teaching Notes and Tips section for tips on setting up the experiment that uses these materials.

200 ml beaker, flask, or similar size clear glass
Drinking straw
50 ml of Bromothymol Blue (BTB) in solution

Printable Materials

Download and print files needed for each lab activity, including images, data tables, and Stop and Think questions.

To download one of the PDF or Word files below, right-click (control-click on a Mac) the link and choose "Save File As" or "Save Link As."

Lab 7 Stop and Think Questions
Word -- educator-only file

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Suggested Answers -- educator-only file

Suggested Answers

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to the Stop and Think Questions

Teaching Notes and Tips

General recommendations for classroom implementation.

General Recommendations:

Students will need to be reminded that a decrease in pH (or a lowering in pH) means an increased acidity. It is very easy for students to get confused.
If unfamiliar with a hands-on activity in this Lab, consider a practice run before implementation.
Print out any paper-based materials before starting the lab.
Have students keep a lab notebook or journal to record important notes, questions, data and findings.
Consider FLIPPING parts of the lessons. This will save you class time and reduce the need to have computer access in your classroom.
Discussion questions, Checking In questions and Stop and Think questions can be adapted and used in a variety of ways based on teachers' needs. For example, some questions might make great "DO Now" activities as students enter the classroom or great "exit quizzes" as students leave.
You may want to spend time projecting graphs and important images on the board and going over the elements (e.g. units of measure, variables on axis, trends, color schemes etc) with them.
In many of the Optional Extensions sections throughout the carbon cycle module, students are prompted to "research the latest research" on important carbon cycle topics pertinent to the lab section they are working in. Rich conversations can ensue when students go to ScienceDaily and/or Phys.org - News and Articles on Science and Technology to find abstracts of new research that supports, contradicts or enhances current understanding on how the carbon cycle works.

Recommendations and tips for the experiment "Does a change in dissolved CO₂ cause a change in pH? What's the evidence?' in Part A.

To save time, you can do the Bromothymol Blue (BTB) experiment as a demo.
For safety concerns, read the Bromothymol Blue MSDS and share any safety concerns with your students.
Bromothymol blue(BTB) is an indicator used to show the presence of an acidic solution. Low levels of acid will result in the BTB solution remaining blue, while higher levels of acid will result in the BTB solution taking on a yellow tint.
Here is background information about The reaction between CO₂ and water if needed.
BTB solution has a limited shelf life so make sure your BTB solution works before you begin the lab.
You can order aqueous solutions of BTB from any school science supply company or you can make your own. Alternatively, you could boil some red cabbage and use that.
If you are doing this lab online, you can have students watch the following Bromothymol Blue + CO₂ video, which shows the same. The video is on Student pages in the Extension section at the bottom of the page. Note that the video was created for another curriculum, so there are questions the narrator asks for another class that are not relevant to this specific lab.

Recommendations and tips for the Virtual Urchin on-line bench experiment in Part B.

The Virtual Urchin on-line lab will works well on a computer but not on a tablet.
This program takes time to load.
The Virtual Urchin Tool has three Parts 1-3. Be sure to familiarize yourself with the Virtual Sea Urchin tool and its three Parts. Students should start out this lesson in PART 2; however, you may decide to have them begin in Part 1. With advanced students, consider giving them Parts 2 and 3 to do at home and then they can bring their data in the next day to graph the class data and write a conclusion.
It is strongly recommended that you go through the tool in Part 2 a couple of times so you understand how the tool works and where your students might have difficulties. Definitely leave the "light bulb" on in the bottom right section of the window.
NOTE: If the Virtual Urchin Lab does not feel like a good fit for your students, you may want to consider substituting this interactive simulation on understanding ocean acidification at the following link
NOTE: If time and computer usage in your room is an issue, have students watch the NOVA program, "Lethal Seas" and follow-up with a discussion. NOVA on PBS - Lethal Seas Viewing "Lethal Seas" online through NOVA is available but only if you have PBS Passport.

Student Notebooks

Suggestions for how to use Student Notebooks for Lab 7.

Here are just a few suggestions for what to include in student notebooks for Lab 7:

Have students write down the learning objectives for Lab 7.
Drawings and notes from videos, animations, discussions and activities
Have students record answers to all Stop and Think questions.
Have students record answers to Discussion questions.
Have students record diagrams they have drawn, with labels and a short description of what the diagram represents.
Have students record important hands-on or minds-on activity components. This could include research questions, data, tables, observations, drawings, graphs, and conclusions.
Have students write down any questions they still have about the content covered in this lab.

Assessment

There are several options for assessment of student understanding of material introduced in this lab. Choose from the following list, or create your own assessments.

Assess student understanding of topics addressed in this investigation by grading their written responses to the Stop and Think questions or by using Stop and Think questions as part of whole-class or small group discussions.
Written Test for Lab 7
Word -- educator-only file

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,
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PDF

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,
Answer Key -- educator-only file

Answer Key

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)
Many lab sections have a "learning assessment" component. While carrying out the learning assessment activity, students are learning important concepts and demonstrating their understanding in a performance assessment. The Virtual Urchin activity in Part B is a performance assessment. Students could write a formal lab report for the Virtual Urchin activity.
Anything that students create such as graphs, diagrams,and conclusions would serve as good assessments.