TE Activity: Breathing Cells
Contributed by: Integrated Teaching and Learning Program, College of Engineering, University of Colorado at Boulder
Summary |
Engineering Connection |
| When toxic materials are spilled into the environment, engineers can use microorganisms, fungi or plants to clean up the spill through a process called bioremediation. The engineers choose an organism that can "eat" the target contamination. One way that engineers can tell whether bioremediation is working or not is by measuring how much the bacteria are "breathing." Engineers measure how much organisms are breathing by changes in pH of the soil or water in which they are growing. Measuring the results of cell activity is usually easier than trying to keep track of the actual amount of toxic material in the environment. |
Contents
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| Grade Level: 7 (6-8) | Group Size: 2 |
| Time Required: 50 minutes |
Activity Dependency  :None |
Expendable Cost Per Group
:
US$ 1 |
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| Keywords: pH, indicator, carbon dioxide, cellular respiration, bioremediation, cells, ions, hydrogen, cabbage, acid, base | |
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Related Curriculum
:
| subject areas | Biology |
| curricular units | Cells |
| lessons | Cellular Respiration and Bioremediation |
Pre-Req Knowledge (Return to Contents)
Students should have a basic understanding of pH. It is also helpful for students to have a basic understanding of cellular respirations, as discussed in the associated lesson, Cellular Respiration and Bioremediation.
Learning Objectives (Return to Contents)
After this activity, students should be able to:
- Describe the effects of cellular respiration on pH.
- Explain how engineers use pH to measure cellular respiration in bioremediation of contaminated soils.
Materials List (Return to Contents)
Each group needs:
- Four small clear plastic cups
- Two straws
- Spoon
- One copy of the Breathing Bubbles Worksheet
To share with the entire class:
- Water
- Red cabbage indicator solution
- Four clear different solutions to measure pH (i.e., diluted lemon juice and/or vinegar, baking soda mixed with water, water, soda pop, etc.)
- pH meter (if available) or pH paper strips (optional)
- Plastic gloves (optional)
Introduction/Motivation (Return to Contents)
What do you know about pH? The pH of a solution is a measure of how much acid or base is in a solution. A low pH corresponds to an acidic solution, and a high pH corresponds to a basic solution. As a point of reference, a neutral pH would be 7. What is an example of a solution with a low pH? This would be anything acidic, such as citrus fruit or vinegar (remember: low pH equals high acidity). What solution has a neutral pH? Distilled water is a solution that has a perfectly neutral pH. What is an example of a solution that has a high pH, or is basic? Basic solutions would include baking soda, ammonia and bleach (remember: high pH equals low acidity, or is basic). pH measures the amount of hydrogen ions in a solution. Lots of hydrogen ions form an acidic solution, and fewer hydrogen ions form a basic solution.
Did you know that cellular respiration has a pH value? When a cell goes through cellular respiration, it consumes oxygen and produces CO2 which lowers the pH of water (forming an acidic solution). On the other hand, when cells go through photosynthesis, they produce oxygen which raises the pH of water (forming a basic solution).
Bioremediation is a process whereby engineers use something living, like a microorganism, fungi or green plant to return a polluted environment back to its original state. During bioremediation, some cells can use certain types of pollution as food for cellular respiration, to create energy for growth, life and reproduction. How do you think engineers can use pH to measure bioremediation? Well, pH tells us about the chemistry of water and soil. Engineers can test the pH of an area to determine if there are bacteria or other cells growing and performing cellular respiration in the area. If the pH is very acidic, then there is most likely cellular respiration going on. The organisms that engineers use for bioremediation are microscopic. So, it is hard to detect them directly. It is much less expensive and faster for engineers to measure the pH that bacteria cells produce when they grow and reproduce in the environment than to develop complicated equipment to detect their presence.
Today we are going to measure the pH of a variety of solutions and then measure how much CO2 we breathe out when we are resting and when we are exercising. First, we are going to test our pH indicator on four different solutions by adding a few drops of the indicator to each solution. Once we have determined which solutions are acidic, basic or neutral, we will try to identify the solutions as a class. Next, we will measure how much CO2 we produce when we are resting and exercising, using the same indicator we used to determine the identity of the four solutions. Lastly, we will think about how we can use pH to help engineers optimize bioremediation.
Vocabulary/Definitions (Return to Contents)
| Carbon dioxide: | CO2; a gas at room temperature that is produced during cellular respiration; when bubbled into water, CO2 lowers the pH of the water creating an acid. |
| Oxygen: | A gas that is consumed during cellular respiration. |
| pH: | A measure of how much acid or base is in a solution; a low pH corresponds to an acidic solution, and a high pH corresponds to a basic solution. A neutral pH is equal to 7. |
| pH indicator: | A solution that changes color depending on the surrounding pH. |
Procedure (Return to Contents)
Background
In this activity, students measure how many breaths it takes to change the color of the indicator to acidic from neutral when they are resting and then after they have been exercising. Their body naturally produces more CO2 when they have been exercising than when they are resting. The indicator should turn to acidic faster after they have been exercising.
Cabbage indicator colors (see Figure 2):
- Acidic pH turns the cabbage juice red.
- Neutral pH keeps the cabbage juice purple.
- Basic pH turns the cabbage juice blue.
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Figure 2. A pH indicator. click for copyright |
Before the Activity
- Gather materials and make copies of the Breathing Bubbles Worksheet.
- Make the red cabbage indicator solution the day before. (Directions: Chop the cabbage into small pieces and steep in boiling water for at least 10 minutes. Then, filter out the cabbage pieces using a coffee filter or tea strainer. You should be left with a bluish/purple solution at neutral pH.)
With the Students
- Pass out materials to students. Have them line up their four cups to receive the "unknown" solutions.
- Pour samples of four unlabeled solutions, one in each cup, to each team of students. Have the students use the indicator to assign identities to four clear solutions by adding a spoonful of indicator into the solution until it turns color. For acidic solutions, the indicator should turn red, and for basic solutions the indicator should turn blue. Have students record their observations on the worksheet.
- Next, have the students thoroughly rinse their cups. Pour cabbage juice indicator into all four of the cups, about halfway full.
- Remind students that CO2 is produced during cellular respiration and O2 is consumed. This results in an acidic solution being created. Have the students record on their worksheet the the color of the cabbage juice indicator before the experiment begins.
- Next have each student breathe into one of the cups of the indicator solution through the straw, remembering not to drink the indicator but blow into it. Record the number of breaths that it takes to turn the indicator to an acidic pH.
- Next, have the students sprint, briskly walk up and down stairs, or do some jumping jacks.
- Have the students repeat the process of breathing into the indicator solution through the straw, and record how many breaths it takes to turn the solution to an acidic color after exercising.
- Have the students report their results to the class and record the results on the board.
- Next, have students answer the results and engineering questions on their Breathing Bubbles Worksheet.
- As a class, discuss how engineers can use a similar technique to measure the amount of microbial activity in the water or in the soil where a toxic spill has occurred. Engineers can save time and money by measuring changes in pH after they have added bacterial cells or plants to a bioremediation site instead of trying to culture organisms in the lab.
Attachments (Return to Contents)
Safety Issues (Return to Contents)
Do not use any toxic liquids for your pH testing; students may inadvertently get some solution on their hands or in their mouths.
Although it is not harmful, the students should be reminded not to drink the indicator solution.
Troubleshooting Tips (Return to Contents)
The students need to thoroughly wash out their four cups after testing the unknown solutions. Any residue left in the cups may affect their breathing experiment.
If the indicator solution does not change color, the students can use pH paper to measure the pH of a solution of water after they breathe into it while resting and then after they have been exercising.
Assessment (Return to Contents)
Pre-Activity Assessment
Class Discussion: The teacher should gauge the students' prior knowledge of the material by asking the following questions:
- What is pH? (Answer: The pH of a solution is a measure of how much acid or base is in the solution.)
- What is cellular respiration? (Answer: The process where cells convert food into energy for growth, survival and reproduction.)
Activity Embedded Assessment
Worksheet/Pair Check: Have the students record measurements and follow along with the activity on their worksheet. After students have finished their worksheet, have them compare answers with their peers.
Post-Activity Assessment
Engineering and Bioremediation Costs: There are many cost and efficiency benefits to bioremediation. Have students think about how the cost and resource put into bioremediation might be different than developing tools and equipment to remove contaminants from soils and water. Have them write a paragraph or have a class discussion comparing bioremediation versus land removal in contamination cleanup.
Engineering Recommendations: Have the students pretend to be a consultant for an engineering firm for one of the following scenarios. Ask the students to make recommendations about how to monitor the bioremediation of the area based on what they learned during this activity.
- A piece of land contaminated with heavy metals and oils from an old industrial factory.
- A former shipyard that has leaking barrels of oil in one area.
- A piece of farmland that has been previously treated with several harmful pesticides.
- A piece of land that has been contaminated with soaps and solvents used by a dry cleaning company.
- A nuclear waste site that has very high amounts of radioactive materials leeching into the soil and groundwater.
Activity Extensions (Return to Contents)
Have the students learn more about monitoring the effects of bioremediation. Several measurements are usually performed, including oxidation reduction potential (redox), pH, temperature, and oxygen content.
The same pH indicator can be used by the students to measure the "breathing" of yeast cells. The class can grow yeast cells in a solution of warm water and sugar and add indicator to the yeast solution in order to watch the pH change as the yeast produce acid when they digest the sugar.
Activity Scaling (Return to Contents)
- For upper grades: have the students describe pH and indicators quantitatively. Have the students create a scale for measuring the pH of different solutions using the cabbage juice indicator.
- For lower grades: do activity as described.
References (Return to Contents)
Helmenstine, Anne Marie, Ph.D. How to make red cabbage pH indicator: Acid base chemistry. Accessed on August 23, 2008. http://chemistry.about.com/library/weekly/aa012803a.htm
Contributors
Kaelin Cawley, Malinda Schaefer Zarske, Janet YowellCopyright
© 2008 by Regents of the University of Colorado. This digital library content was developed by the Integrated Teaching and Learning Program under National Science Foundation GK-12 grant no. 0338326. However, these contents do not necessarily represent the policies of the National Science Foundation, and you should not assume endorsement by the federal government.Supporting Program (Return to Contents)
Integrated Teaching and Learning Program, College of Engineering, University of Colorado at BoulderLast Modified: December 31, 2008