The liver's function is to process and remove waste and toxins. One of the cellular organelles, called peroxisomes, is responsible for detoxifying waste products or foreign toxins within the cell. Peroxisome naturally produces hydrogen peroxide (H₂O₂) during this detoxification process. If this hydrogen peroxide were allowed to build up, it would be harmful to the body. Found abundantly in the liver cells is an enzyme responsible for decomposing the H₂O₂ into harmless reagents, water (H₂O) and oxygen (O₂).

When encountering hydrogen peroxide, liver cells chemically break it into water and oxygen gas (2 H₂O₂ >> 2 H₂O + O₂). Because this reaction releases gas (which we know is oxygen because it is the only gaseous byproduct of the reaction), we can conclude that the liver solution is breaking down the hydrogen peroxide -- and is performing its job! When we add salt (and the same amount of hydrogen peroxide), however, the reaction gives off less gas (produces less oxygen). Therefore, the liver cells are less successful in breaking down the hydrogen peroxide; hence, the liver performs its job less effectively when salt is present.

• Prepare the liver solution.
• Using the eye droppers, place 15 drops of the prepared liver solution into the test tubes. Make enough for each group to have three test tubes with 15 drops of the liver solution in each.
• Prepare the salt solution.
• Divide the prepared salt solution into smaller containers to distribute. Provide each group with one container of salt solution. Label the salt solution so it is not confused with the hydrogen peroxide.
• Divide the hydrogen peroxide into smaller containers to distribute. Provide each group with one container of hydrogen peroxide. Label the hydrogen peroxide so it is not confused with the salt solution.
• Make copies of the Living with Your Liver Worksheet, one per student.

This butcher holds a whole frozen cow liver. click for copyright

1. Review the functions of the liver with students. Explain that hydrogen peroxide (H₂O₂) is a toxin that the liver breaks down to remove it from the body. Hydrogen peroxide can be present in the body as a natural byproduct of cellular detoxification of other materials. Be sure students understand that this reaction produces bubbles as the toxin is altered into other substances.
2. Divide the class into teams of two students each. Distribute materials to each group (test tube with 15 drops of liver solution, salt solution, hydrogen peroxide, eye droppers and worksheets).
3. Have each group decide how many drops of salt solution (between 0 and 30) they will add to each test tube. Remind the students that a wider range provides more interesting results. (Optional: Use tape and markers to identify how many drops will be placed in each test tube.)
4. Tell students to add their specified number of drops of salt solution to each test tube of liver solution. Remind students to record these values on their worksheets.
5. With timers ready, have students add 15 drops of hydrogen peroxide to one of their test tubes. Add the drops relatively quickly. Have students time how long it takes the liver solution to react. Remind students to record their observations about this reaction.
6. Repeat step 4 for the second test tube. Remind students to compare and note the differences between this reaction and the previous.
7. Repeat step 4 for the third test tube. Remind students to compare and note the differences between this reaction and the previous two.
8. Have students finish the activity by completing the worksheet questions. (Optional: Have students graph their data results on the back of their worksheets, comparing number of salt drops versus time of reaction. See post-activity assessment on graphing in the Assessment section.)
9. Conclude by leading students in a discussion drawn from their worksheet answers, as well as post-activity questions and answers provided in the Assessment section.

Prediction: Have students predict the outcome of the activity before the activity is performed.

• What will happen to the liver's ability to function (break down hydrogen peroxide) when salt is added to the liver?

Question/Answer: Ask students questions and have them raise their hands to answer.

• What function does the liver perform? (Answer: The liver is responsible for removing waste materials and toxins, and storing vitamins in the human body.)
• Biomedical engineers have determined that the liver is one of the few organs that can be regenerated. What does this mean? (Answer: Regeneration is the ability to re-grow lost or damaged cells.)
• What might happen if a liver stops functioning? (Answer: If a liver stops functioning properly or encounters too many toxins it can die. In this case, a person needs a liver transplant to help his/her body regulate the wastes and toxins, and acquire essential vitamins.)

Worksheet: Have students complete the Living with Your Liver Worksheet. Review their data table and answers to gauge their understanding of the concepts.

Graphing: Have students graph their results on the back of their worksheets, comparing number of salt drops versus time of reaction. How does the amount of salt affect the rate of reaction? Based on the graph, what would happen to the rate of reaction if you added more salt? Less salt?

Class Discussion: Have students raise their hands to share their answers to the worksheet questions. Talk about how salt affects the liver's ability to break down the toxin hydrogen peroxide. (Point to make: When salt was added to the liver, its ability to function [break down the hydrogen peroxide] was reduced.) Ask students to give advice to someone who has a very high salt content in his/her diet. (Example advice: Because a diet high in salt reduces the liver's ability to break down toxins, it is important to consume moderate amounts of salty foods). Point out that excessive alcohol can cause similar harmful effects to the liver's ability to break down toxins. Ask students to think about how salt might affect a biomedical engineer's development of tissue replacement processes. (Possible examples: Biomedical engineers may want to develop liver tissue that can withstand high salt content.) What types of things might an engineer need to consider when developing replacement liver tissue for a person with high salt content in their environment? (Possible considerations: Material characteristics such as replacement tissue size, material cell size, support structure size, rate of diffusion and degradation [how fast the material breaks down] within the human body.)