Lesson
Purpose of the work:
- to determine how physical and chemical factors influence the activity of the enzyme catalase in plant tissues.
Expected results:
After completing the work, students can:
- develop teamwork skills
- be able to analyze and summarize the information received
- draw logical conclusions
Teacher’s Guide:
- The task is performed in groups of 3-4 people
- Before starting laboratory work, please read the safety rules by following the link:
- To download the worksheet, follow the link:
Theory
Enzymes are biological catalysts of protein nature. They accelerate chemical reactions without being consumed in the process.
Catalase is an enzyme present in almost all living cells. Its main function is to decompose toxic hydrogen peroxide into water and oxygen:
2H2O2→2H2O+O2↑
Enzyme activity depends on environmental conditions: temperature, pH, and the presence of substances that can alter the structure of the protein.
- Heating above the optimum (~40 °C) leads to denaturation of the enzyme and loss of its activity.
- Surfactants (liquid soap) disrupt the structure of the enzyme and decrease its activity.
- Heavy metal salts (such as CuSO₄) bind to the enzyme’s active sites, causing inhibition of the reaction.
Practical part
Step 1. Grate fresh potato on a fine grater and squeeze the juice through gauze into a clean container.
Step 2. Dilute the obtained juice with water in a 1:1 ratio.
Step 3. Prepare 4 test tubes and pour the diluted juice evenly into each.
Step 4.
- Tube №1 — control sample (no treatment).
- Tube №2 — heated sample: place in a water bath for 1–2 minutes, then cool.
- Tube №3 — add 1–2 drops of liquid soap (Fairy).
- Tube №4 — add 1–2 drops of copper(II) sulfate solution (CuSO₄).
Step 5. Add the same amount of 3% hydrogen peroxide (H₂O₂) to each test tube (for example, 1 ml or 5 drops). Mix gently.
Step 6. Observe the reaction for 10 minutes and record:
- intensity of foam formation (strong / weak / none);
- any change in color;
- foam height (mm) after 10 minutes.
Record the results in the worksheet.
Conclusion
In this experiment, students confirmed that the activity of catalase depends on external conditions. Thus, they demonstrated that enzymes are sensitive to environmental changes and can lose their activity when their structure is disrupted.