Catalase Kinetics With Microplastics

ISEF Category: Biochemistry

Subcategory: General Biochemistry  ·  Difficulty: Intermediate  ·  Setup: School Lab  ·  Time: 1 to 2 Months

The Hook

A few plastic bits can change how fast an enzyme works. Catalase breaks down hydrogen peroxide, and you can track that reaction with simple foam or oxygen data. If microplastics change the rate, you have a real test of how pollution can reach basic cell chemistry. You can compare potato, liver, and yeast to see whether every source behaves the same.

What Is It?

Catalase is an enzyme, which means it is a protein that speeds up a chemical reaction. Its job is to break down hydrogen peroxide into water and oxygen. You can think of it like a cleanup crew that helps cells get rid of a harmful chemical before it builds up.

Microplastics are tiny plastic particles that can enter water, soil, and food. In this project, you test whether those particles change how catalase works. You would measure enzyme activity, then fit the data to Michaelis-Menten models, which describe how reaction speed changes as you add more substrate. You can also test inhibition models, which help you see whether the plastic acts like a blocker or changes enzyme behavior in some other way.

Why This Is a Good Topic

This is a strong science fair topic because you can measure a real biological process, change one factor at a time, and turn your results into clear graphs and model fits. It connects to pollution, food, and cell stress, so the topic feels current and useful. You can learn enzyme kinetics, controls, and basic statistical analysis without needing a university lab.

Research Questions

• How does microplastic concentration affect the apparent Vmax of catalase from potato, liver, and yeast?
• What is the effect of microplastic particle size on catalase reaction rate?
• Does microplastic type change the Km value of catalase under the same assay conditions?
• To what extent does pre-exposure to microplastics alter catalase activity compared with direct mixing during the assay?
• Which catalase source shows the strongest inhibition pattern in the presence of microplastics?
• How does microplastic concentration affect the shape of the Michaelis-Menten curve for catalase?
• What is the effect of microplastic exposure on the oxygen production rate of catalase samples?

Basic Materials

• Fresh potato, liver, and dry yeast samples.
• Hydrogen peroxide solution from a school lab or pharmacy grade source.
• Microplastic beads or controlled plastic particles of known type.
• Test tubes or small clear reaction cups.
• Graduated cylinders.
• Digital kitchen scale with 0.1 g accuracy.
• Pipettes or disposable droppers.
• Stopwatch.
• Thermometer.
• Measuring spoon or small balance for sample prep.
• Stirring rods or clean wooden sticks.
• Phone camera for recording foam height or bubble output.
• Safety goggles.
• Disposable gloves.
• Paper towels.

Advanced Materials

• Microbalance or analytical balance.
• Spectrophotometer with cuvettes.
• Gas syringe or oxygen sensor.
• Temperature-controlled water bath.
• Magnetic stir plate.
• pH meter.
• Centrifuge for sample clarification.
• Standard microplastics with documented polymer type and size.
• Laboratory homogenizer.
• Statistical software and graphing tools.
• Image analysis setup for foam or bubble quantification.
• Fume hood or designated wet lab bench.

Software & Tools

• Google Sheets: Organizes trial data, calculates rates, and makes basic graphs.
• Python: Fits Michaelis-Menten and inhibition models with custom analysis code.
• ImageJ: Measures foam height, bubble area, or other image-based signals from photos.
• R: Runs curve fitting, statistical tests, and confidence interval analysis.
• JASP: Lets you compare groups with a free, point-and-click statistics interface.

Experiment Steps

1. Define which catalase source you will test first, and keep the tissue prep method the same across all samples.
2. Choose one way to measure enzyme activity, then make sure it gives a repeatable rate signal instead of just a yes-or-no result.
3. Set up a control series with no microplastics so you can see the normal kinetic curve before adding any exposure condition.
4. Plan a concentration series for the microplastics, and decide whether you will test direct mixing, pre-exposure, or both.
5. Build an analysis plan that converts your raw signal into reaction rates, then fit the results to Michaelis-Menten and inhibition models.
6. Choose the statistics you will use to compare catalase sources and exposure levels, and decide how you will show uncertainty in each graph.

Common Pitfalls

• Using uneven potato, liver, or yeast prep, which makes enzyme concentration drift between trials.
• Letting microplastic particles clump together, which changes the real exposure level in each tube.
• Reading foam height by eye under different lighting, which makes the signal hard to compare across runs.
• Skipping a no-plastic control, which makes it impossible to tell whether the plastic changed the enzyme at all.
• Fitting Michaelis-Menten curves to too few substrate points, which gives unstable Km and Vmax values.

What Makes This Competitive

A competitive version of this project does more than compare rates. You would separate surface effects, dose effects, and enzyme-source differences with clean controls. Strong analysis matters too, especially if you compare multiple model fits and report confidence intervals instead of just one best-fit line. The best entries ask whether microplastics act like a true inhibitor, a physical blocker, or a sample-mixing problem.

Project Variations

• Test only one catalase source, then compare several microplastic polymers such as polyethylene and polystyrene.
• Swap foam height for oxygen sensor data, which gives you a cleaner kinetic signal.
• Compare pre-exposure of the enzyme source with direct exposure during the reaction, which can separate long-term and short-term effects.

Learn More

• NCBI Bookshelf: Search for free textbook chapters on enzymes, catalysis, and Michaelis-Menten kinetics.
• PubMed: Look for review articles on microplastics and enzyme inhibition in biological systems.
• NIH NCBI Primer: Use the database for background on protein function and kinetic analysis terms.
• NOAA Marine Debris Program: Read background on microplastics and environmental exposure pathways.
• MIT OpenCourseWare: Find free biochemistry and kinetics lecture material for model building and graph interpretation.