Yeast Stress Assay for Metabolic Interactions

ISEF Category: Translational Medical Science

Subcategory: Pre-Clinical Studies  ·  Difficulty: Intermediate  ·  Setup: School Lab  ·  Time: 1 to 2 Months

The Hook

A tiny change in fuel can flip a cell from thriving to struggling. Yeast is a simple model, but it reacts to stress in ways that can mirror bigger biological systems. That makes it a smart place to study how sugar, caffeine, and nicotine interact. You can measure the change with a phone and a clear plan.

What Is It?

This project studies how baker's yeast grows when you change the mix of glucose, caffeine, and nicotine. Yeast is a single-celled fungus that uses sugar as fuel. If you think of the cell like a tiny factory, glucose is the power supply, caffeine and nicotine are stressors that can slow the machinery down, and growth becomes the output you can measure.

You do not need to prove anything about people. You are building a model system. That matters because model systems let you test a biological idea in a simpler setting before anyone tries to apply it to more complex cells. In this case, you can ask whether the stress from two compounds together is just the sum of each one alone, or something stronger or weaker.

Why This Is a Good Topic

This is a strong science fair topic because you can change one thing at a time and measure a clear outcome. Yeast grows fast, costs little, and gives you repeatable data without a medical lab. The project also connects to real questions about metabolic stress, drug interactions, and how cells respond to mixed exposures. You can learn how to design controls, build a dose-response curve, and compare single-factor effects to combination effects.

Research Questions

• How does glucose concentration change yeast growth under baseline conditions?
• What is the effect of caffeine on yeast growth at a fixed glucose level?
• What is the effect of nicotine on yeast growth at a fixed glucose level?
• To what extent does the combination of caffeine and nicotine inhibit yeast growth more than either compound alone?
• How does changing glucose level alter the strength of caffeine and nicotine inhibition?
• Which combination of glucose, caffeine, and nicotine produces the largest drop in OD600?
• To what extent do growth curves differ between single-stressor and mixed-stressor treatments?

Basic Materials

• Active dry baker's yeast.
• Glucose or table sugar.
• Caffeine source with known concentration, such as laboratory caffeine powder or a standardized caffeine solution.
• Nicotine source approved for school use, with adult supervision and school safety review.
• Sterile test tubes or culture cups.
• Measuring spoons or graduated cylinders.
• Digital kitchen scale with 0.1 g accuracy.
• Micropipettes or disposable transfer pipettes.
• Distilled water.
• Incubator or warm, controlled storage space.
• Smartphone with a stable camera.
• Homemade phone holder or improvised densitometer setup.
• Printed white background and light box or consistent lamp.
• Labels and permanent marker.
• Gloves, goggles, and lab coat.

Advanced Materials

• Spectrophotometer capable of OD600 readings.
• Autoclave or sterile filtration setup.
• Erlenmeyer flasks with breathable closures.
• Analytical balance.
• pH meter.
• Microcentrifuge tubes and sterile culture tubes.
• Molecular-grade glucose, caffeine, and nicotine standards.
• Incubator shaker.
• Plate reader, if available.
• Image calibration card for smartphone-based color correction.
• R or Python for data analysis.
• GraphPad Prism, if your lab already has access.

Software & Tools

• ImageJ: Measures image brightness or color intensity from your phone setup and helps you compare samples consistently.
• Python: Organizes OD600 data, fits dose-response curves, and tests interaction effects.
• R: Runs statistical tests and makes clear plots for growth comparisons.
• Google Sheets: Tracks sample labels, treatment groups, and replicate measurements.
• NIH Image Analysis resources: Offers free guides for image-based measurement methods and calibration ideas.

Experiment Steps

1. Define the biological question, then decide whether you are testing single compounds first or jumping straight to combinations.
2. Choose a measurement plan, then decide how you will convert phone images into a repeatable growth signal.
3. Map out your treatment matrix, then balance controls, single-stressor groups, and mixed-stressor groups.
4. Plan your calibration strategy, then decide how you will check that your signal changes with cell density instead of lighting drift.
5. Select the statistics before you collect data, then choose how you will test for additivity or interaction between glucose, caffeine, and nicotine.
6. Build a replication plan, then decide how many independent trials you need to trust the pattern you see.

Common Pitfalls

• Using different lighting for each photo, which changes the apparent OD600 signal even when the yeast growth is the same.
• Treating table sugar as a perfect stand-in for glucose without checking whether your concentrations match the intended comparison.
• Skipping single-stressor controls, which makes it impossible to tell whether the mixture effect is real.
• Letting yeast clump or settle before imaging, which makes the densitometer reading vary from sample to sample.
• Choosing nicotine materials without a clear school safety plan, which can create handling and disposal problems.

What Makes This Competitive

A stronger version of this project does more than compare a few growth curves. You can test interaction effects, not just single effects, and use a model that checks whether the compounds act additively, synergistically, or antagonistically. You can also improve the measurement by calibrating your smartphone signal against known density standards. Clear replication, clean controls, and a thoughtful analysis plan make the project feel much more like real pre-clinical research.

Project Variations

• Use caffeine with glucose only, then compare the interaction across low, medium, and high sugar conditions.
• Swap nicotine for another mild stressor, such as salt or ethanol, to see whether yeast responds the same way.
• Measure growth by colony size or turbidity plate images instead of OD600, then compare which readout gives the cleanest signal.

Learn More

• PubMed: Search for review articles on Saccharomyces cerevisiae stress response, caffeine toxicity, nicotine effects, and yeast growth assays.
• NIH PubMed Central: Find free full-text papers on yeast as a model organism and on optical density measurement methods.
• NCBI Bookshelf: Read free biology texts and background chapters on yeast metabolism and cell stress.
• MIT OpenCourseWare: Search for free course materials on molecular biology, genetics, and experimental design.
• NOAA Science Literacy: Use it for plain-language help with variables, controls, and data interpretation, even though the topic is biology.
• ImageJ Documentation: Learn how to measure brightness, calibrate images, and compare samples from smartphone photos.