Tetrahymena Phagocytosis Under Stress

ISEF Category: Cellular and Molecular Biology

Subcategory: Cellular Immunology  ·  Difficulty: Intermediate  ·  Setup: School Lab  ·  Time: 1 to 2 Months

The Hook

Your immune cells are not the only cells that eat things. Tetrahymena, a tiny single-celled organism, can swallow particles too. That makes it a handy stand-in for studying phagocytosis, the process cells use to engulf and digest material. You can turn that into a real experiment with cheap imaging and clear numbers.

What Is It?

Phagocytosis means a cell surrounds a particle, pulls it inside, and breaks it down. You can think of it like a cell-sized garbage truck. In this project, you watch Tetrahymena take up India ink or fluorescent beads, then count how many particles end up inside the cells.

That gives you a simple readout of cell behavior. If the cells are under stress, exposed to caffeine, or treated with a yeast cell-wall signal such as β-glucan, their uptake may change. You are not testing human immunity directly. You are using a model organism that is easier and safer to grow, but still gives you a live-cell system with measurable responses.

Why This Is a Good Topic

This is a strong science fair topic because you can change one factor at a time and measure a real biological response. You do not need a hospital lab or expensive equipment to see whether uptake changes. The project connects to cell signaling, immune-like behavior, and environmental stress, so it has real-world relevance. You can also build useful skills in microscopy, image analysis, controls, and data comparison.

Research Questions

• How does caffeine concentration affect the phagocytic uptake rate of Tetrahymena?
• What is the effect of β-glucan exposure on the number of particles internalized per cell?
• Does osmotic stress change the fraction of Tetrahymena cells that perform phagocytosis?
• To what extent does temperature stress alter the speed of India ink uptake in Tetrahymena?
• Which treatment, caffeine, β-glucan, or environmental stress, produces the largest change in phagocytosis index?
• How does particle type, India ink versus fluorescent beads, affect the measured uptake rate under the same conditions?

Basic Materials

• Tetrahymena culture from a biology supplier or classroom stock
• Compound microscope with camera or smartphone adapter
• Smartphone with manual camera controls
• India ink or carbon suspension
• Fluorescent microspheres or dye-labeled beads
• Well plates or small clear culture containers
• Transfer pipettes
• Graduated cylinders or disposable pipettes
• Distilled water
• Yeast-derived β-glucan source or a teacher-approved substitute
• Caffeine source with known concentration from a school lab or approved stock solution
• Timer
• Disposable gloves
• Lab notebook
• ImageJ or similar free image analysis software

Advanced Materials

• Fluorescence microscope with camera attachment
• Hemocytometer or cell counter
• Fluorescent microspheres in multiple sizes
• Purified β-glucan standards
• Controlled incubator or temperature stage
• Microcentrifuge tubes
• Plate shaker or gentle mixer
• Spectrophotometer or plate reader for validation
• Live-cell staining dyes approved by your lab supervisor
• ImageJ with particle analysis tools
• R or Python for statistical analysis and plotting

Software & Tools

• ImageJ: Measures particle uptake and cell counts from microscope images.
• Google Sheets: Organizes replicate data, calculates averages, and makes quick charts.
• R: Runs statistical tests and compares treatment groups.
• Python: Helps automate image counting or plot uptake patterns across conditions.
• Snapseed: Adjusts image brightness only if you need a consistent viewing workflow, not to change the data.

Experiment Steps

1. Define one clear response variable, such as particles per cell or percent of cells with visible uptake.
2. Choose one main treatment axis first, then build separate groups for caffeine, β-glucan, and stress.
3. Set up a control group that matches every condition except the factor you are testing.
4. Plan how you will standardize imaging, cell density, and particle visibility before you collect data.
5. Build a scoring method that turns microscope images into counts you can compare across replicates.
6. Decide in advance which statistical test and graph type will answer your research question cleanly.

Common Pitfalls

• Using uneven lighting during smartphone microscopy, which makes bead counts hard to compare between images.
• Letting Tetrahymena density drift between groups, which changes uptake just because more cells are crowded together.
• Treating India ink or beads as if every particle is identical, which can hide size or clumping effects.
• Confusing particles stuck outside the cell with particles fully inside the cell, which inflates your phagocytosis score.
• Changing more than one stress condition at once, which makes it impossible to tell which factor caused the response.

What Makes This Competitive

A stronger project goes beyond a simple before-and-after comparison. You could compare two particle types, test more than one stressor, or use image analysis to score uptake in a way that other students can repeat. Strong controls matter a lot here, especially for cell density, lighting, and particle size. A careful statistical analysis with enough replicates can turn a neat demo into a project with real biological insight.

Project Variations

• Test whether different particle sizes change the uptake pattern in Tetrahymena under the same stress condition.
• Compare India ink with fluorescent beads to see which gives cleaner smartphone-based counts.
• Swap caffeine for another environmental stress, such as salt or pH change, and compare the phagocytosis response.

Learn More

• NIH PubMed: Search review articles on phagocytosis, protozoa as model systems, and cell uptake assays.
• NCBI Bookshelf: Look for free textbook chapters on cell biology and membrane trafficking.
• University OpenCourseWare: Search for cell biology or microscopy course notes that explain image-based measurement.
• ImageJ documentation: Find free tutorials on particle analysis, thresholding, and cell counting.
• NOAA Education Resources: Search for background on environmental stress and how organisms respond to changing conditions.