Mimosa Leaf Rhythm in Light And Dark

ISEF Category: Plant Sciences

Subcategory: Plant Physiology  ·  Difficulty: Intermediate  ·  Setup: Home Setup  ·  Time: 1 to 2 Months

The Hook

Some plants keep time even when the sun disappears. Mimosa pudica, the sensitive plant, can fold and reopen its leaves on a daily rhythm. That makes it a great model for asking whether an internal clock still runs in constant light or constant dark. You can track that rhythm with a smartphone and real data analysis.

What Is It?

Circadian rhythms are internal 24-hour cycles that help living things keep track of day and night. In plants, these rhythms can control leaf movement, opening and closing of flowers, and the timing of growth. Think of it like a quiet alarm clock inside the plant. If the clock keeps running without outside light cues, the movement should still repeat with a near-daily pattern.

Mimosa pudica is a good plant for this because its leaves react in a visible way. The leaflets fold and reopen, so you can measure movement without special sensors. Instead of guessing by eye, you can record time-lapse video and turn the motion into numbers. Fourier analysis helps you find repeating cycles in the data, like spotting a beat in a song.

Why This Is a Good Topic

This topic works well for a science fair because you can see the phenomenon, measure it, and test a clear question. You do not need a professional lab to collect the data, but you do need careful recording and analysis. The project connects to plant biology, sleep-like timing systems, and how living things respond when environmental cues disappear. You can learn experimental design, video analysis, and pattern detection from one project.

Research Questions

• How does constant light affect the period of leaf movement in Mimosa pudica compared with a normal day-night cycle?
• How does constant dark affect the amplitude of Mimosa pudica leaf movement compared with a normal day-night cycle?
• What is the effect of light condition on the phase shift of Mimosa pudica leaf movement over 24 hours?
• Does the strength of the circadian signal in Mimosa pudica differ between constant light and constant dark?
• To what extent do individual Mimosa pudica plants vary in the persistence of rhythmic leaf movement under constant conditions?
• Which time series feature, peak height, period, or regularity, best separates constant light from constant dark in Mimosa pudica?

Basic Materials

• Mimosa pudica plant or multiple small plants.
• Smartphone with time-lapse or interval video mode.
• Stable phone stand or tripod.
• Consistent light source for the control setup.
• Opaque box or dark cover for constant dark treatment.
• Timer or clock with visible timestamps.
• Notebook or spreadsheet for observations.
• Ruler or printed scale for video framing.
• Household thermometer to track room conditions.

Advanced Materials

• Mimosa pudica plants grown under matched conditions.
• Light meter or PAR sensor.
• Programmable growth chamber or isolated light box.
• Infrared-safe camera setup for dark-condition recording.
• Digital calipers or image-based measurement calibration target.
• Data logger for temperature and humidity.
• Lab-grade LED light source with adjustable intensity.
• Computer with analysis software for time-series processing.

Software & Tools

• ImageJ: Measures leaf position or angle frame by frame from time-lapse images.
• Python: Cleans the time series and runs Fourier analysis on movement data.
• Google Sheets: Organizes observations and calculates summary statistics.
• R: Tests differences between treatment groups and helps make plots.
• FFmpeg: Converts video clips into a format that is easier to analyze frame by frame.

Experiment Steps

1. Define the movement signal you will measure, such as leaf angle, leaflet opening, or a visible position score.
2. Choose the comparison that matters most, constant light, constant dark, and a normal light-dark control.
3. Plan how you will keep temperature, watering, and camera position steady so light is the main change.
4. Build a scoring system or tracking method that turns each frame into a numeric time series.
5. Set up your analysis plan before filming, including how you will find period, amplitude, and phase.
6. Decide how you will compare plants and how many repeated trials you need for a fair test.

Common Pitfalls

• Changing camera angle between days, which makes leaf movement look larger or smaller than it really is.
• Letting room light leak into the constant dark setup, which breaks the treatment without you noticing.
• Using plants that differ too much in size or health, which adds noise that can hide the rhythm.
• Measuring only one leaf pair, which can make a single damaged leaf stand in for the whole plant.
• Skipping the control condition, which makes it hard to tell whether the rhythm comes from the plant or from the environment.

What Makes This Competitive

A stronger project will not just say whether the rhythm exists. It will quantify how strong the rhythm stays, how the period changes, and how different lighting regimes shift the signal. You can raise the level by using multiple plants, preplanned statistics, and a clean comparison between constant light, constant dark, and a normal control. A careful signal-processing approach makes the work look much more like real plant physiology research.

Project Variations

• Test whether different light intensities change how long the rhythm stays detectable in Mimosa pudica.
• Compare leaf movement rhythms in young plants versus mature plants under the same constant condition.
• Use image tracking to compare leaflet angle with whole-leaf position as two different movement signals.

Learn More

• PubMed: Search review articles on plant circadian rhythms and Mimosa pudica movement to find peer-reviewed background reading.
• NIH Bookshelf: Look for free textbook chapters on biological clocks and circadian regulation in plants.
• NASA: Search for educational material on circadian biology and how organisms respond to light cycles.
• MIT OpenCourseWare: Use free course materials on data analysis or signal processing if you want help with Fourier methods.
• USDA National Agricultural Library: Search for plant physiology and photoperiodism resources and literature summaries.