I'm looking for suggestions for instant-gratification experiments/demonstrations for elementary to high school kids. There are loads of awesome experiments kids can do that take a few days, but what about ideas that can be completed in one lesson?

Here are some ideas I've already come across:

  • Shine a bright light pattern on a leaf, observe the after-image (eg here or here)
  • Extract DNA from a strawberry
  • Re-water a wilted plant

Other ideas take a bit of preparation, but still are pretty cool to finish up in a classroom, like:

  • UV mutagenesis of algae cells, then get the kids to search the colonies for color/morphology mutants
  • Present data (growth +/- external carbon, fluorescence, pigments, etc) for "unknown" mutants (eg a PSI mutant, PSII mutant, chlorophyll mutant), and get the kids to puzzle out which one is which

What's your favorite go-to experiment for inspiring young plant biologists?