Designing a Shampoo Concentration Experiment for 7th Grade Science

A controlled experiment testing shampoo's effect on bean growth needs a clear gradient of concentrations, replication, and measurable outcomes. Here's a robust design:

Experimental Setup

• 6 treatment groups: 0 tsp (control), 1, 3, 5, 7, 9 tsp shampoo per quart water
• 5 pots per group (30 pots total) for statistical validity
• 4 bean seeds per pot, planted ¼ inch deep in identical potting mix
• Randomized placement under identical light/temperature conditions

Measurements

Track weekly for 4–6 weeks:

• Germination rate (%)
• Plant height (cm)
• Leaf number and area
• Visual health rating (1–5 scale)

Resources

Review the NCEAS student project (link) for methodology inspiration. Contact them via their "contact" link for specific mixture details.

Most shampoos contain surfactants that disrupt membrane integrity at high concentrations. Expect a dose-response curve: stimulation at very low doses (hormesis), inhibition at higher doses.