Growing seeds in a zip-lock bag on the window — the classic bean-in-a-bag experiment — gives children a transparent view of germination that a soil-planted seed never provides. They can watch roots emerge, observe the direction of growth, and see the seed coat split. Comparing two bags — one in light, one in a dark cupboard — introduces the concept of a controlled experiment: one variable changed at a time to see its effect.

Basic Bean Bag Germination

1. Wet a paper towel thoroughly and place inside a zip-lock bag.
2. Press 2–3 large bean or pea seeds against the wet towel near the clear wall of the bag.
3. Seal the bag and tape to a sunny window. Seeds should be visible.
4. Observe daily: the radicle (root) emerges in 3–5 days, always growing downward regardless of seed orientation.

Comparison Experiments

• Light vs. dark: Two identical bags — one on the window, one in a dark cupboard. Same water, different light. Which sprouts first? Are the sprouts the same color?
• Warm vs. cool: Identical bags — one in a warm spot, one in the refrigerator. Which sprouts first?
• Wet vs. damp: One bag very wet, one just slightly damp. Which works better?
• Seed type comparison: Bean, pea, lentil, sunflower — which germinates fastest?

Frequently Asked Questions

Why do roots always grow downward?

Roots grow downward due to gravitropism (also called geotropism) — the response of plant parts to gravity. Roots contain specialized cells called statocytes that contain dense starch granules (statoliths). These granules settle under gravity, signaling the root to grow in the direction gravity pulls them — downward. If you flip a sprouted seed upside down, the root will bend to continue growing downward within hours. Shoots show negative gravitropism — they grow upward, away from gravity.

Related activities: Collect and Sort Seeds | Evaporation Experiment | Homemade Weather Station