For a seed to successfully grow it must have water, sunlight and soil, just like its parent plant – whether it is a daisy or a redwood. However, it is not always ideal for a seed just to drop to the ground under the parent plant. If it sprouts and grows right next to the parent plant it will be competing for water, nutrients and light (unless it is an annual that will not come back the next season). Ideally the plant wants to spread its seeds as far and wide as possible. This will allow more offspring to spread throughout the habitat and not compete with its own resources.
Plants have developed many ingenious ways to successfully disperse their seeds. We will look at some of the structures they have developed to accomplish those goals and how they work.
Objectives:
Students will observe, study and hypothesize about the adaptations of seed structures to aid in their dispersal.
Materials:
- Hand lens for each team (pair of students)
- Paper plates for each seed
- Seed samples displayed at different stations (acorns, maple seeds, burrs, nuts in shells, coconut, milkweed pod and seed, berries, grass seeds off wild grass – the more the better)
- Fuzzy sock or material at each station
- A bowl or cup of water at each station
- Paper on clipboards and pencils
Optional: provide a puffball mushroom that is ready to puff out spores for students to see.
Procedures:
- Inspect each seed with the hand lens.
- Draw a picture of what you see.
- Describe its shape and structures.
- Explain how these might help it move away from the parent plant.
- Does it have structures that will help it move by wind, water, attach to animals, be consumed by animals or be planted by animals? Explain.
Experimenting with Dispersal:
- Try touching seed to the sock. Does it stick?
- Hold the seed at arms length over the plate and drop it. Does it drop straight down onto the plate, or move away.
- Hold the seed in the palm of your hand and blow lightly on it. Does it float away?
- Drop the seed in the bowl of water. Does it float? Blow on the water. Does the seed move away in the water?
- Is the seed edible to an animal? If the animal eats it, how will this affect where it is dispersed?
- If the animal “hides” it (buries it in the ground), how will this affect where it is dispersed?
Discussion:
Be prepared to discuss each seed and how it responds to your “dispersal” techniques.
