Lesson by Esther Zack
Students will become aware of the differing methods of seed disperal of various plants in their local area and the reason for seed disperal mechanisms.
Seed dispersal mechanisms in this lesson will illustrate dispersal by wind, by being carried by animals or people, or by fruits and nuts that are eaten and stored by either animals or people. Wind disperses seed that have hairs or fluff attached (called a "pappus"), as well as those that have papery wings. Seeds that hitchhike on people and animals have burrs, hooks, or awns that stick into clothes or fur. Seeds dispersed by being eaten are fleshy fruits or nuts. Fruit seeds are sometimes passed through the digestive system of animals and deposited in areas where they sprout. Nuts are often buried by animals and forgotten, where they eventually begin to grow.
To collect seeds locally, visit vacant lots (if you have socks on you'll get quite a few) or walk through your neighborhood keeping an eye out for trees or plants that have the type of seeds described below. Of course, all types of seeds are not available at all times of year.
- Collection of local seeds (children can help in bringing some in as well), enough for one per student
Examples: Fluff-type--dandelion, thistle, goldenrod, milkweed Burr-type--foxtail, sticktight, burdock, wild carrot Fruit--peach, plum, apple, pear Nut--walnut, almond, acorn
- Hand lense, if possible (enough for each group of 3-4 students to have 2)
- Chart paper for Seed Chart with regions marked out for: "Airborn Seeds, Hitchhikers, Fruit, Nuts"
Ask students to suggest ways they travel (cars, buses, planes, bicycles, feet), as well as reasons why they travel (shopping, school, vacations, etc.). Ask them if anyone has ever traveled for the purpose of moving to a new home. Say that plants also travel to find new homes.
Give students a brief understanding (if necessary) that plants make seeds to "reproduce" themselves (make new plants). Ask them what would happen if a plant could drop its seeds only beneath itself. (Overcrowding, too much competition for sunlight and soil nutrients, excessive shading by parent plant, resulting in failure of many new seedlings.)
Tell them they are going to investigate several ways in which plants move to new homes--a process called "seed dispersal."
- Divide students into groups of 3-4. Give each group 3-4 different types of seeds (with seed dispersal mechanisms still attached) and the hand lenses. Ask them to observe the seeds closely and determine how the seed could move away from the "parent" plant to seek a new home.
- Students should trade seeds within the group so they can all hypothesize on the dispersal mechanisms of their group of seeds.
- Have each group report to the class about their seeds and how they think they are dispersal.
- Explain the various seed dispersal methods mentioned above in the background material. Analogies with parachutes for airborne seeds and velcro for sticking-type seeds can be made. For fruit, explain that animals and people eat the fleshy parts, often discarding the seeds, or as in the case of animals, the seeds pass through their bodies and get deposited various places. Nut often get buried by animals, a process which simulates planting the seed.
- Students should the glue their seeds on the chart in the correct regions. (See "Materials" Section.) In the case of friuts and nuts, they can either tape them on or lay them out in a display. Note: lemon juice on an apple or pear will deter browning for a while.
- What would make one type of plant have an "airborne" seed, and another have seeds with stickers? (Taller plants can release their seeds in the wind, shorter plants need help in dispersal.)
- Can you think of any other ways seeds disperse? (By just dropping, by shooting out of a pod when mature, as violet seeds do, or by being carried on or in the water)
- Have you observed any signs of seed dispersal in your yard or neighborhood where certain plants sprang up which were not planted by people? (Weeds!)
- How do plants get to remote island? (Transported by birds, on air currents, on water, brought by people)
- Note to students that Velcro was invented by inspiration from seeds with hooks on them.
Social Studies: Research how plants traveled to the Hawaiin Islands. Art: Gather or buy seeds and make a seed collage or a picture using various colors of seeds Science Clear a patch of ground (about 1 sq. yd.) thoroughly of all vegetation. Make sure ground is clear of all seeds or plant parts. Have students observe this area once a week for the entire semester or year. They should record their observations in a "Plot Observation Record Book."