BACKGROUND:

Seeds insure that plants will continue to live on this Earth. It may take years before a seed will germinate, but this is a survival strategy. Plants have developed different methods to make sure their seeds find a suitable location to grow. Since plants themselves are not mobile they must have a mechanism to disperse, otherwise, all plants would grow in one area.

There are four basic methods of seed dispersal including by wind, by attachment to fur or feathers, by passing through an animal's gut, or by animals moving the seeds. Wind dispersal allows seeds to travel with the wind. Sometimes the distance that seeds travel can be long. For instance, if a seed gets into the upper atmosphere it can travel along the jet stream and travel hundreds, if not thousands of kilometers. Attachment to the fur of mammals or the feathers of birds helps seeds to "walk" or "fly" to a new location. The seeds may drop and fall into a suitable location to grow. When an animal eats a seed, sometimes its stomach cannot digest the outer portion of the seed and the seed is passed through the animal’s digestive system intact. Some animals move seeds purposely for storage and later consumption. Animals can drop seeds by mistake resulting in germination at that spot.

PROCEDURE:

1. Seeds require water for growth. Discuss with students this need for water and if you’d like, you can fill a jar with seeds add water and seal this tightly. At some point, if the glass is not too thick, it will break due to the pressure of the expanding seeds. Another way to make the same point is to measure the level of dry seeds in a jar, and measure how high they reach after soaking overnight. In any case, the seeds to be examined need to be soaked overnight. Have the children compare the size of a dry seed and of a wet seed and ask the students to figure out how the water got into the seeds. The PRE LAB worksheet illustrates the micropyle which is where water penetrates the seed coat.

2. Soak the beans and corn (if dried) prior to the lab. Give students a toothpick and have them dissect the seed. Let each child take a pinto bean apart and identify the three parts of the seed (seed coat, root, food storage). The corn seed will be trickier. The important thing for them to notice is that the corn seed appearance is different. With help, they should be able to find the root, the food storage and the seed coat, but they may have trouble finding the leaf in the root portion.

3. Discuss the fact that ferns produce spores instead of seeds. Have the students examine the back of the fern with their magnifying glasses.

4. Discuss the four methods of seed dispersal including by wind dispersal, by attachment to fur or feathers, by passing through an animal's gut, or by animals moving the seeds. Give the children at least one seed using each method of dispersal and see if they can guess which one uses which method.

corn seed
dandelion or other fuzzy seed (wind dispersal)
spores (wind dispersal)
maple, sycamore, conifer (food for animals, wind, gut)
elm seeds (wind dispersal)
burrs or other seeds that can attach to fur or feathers (or socks)
berry, cherry, apple and/or orange seeds (pass through animals, or stick to beak of birds, like berries)
acorns, other nuts (squirrels hide them and forget)
dried pea pods and other propulsive seeds (the two sides of the pod dry unevenly, so that the pea flips out)