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:
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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 o f 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.
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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.
-
Discuss the fact
that ferns produce spores instead of seeds. Have the students examine
the back of the fern with their magnifying glasses.
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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)
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