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Back to Those That Sting: Teachers!
Sea Drifter Sun Catchers
Don't forget to print the patterns
with these instructions!
Lesson at a glance:
Students will be able to recognize the structure and function of a jelly by completing this activity.
Benchmarks and Common Curriculum Goals:
These national standards and benchmarks come from the Content Knowledge Home Page, an effort by the Midcontinent Regional Educational Laboratory (McREL) to consolidate the many national, state and local efforts at defining what a student needs to learn. You can find them on the WWW at http://www.mcrel.org/standards-benchmarks/. Your state or district may have additional standards or benchmarks that may apply.
Life Sciences
Science Standard 4: Knows about the diversity and unity that
characterize life.
Grade k-2 Benchmark: Knows that plants and animals have features that
help them live in different environments.
Science Standard 5: Knows the general structure and function of
cells in organisms.
Grade 3-5 Benchmark: Knows that each plant or animal has different
structures which serve different functions in growth, survival, and reproduction
(e.g., humans have distinct structures of the body for walking, holding, seeing,
and talking).
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Background:
Jellies are plankton. In fact, some species are some of the largest types of plankton on earth. When we think of plankton, we think of microscopic plants and animals, so how does a jelly get to be plankton? Scientists classify plankton as a plant or animal at the mercy of the currents¾something that can’t swim against the currents under its own power. This makes a jelly a kind of zooplankton.
But jellies are so much more. Jellies belong to the phylum Cnidaria. They range in size from an eighth of an inch across to eight feet! All cnidarians share similar characteristics. They are radially symmetrical (they can be cut into equal parts like a pizza or a pie), they have a ring of tentacles that surrounds their mouths, and they have no true organs, only tissues. In fact, jellies are 95 percent water!
Scientists call their body shape a medusa. It resembles the Medusa of Greek mythology. In the legend, Medusa’s face was surrounded by a ring of snakes, similar to the tentacles of a jelly. Instead of biting snakes, however, each tentacle of a jelly is filled with stinging cells called cnidocytes. These specialized cells are used for defense and feeding and contain small stinging structures full of toxins called nematocysts. Some nematocysts carry a sting so strong that they are deadly to most animals, including humans.
Most jellies have four stomachs that receive their food through a central mouth. Prey is stung by the tentacles around and on the bell of the jelly and then transferred to the four oral arms that surround the mouth opening. From there the food travels up into the stomachs, where it is digested. Any undigested food is then passed back through the mouth opening and out into the water.
To move, the jelly contracts a sheet of muscles near the rim of the bell. As it relaxes, the water fills the cavity of the bell; when it contracts, it happens quickly, and the water is forced out, moving the jelly in the opposite direction. Even though it can move up and down in the water column, it is no match for the ocean currents.
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