Applied Science - Science and Math (3A) Post Lab
 OBJECTIVES: Comparing and contrasting objects. Investigating how to compare objects systematically. VOCABULARY: characteristics shape shell spiral MATERIALS: worksheet snail clam Students compare a clam and a snail. Gastropods are spiral
BACKGROUND:

Nature for some reason likes symmetry. Many organisms display a beautiful pattern in their group. Early philosophers would write about why nature is so consistent. For instance, to the left is a picture of fuchsia, which grows in multiples of four. So even a plant, knows its time tables! We call this 4-part symmetry.

Other organisms have bilateral symmetry, which is a mirror image of one side. Bilateral symmetry is characteristic of many animals, including insects, fishes, amphibians,  reptiles, birds, mammals, and many crustaceans.

Some organisms have a 5-part or pentagonal symmetry. Echinoderms including sand dollars, sea urchins, and sea stars have this "star" symmetry.

Other organisms have no symmetry or asymmetrical. Spiral symmetry, like a snail, is asymmetrical. A circle has radial symmetry, which is no matter how you cut it through the center, one side will look like the other.

PROCEDURE:
1. Pass out the student worksheets. Ask the students to look at the shells and then describe the differences orally.  Many will find it difficult.  Record their responses on the board.

2. Instruct students to begin working on the exercise. Give students guidelines to help them compare objects.  First ask students to compare:  color, length, width, lines, and shape.

3. Color is dependant on the real clam or snail you give them.  You may want to use real objects for the entire exercise. Their answers will differ depending on the color of their sample.
4. The shape of these two objects can be divided into two groups: bilateral and spiral.  Bilateral objects can be split in two leaving two objects that mirror each other.  A spiral object cannot be divided into any parts that look like the other side (asymmetrical).

5. Review their charts when finished.  Use the following chart as a guideline. Discuss the similarities and differences.
 CLAM SNAIL length 5.5 cm 7.5 cm width 6.3 cm 4 cm lines across, up and down up and down color depends on sample depends on sample shape bilateral spiral