**BACKGROUND:
**
**Symmetry** refers to, "the correspondence
in size, form, and arrangement of parts on opposite sides of a plane, line,
or point." If you look at the word in the dictionary, you will notice a
list of definitions for subjects as diverse as geometry, botany, physiology,
chemistry, and geology. Symmetry can refer to two dimensional as
well as three dimensional objects. Some objects can have one or more
symmetries. In nature symmetry is not always perfect, but the terms
are still applicable.

**
Bilateral symmetry** is when one side looks
like the other or is a mirror imagine. Humans are bilaterally symmetrical
. If you make an imaginary line from the head to the ground; one
side basically looks like the other. However if you look at the organs
inside a human, they are not bilaterally arranged.

**Radial symmetry** is when all segments are equal
that radiate from a point. A ball or a circle has radial symmetry.
Note that all objects that have radial symmetry also have bilateral symmetry.

**Pentagonal symmetry** reflects a five-part symmetry.
The echinoderms (sea stars, sand dollars) are an excellent example of pentagonal
symmetry. This is easily recognized as a “star” shape. Internally,
echinoderms also have a five part symmetry.

There are other ways of dissecting symmetry
including ** hexagonal symmetry** (six-part) and ** cubic symmetry ** (three-dimensional
square). Symmetry is all around us if we just look and describe.

**PROCEDURE:
**

- The objectives of this week's
activities are to illustrate the difference between symmetry in nature. The first exposure to these concepts will give
students a new vocabulary power to describe and observe the world.
Go over each of the above vocabulary words and illustrate with examples.
Reinforce the types of symmetry so children can learn by experience.
Listed below are a few ideas.

- Use a construction type set that can help illustrate
the different types of symmetry. Include bilateral, radial, pentagonal,
hexagonal, and cubic. Construct these examples before class so you
can show students.
Draw the different types of symmetry on the board and have students think
of examples. Reinforce the words using a model and do not expect students
to learn with just one introduction.

- Students will continually use these
terms throughout this program. This is only an introduction to symmetry.
Start them off right!

The worksheet will help illustrate different
types of symmetry using models. Look at your worksheet and have students
color in the different types of symmetries. If you have any of the
construction type kits or paper models you may want students to make one
of the different shapes.

1. bilateral symmetry = one side looks like
other

2. radial symmetry = radiate from a point

3. pentagonal symmetry = 5 part symmetry

4. hexagonal symmetry = 6 part symmetry

5. cubic symmetry = 4 part symmetry