How many ways could you fold the triangle? This is bilateral symmetry

How many ways could you fold the circle? This is radial symmetry

How about this shape? This shape has NO lines of symmetry It is called asymmetrical

Animals have three types of symmetry in body structure. -BILATERAL -RADIAL -ASYMMETRICAL Copyright © 2010 Ryan P. Murphy

Bilateral symmetry = 1 line of symmetry. Same on both sides. Copyright © 2010 Ryan P. Murphy

Bilateral symmetry. Same on both sides. Copyright © 2010 Ryan P. Murphy

With its wings closed, a bright and colorful butterfly perches lightly on a flower, drinking nectar. Its delicate but strong wings are motionless while it drinks. Then, suddenly, those fragile-looking wings begin to move, and they lift the butterfly, seemingly effortlessly, into the air. As you can see, a butterfly’s body has two halves, and each half looks almost like a reflection of the other. This balanced arrangement is called symmetry. A butterfly’s symmetry contributes to its pleasing appearance. more importantly the balanced wings help the butterfly to fly more easily.

The Mathematics of Symmetry As you saw, the line drawn down the middle of the butterfly produces two halves that are the same -- they are mirror images. This dividing line is called symmetry. An object has one line symmetry, or bilateral symmetry, if there is a line that divides it into halves that are mirror images. So do….. and… also…

SYMMETRY Bilateral Symmetry Characteristics: Having mirror image in one plane, (eg. left-right sides.) Advantage: Predatory. Fast - accumulation of nerves leading to development of a brain. Disadvantage: Defends in only one direction.

Animals with Bilateral Symmetry Most of the familiar animals have bilateral symmetry. In general: bilaterally symmetrical animals are larger and more complex than those with radial symmetry. Have a front end that goes first as the animal moves along. Move more quickly and efficiently - bilateral symmetry allows for a streamlined, balanced body. Have sense organs in their front ends..

Other Organisms with Bilateral Symmetry

Let’s contrast the butterfly’s symmetry to that of a sea anemone. A sea anemone is circular if you look at it from the top. Any line drawn through its center will divide the sea anemone into two symmetrical halves. Like the sea anemone, many circular objects exhibit…… radial symmetry.

Radial Symmetry. Copyright © 2010 Ryan P. Murphy

Radial Symmetry. Arranged equally in all directions from a central point. Copyright © 2010 Ryan P. Murphy

Symmetry in Animals The bodies of complex animals all have either radial or bilateral symmetry.

RADIAL SYMMETRY Radial Symmetry: Having round bodies Will have mirror images when cut in any plane. Advantage: Defend in all directions Disadvantage: Slow nerve net. Not centrally controlled. (No brain means slower response!)

Animals with Radial Symmetry Animals with radial symmetry have external body parts that are equally spaced around a central point. (eg.: spokes on a bicycle wheel) Because of this radial symmetry, these animals (such as jellyfish, sea urchins, and sea anemones) do not have distinct front or back ends.

Animals with radial symmetry have several characteristics in common. All of them live in water Most do not move very fast stay in one place move along by currents creep along the bottom Watery environment carries food to them. Learn about their environment primarily through senses of touch and taste which function on the surface of their body.

Asymmetrical. Having no symmetry. Copyright © 2010 Ryan P. Murphy

Symmetry in Animals There are a few animals, such as sponges, that exhibit no symmetry. These asymmetrical animals generally have very simple body plans. Sponges have no hearts, brains, kidneys, or nerve cells.

Wrap - Up

QUESTIONS A soccer ball has what type of symmetry? (radial or bilateral) An airplane has what type of symmetry? (radial of bilateral) How can bilateral symmetry be an advantage to a predator?

Quiz 1-10 Name the type of symmetry Word bank: Bilateral, radial, asymmetrical. “Let’s do it with symbols” One finger “Index Please!” (Bilateral) All five fingers (Radial) Just a fist (asymmetrical) Copyright © 2010 Ryan P. Murphy

Clam OpenClam Shut

Bonus – Name this movie? ?

Bonus –TWILIGHT?