Objective:

• The student will be able to identify what luminescence is and some possible reasons for its biological purpose or function.

• The student will be able to define the terms photophore, luminescent, and counterillumination.

Materials:

• flashlight (for each individual or one to share in a small group)
• masking tape graphic organizer for taking notes (optional) (included)
• drawing paper or picture of squid (optional)
• glow in the dark crayons (optional)

Procedure:

1. To pique the students' interest, ask questions such as the following:
   • How many of you have ever played flashlight tag?
   • When during the day do you play this game?
   • Could you play this game at noon? Why not?
   • What is the object of the game?
   • Could you play it without the flashlight at night? Why not?

2. Lead students to the realization that the flashlight has a purpose in this game, and the only time they can really effectively use the flashlight is in the dark.

3. Ask if students can think of other ways we use lights, besides playing games in the dark. Some possible responses might be for illumination, so we can see; to decorate, as during holidays or at a carnival to decorate a Ferris wheel; for warnings, such as a traffic light; for signaling, as at an airport to signal to planes.

4. Ask students if they know of any land animals, including insects, that have lights on their bodies. Students will probably mention fireflies. Ask the students if they know where the light comes from. (The light is produced by the breakdown of a protein called luciferin in the firefly's body. This is done by the action of a enzyme called luciferase.) Tell the students that there are many sea animals which have lights on their bodies, also generated by luciferin. A creature or an object that produces light is said to be luminescent.

5. Ask students if they can figure out where luminescent sea creatures live and why. Refer to the discussion that was previously held about ways that people use lights, and ask the students if they can think of reasons why deep sea creatures would have lights. Tell the students that even today we do not know all the ways that these animals use their lights.

6. Tell the students that they are going to pretend that each of them is a luminescent squid. Luminescent squid have light producing organs called photophores. Ask the students if they can figure out what the prefix "photo" means. Give examples of words to help them figure out the meaning such as photography, photogenic, photosynthesis, photographer. Be sure students understand the prefix "photo" before continuing.

7. Pass out the flashlights. Tell the students that these are their photophores. Have the students label the flashlight with the word "photophore," using the masking tape for the label. (Option: If there are not enough flashlights for all students or for small groups, choose a few students to be the demonstrators in front of the class with the available flashlights.)

8. Tell the students that you are going to give them three situations (see below) where they must decide whether or not to use their photophores (flashlights) . They must be able to give reasons why they did or did not turn on their photophores. Remind students that they are luminescent squid and that they need to think like a squid. They live in the deep dark sea.

   Turn off the lights and draw the blinds. If not demonstrating in front of the class, students are to remain in their seats. Present the following situations:

   • You want to capture a fish.
   • You want to make yourself attractive so that you can attract a mate.
   • You want to escape from an enemy.

   After each example, ask students why they turned their "photophores" on or off. Some possible students' responses might be that they turned their photophores off to trick the fish so that it could not see them, or they turned them on to lure the fish. To attract a mate, they would probably turn on their photophores so that they would be visible. To escape from an enemy, they might turn their photophores off to flee in the dark, or they might turn them on to scare their enemy. There are no correct answers. It is important to explore the reasons why light would be used. Tell the students that squids sometimes pulse their lights, rather than just let them glow.

   Tell the students that you are going to show them another very important reason why a squid might have photophores. Open the classroom door and place a student in front of the door. The classroom should still be dark, but the hallway is lit. Say to the students, "See how easy it is to see this 'squid'? Squid are easy to see from below because they cast a silhouette. What do you think would happen if the squid could light up underneath to match the light overhead?"

   Lead the students to realize that by matching the light overhead, the squid would be difficult to see and thus protected from its enemies. Illuminating the underside of an animal so that it makes its silhouette disappear is called counterillumination.

9. Put away the flashlights and turn on the classroom light. Have students pair with another student and review the following: photophore, what "photo" means, luminescent, reasons for luminescence, counterillumination and the purpose it serves.

Extension:

Give further notes about luminescence and counterillumination in squid. (See the Background Content for Teachers.) Students may use the accompanying graphic organizer or any other method of the teacher's choice.

Give students pictures of squid or have them draw their own. Have them use glow in the dark crayons to draw photophores on the squid.