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Creatures of Darkness

Instructional Objectives
Background Information
Activity
Procedures
Evaluation
Extension for Lower Grades


Topic: Bioluminescence

Instructional Objectives:

Students will:

  1. Learn about the function of bioluminescence among some marine animals.
  2. Conduct an experiment to test the function of bioluminescence as camouflage.

Background Information:

Bioluminescence, light given off by living organisms, is common among creatures of the sea. In the deep sea, where little or no sunlight penetrates, a variety of fishes live out their lives dependent upon bioluminescence. Among these fishes, light organs have evolved to serve a number of purposes.

The hatchetfish, for example, is decorated with a dazzling array of photophores-specialized light organs. These are believed to act as camouflage in mid-water depths where some sunlight penetrates and it is necessary for survival to blend an otherwise black silhouette into the background of scattered light.

Activity: Surviving the Darkness of the Depths

Time Needed For Activity: one 45-minute period

Target Grade Level: High School

Materials:

  • shoe box
  • black spray paint
  • flexible desk lamp
  • large pin
  • black construction paper
  • scissors

Procedures:

  1. Spray paint the inside of a shoe box black.
  2. Use a large-gauge pin to poke plenty of holes in one end of the box. Cut round peephole in the opposite end.
  3. Fold a sheet of black construction paper in half and cut out two dentical fish-shaped silhouettes a few inches in length.
  4. Using the same pin, poke lots of holes in one of the silhouettes.
  5. Suspend the fish silhouette without holes inside of the box so that it hangs perpendicular to the line of sight through the peephole. Use a strip of black paper to suspend it, taped to the inside surface of the box. Close the lid, hold the punctured end of the box up to the light, and peep through the hole at the other end. Record observations.
  6. Next, suspend the fish silhouette with holes inside of the box in the same way and repeat the observations. Record results.

Evaluation:

When viewed against a background of scattered light, such as that reproduced in the shoe box, a fish without photophores is likely to appear as a solid black silhouette, interrupting the background of light. Such a fish is likely to be noticed by predators in the darkness and quickly gobbled up.

Photophores, on the other hand, can act to blend the fish into the background just as the holes in your silhouette will allow light to pass through them as light passes through the box. It is this principle that helps some deep-sea fish use bioluminescence as camouflage.


Extension for Lower Grades:

Think of other kinds of animals that use camouflage to help them survive. Look through magazines for photographs of examples. Cut out pictures of predators, prey and their habitats. Don't limit yourself to the marine environment. Consider other examples such as: lions, zebras and grasslands; tigers, deer and tropical woodlands; sharks, sardines and the open ocean. How does a habitat help determine a camouflage? How does the predator take advantage of its camouflage? How does the prey survive using its camouflage? When is it better to be seen than unseen? Can you find examples? Hint: many highly venomous animals, both marine and terrestrial, have highly colorful markings. Why?


Sea Dwellers
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