Lesson Objectives Students will be able to:

1. Lesson ObjectivesStudents will be able to: • Explain why chemical toxins are used by animals; • Name two ways that animals acquire toxins; • Explain why adult and larvae fireflies use bioluminescence; • Define chemiluminescence and bioluminescence; • Identify the three components necessary for an animal to produce bioluminescence; • Explain how light is produced from an atom; • Identify the difference between ground state and excited state; • Explain how emission spectra is produced.

2. Chemical Defenses Chemical toxins are used by animals to make themselves inedible and warn predators through: ■ Bad Taste ■ Sickness and/or death The predator will learn to avoid the bad tasting prey, the prey that makes it ill, or in a worse case scenario, the predator will die from ingestion of the toxin.

3. Where do these toxins come from? • Animals can make or synthesize toxins or irritating chemicals through a series of reactions that occur within its body; • They can acquire and accumulate toxins by eating food that already contains the poison.

4. Animals manufacture toxins • The sea slug produces a mixture of hydrogen peroxide, ammonia and acids. When it is threatened by predators, it defends itself by secreting these chemicals into the water. http://www.sciencedaily.com/releases/2005/12/051217005143.htm Aplysia (Aplysiacalifornica) sea slug

5. Animals borrow toxins • Most poisonous snakes make their own toxin to deter predators, but this Asian snake, Rhabdophistigrinus, eats poisonous toads and borrows it toxin. The snake stores the toxin in its neck glands. When it is threatened, it releases the poison. A Rhabdophistigrinus snake http://www.sciencedaily.com/releases/2007/01/070130184641.htm

6. Some animals manufacture and borrow toxins: Fireflies • Some species of fireflies chemically manufacture their own toxins. http://www.news.cornell.edu/chronicle/99/8.19.99/lizards.html

7. http://www.flickr.com/photos/charlestilford/2953526518/ Photuris: The femme fatale species of firefly Some species of fireflies borrow toxins by eating the firefly that produces the chemicals.

8. Why would fireflies need a chemical defense? • The flickering light of the firefly advertises its position to potential predators, and, without a chemical defense, it would become an easy, tasty meal. http://static.howstuffworks.com/gif/willow/firefly-info0.gif

9. What is in the firefly toxin? • Defensive chemicals called lucibufagins are released in firefly blood. • Lucibufagins deter predatory spiders, insects and even predatory bats. • The chemical also protects firefly eggs. http://www.news.cornell.edu/releases/Aug97/luredandliquidated.hrs.html

10. Why do fireflies light up? • Fireflies glow in a process called bioluminescence, a living organism produces and emits lights through chemical reactions. • Adult fireflies flash to attract their mates through the process of bioluminescence.

11. The larvae of firefly glow and act as a warning sign to predators that they will make an unpleasant meal. http://www.bio.davidson.edu/people/midorcas/animalphysiology/websites/2006/cahermes/larvae.htm

12. Bioluminescence: What is it?Chemiluminescence in a living organism=bioluminescence Chemiluminescence: light produced from a chemical reaction Bioluminescence: light produced from a chemical reaction in a living organism http://coris.noaa.gov/glossary/chemilumin_186.jpg http://www.flmnh.ufl.edu/fish/education/adapt/biolum.JPG

13. How does chemiluminesence work? • A chemiluminescentreaction occurs when an electron in a molecule absorbs enough energy from an external source to promote the electron into a higher energy orbital. This is called its excited state. • The excited state is not stable. When the electron returns to its original lower energy orbital, called the ground state, energy is releasedfrom the molecule as a photon of light.

14. How does bioluminescence work? • Bioluminescent organisms convert chemical energy to light energy. • Bioluminescence requires 3 components: • Luciferin: a light emitting organic molecule • A source of oxygen • Luciferase: a protein catalyst Bioluminescence works on the same principle as chemiluminesence: electrons gain energy and jump to a higher orbital, as they fall back down they emit the energy in form of light.

15. The chemistry of the flash: How does the bioluminescent reaction work in fireflies? “Luciferin reacts with adenosine triphosphase (ATP) - a chemical all cells use for energy-including ours. The reaction occurs in the presence Mg2+ ions and an enzyme known as luciferase. Luciferase acts as a catalyst. The reacting species bind to the enzyme, where the reaction takes place. This produces a species known as adenylluciferin (also called luciferyl adenylate) and pyrophosphate. Adenylluciferin combines with oxygen to release form oxyluciferin and adenosine monophosphate (AMP). “ http://www.elmhurst.edu/~ksagarin/color/discussion8.html

16. The light emitting chemical (luciferin) in fireflies and the excited state molecule, oxyluciferin, are shown below. When the electrons in oxyluciferin fall back down to their ground state, light is emitted from the firefly. Oxyluciferin in its excited state Firefly luciferin http://www.elmhurst.edu/~ksagarin/color/discussion8.html

17. View a Tuft University student research project on fireflies: “Firefly flashing: What’s the cost?” • http://www.youtube.com/watch?v=cGfagRjCXDU

18. Light emission can also be demonstrated in an atom. The electron gains energy and is promoted to a higher energy level, the excited state. When the electron returns to its original ground state, it releases the energy in the form of light. http://www.mut-group.com/uploads/pics/3001-Photonenemisssion_02.jpg

19. Excitation of Hydrogen Atoms Zumdahl, Zumdahl, DeCoste, World of Chemistry2002, page 328

20. Return to Ground State Zumdahl, Zumdahl, DeCoste, World of Chemistry2002, page 328

21. An explanation of Atomic Spectra

22. Where does the electron start? • When we write electron configurations, we are showing the electrons in their lowest energy state-the ground state.

23. Outside sources of energy can move the electron up energy levels. Changing the energy levels in a hydrogen atom

24. As the electron falls back to its ground state it gives the energy back as light.

25. The energy change may occur in steps, each with a different energy change.

26. { Ultraviolet Visible Infrared { {

27. The further the electron falls, the greater the energy, and the higher the frequency. • Each orbital inside the energy level has a different energy, and all the electrons can move around. http://homepage.mac.com/dtrapp/chemGraphics.f/HydrogenSpectra.jpg

28. Summarize • Why are chemical toxins used by animals? • Name two ways that animals acquire chemical toxins. • Why do adult fireflies light up? • Why do firefly larvae light up? • What is chemiluminescence? • What is bioluminescence? • What three components are necessary for an organism to be bioluminescent? • How is light produced in an animal? • Explain the terms ground state and excited state. • How does an electron move from its ground state to its excited state? • How is an emission spectra produced?

29. Teacher Resource • Demo chemiluminescence for your students. Directions at: http://www.digitaldapp.org/demos/documents/chemiluminescence.pdf