Academic journal article The Science Teacher

Ask the Experts

Academic journal article The Science Teacher

Ask the Experts

Article excerpt

How do fireflies get their light power?

Gilberto Monarez NASA/JPL Solar System Ambasdor Austin High School Austin, Texas

Fireflies do not harvest light like photosynthetic plants, so it would probably be better to say they "produce" light rather than "get" it. How this happens is a very interesting story.

First, let's analyze various light-producing processes. In an incandescent lightbulb, the tungsten filament becomes very hot as electricity flows through it, producing white light. This is inefficient in that a lot of heat emanates, too. Ideally, we would have a system that could convert the input energy into light energy with no loss of electromagnetic radiation outside the visible spectrum. Fireflies convert chemical energy into light energy by a very efficient process called chemiluminescence. Because the firefly is living, we call this special form of chemiluminescence bioluminescence.

These special reactions produce a product in an electronically excited state. Electrons of atoms in the reacting molecules start off in the ground (lowest energy) state. As the bonds break and reform, one of the products contains electrons in an excited (higher energy) state. This is unstable, so the electrons return to the ground state, releasing the absorbed energy by emission of a photon of visible light.

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This happens when you break a light stick and it glows. In fireflies, the same sort of thing happens. When the firefly lantern organ is stimulated by nervous signals from the firefly's tiny brain, those signals result in mixing of the reactants--luciferin, ATP, and oxygen (from the air). …

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