#phospherescence

I thought I'd stray a bit from my usual writings and explore a topic that has been on my mind recently: bioluminescence.

For all of those doing biology A level in the UK, I can say certainly that it is something of an understandable nature, even for our level.

Simply put, bioluminescence is light produced by a chemical reaction within a living organism. Hence bioluminescence is a type of chemiluminescence.

It is know as a "cold light" because less than 20% of the light generates thermal energy. And it is mostly produced in the ocean by marine species, ranging from fish to bacteria. Some are found on land, like fungi or fireflies (who use short outbursts of bioluminescence to attract partners), with also nearly none bioluminescence species in freshwater environments.

Now for the chemistry. Luciferin and luciferase are the two chemicals that are required for this reaction. Luciferin is the compound that actually produces the light after acting as a substrate for the compound that catalyses the reaction, the luciferase (you can notice that endings with -ase usually refer to biological enzymes).

The luciferin becomes oxidised and light is produced with an inactive oxyluciferin. Fresh luciferin is acquired through diet or it is internally synthesised.

What makes this even more interesting is that this is not the only combination of chemicals that can produce bioluminescence. A photoprotein unit can form in living organisms from the luciferin, luciferase and oxygen. This unit can be triggered to produce light when an ion is added to the system, with it usually being calcium ions (Ca2+ ions).

Do not get mixed up with fluorescence, which refers to energy being absorbed from an external source and almost immediately reemitted. Or equally with phosphorescence, where the energy absorbed and released as light can be delayed, resulting as a glow after the light has been removed (serves as the basis of glow in the dark items). Bioluminescence is internally produced, without the aid of any external sources.

I mentioned before how fireflies use this adaptation for mating, well it is used in a wide range of scenarios. Defensive adaptations may include here to defend against prey. For instance the vampire squid ejects sticky bioluminescent mucus to startle and delay predators upon escape. In defence, some organisms use counterillumination to disguise their shadows by matching the light from above to the light from their undersides, with this they become virtually invisible when predators look up. Particularly exhibited by hatchets that protect themselves from sharks that look up (I tried to imagine a shark looking up here, well that was a fascinating image).

For the offensive, the infamous anglerfish uses its dangling light (called esca) to lure smaller fish, who are curious about the spot of light amidst the darkness. But generally the small fish is greeted by the gigantic, dark jaws of the anglerfish.

Humans take advantage of bioluminescence. Green Fluorescent Protein (GFP) behaves as a reporter gene for biologists and engineers to attach to genes they are studying, as it is easily identifiable. It may help scientists to monitor the cell's activity; its expression and interaction with chemicals.

Who knows, perhaps in the future street lights will use bioluminescence to reduce the need of electricity. Or crops and plants would glow when requiring water or nutrients, which would reduce the strain on agribusiness (and myself, for I never know when to water my plants!).