Welcome to Brainstuff, a production of iHeartRadio, Hey Brainstuff Lauren vogelbomb here. Animals that use their sense of sight to navigate generally have a hard time getting around without light, so there are a lot of adaptations out there to help. For example, owls have very large, tubular eyes that they use to collect a lot of light. Cats have a layer of highly reflective material deep in their eyes to give their light receptors a second chance at gathering it.
Humans have put a lot of effort into creating portable, often artificial light sources, from torches to light bulbs and LEDs. Some bioluminescent life forms have an entirely different approach. They make their own light and carry it around in their bodies. Some of these animals use the light they produce the same way that people use flashlights or searchlights, but bioluminescent animals produce light very differently from the way that traditional
light bulbs do. Traditional light bulbs and fires, for that matter, create light through incandescence. A material like wood or a filament inside a bulb gets very hot and emits light. This process isn't particularly efficient, since generating enough heat to create light wastes an enormous amount of energy. That's why led light bulbs have become so popular. They use what's called electroluminescence to basically use a low amount of electrical
current to produce photons. When that current is run through certain semiconductive substances, it produces light but wastes a lot less energy. In life forms that use luminescence, chemical compounds mixed together to produce a glow. It's a lot like the way that substances inside a light stick combine to make light. Illuminescence of any kind is far more efficient than incandescence. It neither requires nor generates much heat, so it's sometimes known as cold light, hot or cold. A
light generally comes from one source, an excited electron. Basically, energy causes an electron to move up a level in its atomic orbit. When the electron settles back down, it releases a photon, or a tiny packet of light. The result in various life forms can be beautiful alike the twinkling of fireflies, or a little eerie, like the glow
of foxfire. It can have all kinds of uses, from protection to predation to we're not really sure what today, let's talk about the basic process behind bioluminescence and how different life forms use it to their advantage. You can find bioluminescent life forms all over our planet. On land. The aforementioned foxfire comes from glowing species of fungi that feed on rotting wood, creating an ectoplasm green carpet of
light in Appalachian and other forests at night. In some types of fungus, the whole structure glows, in others only parts, like the aptly nicknamed jack o lantern, mushrooms, gills. Then there are various land animals, including some insects, centipedes, millipedes, and worms. You know fireflies and glowworms, which are the larvae of various species of flies and beetles. But most of the world's bioluminescence exists in the oceans, and particularly
in the depths known as the twilight zone. This has nothing to do with rod sterling that I know of. In this zone, which extends from about six hundred and sixty to three thousand, three hundred feet which is two hundred to one thousand meters, some light but very little penetrates from the surface. The water above this zone absorbs wavelengths red, orange, and yellow sunlight and scatters violet light, so the light that reaches the twilight zone is bluish
green in color. At this depth you can find lots of bioluminescent jellyfish, squid, shrimp, krill, marine worms, and fish. Most make light that matches that blue green sunlight that exists in this zone. The animal's glow can travel a long way and it can blend in with the light above. In some places, these animals, not the sun, are the primary source of light, So that's weird. Next question, why Hypothetically the evolution of something that requires a body to
use precious resources usually has a reason. Like I said a minute ago, we don't know all of them yet. For example, several species of earthworm secrete luminescent stuff that doesn't have an obvious purpose. We think that some mushrooms glow to attract insects to help spread the mushrooms spores. But yeh, a few animals light up when nearby animals start to glow, and there's not always a clear reason
for this behavior. One of my favorite examples is the phenomenon known as the milky sea Awhere in the surface of the ocean glows at night. Okay, so some species of single celled plankton glow when they're disturbed. Tides, storms, swimming marine life, and passing ships can cause large numbers of these plankton to produce light simultaneously. In some cases, this glow is so bright that it interferes with marine navigation. There's a hypothesis that this works sort of like a
burglar alarm to help the population of plankton survive. The idea goes that if a small fish begins to feed on the plankton, the disturbed plankton emit a flash of light. The light attracts larger fish, which are likely to be the smaller fish as predators, and will thus prevent more of the plankton from being eaten by eating those smaller fish. However, this system doesn't seem to be as fool proof as some of the better understood uses for bioluminescence. So what
do we know. We know that some animals use bioluminescence for communication. Of Fireflies flash at one another in species specific patterns, often in order to find a mate, but attraction isn't always benevolent. In the twilight depths, of the ocean. Some fish species, like the anglerfish, use aluminescent lure to attract prey. Some twilight zone fish species use their luminescence
more like a spotlight to find prey. A one species of loose jawfish produces red wavelengths of light because red is uncommon at those depths, many deep water species didn't evolve to see it, so we think the loose jaws red light may allow it to spot and sneak up on prey. Bioluminescence can also be used for camouflage and mimicry. Okay, in the darker parts of the ocean, it's hard to see anything below you, but easy to see the silhouette
of what's above you. For this reason, some species produce spots of light on their undersides, which blur their outlines and allow them to blend in with the light coming from above. This is also known as counter illumination. Or take for example, the cookie cutter shark, which has one unlit patch on its underside, and that patch resembles a
smaller fish when viewed from below. Thus, a predator may approach and this shark can take a bite out of it and then flee which allows the cookie cutter shark to prey on animals that are much larger and more powerful. Bioluminescence can also be used for self defense when threatened. Some animals release a cloud of bioluminescent fluid, similar to the way that squid defend themselves with a cloud of anis.
Others use a bright flash to temporarily blind predators. But okay I said earlier that bioluminescence comes from chemical reactions. For all of these different uses of light in all of these different organisms, the actual compounds at play can be different, but the basic formula is the same. In general, bioluminescence involves the combination of two types of substances in a light producing reaction, a luciferin and a luciferase. Luciferns
are a category of light producing substances. Luciferases are a category of enzymes that catalyze the reaction. Often the process requires the presence of other substances, like oxygen or a denticine triphosphate that's ATP, a molecule that stores and transports energy in living cells. The luciferase basically allows the oxygen or whatever to interact with the dormant luciferin, thus prompting it to produce photons of light. The terms both come
from the Latin term lucifer which means light bringer. Lots of different substances can act like luciferins and luciferases. For example, those milky seed plankton obtain their energy through photosynthesis, and they have a luciferin that resembles chlorophyll. Some shrimp and fish appear to manufacture their lucifern from the food that they eat, but not all bioluminescent life forms produce their
own light. Some animals create these substances in their own bodies, but others have developed a symbiotic relationship with light producing bacteria. These bacteria typically live in a specialized organ in the host organism's body. The bacteria produce light all the time, so in order to turn their lights on and off, some animals can pull and push their light producing organs into and out of their bodies. Others cover them with
membranes of skin to eyelids. Because of all of these variations and how bioluminescence works, researchers think that this ability to make light evolved independently in multiple forms of life, and although humans didn't evolve by iluminescence, we've been using it to our advantage for thousands of years. In ancient Rome, plenty of the Elder wrote about using jellyfish goo to paint a walking stick and making it into a cold torch.
People around the world have picked foxfire fungi to use his lanterns, or cultivated them along pathways to light a trail. During World War Two, the Japanese army harvested and dried tiny bioluminescent crustaceans that, when crushed by soldiers in the field, provided just enough light to say, read a map, without giving their location away to any enemies nearby. Modern navies track milky seed plankton to detect enemy movement, and researchers
can similarly track animals to learn more about them. Researchers have even used luciferins and luciferases to help tag and literally illuminate the workings of different cells and proteins in order to better understand things like nerve damage in Alzheimer's disease and the proliferation of cancers in living bodies. But as I've said, we don't even understand everything there is
to know about these beautiful and useful biological processes. Hopefully future research will help light the way to even more applications a bioluminescence. Today's episode is based on the article how bioluminescence works on how stuffworks dot com, written by Tracy V. Wilson, who you may be familiar with from a little show called Stuff You Missed in History class. Brain Stuff is production of by Heart Radio in partnership with how Stuffworks dot Com and is produced by Tyler Klang.
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