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  • Thanks to Brilliant for supporting this episode of SciShow!

  • Go to Brilliant.org/SciShow to learn more.

  • {♫Intro♫}

  • The world is filled with an abundance of beautiful natural colorsthough, some stand out more

  • than others with super-shimmery blues, whiter than white whites, or darker than dark blacks.

  • And today, we're going to talk about three of the most intensely colored living things.

  • What's really fascinating about these three is that their signature looks are all made

  • without colorful molecules.

  • The color you see when you look at an object or a living thing is determined by the wavelengths

  • of light it reflects back into your eyes.

  • White light, like the light from the sun, contains all the wavelengths we perceive as colors.

  • And when it hits something, that thing absorbs some wavelengths of light and reflects others.

  • For most living things, what's reflected is determined by pigmentsquotecolorful

  • chemical compounds that absorb certain wavelengths of light.

  • Leaves are green, for instance, because they contain chlorophyllspigments that largely

  • absorb all light except for green wavelengths.

  • And that's all well and goodfor most colors.

  • But the most intense colors we see in nature don't tend to come from pigments.

  • They come from a phenomenon called structural coloration.

  • That's when the light reflected or absorbed depends on the microscopic structure of a

  • surface and not the absorption properties of specific molecules.

  • Take the marble berry, for instance.

  • It's the vivid fruit of an African herbaceous plant, and back in 2012, it was heralded as

  • the most intense natural color on the planet.

  • And it's not hard to see why.

  • These small berrieswhich are smaller than blueberriespack a colorful punch.

  • Their bright iridescent surfaces sparkle and shine in stunning blues and purples.

  • But unlike other berries, marble berries don't get their color from pigments.

  • Instead, it comes from unique structures in the outer layers of the fruit.

  • The outermost layer, called the cuticle, is glossy and transparent, allowing light reflected

  • from the tissue belowcalled the epicarpto shine through.

  • The cells in that tissue contain translucent cellulose microfibers stacked in miniature spirals.

  • These act like a series of mirrors, reflecting the light back and forth between them.

  • Depending on the thickness and direction of the spiral as well as the thickness of the

  • cell's wall, each cell reflects red, green or blue wavelengths.

  • Though most of them reflect blue light, causing the berry to have a somewhat speckled but

  • generally blue appearance.

  • Below these cells is a layer of dense brown tannin pigments, followed by a third layer,

  • an even deeper sheet of thin cells.

  • The tannins absorb most of the light that gets to them, while the thin cells scatter

  • what's left to enhance the purity of the color produced by the spirals.

  • In total, the berries reflect 30% of the light that hits them.

  • As for why the berries are such a brilliant bluewell, that's likely to attract berry-lovers like birds.

  • In general, plants that make berries are hoping animals will eat them because that means they'll

  • carry their seeds in their guts for awhile before depositing them in a hopefully-distant location.

  • But marble berries don't contain lots of yummy flesh, so animals have no particular

  • reason to help the plants disperse their seeds.

  • Except, of course, that the berries are so shiny and blue.

  • It's thought the coloration either fools birds into thinking they're a different,

  • more nutritious species, or simply looks amazing.

  • You see, during courtship, lots of bird species decorate nests or other structures to prove

  • they're a high quality mate, so a shiny blue berry could bring their mating display

  • to the next level.

  • Either way, the berries get dragged around, helping the plant reach new areas.

  • While the berries' 30% reflectance is impressive, it's nothing compared to the brilliant 70-plus

  • percent reflectance of Southeast Asian Chypochilus beetles.

  • Their whiteness is so bright that it almost hurts to look at them.

  • And they get this super whiteness from their unique scales.

  • Each is comprised of numerous tiny filaments densely packed together.

  • These fibrils are really good at scattering light, and because the scattering is random,

  • all wavelengths are scattered equally, making the resulting color white.

  • Which is all well and good for the beetles, because it lets them blend in with the white

  • fungi they like to live on.

  • White things are also useful to us, of coursewhich is why researchers have created an artificial

  • white substance that mimics the structure of a Cyphochilus scale.

  • This substance is 20 to 30 times more white than normal white filter paper and retains

  • this clarity of color down to a mere 10 microns thickthat's thinner than a human hair!

  • On the other hand, creating the blackest black requires the exact opposite approach.

  • Black is the absence of all colors, so to make deep, dark blacks, you need something

  • that absorbs most if not all of the wavelengths beaming at it.

  • And that's exactly what the feathers of several birds of paradise do.

  • Some people who have sees these birds up close say looking at their feathers is like looking

  • into a dark void.

  • And that's actually a pretty apt comparison, because the birds' feathers reflect a mere

  • 0.05% to 0.31% of the light that hits them.

  • Compare that to normal black bird feathers, which reflect about 3 to 5%.

  • The difference in blackness comes from modifications to small branches of the feathers called barbules.

  • In most birds, these are relatively flat and thin; all the absorption is done by dark pigments

  • inside the feather.

  • But in the black feathers from birds of paradise, the barbules are curved, dense, and pocked

  • with tiny spikes.

  • These reflect any escaping light back inwards towards the bird, trapping it in the feathers

  • until it's absorbed.

  • You might think something that deep and dark was trying to hide, but that's not what

  • these birds are after.

  • Instead, it's thought the super-black of their feathers helps them highlight the colors

  • of the rest of their plumage, which they use to during courtship to woo a mate.

  • That's why nothing but the blackest black would do.

  • And though there are lots of ways to make beautiful colors, it seems like when nature

  • wants something really intense, light-absorbing compounds just don't cut it.

  • To understand why structural colors are so much more intense, you have to understand

  • how light behaves.

  • And if it's been a little while since your last physics class, don't worryBrilliant.org

  • has you covered.

  • Their course on waves and light can give you a more complete understanding of how light

  • behaves, which will help you dig deeper into this kind of material.

  • And it's just one of their many engaging, interactive courses that teach you science,

  • engineering, computer science and math.

  • And with Brilliant, the learning doesn't stop there.

  • Every day they put out new Daily Challenges which help you take your learning a step further.

  • And they don't take long, so you can give your brain a little workout while waiting

  • for a train to arrive or a pot to boil.

  • You can check out today's challenges right now even if you aren't a member, but with

  • a premium subscription, you get access to the whole backlog of challenges, too.

  • And right now, the first 200 people to sign up at Brilliant.org/SciShow will get 20% off

  • the annual Premium subscription!

  • And that's a pretty great deal if you ask me.

  • {♫Outro♫}

Thanks to Brilliant for supporting this episode of SciShow!

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世界上色彩最濃郁的3種生物。 (3 of the World's Most Intensely Colored Living Things)

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    林宜悉 發佈於 2021 年 01 月 14 日
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