Skin Pigment Scavenger Hunt
Biological Pigments in Plants:
Plant pigments exist in a wide variety of forms, some with highly complex and large structures.
Over 600 naturally occurring carotenoid structures have been identified, as well as over 7,000
flavonoids, including over 500 anthocyanins. Biological pigments such as chlorophyll are
colored organic molecules which owe their color to the presence of unsaturated bonds.
For your next clue go find a specimen with the specific pigment discussed in this section.
Biological Pigments in Animals:
Biological pigments are pigments produced by living organisms. They can be found in many
plants, including flowers, and even in our skin. Bacteria are colored by pigments. All biological
pigments selectively absorb certain wavelengths of light while reflecting others.
Color arises from the way the pigments react with light. Melanin is the main pigment found in
mammals. It is responsible for the color of hair and fur. There are different types
of melanin (eumelanin and pheomelanin), and they produce a huge color range, from black to
sandy to red.
For your next clue go find a specimen that contains the mammal pigment.
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Other Ways Animals Create Color:
Fireflies and bacteria emit light in the form of bioluminescence. Luciferins are a class of lightemitting biological substance found in these organisms.
Although animals do manufacture their own melanin, they can’t make many other pigments.
Plants, however, can produce a range of pigments, so many animals are colored by what they
eat.
The eye-catching colors of many birds aren’t produced by the birds themselves, but by what
they eat. Research into the varied plumage of a House Finch has shown that its colors are
related to the bird’s diet and the pigments it eats. The carotenoid pigments of the tasty berries
that the red Cardinal enjoys in the summer are laid down in the feather follicles. In the same
way, yellow, red, and orange pigments can be absorbed from an array of seeds. The wide
variety of summer fruits and seeds that form the bird’s diet as it prepares for the lean winter
months also provides the pigments in its vibrant plumage. Another factor is the ability of the
bird to metabolize carotenoid pigments to create plumage pigmentation of a different color
than the ingested pigment. So, one type of seed, eaten by a House Finch, might make it appear
yellow, while the same seed eaten by a Cardinal might make it appear pink, as the Cardinal
converts the pigment metabolically to a red pigment. If you kept a colorful wild bird like a
Cardinal or House Finch in captivity and fed it just one type of seed, its feathers would become
progressively duller with each molt.
For your next clue go find the bird who metabolizes red pigment.
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Other Ways Animals Create Color:
Unlike plants, most animals are unable to make green and blue pigments.
Most of their green and blue colors are created through structural effects. A
bluebird manufactures melanin and would look almost black, but tiny air sacs in the feathers
scatter light and make it appear blue, in a similar way to the sky, which appears blue as gas
molecules in the atmosphere scatter light. Peacocks are colored through a combination of
pigments, and the way light interferes when reflected off the feathers to create iridescence.
Examples of colors arising from iridescent and diffractive structures can be found in peacock
feathers, pearls, and mother of pearl. Another brilliant example of structural color in the animal
kingdom is the brilliant blue of the Morpho butterfly. The color of their wings is the result of
their microstructure, although many butterflies have cells that contain pigment as well.
Some beetles with a metallic green sheen show similarly vibrant colors.
Structural color is the result of selective reflection or iridescence, usually because of multilayer
structures. Pigment color differs from structural color in that it is the same for all viewing
angles. Some colors are a combination of pigment, structural color, and diet. Most green colors
in fish, reptiles, amphibians, and birds are created by a reflection of blue light coming through
an over-layer of yellow pigment.
Blue Poison Arrow Frog from South America. Amphibians’ and reptiles’ skin contains three kinds of highly branched
color cells called chromatophores. The chromatophores occur in three discrete layers. The top layer is generally
made of xanthophores bearing yellow pigments; the middle layer includes iridophores; and the bottom layer has
melanophores with black or brown melanin. In the typical green frog, light penetrates to the iridophores, which act
like tiny mirrors to reflect and scatter mostly blue light back into the xanthopores above them. The xanthopores
contain yellow pigments, and act as yellow filters so the light escaping to the skin surface appears green to our
eyes. If a frog lacks the yellow xanthophores, blue light scatters back and the frog appears bright blue. Iridophores
do not synthesize pigments, but reflect and refract color. They contain platelets that produce a scattering effect.
The real advantage to these stacks of pigment cells lies in their potential to create color changes. The animal can
darken its color by moving the melanin pigment. By manipulating the three types of cells, a wide range of colors
can be produced, usually extending from bright green to shades of brown and grey. Generally xanthophores
contain pteridines (synthesized) and are yellow, but they can produce red pigments. Sometimes the top layer may
contain erythrophores as well as xanthophores. Erythrophores contain carotenoids (absorbed through diet) which
produce intermediate colors like orange, reddish-orange, and
yellowish-orange. The distinction is not always made, as
sometimes pteridine and carotenoids are found in the same
cell.
For your next clue go find a specimen with similar
skin layering.
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White animals:
White animals are often found in nature and sometimes the cause is albinism. Melanin is the
primary pigment that determines the color of a mammal`s skin, fur, and eyes. Albinism occurs
in mammals (including humans), fish, birds, reptiles, and amphibians. It is a hereditary
condition; the principal gene which results in albinism prevents the body from making the usual
amounts of the pigment melanin. An animal inherits either a single trait or set of traits that
interrupt melanin production.
Animals with albinism are typically white or very pale. However, not all animals with albinism
are pure white; some traits that control melanin allow forms of the pigment to appear in the fur
of the animal. The many types of melanin are responsible for brown, black, gray, and some
yellow colorations. In some animals, especially albinistic birds and reptiles, ruddy and yellow
hues or other colors may be present on the entire body or in patches (as is common among
pigeons), due to the presence of other pigments unaffected by albinism such as porphyrins,
pteridines, and psittacins, as well as carotenoid pigments derived from the diet. White
peacocks and white lions are examples of animals that appear white, but do not have albinism.
The color of white lions has been attributed to leucism. Leucism is sometimes mistaken for
albinism, but leucism is a condition characterized by reduced pigmentation in animals. It affects
all pigments, not just melanin, and animals with leucism have normal eye color, while animals
with albinism tend to have red eyes.
Big cats may be white through albinism or leucism, but in a related variation they can be black
because they have melanism, an unusually high proportion of melanin. All these conditions
relate back to their genetic makeup. In black leopards and jaguars with melanism, close
examination will show that the markings are still there, masked by the black coloration.
Melanism is known to occur in other species, but is common in cats.
For your next clue find the culprit of albinism.
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Use of Pigments for Camouflage or Defense
Pigmentation is used by many animals for protection, by means of camouflage, mimicry, or
warning coloration. Pigments such as melanins in the skin may serve to protect tissues from
ultraviolet radiation. Pigments may also aid in sexual reproduction, by identifying species and
gender of animals to potential mates, or signaling readiness to breed. It is now believed that
chameleons change color not so much to blend into the surroundings, but rather to signal, fend
off rivals, or attract a mate. The skin of a chameleon is similar to that of a frog and contains
chromophores. The inner layer consists of melanin (melanophores), the next layer (iridophores)
diffracts or scatters the light, and the top layer contains pigments (such as red and yellow). The
expansion and contraction of the color cells is controlled by the chameleon’s brain to cause a
color change. The melanin (which is black or brown) in the inner layer can move closer to, or
farther away from, the skin surface, allowing it to blend in with, blot out, or intensify color from
other cells. Another interesting fact about a chameleon is that they have a different visual
system than humans and apparently have a fourth cone that is ultraviolet sensitive.
For your next clue find something that employs a defense mechanism.
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Squid Ink
Squid, octopi, and cuttlefish are well-known for the jets of ink they squirt out in clouds at their
attackers. This dark cloud distracts and confuses their potential predators. Cephalopods such as
the octopus squirt ink composed primarily of concentrated melanin, produced in an ink sac. To
add to the effect of this defense, the ink can contain among other things the chemical
tyrosinase, a harmful compound that is thought to diminish sense of smell and cause irritation.
While most octopi have ink sacs, some, such as those that live the darkness of the deep sea,
have reduced or absent ink sacs. The melanin in octopus ink is red, but may appear brown or
even black in high concentrations. Nocturnal and deep-sea cephalopods only produce red or
brown ink, but in reduced light it appears black.
Congratulations you are done!
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