The term pigment generally denotes color or dye, but here we will be discussing about biochromes or biological pigments that are produced by living organisms. Simply speaking, biochromes are also known as pigments and are created by living beings that possess color owing to their selective absorption of color from light. In fact, when we talk about biological pigments or biochromes, we refer to the colors produced by animals as well as plants, especially the flowers. Several biological structures in animals, for instance the skin, eyes, hair and fur, also enclose pigments or colors. The pigments found in animals like melanin are present in special cells called chromatophores – cells containing pigments.
Biochromes or the biological pigments produced by living beings, animals, plants as well as lesser organisms like bacteria, differ from the structural color, but appear similar when viewed from different angles. The structural color of the living beings is a result of their selective reflection of light (iridescence) basically due to multi-layer structures of the organisms. In other words, the term iridescence denotes the exhibition of an assortment of colors that glisten and transform due to obstructions as well as scattering when the position of the viewer changes. The wing of a butterfly, which usually encloses structural color, is a case in point. On the other hand, the fact remains that numerous species of butterflies actually have cells that enclose pigments.
As discussed earlier, biochromes or biological pigments produced by living organisms are basically coloring agents. Biochromes are present in several plants, especially their flowers and fruits, while the human skin also possesses this substance. It is interesting to note that even inferior organisms or microorganisms like bacteria are also colored by biochromes.
Pigments in plants
In plants, biological pigments are found in a range of forms – and some of them may be intensely compound as well as large structures. Till date, scientists have been able to categorize in excess of 600 naturally occurring carotenoid structures in plants. In addition to this, over 7,000 flavonoids, counting 500 anthocyanins, have also been identified. For instance, biological pigments or biochromes like chlorophyll are pigmented organic molecules which are caused by the presence of unsaturated bonds in plants.
Precisely speaking, the biological pigments present in plants include a variety of different sorts of molecules, including carotenoids, anthocyanins, porphyrins and betalains. On the face of it, all varieties of biochromes selectively absorb certain wavelengths of light and reflect the other types. In most cases, the light that is soaked up by the plants is utilized to provide energy for chemical reactions. On the other hand, the light wavelengths that are reflected by the plants actually determined the color of the plant as it appears to the viewer. Besides these two advantages of biological pigments in plants, they also help in attracting pollinating agents like insects and birds.
Most of us are aware of the fact that chlorophyll is the major pigment in plants that produce their own food. The fact remains that porphyrin found in the plants help them to absorb the yellow and blue wavelengths of light, while the green wavelength of light is reflected by the porphyrin molecules present in most plants. In fact, the copious presence of chlorophyll in a plant makes the plant look green to the viewer. Precisely speaking, all green plants growing on the land and the green algae actually have two different types of green pigments – chlorophyll a and chlorophyll b. Conversely, kelps, diatoms and other photosynthetic heterokonts (14 classes of which have been identified thus far) contain chlorophyll c instead of chlorophyll b. Unlike the green algae, the red algae only possess chlorophyll a. These diverse varieties of chlorophyll provide the plants with the fundamental means to intercept light to enable them to undertake process called photosynthesis.
Carotenoids are also present in plants in a variety of colors, including red, orange or yellow tetraterpenoids (tetraterpenoids are basically obtained from terpenes and have a vast as well as varied class of hydrocarbons). They perform the role of accessory biological pigments in the plants and facilitate the photosynthesis process by gathering light wavelengths that are not easily absorbed by chlorophyll. Most of us are quite familiar with carotene, an orange colored biological pigment present in carrots. The other familiar carotenoids are lycopene (the red biochrome that is responsible for the color of tomatoes) and lutein (a yellow biological pigment present in many fruits and vegetables). It has been established that carotenoids function as antioxidants. Carotenoids also aid in promoting healthy vision or eyesight in people.
On the other hand, anthocyanins are basically flavonoid pigments that are dissolve in water and appear to possess any color ranging from red to blue depending on their pH level. Anthocyanins may be found in all tissues of the higher plants and the color of the leaves, stems, flowers, fruits and roots of these plants are attributed to anthocyanins. Nevertheless, their presence in the plants is not always adequate and, hence, anthocyanins are often not visible. Precisely speaking, they are most visible in the flower petals wherein they form about 30 per cent of the dehydrated weight of the tissues. Apart from this, anthocyanins are also responsible for the purple color visible on the underside of the tropical shade plants, such as Tradescantia zebrina. The function of anthocyanins in plants that contain them is to absorb the light wavelength that has already passed through the leaf and reflect them back towards the plant areas that enclose chlorophyll. The idea is to make the utmost use of the available light at any specific spot on the plant.
Then again, betalains are red or yellow biological pigments and, much like anthocyanins, they also dissolve in water. However, betalains are also different from anthocyanins in the aspect that they are compounds derived by synthesizing tyrosine and are driven by indole. This type of biochromes is only found in Caryophyllales or Chenopodiales, including amaranth and cactus. It may be noted that betalains are never found in plants that enclose anthocyanins. Significantly, the deep red color of the beets is attributed to the betalains. This deep red color of beets is often used commercially as agents to add color to foods.
Pigments in animals
As mentioned earlier, even animals produce biochromes or biological pigments. Like chlorophyll is the primary biological pigment in most plants, melanin is the main biochrome found in the mammals. In fact, melanin is responsible for the color of the hair and fur of an animal. Like in the case of plant biological pigments, the melanin present in animals also differ in form – for instance, pheomelanin and eumelanin. These different forms of melanin produce a wide range of colors varying from black to red to sandy.
The presence of biological pigments in animals is useful in the sense that they may be helpful in protecting their tissues from the harmful effects of the ultra-violet (UV) rays. For instance, the presence of melanin in the skin protects the mammals from several skin disorders caused by the UV rays. In addition, biochromes in animals are also said to be helpful in sexual reproduction, indicating the preparedness to breed and also to recognize the species and gender of animals to prospective mates.
In addition, several cephalopods (marine molluscs belonging to the class Cephalopoda) utilize the pigmented chromatophores (cells containing pigments) to fulfill their communication requirements.
It is also well known that numerous animals use their biological pigments to protect themselves from predators. In fact, such animals utilize the biochromes as a means of camouflage or disguise, warning coloration and even for mimicry. The chameleons are the best example of this. They use the biological pigments present in their body to match their body color with their surroundings by means of regulating the absorption levels of the electromagnetic spectrum.
Additional ways for organisms to create color
In addition to the biological pigments produced by living organisms, they are also able to create colors by other means. For instance, bacteria and fireflies send out light in the form of bioluminescence. It may be noted that luciferins are a category of biological substance present in these organisms that emit light.
While the animals themselves produce their melanin, they are actually unable to make any other type of pigment. Nevertheless, the plants are able to produce a wide variety of pigments. Therefore, several animals are actually colored by what they ingest.
For instance, flamingos consume planktonic animals (microscopic organisms like algae and protozoa that float and drift in water bodies), especially shrimp. It is interesting to note that neither the flamingo, nor the shrimp are able to produce their own carotenoids. On the other hand microscopic algae produce red and yellow pigments and they basically form the main diet for the small shrimp. Once the flamingo eats the shrimp, the carotenoids progress another step by means of the food change to make the bright pink and orange colors that is seen on their feathers. In fact, most of the zoos enhance the diets of their flamingos with the pigments extracted from plants. In fact, if flamingos were just gray colored, they would lack the visual appeal of bright colors that we generally look forward to from these birds. Likewise, salmon that are farmed are fed on a supplement in order to make them an additionally tempting pink.
Animals without vertebrates, for instance insects, generally demonstrate green colors owing to the porphyrin pigments that they occasionally take in through their diet.
Different from the plants, majority of the animals are not able to produce green and blue pigments. In effect, most of the green and blue colors of the animals are created by means of structural effects. For instance, a bluebird produces melanin and would almost appear to be black, barring for the miniature air sacs in the birds’ feathers that scatter light and make it seem to be blue – something similar in which the sky appears to be blue since the gas molecules in the atmosphere disperse light. On the other hand, peacocks have a combination of pigments that imparts colors to them.
In effect, it is the manner in which the light interferes when it is reflected off the feathers of peacocks that create iridescence (changing colors). Instances of hues occurring from iridescent as well as diffractive (owing to diffraction) structures may also be found in the feathers of peacock, mother of pearl as well as pearls. The luminous blue biological pigment found in the Morpho butterfly is another excellent instance of structural color in the animal kingdom. In fact, the color of the wings of the Morpho butterfly is owing to their microstructure. Nonetheless, several butterflies possess cells that enclose pigments too. In addition, a number of beetles having a metallic green gleam also display equally vivacious colors.
It may be mentioned that by and large the structural color is caused due to selective reflection of light wavelength or iridescence owing to the multi-layer structures. Biological pigments are generally at variance with structural color in the sense that they appear the same no matter from which angle the organism is being viewed. Other than this, there are a number of colors that are a blend of structural color, pigment as well as the diet of the organism. In fact, in most cases, the green color seen in fish, amphibians, reptiles as well as birds are produced due to the reflection of the blue light passing through an upper layer of yellow pigment.
Diseases and conditions
Absence or loss of pigments or pigment cells in humans as well as animals also results in an assortment of ailments or abnormal health conditions. Such diseases and conditions may also arise in humans and animals owing to profuse production of pigments in their body.
- For instance, albinism (deficiency of pigmentation in animals and plants) is actually an inherited disorder that is distinguished by complete or part loss of melanin. ‘Albinistic’ is the term that is used to denote such humans and humans who suffer from albinism. Although occasionally the term ‘albino’ is also used to denote such people, but those suffering from condition are likely to consider this term as offensive.
- Another ailment, known as lamellar iscthyosis (fish scale disease), too is an inherited health condition wherein one of the symptoms include excessive production of melanin. In such cases, the complexion of the skin turns darker and is distinguished by darkened, scaly and arid patches. For instance, melasma is a health condition wherein dark brown patches of pigments surface on the face and they are known to be influenced by hormonal changes. When this condition happens during pregnancy, it is known as the ‘mask of pregnancy’.
- Excessive pigmentation also results in another health condition called ‘ocular pigmentation’. In this instance, excessive pigments accumulate in the eye and this condition may arise owing to latanoprost medication (a medicine applied topically to lessen high intraocular pressure). On the other hand, vitiligo is a health condition wherein there is a loss of cells that produce pigments called melanocytes in patches of the skin.