Thursday, October 20, 2011

Color: It's more than just pretty

Biking along Highway M on my way to work, I am dazzled by the gorgeous rainbow of color.  It started with the red maples in the swamps.  They turned scarlet several weeks ago, brightening up the landscape like nothing else can do.  The interrupted ferns and bracken ferns in the ditches turned yellow, and then a rapid cascade of other plants changed into their fall wardrobes.  Now the forest is mostly orange and gold – from the thick litter of leaves on the ground, all the way up to the crowns of the trees.  In gloomier falls I often quip that this is the season when the sun shines from the ground up.  Recently we’ve been completely surrounded by sunshine, with not a cloud in the sky.

While the colors this fall have been stunning, I like to think about how useful the colors are, too.  Green plants, for example, get their color from chlorophyll, the powerhouse of photosynthesis.  Chlorophyll captures the energy of the sun, uses it to make sugar out of water and carbon dioxide, and supports the entire food chain.  Including us.  We have all known this since grade school science class, but it never ceases to amaze me. 

The yellows and oranges finally revealed during the past couple weeks were always there.  They were just masked by the greater amount of chlorophyll.  When the plant stops producing new chlorophyll, the old is broken down into a colorless chemical, and the other colors shine through.  Yellow and orange aren’t just useless underdogs -- they have important jobs to do, too.

Yellow colored xanthophylls are found in most plants, and they help keep the machinery of photosynthesis from being damaged by absorbing too much light.  Animals get xanthophylls from their food, and we can see them in the color of egg yolks, butter, fat, skin, and even the macula lutea – a yellow spot in our retina where the pigment helps protect our eye by absorbing UV light.

Orange carotenoids (as in carrots) also absorb extra UV light.  In addition, they are antioxidants that capture renegade oxygen molecules.  They are important to human health in the form of vitamin A.

Red anthocyanins aren’t revealed in the same way that yellow and orange are.  They are created from the breakdown of sugars once phosphate has been sucked from the leaf down into the twigs.  Sunlight is necessary to create anthocyanins (and more anthocyanins are needed in sunny weather), which is why sunnier autumns have more brilliant colors.  We see the red color again in the new leaves of spring.  During both seasons, the pigment protects against damaging light at low temperatures. 

Anthocyanins protect humans, too, and have been shown to help stave off cancer, inflammation, diabetes and bacterial infections.  One study even showed that anthocyanins cause cancer cells to die faster!  We don’t eat red maple leaves for our health, of course, but we do eat blackberries, blueberries, cranberries, and many other fruits with plenty of red in their skin and juice.

Speaking of red skin, kayaking on Lake Namakagon for three hours in the sun reminded me about the importance of melanin.  This brown pigment not only protects us, bacteria, and fungus from UV light (it creates our summer suntan), it is also important in the immune systems of invertebrates.

While I think the biochemistry of color is fascinating, there are many other ways that colors provide protection.  As a gray-brown deer materializes from the shadows at dawn, camouflage comes to mind.  The short-tailed weasel (aka ermine) skins in our Collections Room also show this quite well: the summer fur is light brown, and the winter fur is bright white.  In contrast, a bright-orange monarch butterfly fluttering by my paddle vividly warns birds that it would be a bitter mouthful, simply through its colors.

The pale, smooth trunk of a paper birch also has protective coloration – this time from heat.  In winter, trees freeze very carefully to make sure their cells are not damaged by ice.  Darker trees may thaw and then freeze again too quickly, while birches stay cool and safe.

Paddling close to a loon, I am struck by the vibrancy of its glowing red eye.  Even that has a specific purpose.  Since we perceive color based on the wavelengths of light that are reflected off a surface, the loon’s eye is reflecting red light and absorbing all others. Under the water, red is the first light to be filtered out, allowing the loon to still gather as much light as possible with its eyes.

My brown eyes are taking in as much as possible.  Despite my love of science and explanations, I think one of the most wonderful uses of color is the rejuvenation of our hearts and souls in the presence of natural beauty.

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