Nature’s hidden beauty – A tangent from Intro Bio

28 Sep

Photosynthesis is a way that nature observes the first law of thermodynamics.

As we all learn in school, the sun is the primary source of energy on Earth, but only a fraction of Earth’s residents can tap into that energy directly. The rest of us, the heterotrophs (from hetero- other and troph – food), get our energy indirectly. We either eat the plants (or other organisms) that produce their own food, or we eat the things that somewhere down the line got their energy from eating autotrophs (from auto- self).

But, because the first law of thermodynamics states that energy cannot be created or destroyed, but only converted from one form to another, these autotrophs could not make their food from nothing. Instead, they converted (solar) energy from the sun into chemical energy via photosynthesis.

Solar energy, which comes to Earth as photons, has characteristics of both particles and waves (as it turns out everything does). These waves have energy that is inversely proportional to the wavelength of the light- shorter wavelengths transfer more energy than longer ones. I like to think of it this way: Shorter wavelengths mean more waves per unit time. If you were one the beach watching waves come in to shore, if more waves crash on the beach in an hour on Saturday than on Sunday, then more energy was transferred per hour from the ocean waves to the shore on Saturday.


Absorption spectrum of pigments

The visible light we can see only a small slice of the broader electromagnetic spectrum. Because we see only the light that bounces of things, if those things absorb some of that light (such as plants that use the light for photosynthesis), then we see only what they reflect back because it is not absorbed. This explains precisely why most leaves appear green – all but the green light is absorbed by pigment molecules that are collecting energy in the chloroplasts.

We can see this clearly by looking at an absorption spectrum of several pigments found in leaves.

What’s really interesting, is the beauty of flowers. These parts of the plant are not photosynthetic*, but they also contain pigment molecules. Why?

Of course we know this. Flowers are the reproductive organs of plants, and they often require assistance from insects or other animals for pollination. The way they attract pollinators is by giving a reward (nectar) and providing visual cues about where that reward can be found (the colorful flower).


Visual spectrum comparison

But, it turns out that bees (a common pollinator) don’t see the same visual spectrum as we humans do. Instead, their spectrum is shifted slightly in the ultraviolet direction.

Naturally, this would have consequences. If bees can see UV light, it would be reasonable to expect that some flowers use pigments that make them visible at UV wavelengths. In fact, this is exactly what we see – well, what we would see if we could see UV. Here’s a representative flower shown as we see it and as a bee may see it – with a UV colored landing area right where the pollen and nectar are found.


Natural Light / UV Light

*At least I think they aren’t. If anyone can provide an example of flower petals that photosynthesize, that would be greatly appreciated.


Posted by on September 28, 2012 in Uncategorized


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6 responses to “Nature’s hidden beauty – A tangent from Intro Bio

  1. Piter Keo

    September 29, 2012 at 11:55 pm

    Excellent post! I like the way you linked so many subjects as photosynthesis, vision and pollination. I will certainly add a link to your blog on mine and follow it from now on. Thank you again for your comments on Earthling Nature and for making me know your blog.

  2. standingoutinmyfield

    April 26, 2013 at 12:59 pm

    Most flowers don’t photosynthesize, but of course there are exceptions and low rates of photosynthesis have been shown in a number of flowers. So it happens, but at a much lower rate than in the leaves.

    • downhousesoftware

      May 4, 2013 at 8:51 am

      Thanks for the comment. It seems logical that some photosynthesis would occur in flowers simply because the flower part is relatively new in evolutionary terms, so why shut off photosynthesis entirely unless that provided a benefit itself? (yet, I can also imagine this being the case because of the coloration….)

  3. Ratabago

    September 12, 2013 at 8:26 am

    I know I’m responding to a bit of ancient history here, but you might like to look up Hellebores (maybe Helleborus viridis). Their flowers start off with petal like structures in white/pinks/reds. But after fertilisation they thicken, loose the colour and start producing chlorophyll, and become somewhat like a cross between a leaf and a sepal. In fact, they are usually referred to as sepals. IIRC some studies have suggested that during parts of the life cycle the flowers are responsible for providing up to 60% of the plant’s carbon.

    • downhousesoftware

      September 14, 2013 at 11:52 pm

      Thanks for the comment. I’ll certainly look this up.


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