Photosynthesis: A Love Song
Lyrics by Bette Korber, sung to the old Irish melody Samhradh, Samhradh
Warning: If you are allergic to the use of adjectives in scientific discourse, discontinue reading. Symptoms may include eye-rolling, nervous tics, uncontrollable finger-drumming, heavy sighs, and apoplectic seizures.
Photosynthesis. I was first introduced to this beautiful chemistry, photosynthesis, in a college class. I had known the word, of course, but hadn’t really registered the depth of its centrality to Life until I fussed and fretted with locking the details of its cycles into my memory for a college midterm. Taking a step back from memorizing the lines and the letters that we use to symbolize the chemistry, in a moment of clarity I looked deeper at the implications, and I fell in love.
I changed my major from English to Chemistry.
Photosynthesis transforms inorganic molecules into the stuff of life, and tracing its cycles is one of many paths towards appreciating how deeply entwined is all life on Earth. When you next step out-of-doors and into the morning sun, consider for a moment that each leaf and each blade of grass you see is incredibly busy catching sunlight to construct the chemical framework of life. As leaves do this, they create oxygen, the breath of life in the animal kingdom. When I slow down enough to remember this bit of knowledge it never fails to move me -- a jumble of words that describe this feeling are gratitude, awe, comfort, and delight. So, this song is about sharing this good feeling with people who have not had the opportunity to consider the enormity of the green leaf in our world, or perhaps to reawaken the idea for a moment’s contemplation in those who already share my appreciation.
You don’t need to understand the chemical details to enjoy the science, although it is a tribute to human ingenuity that the chemistry has been worked out precisely. Here are the basics:
What comes into and out the photosynthetic reactions.
Photosynthesis includes two intimately linked cycles. Energy and energy carriers swirl between the two, spinning life from air, water, and light. First are the light reactions, fed by water and sunlight. Water is taken up by plants through the earth by their roots, and brought up into the leaves through transpiration -- essentially water moves up through the plant as it evaporates into the air through microscopic pores on the leaves’ surface, called stomata. Plants breath through their stomata, and hundreds of thousands of stomata can be found on even a single tiny leaf. Trees can open and close these pores to control the flow of water through their giant bodies, and they balance not losing too much water in the heat of the day or times of drought with keeping enough water moving through leaf in the daylight to enable Earth’s sweet alchemy, photosynthesis. Trees are a vital part of the great cycle that moves water from earth to cloud, they are living water channels to the sky. The water then cycles back again to Earth through rain and fog and snow. As water flows through the leaves on route from root to sky, some of it is captured by the leaves for use in the light reactions of photosynthesis. The leaf deftly uses this water and the energy in sunlight to charge up two molecules (called ADP and NADP+) to become energy-carriers and electron porters (called ATP and NADPH). CO2 also plays a vital role in the light reactions, enabling the flow of electrons. In charging up ATP and NADPH, water is transformed, and oxygen released -- and so, thank you leaf, we breathe.
The energy carriers from the light reactions deliver energy and electrons into the path of the dark reactions of photosynthesis, called dark as this cycle doesn’t depend on sunlight (the dark reactions are also called the Calvin cycle, named for Melvin Calvin, who together with Andrew Benson sorted out much of the chemistry). The dark reactions build CO2 taken in through the stomata, and more water, into glucose (sugar), the energy-rich organic molecule at the center of life. As glucose is assembled, ATP and NADPH revert back to ADP and NADP+, and circle back into the light reactions to be recharged once more by the sun.
The two cycles themselves seem miraculous, prayer wheels spun by the touch of the sun.
So, the leaf uses sunlight’s energy to weave simple water (H2O) and carbon dioxide (CO2) into life by channeling electrons, remixing oxygen, carbon, hydrogen, to re-frame them as glucose. Glucose is primed to enter the metabolic pathways of Life on this Earth, and we all build from this foundation the many complex molecules needed by our cells, our organs, our bodies to become a living being.
Our atomic composition is not quite so simple, we are not composed of just the elements carbon, hydrogen, and oxygen, but also hold nitrogen, phosphorus, calcium, and many other essential traces of stardust. Still, the transition of the inanimate towards life begins on the carbon backbone of glucose that emerges from photosynthesis. First, a plant taps light, water and air to builds itself. The herbivore eats the leaf, the carnivore eats herbivore, and we omnivores eat everything we can. And we thrive on every breath that brings us the oxygen that was also created in leaf -- oxygen carried by our blood cells to all the cells of our body, keeping our muscles moving, our hearts beating, our nerves firing, our thoughts swirling.
All this born in a sun-kissed leaf.
This song was nominated in the World Music Category in the 2023 New Mexico Music Awards.
Note: with thanks to Professor Govindee Govindee for carefully reading these comments and kindly offering some helpful editing suggestions. He sent a remarkable reading list, you can find links to his writing on his web page. Also with gratitude to Professor Hartmut Lichtenthalar, a botanist who founded a research institute at the University of Karlsruhe where the science of photosynthesis was advanced. He sent along these very kind words that made my heart sing:
"Thanks for your song and music on nature, plants, on Photosynthesis and Melvin Calvin. ... I worked two years in Melvin Calvin’s Laboratory in Berkeley from 1962 to 1964. He was a great scientist and wonderful person. He would have liked to hear your music and to see the photos and his photo being included. As I knew him very well, I am very sure on that."
-- Hartmut Lichtenthaler, 2022-09-16
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