Farm Biology 101

The Good/Evil piece is still on the drawing boards. I wrote this post for a local sustainable/organic farming group to put on their Web site and thought you might be interested. We are, after all, the beneficiaries of a sun in the cosmos.

Each of us values the many bounties brought to us by our dedicated local farmers, but what about the underlying and fascinating biology that paves the way to harvest? This series of articles will take us on a journey from sun to seed and beyond.

The Harvest

Farmers harvest crops; plants harvest sunlight

We all know that plants need sunlight to grow and produce the bounty that we buy at market and savor at our tables. But just how does sunlight assist in serving up this cornucopia? Living requires energy, your eyes and brain are using energy to read what you’re reading right now, and plants need energy to live and produce he food we eat. Sunlight is the source of life’s energy. The leaves of green plants are very sophisticated solar panels. Green plants, including farm crops, harvest the sun’s energy and package it into sugar molecules that they, and we, need to stay alive. Without the conversion from light energy to chemical energy we wouldn’t be here.

But where does the sugar come from? Sugar is a form of matter but sunlight is pure energy, there’s no matter in it. The matter in sugar comes from two simple ingredients, water and carbon dioxide. Recall that water is H₂O, that is, two hydrogen atoms attached to an oxygen atom, and those hydrogen atoms really like staying attached to the oxygen atom. It takes a lot of energy to strip them away. That’s where the Sun’s energy comes in. Plants use some of the energy that they receive from sunlight to pull the hydrogen of of oxygen, making the hydrogen available for combining with carbon dioxide. That’s what sugar is made of, hydrogen combined with carbon dioxide. Plants use another portion of the light energy to fashion the chemical bonds that hold the atoms in the sugar together. Those bonds contain energy that originally came from the Sun, so, in this sense, we are all solar powered!

And, you’re breathing the leftover from water right now; it’s the oxygen that was attached to the hydrogen atoms in H₂O. We need oxygen, as do living crops, to extract the Sun’s energy that was packaged in sugar molecules. That unpackaging results in the very ingredients we started with, carbon dioxide and water. You’re exhaling them as you breathe. The cycle goes on as long as plants do what they do with sunlight.

Next: Nitrogen nitrogen everywhere but not a drop to drink.

© R. E. Morel 2009