Eco-Farm: An Acres U.S.A. Primer — Lesson 1: Photosynthesis, Part 3
This is an excerpt from Charles Walters’ Eco-Farm — An Acres U.S.A. Primer, available from the Acres U.S.A. bookstore at bookstore.acresusa.com. Read more excerpts from this book using the category “Eco-Farm.”
8. The “?” at the end
Certain bacteria handle the business called photosynthesis. In plant cells, chloroplasts work with the sweep of the sun to manufacture the oxygen we breathe. There is also a purple bacteria that carries out photosynthesis much like chloroplasts in plants, using carbon dioxide as a raw material. Unlike the chloroplasts, purple bacteria use no water. They use hydrogen sulfide, H2S, a gas compound that smells like rotten eggs. (Parenthetically, it might be noted that recent research has also uncovered the presence of purple protein inside the placenta which supplies the beginning colostrum nutritional needs of developing embryos. Umbilical systems for nutrition are not the only conduit for embryo requirements.)
It remained for an American biologist, C. B. Van Niel, to fit into place a last stone of the mosaic started when van Helmont planted his willow tree. Van Niel suspected that purple bacteria were doing exactly the same thing chloroplasts were doing in green leaves, using carbon dioxide plus hydrogen sulfide instead of carbon dioxide and water. The equation for green plants read CO2 + H20 –> glucose + O2. The equation for purple bacteria read CO2 + H2S –> foodstuff + ?. That purple bacteria made another foodstuff, not glucose, didn’t matter. What mattered was whether the “?” at the end of the purple bacteria equation read oxygen or not. A positive answer meant that oxygen released during photosynthesis came from carbon dioxide. If the “?” meant sulfur, then, indeed, the oxygen byproduct of photosynthesis came from water.
Van Niel knew the answer in terms of purple bacteria: it was sulfur. This was confirmed by isotope studies hardly more than three decades ago. By using water with oxygen-18, and carbon dioxide with oxygen-16, and exposing the one cell Chlorella plant to the water, it was possible to measure oxygen released. Mass spectrometer reading revealed that the released oxygen indeed was oxygen-18, the isotope found in the experimental water.
Picture the irony. It had taken 2,000 years to scratch the surface on how plants fed, and another 200 years to solve a relatively simple question—where the oxygen byproduct of photosynthesis came from. In the process, the world learned something about the absurdity of single factor analysis, about the tragedy of legislating what is true or false in science, about the curse that descends on science when practitioners are not well grounded in logic.
9. Limiting factor
There is a limiting factor in almost everything that concerns farming, and a limiting factor often has absolute power. Light is a limiting factor in photosynthesis. Temperature, water, certain earth minerals, all serve up limitations. The green pigment called chlorophyll gives off a reddish light when leaves are placed in acetone, and the chlorophyll in chloroplasts goes into solution. Why is this? No reddish glow can possibly be seen when chlorophyll remains in the chloroplasts. The answer is absurdly simple— and complicated!
There are energy exchanges involved here. Molecules are formed, as is the case with glucose—C6H12O6. Orbits of electrons are different when chlorophyll goes into an acetone solution from when it remains in the chloroplasts. There is an energy differential when electrons are excited. As electrons are raised to higher orbitals and fall back to lower ones, green plants manage to trap the energy into energy-rich chemical compounds. Light figures in creating this excitement that splits water molecules and presides over energy-rich compound production. These many energy-rich compounds in effect power food production once light no longer has a role to play.
It is the function of plants to produce more than they themselves require. That is why the farmer can harvest directly, or harvest to feed animals for later human consumption.
People who make computations on such things say that only about one part in 2,000 of sunlight reaching the earth is ever absorbed by plants. This seems a very low efficiency ratio. This equation becomes even more awesome when we consider that grass, trees and farm crops account for only 10% of the photosynthesis going on. At least 90% of this activity is carried on by algae, which are small single cell plants living in the lakes, streams and oceans of spaceship earth. However, once chlorophyll molecules in a green plant get a hammerlock on light energy, fantastic efficiency is invoked. Over half the absorbed energy is locked up into the energy-rich molecules we’ve been discussing.
As Gene Poirot so aptly put it, nature creates life using air, water, sunshine and earth minerals. What is even more astounding is the fact that a typical crop of corn—one of the simpler monocot grasses—is 95% air, water and sunshine, and only 5% earth minerals. Nature furnishes air, water, sunshine with little or no variance, apparently leaving the farmer to concentrate most of his management capabilities on 5% of the nutrient traffic. Yet it stands to reason that we need to deal with function and nutrition in the 95% range, where results can be proportionately better than in the 5% range.
Thomas A. Edison was once asked what he thought was the greatest invention. The wise old inventor pondered the question, then answered, “A blade of grass.” And then he added, “Do you really understand what makes it grow?”
