Nature's Solar Batteries

Scientists have had a hard time explaining photosynthesis, the action of chlorophyll, on which plant, animal and human life depends. They knew that chlorophyll by itself has no photosynthetic power. Only when it is contained in extremely small structures found in green leaves can it use the energy of light to release hydrogen from water, the first step in photosynthesis. The orderly pattern of the molecules in these bodies, say Drs. Melvin Calvin and Power B. Sogo of the University of California at Berkeley, is the key to the process.

The electron microscope shows that in green leaves the chlorophyll is arranged in flat disks like piles of plates. Biologists suspected that this delicate laminated structure had something to do with photosynthesis, but they could not make sense out of it until Bell Telephone Laboratories invented its solar battery, an electronic device made of thin layers of treated silicon. When sunlight hits the battery, it knocks electrons out of one of the silicon layers. Caught by another silicon layer, the electrons turn into a useful electric current. Hearing about this principle, Dr. Calvin and other scientists speculated that the thin layers of chlorophyll might capture light energy in somewhat the same way.

To prove the theory. Researcher Calvin spelled out a delicate test: searching for free electrons in laminated chlorophyll exposed to sunlight. B. Commoner, J. J. Heise and J. Townsend of Washington University at St. Louis were the first to offer evidence that such electrons exist, but critics did not accept their experiment as conclusive. It was performed at room temperature, and under such conditions many chemical processes having nothing to do with photosynthesis can produce free electrons.

To meet this objection, Drs. Calvin and Sogo cooled their apparatus down to -- 140DEGC., close to the temperature of liquid air, so that electron-yielding chemical reactions could not happen. Then they placed deep-frozen chlorophyll in a magnetic field and shot extremely high-frequency radio waves through it. When strong light was shone on the chlorophyll, some of the radio energy was absorbed. This proved to Dr. Calvin that chlorophyll exposed to sunlight contains free electrons, and is therefore capturing light energy by the layer-to-layer method. Nature's green plants. Dr. Calvin believes, have turned out to be electronic solar batteries invented millions of years before human scientists ever thought of electronics.

This file is automatically generated by a robot program, so reader's discretion is required.