Gray • Our Bridge from the Sun 



stitutes more than 99.999 per cent of 

 the Universe. 



Embedded in the stupendous set- 

 ting of ph}sical Nature is an entirely 

 different order of creation which scien- 

 tists call the organic world— the film of 

 life which covers much of the land sur- 

 face of our planet and populates the 

 waters with a rich and varied flora and 

 fauna. TTiis realm of living things is 

 entirely distinct from the physical in 

 organization and in the ways in which it 

 expresses its existence; and yet the or- 

 ganic world is completely dependent 

 on the inorganic for the chemical ele- 

 ments with which to maintain its life 

 processes. It needs carbon and hydro- 

 gen in forms which will serve as fuel to 

 burn with oxygen and release energy. It 

 also needs nitrogen, calcium, and 

 dozens of other elements to combine 

 with carbon, hydrogen, and oxygen in 

 the myriad molecular forms which go 

 into the construction of cells, their 

 extension into tissues, and the constitu- 

 tion of the fluids which bathe the cells 

 and serve as their transports for food 

 and wastes. 



These chemical elements exist in 

 profusion in the physical world around 

 us: the great storehouse of all the atoms 

 that we, the animals, the plants, and 

 the micro-organisms require to build 

 and sustain our living systems. The 

 difficulty is that the atoms are locked 

 up in a quite literal sense— for the 

 bonds which hold hydrogen to oxygen 

 in HoO are among the most powerful 

 known to chemistry, and the same can 

 be said of the attachment of carbon 

 to oxygen in COo. Such tightly locked 

 structures can be broken into only by 

 force. 



There is no dearth of force. Calcu- 

 lation shows that the solar rays falling 

 in a day on each IV2 square miles of 

 the Earth's surface carry as much en- 

 ergy as an atomic bomb of the Hiro- 

 shima type. These ravs continually 

 stream through the water vapor and 



103 



carbon dioxide of the atmosphere, and 

 if only a tiny fraction of their energy 

 were effectively utilized, it would be 

 sufficient to break the molecular bonds 

 and release the atoms of hydrogen, 

 carbon, and oxygen for use by man and 

 the other creatures of the organic 

 world. But the gases of the atmosphere 

 are nearly transparent, and light pro- 

 vides chemical energ)' only when it is 

 absorbed. 



It is here that the green plant as- 

 sumes a key role in the drama of life, 

 for its chlorophyll serves both as an 

 absorber of sunlight and as a mecha- 

 nism to convert the absorbed light into 

 chemical energy. Operating on the 

 water molecules from its surroundings 

 and on the carbon-dioxide molecules 

 from the air, the plant reshuffles the 

 atoms of these compounds to make 

 that most basic of all foods, the carbo- 

 hydrates. (Sugar is the familiar exam- 

 ple.) As a by-product of this photo- 

 synthesis, the plant releases the surplus 

 oxygen not used in fabricating sugar, 

 and thus continually replenishes the 

 air with fresh breathing material. 



Sugar is found in most living crea- 

 tures, from man to microbe. It is one 

 of life's early inventions, a molecule 

 made up of carbon, hydrogen, and oxy- 

 gen with the atoms so proportioned 

 among the three and so loosely linked 

 together that in the presence of free 

 oxygen they dissociate and reunite in 

 more stable combinations, with the re- 

 lease of energy. In other words, sugar 

 will bum. In our bodies it is the pri- 

 mary fuel. Its burning supplies the en- 

 ergy to activate our muscles, to power 

 the pulsations of the heart and lungs, 

 and to generate the currents which 

 course through our nerves. As the Brit- 

 ish chemist F. G. Donnan has ex- 

 pressed it in his oft-quoted phrase, 

 "Without that sugar and oxygen there 

 could be no thought, no sweet sonnets 

 of Shakespeare, no joy and no sorrow." 



Photosynthesis thus occupies a pri- 



