Evening star., 1937-08-14
STARS, MEN AND ATOMS
Notebook Of Science Progress in Field.
Laboratory and Study.
BY THOMAS r. HENRY,

A step toward eventual explanation of
one OF the basic biochemical reactions
which makes possible all life on earth
is reported bv E. D. McAlister, Smith
sonian Institution physicist.
This is photoSynthesS-the creation Of
carbohydrates out OF carbon doxide and
water. 1t can be ACCOMPLISHED only by
green plants These have in their leaves
small amounts Of a very complex chem
ical chlorophyll. The molecule OF chlor-
phvll has the unique property with one
possible exception. of trapping photons
OF light and using their enormous ener-
gies TO combine the water and carbon
dioxide into very complex carbon hydro
gen-oxy9en molecules.
These constitute the Starches and
sugars which serve as the fuel of life.
The animal body is essentially heat
engine with carbohydrates serving as
fuel. Coal, oil and gasoline are carbo-
hydrates Practically all food contains
them. In each carbohydrate molecule is
shut up little bit of solar energy which
may have hit the earth millions of
years ago. Carbon dioxide and water in
themselves are lifeleSs things. They
have no capacity for sustaining life. ex-
CSpI III Doullu tOsCtliCl ny
trapped solar energy.
The chlorophyll itself does not enter
into the carbohydrate combination. Its
job is that of trapping the sunlight and
passing it on in the proper fashion. The
actual mechanism of the phenomenon
has puzzled chemists for century since
the process Of photosynthesis was first
suspected 1t seemed to violate all laws
of chemistry. 1t looked as if what was
taking place was something unique in
nature.
To explain several effects it seemed
necessary to assume that at one point
in the process approximately ! 900 chloro-
phyll molecules were entering into
temporary combination with a single
carbon dioxide molecule. The comblna-
ton was known as the "photosynthetlc
unit" 1t verged on the mystical.
Assumption of the existence OF this
photosynthetic unit, DR.. McAlister
explains, has rested on several lines OF
evidence. The simplest is the fact that
in an inclosed chamber containing
measured amount of carbon dioxide far
beyond that of the air and placed under
illumination much more intense than
sunlight the number of molecules OF the
gas which are taken up by the plant,
per light quantity absorbed as determined
by precise analysis, is only about one per
thousand of the calculated number of
Chlorophyll molecules in the plant itself.
Dr. McAlister worked with device OF
his own invention which makes possible
continuous Quantitative determination
of the precise amount of carbon dioxide
in the air of the closed chamber sur
rounding a plant BY this means it is
possible to tell what is happening from
second to second. The device Is based
on the. principle that carbon dioxide
absorbs specifically certain wave lengths
Of light, 50 that the intensity OF light
of these wave lengths varies very pre-
cisey with the proportions Of the gas
in the atmosphere through which 1t
passes.
He found contrary to the long -estab-
lished belief, an almost one to-one rela-
tionship between the calculated number
Of chlorophyll molecules and the con-
tinuous carbon dioxide decline in the
atmosphere OF the closed chamber. That
is. every molecule of the chlorophyll was
attaching to itself under illumination
one molecule Of the gas, or something
of that order
DR.. McAlister determined by his meas
urements another phenomenon which
opens up new paths in the study Of
photosynthesis. A plant was kept in
the dark for varying periods. Without
illumination there is no photosynthesjs.
Upon turning on the light. he found.
the rate Of absorption II carbon dioxide