44
HENRY EYRING, RICHARD P. BOYCE AND JOHN D. SPIKES
siderable absorption and re-emission, the energy hv is radiated from the
surface of the sun as sunlight. The spectral distribution shows the
maximum to be at 0.48μ. This radiation represents the large pool of
free energy from which organisms must draw, directly or indirectly,
in order to exist.
2. Accumulation of Free Energy by Autotrophs
The autotrophs are those organisms capable of drawing directly
from the free energy pool to manufacture energy-rich compounds using
C0 2 as the only source of carbon. This class includes all photosynthesizing plants. The over-all reaction for photosynthesis is sometimes
depicted schematically as
C0 2 + H 2 0 + kv -> (CH 2 0)* + 0 2
The modern trend, however, is to break the above equation into two
parts in accordance with van Niels' (7) suggestion. Thus, the first reaction may be written
H 2 0 + kv -» [H] + [OH]
In green plants and other 0 2 -producing organisms, the oxidizing agent
is disposed by conversion into molecular 0 2 :
2[OH] -* i0 2 + H 2 0
The reducing agent [H] is used in the reduction of the C0 2 to
produce ultimately all of the carbon compounds of the photoautotropic
organisms. The second reaction may be depicted as
C0 2 + 4[H] -> (CH 2 0), + H 2 0
Intense work with radioisotopes has greatly clarified the actual pathway of carbon in gr^en plants (8).
3. Expenditure of Free Energy
Only a small fraction of the total energy output of the sun is captured by living organisms. This energy is stored as chemical potential in
carbon compounds for longer or shorter periods. Eventually, this
chemical potential is released as free energy during exergonic chemical
reactions, and a portion is utilized for the activities characteristic of life.
It must be realized, of course, that the chemical potential of these
carbon compounds may be used directly by the plant which produces
them for its own designs, or that they may be ingested by the other
large class of organisms, the heterotrophs. This class comprises those
organisms which are incapable of manufacturing their own food, and
therefore, depend upon the autotrophs.
HENRY EYRING, RICHARD P. BOYCE AND JOHN D. SPIKES
siderable absorption and re-emission, the energy hv is radiated from the
surface of the sun as sunlight. The spectral distribution shows the
maximum to be at 0.48μ. This radiation represents the large pool of
free energy from which organisms must draw, directly or indirectly,
in order to exist.
2. Accumulation of Free Energy by Autotrophs
The autotrophs are those organisms capable of drawing directly
from the free energy pool to manufacture energy-rich compounds using
C0 2 as the only source of carbon. This class includes all photosynthesizing plants. The over-all reaction for photosynthesis is sometimes
depicted schematically as
C0 2 + H 2 0 + kv -> (CH 2 0)* + 0 2
The modern trend, however, is to break the above equation into two
parts in accordance with van Niels' (7) suggestion. Thus, the first reaction may be written
H 2 0 + kv -» [H] + [OH]
In green plants and other 0 2 -producing organisms, the oxidizing agent
is disposed by conversion into molecular 0 2 :
2[OH] -* i0 2 + H 2 0
The reducing agent [H] is used in the reduction of the C0 2 to
produce ultimately all of the carbon compounds of the photoautotropic
organisms. The second reaction may be depicted as
C0 2 + 4[H] -> (CH 2 0), + H 2 0
Intense work with radioisotopes has greatly clarified the actual pathway of carbon in gr^en plants (8).
3. Expenditure of Free Energy
Only a small fraction of the total energy output of the sun is captured by living organisms. This energy is stored as chemical potential in
carbon compounds for longer or shorter periods. Eventually, this
chemical potential is released as free energy during exergonic chemical
reactions, and a portion is utilized for the activities characteristic of life.
It must be realized, of course, that the chemical potential of these
carbon compounds may be used directly by the plant which produces
them for its own designs, or that they may be ingested by the other
large class of organisms, the heterotrophs. This class comprises those
organisms which are incapable of manufacturing their own food, and
therefore, depend upon the autotrophs.