Page 39 - Biofuels Refining and Performance

22 Chapter One

These examples are sufficient to indicate that if gastric mucosa is
connected to the intravenous system, a potential difference or an EMF
will be experienced. Likewise, if the root tissue and the fruit of a tree
are short-circuited, current (however feeble) will be experienced. This
information is not worth much at this present state of the art because
the magnitude of instrumentation will appear prohibitive. But in space
research, there was no alternative left but to develop solar cells, and sil-
icon cells have found their place despite their cost. Because roughly
4 kcal of energy is available per gram of coal or hydrocarbon, this tech-
nique is of limited value at present. However, with enhanced improve-
ment, the renewable resources of flora and fauna may be sources of
direct energy when we run out of oil and coal and will also appear inex-
pensive under those circumstances.

1.9 Plant Cells Are Unique
Whether they are green algae (chlorella) or the higher plants, autotrophs
in general are gifted in nature to fix carbon dioxide and produce biomass.
In ecologic terms, these are producers. The dominant autotroph is pho-
totrophic. Photosynthesis has two distinct aspects: the light dependent
step, where photolysis of water takes place:

680 nm (52 kcal) 1

NADP H O ⎯⎯⎯⎯⎯⎯→ H NADPH O 2
2
2
8 kcal
ADP P ⎯⎯→ ATP
i
During this reaction, oxygen is set free, Co II is reduced and phosphory-
lation of ATP takes place. The photoenergy is chemically utilized twofold.
In the next step, through a very complex enzymic sequence, CO is
2
incorporated into the existing metabolite pool and higher carbohydrates
are biosynthesized. This step of the reaction finds variation in different
species; carbohydrates, proteins, and lipids are biosynthesized. Then, the
first part of the reaction makes the autotrophs unique. Light falling on
chloroplasts develops an electrical field across the membrane.
In the presence of the pigments in chloroplasts, the light energy is
trapped and activates water and lyses it. Ideally, water, if converted into
its elemental components, requires (at 25 C) 68.3 kcal/mol (from liquid)
or 57.8 kcal/mol (from vapor). Thermal energy is not sufficient to bring this
change. During photolysis, the plant pigment augments electron flow, and
the electron flow system culminates in the two energy-rich chemical prod-
ucts (reduced Co II, ATP, and O ), as already mentioned (see Fig. 1.7).
2
Lester Packer’s group at the University of California at Berkeley has
shown the steps of the pathway with chloroplasts from spinach leaves,