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Photosynthetic Plants as Renewable Energy Sources 49

3. Photophosphorylation This is the stage of formation of ATP from
ADP

ADP Pi → ATP

2.3.2 Blackman’s reaction (dark reaction)
The dark reaction is independent of light. This reaction is purely enzy-
matic and is carried out in the stoma portion of the chloroplast. Ribulose-1,
5-diphosphate (RuDP), a pentose phosphate present in plant cells, acts
as the initial acceptor of CO and changes thereby into a very unstable
2
C . The latter is converted into 3-phosphoglyceric acid (3-PGA), which
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is transferred to 3-phosphoglyceraldehyde. For this reaction, ATP and
NADPH (produced in the light reaction) are necessary as cofactors.
2
Three molecules of RuDP combine with three molecules of CO to give
2
rise to six molecules of PGA. Three molecules of RuDP utilized initially
as CO acceptors are regenerated by five molecules of phosphoglycer-
2
aldehyde through different intermediates like xylulose-5-phosphate and
ribulose-5-phosphate. The only molecule of phosphoglyceraldehyde is
converted into fructose-1,6-diphosphate, which may be transformed into
sucrose and starch through other reactions.

2.3.3 Efficiency of photosynthesis
While there are several factors that affect photosynthetic rate, the three
main factors are light intensity, carbon dioxide level, and temperature.
The net efficiency of photosynthesis is estimated by the net growth of
biosynthesis and the amount used for respiration. The requirements for
achieving high energy conversion are optimal temperature, light, nutri-
tion, leaf canopy, absence of photorespiration, and so forth. Many plant
species can be distinguished by the type of photosynthetic pathway they
utilize. Most plants utilize the C photosynthesis route. C determines
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the mass of carbon present in the plant material. Poplar, willow, wheat,
and most cereals are C plant species. Plants such as perennial grass,
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Miscanthus, sweet sorghum, maize, and artichoke all use the C route
4
of photosynthesis and accumulate significantly greater dry mass of
carbon than the C plants. Advances in crop production, agricultural
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techniques, and so forth have led to potential applications in low-cost bio-
mass production with high conversion efficiencies. Further, introduction
of alternative nonfood crops on surplus land and the use of biomass as a
sustainable and environmentally safe alternative make biomass an
attractive renewable energy resource. The potential of biomass energy
derived from forest and agricultural residues worldwide is estimated at
about 30 EJ/yr. For the adoption of biomass as a renewable energy