Carbon
Cycle -The
most
important
element
in
the
biological
realm
and
a
component
of
an
cell
structures
is
carbon.
It
constitutes
about
50
per
cent
of
all
living
organisms
and
undergoes
a
cyclic
change
from
an
oxidized
to
a
reduced
state.
Carbon
dioxide
is
reduced
into
organic
carbon
compounds
mainly
by
the
process
of
photosynthesis.
Green
plants
and
the
photosynthetic
algae
are
the
most
important
agents
of
CO2
fixation.
It
is
estimated
that
about
1.3
X
1014
kg
CO2
is
fixed
annually
in
the
biosphere.
To
a
lesser
extent,
CO2
is
also
fixed
through
the
agency
of
photosynthetic
bacteria
and
certain
other
chemolithotrophs
the
carbon
cycle
which
revolves
around
CO2
fixation.
