ergy that occur in living organisms.
Typically, the amount of energy that
an organism takes in (from food or
sunlight) is measured and divided
into the amount used for growth of
new tissues; that lost through death,
wastes, and (in plants) transpiration;
and that lost to the environment as
heat (through respiration).
biofuelA gaseous, liquid, or solid
fuel that contains an energy content
derived from a biological source. The
organic matter that makes up living
organisms provides a potential
source of trapped energy that is be-
ginning to be exploited to supply the
ever-increasing energy demand
around the world. An example of a
biofuel is rapeseed oil, which can be
used in place of diesel fuel in mod-
iÜed engines. The methyl ester of
this oil, rapeseed methyl ester (RME),
can be used in unmodiÜed diesel en-
gines and is sometimes known as
biodiesel. Other biofuels include
biogas and gasohol.
biogas A mixture of methane and
carbon dioxide resulting from the
anaerobic decomposition of such
waste materials as domestic, indus-
trial, and agricultural sewage. The de-
composition is carried out by
methanogenic bacteria; these oblig-
ate anaerobes produce methane, the
main component of biogas, which
can be collected and used as an en-
ergy source for domestic processes,
such as heating, cooking, and light-
ing. The production of biogas is car-
ried out in special digesters, which
are widely used in China and India.
As well as providing a source of fuel,
these systems also enable sewage,
which contains pathogenic bacteria,
to be digested, thereby removing the
danger to humans that could other-
wise result from untreated domestic
and agricultural waste.
bioinorganic chemistryBiochem-
istry involving compounds that con-
tain metal atoms or ions. Two
common examples of bioinorganic
compounds are haemoglobin (which
contains iron) and chlorophyll
(which contains magnesium). Many
enzymes contain metal atoms and
bioinorganics are important in a
number of biochemical processes, in-
cluding oxygen transport, electron
transfer, and protein folding.
bioluminescenceThe emission
of light without heat (see lumi-
nescence) by living organisms. The
phenomenon occurs in glow-worms
andÜreÛies, bacteria and fungi, and
in many deep-seaÜsh (among oth-
ers); in animals it may serve as a
means of protection (e.g. by disguis-
ing the shape of aÜsh) or species
recognition or it may provide mating
signals. The light is produced during
the oxidation of a compound called
luciferin(the composition of which
varies according to the species), the
reaction being catalysed by an en-
zyme, luciferase. Bioluminescence
may be continuous (e.g. in bacteria)
or intermittent (e.g. inÜreÛies).biomarkerA normal metabolite
that, when present in abnormal con-
centrations in certain bodyÛuids,
can indicate the presence of a partic-
ular disease or toxicological condi-
tion. For example, abnormal
concentrations of glucose in the
blood can be indicative of diabetes
mellitus (see insulin).biomoleculeAny molecule that is
involved in the maintenance and
metabolic processes of living organ-
isms (see metabolism). Biomolecules
include carbohydrate, lipid, protein,
nucleic acid, and water molecules;
some biomolecules are macromole-
cules.biopolymerA polymer that occurs69 biopolymer
b