Biochemistry is the study of the chemistry of living organisms, of the
ways in which food is used to serve all the many needs of the body.
Biochemistry is closely connected with nutrition, the study of the types
and amounts of various materials required in the diet. Biochemistry is
also inextricably int rtwined with endo- crinology, the study of
hormones, for most of the hormones exert their actions by altering the
behaviour of chemical reactions within the body. The central problem in
biochemistry is that of the supply of energy. Energy is needed for a
multitude of purposes of which muscular activity is the best known.
Energy is required for digestion, and for the functioning of the kidney,
the liver, the brain and all the other organs in the body. Energy is
also essential for the building up of the complex organic molecules of
which the body is con- structed. Ultimately, most of the energy utilized
on earth comes from the sun. Plants are able to tap this energy source
directly by the process of photosynthesis. By using pigments, notably
the green chlorophyll, plants can trap the energy of sunlight and use it
to build up complex substances such as fat, carbohydrate, protein and
nucleic acids. The only raw materials required are carbon dioxide, water
and simple inorganic substances such as nitrates which can be extracted
from the soil.