Metabolism 2

Metabolic reactions
occur continuously in every living
organism. (a) Relationships of some
metabolic activities. Some of the
nutrients provided by proper nutrition are used to synthesize needed
materials and cell parts; other nutrients are used as fuel for cellular
respiration, a process that captures
energy stored in food. This energy
is needed for synthesis and for
other forms of cellular work. Cellular respiration also requires oxygen,
which is provided by the process of
gas exchange. Wastes from the @115
such as carbon dioxide and water
must be excreted from the body.
(b) Like most organisms

Metabolism

In all living organisms chemical reactions take place that are essential to
nutrition, growth and repair of cells, and conversion of energy into usable
forms. The sum of all the chemical activities of the organism is called metabolism. Metabolic reactions occur continuously in every living organism
(Figure 1-3); when they cease, the organism dies.
Each individual cell of an organism constantly takes in new substances,
alters them chemically in a variety of ways, and builds new cellular

Specific Organization

The cell theory, one of the fundamental concepts of biology, states that all
living things are composed of basic units called cells and of cell products.
Although organisms (living things) vary greatly in size and appearance, all
(except the viruses‘) are composed of these small building blocks. Some of
the simplest organisms, such as bacteria, are unicellular; that is, they consist of a single cell. In contrast, the body of a human or an oak tree is made
of billions of cells. In such complex multicellular organisms the processes
of the entire organism depend on the coordinated functions of the constituent cells