Environmental Engineering Reference
In-Depth Information
Living Organisms
Autotrophic
Heterotrophic
Phototrophic
(photosynthesis)
and
Chemoautotrophic
organisms
Viruses
Bacteria
Fungi
Animals
Oxidation-Reduction
Figure 6.3
Autotrophic and heterotrophic organisms in relation to their means of obtaining energy.
Metabolism
Metabolism
refers to the bacteria's ability to grow in any environment. The
metabolic process refers to the chemical reactions that occur in living cells.
In this process,
anabolism
works to build up cell components and
catabolism
breaks down or changes the cell components from one form to another.
Metabolic reactions require energy, as does locomotion and the uptake of
nutrients. Many bacteria obtain their energy by processing chemicals from
the environment through
chemosynthesis
. Other bacteria obtain their energy
from sunlight through
photosynthesis
.
Chemosynthesis
Chemosynthesis is the synthesis of organic substances such as food nutrients
using the energy of chemical reactions. A bacterium that obtains its carbon
from carbon dioxide is called
autotrophic
. Bacteria that obtain carbon through
organic compounds are called
heterotrophic
(see
Figure 6.3
).
Autotrophic Bacteria
Organisms that can synthesize organic molecules necessary for growth from
inorganic compounds using light or another source of energy are
autotrophs
.
For their carbon requirements, autotrophs are able to use (fix) carbon dioxide
to form complex organic compounds.
Heterotrophic Bacteria
Most bacteria are not autotrophic. They cannot use carbon dioxide as a major
source of carbon and therefore must rely upon the presence of more reduced,
complex molecules (mostly derived from other organisms) for their carbon
