Obtaining Food and Energy
Bacteria obtain energy and nutrients from a variety of different methods. Bacteria known
as decomposers break down wastes and dead organisms into smaller molecules to obtain
nutrients and energy.
Photosynthetic bacteria use the energy of the sun, together with carbon dioxide, to make
their own food (discussed in theCell Functionschapter). Briefly, in the presence of sun-
light, carbon dioxide and water is converted into glucose and oxygen. The glucose is then
converted into usable energy. Glucose is, in essence, the ”food” of the bacteria. An example
of photosynthetic bacteria iscyanobacteria,as seen inFigure8.6.
Figure 8.6: Cyanobacteria are photosynthetic bacteria. These bacteria carry out all the
reactions of photosynthesis within the cell membrane and in the cytoplasm; they do not
need chloroplasts. ( 10 )
Bacteria can also be chemotrophs.Chemotrophsobtain energy by breaking down chemical
compounds in their environment, such as nitrogen-containing ammonia. They do not use
the energy from the sun. This process is important, for example, for the cycling of nitrogen
through the environment. As nitrogen can not be made by living organisms, it must be
continually recycled. Organisms need nitrogen to make organic compounds, such as DNA.
Some bacteria depend on other organisms for survival. For example, mutualistic bacteria live
in the root nodules of legumes, such as pea plants, and make nitrogen available to the plants;
in this relationship both the bacteria and the plant benefit. Other bacteria are parasitic and