Cell Respiration - 1
All cells must do work to stay alive and maintain their cellular environment.
energy needed for cell work comes from the bonds of ATP.
Cells obtain their ATP
by oxidizing organic molecules, a process called cellular respiration.
many organic molecules can be oxidized, glucose, a main product of
photosynthesis, is the primary fuel molecule for the cells of living organisms.
Every living organism, autotroph and heterotroph, must do cell respiration. In fact,
the metabolic pathways used in the process of cellular respiration are the same in
virtually all eukaryotic organisms as well as most prokaryotic organisms.
that organisms that do photosynthesis (or properly, manufacture their own fuel
molecules) are called autotrophs.
Heterotrophs obtain their fuel molecules
"pre-formed" by other organisms.
Animals, fungi and many protists are
heterotrophs, as are most bacteria.
Plants and some protists are autotrophs, as
are some bacteria.
Most eukaryotic organisms are aerobic (oxygen requiring).
respiration is required in order to obtain enough energy (ATP) from the
oxidations of fuel molecules for these organisms to survive.
In aerobic respiration
glucose is oxidized to water and carbon dioxide.
Oxygen is required as the final
electron acceptor for the oxidations.
Most organisms are obligate aerobic
O + 6CO
+ 686 kcal energy (ATP + Heat)
Not all cell respiration is aerobic.
All organisms do some type of anaerobic
respiration during times of oxygen deficit, although it may not be sufficient to
sustain the organism's ATP needs for many species.
Fuel molecules oxidized
without oxygen yield smaller amounts of ATP.
The fermentations involve the partial breakdown of glucose without using
Many prokaryotes have a variety of fermentation pathways, using a
number of different fuel molecules.
By definition, the end product for the
fermentations is an organic molecule.
In aerobic cellular respiration, the final
electron acceptor is oxygen, hence, the emphasis on oxygen in aerobic cell
In addition, some prokaryotes use anaerobic electron transfer
respiration pathways in which their final electron acceptor is an inorganic
molecule such as sulfate, iron, or nitrogen compounds.
Some organisms are obligate anaerobes.
They cannot survive in the presence
bacteria that cause botulism poisoning, tetanus and
gangrene are obligate anaerobes.
Other anaerobes are metabolic anaerobes;
they lack the enzymes needed to do aerobic cell respiration.
Many of our intestinal
bacteria, such as the
bacteria, are metabolic anaerobes.
organisms will survive nicely in the absence of oxygen but will do aerobic
respiration when oxygen is available.
Yeast organisms and
are two such