Releasing Energy From Food: Cellular Respiration
I. How do organisms transform energy to maintain life?
A. Organisms release energy from carbohydrates, capturing it to do cell work.
• Organisms, such as plants and humans, use a process called cellular respiration to
release the energy stored in carbohydrates, specifically glucose, and the energy is
used to power the reactions characteristic of life
• Aerobic cellular respiration is so named because the last electron acceptor in the
process is oxygen
• Aerobic cellular respiration uses oxygen and produces carbon dioxide
• Certain bacteria and yeasts use anaerobic electron transport or fermentation, which
does not require oxygen, to produce ATP
• In anaerobic electron transport, other compounds, such as nitrate or sulfate, are
used as the terminal electron acceptors
• Fermentation consists of glycolysis and one or two additional reactions, in which
the atoms in the glucose molecule are rearranged, with the release of a small
amount of energy
• Fermentation requires much more glucose than does aerobic or anaerobic
• Cells that utilize fermentation produce a variety of byproducts, including carbon
dioxide (yeasts), alcohol (yeasts), and lactic acid (human muscle cells)
II. Hoe do organisms release energy from food?
A. During aerobic cellular respiration, glucose is broken down, yielding
• The overall summary reaction of cellular respiration:
Glucose + 6 oxygen 6 carbon dioxide + 6 water
• This is an exergonic reaction that releases enough energy to produce 36 molecules
• The ATP that is produced is available to power any of the endergonic reactions
used by the cell to do work
• The complex series of reactions of cellular respiration can be divided into three
B. Food is converted into substrates that can enter the pathways of aerobic
III. What are the chemical pathways that release energy from glucose?
A. Some energy released from glucose is captured in ATP molecules during
B. The remaining energy in glucose is captured during the Krebs cycle.
C. The electron transport chain produces ATP from reduced electron carriers
D. Fermentation takes place without oxygen.