Energy is required to maintain life. All organisms have processes that utilize
energy sources to maintain high levels of organization.

Supporting Ideas:
1. Organisms utilize a series of cyclic energy conversion reactions to meet their
needs. Autotrophs convert energy from the sun or energy from inorganic
compounds into energy-rich organic compounds. Heterotrophs obtain energy by
consuming energy-rich organic compounds from other organisms.
2. Experiments have shown that chlorophyll and other pigments in autotrophs
absorb light energy and are able to transfer the energy to complex organic
reactions.
3. Photosynthesis in autotrophs includes a light-dependent stage in which energy is
captured, Adenosine triphosphate (ATP) is generated, and free oxygen is
released. In the light-independent stage (Calvin cycle), the energy is used to
make glucose from carbon dioxide.
4. In cells, ATP acts as an energy-transferring molecule that is repeatedly built up
and broken down.
5. The products of photosynthesis provide the raw materials for cellular respiration
and the products of cellular respiration provide the materials for photosynthesis.
6. During cellular respiration, all organisms obtain energy by breaking down the
complex chemical compounds in foods and by synthesizing ATP molecules.
7. In the absence of oxygen, ATP can still be produced through glycolysis and
fermentation.
8. Aerobic respiration produces more ATP for cell activity than does anaerobic
respiration.