Chap 9 Ap Bio
...their many tasks, living cells require energy from outside sources.
• Energy enters most ecosystems as sunlight and leaves as heat.
• Photosynthesis generates oxygen and organic molecules that the mitochondria of eukaryotes use as fuel for cellular respiration.
• Cells harvest the chemical energy stored in organic molecules and use it to regenerate ATP, the molecule that drives most cellular work.
• Respiration has three key pathways: glycolysis, the citric acid cycle, and oxidative phosphorylation.
A. The Principles of Energy Harvest
1. Cellular respiration and fermentation are catabolic, energy-yielding pathways.
• The arrangement of atoms of organic molecules represents potential energy.
• Enzymes catalyze the systematic degradation of organic molecules that are rich in energy to simpler waste products with less energy.
• Some of the released energy is used to do work; the rest is dissipated as heat.
• Catabolic metabolic pathways release the energy stored in complex organic molecules.
• One type of catabolic process, fermentation, leads to the partial degradation of sugars in the absence of oxygen.
• A more efficient and widespread catabolic process, cellular respiration, consumes oxygen as a reactant to complete the breakdown of a variety of organic molecules.
In eukaryotic cells, mitochondria are the site of most of the processes of cellular respiration.
• Cellular respiration is similar in broad principle to the combustion of gasoline in an automobile engine after oxygen is mixed with hydrocarbon fuel.
Food is the fuel for respiration. The exhaust is carbon dioxide and water.
• The overall process is:
organic compounds + O2 CO2 + H2O + energy (ATP + heat).
• Carbohydrates, fats, and proteins can all be used as the fuel, but it is most useful to consider glucose.
C6H12O6 + 6O2 6CO2 + 6H2O + Energy (ATP + heat)
• The catabolism...
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