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Unformatted text preview: Cell Respiration - 1 All cells need energy to stay alive and maintain an ordered cellular environment. In addition to the routine maintenance of the cell required for the cell to function, cell growth, development, and reproduction all require energy. Movement of materials through membranes often requires energy, as do intracellular movements and locomotion. Cells obtain the energy to do work by oxidizing organic "fuel" molecules, a process called cellular respiration*. In general, molecules rich in hydrocarbons are excellent sources for the oxidations of cell respiration because they have a source of hydrogen electrons that are readily oxidized, and we ultimately obtain our energy from those oxidized electrons. Although many organic molecules can be oxidized, glucose, the main product of photosynthesis, is the primary fuel molecule for the cells of living organisms; hence the pathways of cell respiration are commonly referred to as Glucose oxidation or Glucose metabolism. * The term, cellular respiration, is properly restricted to the aerobic respiratory pathways of glucose metabolism that occur in the mitochondria of eukaryotic organisms. The chemical end products, H 2 0 and CO 2 are inorganic. Fermentation is used to describe the respiratory processes that occur without the use of oxygen and have organic end products. Both aerobic respiration and fermentation start with Glycolysis, a cytoplasmic pathway that oxidizes glucose to the 3-carbon molecule, pyruvate. Anaerobic respiration is used by some prokaryotes whose respiratory pathways do not involve oxygen and have inorganic waste products. Cell respiration pathways are catabolic – the end products have less energy than the reactants. Some of the energy released during cell respiration is heat energy; the rest is used to make molecules of ATP. All organisms, autotrophs and heterotrophs, must have some cell respiratory pathway (aerobic, fermentation or an anaerobic respiration). Organisms that manufacture their own organic fuel molecules by the endergonic process of photosynthesis, or for a very few, chemosynthesis, are called autotrophs. Heterotrophs obtain their fuel molecules "pre-formed" by other organisms. Animals, fungi, many protists and many bacteria are heterotrophs. Plants and some protists are autotrophs, as are some bacteria, in particular, the cyanobacteria. However, both autotrophs and heterotrophs must do respiration. They differ only in how they obtain their fuel molecules needed for respiration. The cell respiration processes of all organisms have common elements: • Cell respiration is an exergonic process that produces ATP. • The chemical reactions of glucose metabolism involve metabolic oxidation- reduction pathways with electrons moving down an energy gradient....
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This document was uploaded on 01/06/2012.
- Winter '09