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BIO 2 - Cell Respiration 1 All cells must do work to stay...

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Cell Respiration - 1 All cells must do work to stay alive and maintain an ordered cellular environment. Movement of substances through membranes, manufacture of the organic molecules needed for structure and metabolism and cellular movement are some of the activities that require energy in each cell. Cell growth, development and reproduction all require energy. Cells obtain the energy to do work by oxidizing organic molecules, a process called cellular respiration . Although many organic molecules can be oxidized, glucose, the main product of photosynthesis, is the primary fuel molecule for the cells of living organisms. 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 use to make molecules of ATP . Both autotrophs and heterotrophs must do cell respiration. In fact, the metabolic pathways used in the process of cellular respiration are the same in virtually all eukaryotic organisms. Recall 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 many bacteria. Plants and some protists are autotrophs, as are some bacteria. The metabolic pathways of cell respiration are variable, depending on the type of organism, the enzymes the organism has, and what the final product molecule in the cell respiration process is. We will focus on the metabolism of glucose in cell respiration, but we shall also discuss how alternative fuel molecules fit into the cell respiration. Most eukaryotic organisms are aerobic (oxygen requiring). In aerobic cellular respiration, which is the complete metabolism of glucose, electrons removed from glucose move down an electron transport system to a final electron acceptor, oxygen , hence, the emphasis on oxygen in cell respiration. Most organisms are obligate aerobes . They cannot survive without the oxygen needed for aerobic cell respiration. For complete aerobic respiration, glucose is broken down into water and carbon dioxide. This process requires oxygen. C 6 H 12 O 6 + 6O 2 Æ 6H 2 O + 6CO 2 + 686*kcal (ATP + Heat) {*720kcal within cells ( G= -720kcal)}
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Cell Respiration - 2 Not all cell respiration is aerobic. Organisms that do cell respiration without oxygen are said to be anaerobic . Fuel molecules can be oxidized without oxygen to yield smaller amounts of ATP. The fermentations involve the partial breakdown of glucose without using oxygen. Many prokaryotes have a variety of fermentation pathways, using a number of different fuel molecules. The final electron acceptor for the fermentations is an organic molecule.
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