Photosynthesis211S - Photosynthesis 1 The energy needed for...

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Photosynthesis - 1 The energy needed for life on our planet originates with the sun. As we have discussed, living organisms require a source of organic fuel molecules to provide energy for cell functioning. Organisms that can use energy from the sun and carbon from their physical surroundings to produce their own organic molecules, including fuel molecules, are autotrophs. The majority of autotrophs produce their organic molecules by the process of photosynthesis. Photosynthesis transforms light energy into chemical energy, and uses that chemical energy to produce organic molecules, typically glucose, from water and carbon dioxide. Most photosynthetic organisms (or photoautotrophs) are plants or protists that contain chlorophyll. Many prokaryotes are also photosynthetic. The cyanobacteria have chlorophyll pigments. Some bacteria, such as the purple sulfur bacteria, have different light-capturing pigments and photosynthetic mechanisms. They are studied in microbiology. Recall that heterotrophs are organisms that obtain their organic fuel molecules pre-formed from the environment. Animals, fungi, many protists and many bacteria are heterotrophs. Not all autotrophs are photosynthetic; a tiny proportion of living organisms, the chemoautotrophs, manufacture organic fuel molecules by chemosynthesis. Chemosynthetic autotrophs (or chemoautotrophs) use energy from chemical reactions involving inorganic atoms and molecules, such as S, Fe, H and N, to make organic compounds. Chemosynthesis sustains some deep seabed ecosystems that surround sulfur vents. To be complete, some green and purple non-sulfur bacteria are photoheterotrophs, using light to reduce organic compounds. Bacterial energy and carbon source versatility are discussed in microbiology. The products of photosynthesis, along with a number of inorganic atoms and molecules, are the basis for the biological molecules used for structure and metabolism for all living organisms as well as the fuel molecules we use in cell respiration. The process of photosynthesis also produces oxygen gas as a "by-product", the very same molecule that is used in aerobic cell respiration, without which most organisms on earth would not survive. Photosynthesis produces about 160 billion metric tons of carbohydrate annually, an amount most of us can't even imagine. Plants being efficient organisms use less than they produce and we depend on the plants "leftovers" for survival. This dependence, for humans, is greater than just obtaining food directly from an autotroph or processed through the food chain by a series of heterotrophs, many of which use tremendous amounts of photosynthetic output to make those conversions. Our lifestyles depend on products of or past products of photosynthesis, too. As you read and learn the photosynthetic pathways, consider that you would not be here without it!
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Photosynthesis - 2 The Process of Photosynthesis As stated, photosynthesis involves the transformation of light energy to chemical energy.
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Photosynthesis211S - Photosynthesis 1 The energy needed for...

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