LYCOS RETRIEVER 
Photosynthesis
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Photosynthesis is a two stage process. The first process is the Light Dependent Process (Light Reactions), requires the direct energy of light to make energy carrier molecules that are used in the second process. The Light Independent Process (or Dark Reactions) occurs when the products of the Light Reaction are used to form C-C covalent bonds of carbohydrates. The Dark Reactions can usually occur in the dark, if the energy carriers from the light process are present. Recent evidence suggests that a major enzyme of the Dark Reaction is indirectly stimulated by light... the term Dark Reaction is somewhat of a misnomer. The Light Reactions occur in the grana and the Dark Reactions take place in the stroma of the chloroplasts.
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Photosynthesis is the physico-chemical process by which plants, algae and photosynthetic bacteria use light energy to drive the synthesis of organic compounds. In plants, algae and certain types of bacteria, the photosynthetic process results in the release of molecular oxygen and the removal of carbon dioxide from the atmosphere that is used to synthesize carbohydrates (oxygenic photosynthesis). Other types of bacteria use light energy to create organic compounds but do not produce oxygen (anoxygenic photosynthesis). Photosynthesis provides the energy and reduced carbon required for the survival of virtually all life on our planet, as well as the molecular oxygen necessary for the survival of oxygen consuming organisms1 . In addition, the fossil fuels currently being burned to provide energy for human activity were produced by ancient photosynthetic organisms. Although photosynthesis occurs in cells or organelles that are typically only a few microns across, the process has a profound impact on the earth's atmosphere and climate. Each year more than 10% of the total atmospheric carbon dioxide is reduced to carbohydrate by photosynthetic organisms.
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Photosynthesis uses the energy of sunlight to produce sugars and other organic molecules. These molecules in turn serve as food for other organisms. Many of these organisms carry out respiration, a process that uses O2 to form CO2 from the same carbon atoms that had been taken up as CO2 and converted into sugars by photosynthesis. In the process, the organisms that respire obtain the chemical bond energy that they need to survive. The first cells on the earth are thought to have been capable of neither photosynthesis nor respiration (see Chapter 14). However, photosynthesis must have preceded respiration on the earth, since there is strong evidence that billions of years of photosynthesis were required before O2 had been released in sufficient quantity to create an atmosphere rich in this gas to support respiration.
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Photosynthesis occurs in green plants, seaweeds, algae, and certain bacteria. These organisms are veritable sugar factories, producing millions of new glucose molecules per second. Plants use much of this glucose, a carbohydrate, as an energy source to build leaves, flowers, fruits, and seeds. They ... convert glucose to cellulose, the structural material used in their cell walls. Most plants produce more glucose than they use, however, and they store it in the form of starch and other carbohydrates in roots, stems, and leaves. The plants can then draw on these reserves for extra energy or building materials.
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Photosynthesis is carried out in two steps, first in two light-dependent photosytems and then in a carbon fixation cycle (Calvin Cycle). Through this process, the plant is able to convert sunlight, water, and CO2 into glucose and ATP. As a byproduct of this process, O2 is released. The plant's ability to convert water and CO2 into glucose and O2 ... provides great benefit for animal species that depend on glucose for energy. The photosynthetic reaction can be summarized as follows:
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Photosynthesis is divided into two sets of reactions: the light-dependent (light) reactions and the light-independent (dark) reactions. As their names imply, the first set depends directly on light, whereas the second set does not. Nevertheless, even the dark reactions will cease if the plants are deprived of light for too long because they rely on the products of the light reactions.
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Photosynthesis