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Photosynthesis, the reverse of respiration

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Photosynthesis, the reverse of respiration Jugal Vansia In some aspects, I would agree that photosynthesis is in fact the reverse of respiration, as by looking at the two equations: Photosynthesis: 6CO2 + 6H2O -----------> C6H12O6 + 6O2 Respiration: C6H12O6 + 6O2 -----------> 6CO2 + 6H2O But as we look at them from a more accurate angle, many aspects of photosynthesis and respiration differ, as will be discussed below. We can surely understand that photosynthesis and respiration are not exactly the reverse of each other as they involve different processes. But these processes share both similarities and differences. The most obvious differences in the processes are the energy sources, Photosynthesis uses light or carbon dioxide as its energy sources while respiration requires oxygen and carbohydrate as its energy sources. Photosynthesis involves the conversion of light energy to chemical energy, which occurs in the chloroplasts of plants, while respiration involves the conversion of chemical energy to metabolic energy, which occurs in mitochondria. These conversions of energy require different pigments/proteins like chlorophyll in chloroplasts, and cytochromes in the membranes of mitochondria. Photosynthesis has two phases, the light and dark stages. ...read more.


The second process of photosynthesis is the dark stage and occurs the stroma of the chloroplasts. It is called this, as it does not require light to occur. The process that occurs is called the Calvin Cycle. Here, carbon dioxide from the atmosphere diffuses into the cytoplasm of the cells and combines with the 5-carbon compound called ribulose bisphosphate (RuBP) and form an unstable 6-carbon compound. This compound then breaks down into two 3-carbon molecules of glycerate-3-phosphate (GP). ATP produced from the light stage is used to convert GP into glyceraldehyde 3-phosphate (GALP) or triose phosphate. Reduced NADP from the light stage is also required for this conversion, this leaves NADP+, which returns to the light stage to accept more hydrogen. Pairs of this triose phosphate combine to form an intermediate hexose sugar which is then polymerised to form starch, which is stored by the plant. But some triose phosphate is used to regenerate RuBP, using more ATP from the light stage. Respiration involves the three main stages of Glycolysis, The Krebs Cycle and the Electron Transport System. In Glycolysis, a hexose sugar, usually glucose is broken down into two molecules of the 3-carbon compound private or pyruvic acid. ...read more.


But each process uses the electron transport chains in different ways. In photosynthesis, the photosystems absorb light and release excited electrons which are then taken to the electron transport chains via electron acceptors. In respiration, the electrons come from the hydrolysis of water, which is sent along the electron carriers, giving out its energy as it does so, providing energy for the formation of ATP. Both processes use NADP as reducing an agent, respiration uses it to carry hydrogen to the electron transport chains, while photosynthesis uses it to reduce GP to triose phosphate. They both use ATP at certain stages of the reactions, and both make it via phosphorylation. In respiration, ATP is used to begin the reactions by providing the energy required, in photosynthesis, it is made during the light stage and used later in the dark stage. ` The use of glucose is also a reverse in the processes. Photosynthesis produces glucose and may store it as starch. Respiration uses glucose, breaking it down by glycolysis to get the energy for the process. In both cases however, and intermediate 3-carbon compound is formed. And so as we can see, only certain areas of the reactions are considered to be reversed, but others are clearly different. ...read more.

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