Photosynthesis and respiration are two fundamental biological processes. Compare and contrast these two processes

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Photosynthesis and respiration are two fundamental biological processes. Compare and contrast these two processes. [MAY, 2002] Photosynthesis and respiration both involve many reactions and a variety of enzymes. Thus both are affected by temperature. Although both occur within membrane-bound organelles, aerobic respiration occurs within the mitochondrion and photosynthesis within the chloroplast. Respiration occurs in all organisms while photosynthesis occurs only in autotrophic ones. Photosynthesis requires light energy to proceed whereas respiration does not. In photosynthesis light energy is converted into chemical energy in the form of organic molecules, mainly carbohydrates. In respiration glucose, fats or amino acids are used to release energy in the form of heat and ATP. ATP is also released in photosynthesis during photophosphorylation. Chemiosmosis is the process involved in ATP release in both respiration and photosynthesis. For ATP to be released by chemiosmosis, a gradient of hydrogen ions must be present across a membrane. Hydrogen ions are pumped into the intermembrane space in mitochondria and inside the thylakoid interior in chloroplasts. A molecule of ATP is released as three hydrogen ions move down their concentration gradient through a complex channel protein which is attached to ATPsynthase. The energy to pump the hydrogen ions is obtained from energy released by high-energy electrons as they move down an electron transport chain (ETC). Both photosynthesis and respiration involve ETC to carry high- energy electrons from one carrier to the next. Cytochromes are the components of the electron transport chains, but these differ in the two processes being compared. Cytochrome f is part of the ETC in photosynthesis while a, b and c in respiration. There are two sets of ETC in photosynthesis while only one in respiration. The electron which is depleted of its energy is accepted by oxygen in respiration but by NADP in photosynthesis. In both processes,