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How occure light and dark reaction in plant |
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Answer» https://www.toppr.com/guides/biology/photosynthesis-in-higher-plants/light-reaction/. Bhai here you can understand easily.... The light reaction of light dependent reaction occurs in the chloroplast of the mesophyll cells of the leaves. The chloroplasts are double-membraned cell organelles that are comprised of stacked disc-like structures known as thylakoids. The pigment, chlorophyll, which is required for the process is present on the membrane of these thylakoids and this is where the light reaction occurs.The Steps Involved in the Light ReactionThe main purpose of the light reaction is to generate organic energy molecules such as ATP and NADPH which are needed for the subsequent dark reaction.Chlorophyll absorbs the red and blue segment of the white light and photosynthesis occurs most efficiently at these wavelengths.When the light falls on the plant, the chlorophyll pigment absorbs this light and electrons in it gets excited.This process occurs in a complex protein system which is collectively called as a photosystem. There are two closely linked photosystems known as PSI and PSII.The chlorophyll pigments which are excited give up their electrons and to compensate for the loss of electrons, water is split to release four H+ ions and four electrons and O2. The electrons that are lost from the PSII enter into an electron transfer chain or ETC.The electrons finally reach the reaction centre where they combine with NADP+ and reduce it to NADPHWhile the electrons are taken care of, the built up of H+ ions inside the thylakoid lumen is of equal importance.The hydrogen ions building up inside the lumen creates a positive gradient and in the presence of the enzyme ATP synthetase, these H+ ions combine with the ADP in the nearby region to form ATP.The oxygen that is a waste product is released by the plant into the atmosphere and some of it is used in photorespiration if the plant needs to.To summarise the light reaction, we can write it down as the following reaction:2H2O + 2NADP+ + 3ADP + 3Pi → O2 + 2NADPH + 3ATPFor any plant performing photosynthesis, four factors influence this process. CO2, water, light, and chlorophyll are the raw materials for photosynthesis. But, in case of light dependent reaction or light reaction of photosynthesis, it is most influenced by presence or absence of light. The other three factors do not play a critical role in it. The "light-independent" or dark reactions happen in the stroma of the chloroplasts. This is also known as the Calvin Cycle. Since these processes can only happen in the chloroplast (a chlorophyll filled plastid in green plants), photosynthesis "light reaction" "light dependent" can only happen in green plants! |
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