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| 1. |
Discribe the photosynthesis in higher plants |
| Answer» Photosynthesis in higher plants involves the following processes:\tLight Reaction\tDark ReactionLight Reaction\tThis phenomenon occurs in the presence of light.\tThe pigment absorbs light and produces energy in the form of ATP.\tThe process involves- absorption of light, water splitting, the release of oxygen, and formation of ATP and NADPH.\tThe protein-bound pigment molecules form the light-harvesting complexes present within two photosystems- PS-I and PS-II. Each photosystem has a reaction centre consisting of chlorophyll a molecule, and antennae containing accessory pigments.\tThe reaction centre for PS-I is P-700 because the absorption peak for chlorophyll a is at 700 nm while that for PS-II is P-680 because the absorption peak for chlorophyll a is at 680 nm.PhotophosphorylationThe formation of ATP in the presence of sunlight is called photophosphorylation. It is of two types:\tNon-cyclic photophosphorylation\tCyclic photophosphorylationNon-cyclic Photophosphorylation\tPS-II absorbs light at a wavelength of 680 nm and causes excitation in the electrons. These excited electrons are accepted by an electron acceptor and transferred to the electron transport system.\tThe electrons from the electron transport system are transferred to the PS-I. At the same time, the electrons at PS-I receive a wavelength of 700 nm and get excited.\tAn electron from the electron acceptor is added to NADP+, which is then reduced to NADPH+ H+.\tThe electrons lost by PS-II does not return to it and hence named non-cyclic photophosphorylation.\tIn this, both the photosystems are involved.Cyclic Photophosphorylation\tIn cyclic photophosphorylation, only PS-I is involved.\tThe electrons circulate within the photosystem which results in a cyclic flow of electrons.\tThis only forms ATP and not NADPH+ H+.\xa0Water SplittingThe light-dependent splitting of water is called photolysis. This process is associated with PS-II in which manganese and chlorine play an important role. The electrons lost from P680 are replaced by the electrons formed in this process. A molecule of water splits to release oxygen upon the absorption of light by P680.Dark ReactionThis process occurs in the absence of light in the stroma of the chloroplasts.\xa0The following cycles are involved in the process:Calvin Cycle (C3 Cycle)This cycle involves the following steps:\tCarbon-fixation: Ribulose-1, 5-bisphosphate combines with carbon dioxide to fix it to a 3 carbon compound 3-phosphoglyceric acid. The enzyme RuBisCO is involved in the process.\tReduction: 2 molecules of ATP and NADPH fixes one molecule of carbon dioxide to form glyceraldehyde-3-phosphate.\tRegeneration: Some glyceraldehyde-3-phosphate molecules undergo a series of reactions to form glucose while the RuBP regenerates to continue the cycle. | |