In this screencast video lecture, we will try to understand about the photosynthesis process that happens in the living organism. It is one of the important and primary carbon assimilation process that have been operating at the very base level of Earth. This can be carried out by the plant system or in the category of bacteria, it can be carried out by the sign of bacteria as well as other group of bacteria such as purple sulfur bacteria and green sulfur bacteria. Here in this process involves conversion of light energy into chemical energy and the organism that is carrying out this process is referred as a photosynthetic organisms. Organism that is carrying out this photosynthesis or commonly referred as a phototrust, they could be of a two kinds which I have already narrated. One is the purple and green sulfur bacteria that are commonly involved in the unoxygenic kind of photosynthesis process. Whereas, the other one is a sign of bacteria, all the and the green plants that are involved in the oxygenic way of photosynthesis. Here the difference between these two groups is existing there in the utilization of the reducing power. Whereas, the other two processes that is carbon fixation and energy generation are same to both the group of the organisms. If you look at into the unoxygenic group of photosynthetic organism, the electron is being available or obtained there from the reduced molecules such as hydrogen sulfide. Whereas, if you look at that into the oxygenic group of photosynthetic organism, the electrons are commonly obtained there by the photolysis of water. That in turn results the formation of oxygen. That is the reason why it is referred as a oxygenic photosynthesis. Whereas, in the other group, oxygen is not produced there. It is only oxidized form of other inorganic compounds are formed. So it is referred as an anoxygenic photosynthetic groups. For both this process, light is the only thing that is used as an energy. But it has been effectively intercepted and converted into chemical energy with the help of chlorophyll molecules or bacterial chlorophyll molecules. They are found to contain certain protein complexes that are known as a photochemical reaction centers which are intercepting the light and it is used for the production of generation of ATP and NADPH. This ATP and NADPH are further used there in the carbon fixation process. This could be very clearly explained in this diagram. If you look at the first step involved, production of ATP as well as NADPH. And this step is commonly referred as the energy and the reducing equal and synthesizing phase which commonly happens through photo phosphorylation process. The phase following this energy as well as reducing equal and synthesizing phase is the carbon reduction phase or carbon fixation phase. You can look at here the NADPH and ATP that is formed in the photo phosphorylation phase having utilized here for fixing carbon dioxide into cell carbon. Now we look at in some detail about the first phase that is the energy and reducing equal and synthesizing phase. It is operating there in the thylacoid membranes. This thylacoid membrane will be present there in the plant system that is inside the chloroplasts or else this thylacoid like membranes could be present there in the sino bacteria in which it can be taking place. Here it is analogous to the top of the oxidative phosphorylation that is the electron transport will be operating here and finally the ATP has been synthesized here. And this particular process will be commonly taking place only in the presence of light. That is the reason why the reaction involved here are all collectively referred as a light dependent reaction. What is the important reaction that will be taking place here? On the sun's light is intercepted by certain special photo systems here. Photo system 2 as well as photo system 1. They are involved in gathering the sunlight that helps in the splitting of the water molecule. That is photolysis of water as a result oxygen have been involved there. So this particular process of photo phosphorylation is referred as the oxygenic photosynthesis process. As oxygen have been involved there and it is commonly referred as the NAD cyclic photo phosphorylation. The reason is the electron that are being donated there in the photolysis process of water will not be again returning back into the system. This kind of non-cyclic photo phosphorylation is usually happening there in the plant system and also in the sino bacteria. Whereas another kind of a photo synthesis that is an oxygenic photosynthesis usually involves the cyclic photo phosphorylation process which would be commonly happening there in the organisms such as a purple sulfur bacteria as well as green sulfur bacteria or classical examples of this cyclic photo phosphorylation process. Here in this phosphorylation it involves the pigment of bacterial chlorophyll instead of chlorophyll that have been involved there in the oxygenic photosynthesis. Here again the reaction centers of the bacterial chlorophyll will get excited. Through sunlight and the electron will be moving there in a cyclic process and finally it reaches back to the bacterial chlorophyll molecule itself that is to its reaction center itself. But during this particular movement a cyclic flow of this electron results in the generation of a proton motif force that could be successfully harness for ATP synthesis. So far we have seen the points later to the photoposporylation which could be of a non-cyclic that is in the oxygenic photosynthetic organisms of sino bacteria and plant system and which could be of a cyclic when it is an anoxygenic photosynthesis process that operates in the green sulfur bacteria as well as purple sulfur bacteria. So whatever the process finally it gets a lot of energy as well as reducing equivalent that will be channelled into the next process that is for the carbon fixation process which usually involve the Kelvin-Benson cycle that is there in the sino bacteria as well as in the plant system whereas other cycles such as a hydroxy propionate pathway or acetal cohe pathway could be involved there in the anoxygenic photosynthetic corollizum. Usually the reactions of this carbon cycles are light independent reactions that is light energy is not necessarily required for the reactions. The total cycle can be divided into three steps. One involves carbon fixation and the next one involves reduction and production of other sugars or manufacturing of other sugars and the third step involves the regeneration of ribulose disposizione which is an essential molecule for the carbon fixation process to get continued. In an actual if you look at the light independent reaction or carbon fixation reaction, six molecules of carbon dioxide will be converted into one molecule of carbon that is glucose molecule. These glucose molecules further help in building the other molecules of the cell. One molecule of carbon dioxide combines there with its acceptor organic molecule that is ribulose disposizione. This helps in the forming of three phosphoglycerate molecules. In the next step, phosphoglycerate form is reduced into glycerolidate three phosphate. This involves a lot of ATP as well as NADPH that is reducing equivalent that have been previously synthesized by a cyclic or non-cyclic photoposporylation process. So finally, about one sixth of the glycerolidate three phosphate is used to make the sugars that is to make glucose and other sugars such as amylose or cell-lose there in the plant system. Whereas the five sixths of the glycerolidate three phosphate molecule are further processed by complex reactions in order to produce the ribulose monopospate. Again, with the help of ATP requirements, the ribulose monopospate is converted into ribulose disposizione, which is the actual molecule which accepts the carbon dioxide and involved in the continuation of the carbon cycling process.