 fermentation, first the contents, definition of fermentation, types of fermentation, alcoholic fermentation, latex fermentation, and why there is a need for fermentation. So first the fermentation. So fermentation is basically the process by which the pyruvate which is produced during glycolysis is further metabolized in the absence of oxygen. Students, if I clear it a little bit, most students consider glycolysis as fermentation. Basically, glycolysis is an energy production step in cells in which glucose is broken down into pyruvate. Now when pyruvate is formed, then the cell has two options, conditions. The first condition is that oxygen is available. If this oxygen is available, then this pyruvate will be taken into the crab cycle. And it will produce further energy in the crab cycle. The crab cycle will run, the electron transport will run, the chain will run. So this is how aerobic respiration will run. But if oxygen is not available, there is anaerobic environment, then in anaerobic environment, pyruvate is converted into electric acid or ethanol or alcohol. So the process of pyruvate converted into electric acid or alcohol is called fermentation. So if we look at the reaction diagram of the ovaryl, then basically pyruvate plus NADH, NADH is also produced during the glycolysis. So when pyruvate and NADH are reacting together, then pyruvate is converted into electric acid or ethanol. So both of them will be converted into a reduced compound. And NADH is converted into NAD. In the last space, NADH is converted to NAD. This is basically the special importance of fermentation. Types of fermentation. Just like we said that if oxygen is not available, then pyruvate which is formed during the glycolysis either has to be converted into electric acid or alcohol. Similarly, if an organism is formed by pyruvate with electric acid, then we will say that electric acid fermentation is taking place. And if an alcohol is formed by pyruvate in a cell, then we will say that it is alcoholic fermentation. So we will consider the type of fermentation that will be made. So first the electric acid fermentation. So electric acid fermentation is actually the process during which pyruvate is converted into lactate or lactate acid. I have used the word lactate from here itself. So when you read books or often you will see that you will get very less electric acid. Often you will get lactate. Why? Because in living cells, the acids are ionized and come into the form of the acid. Like from the lactate acid, it becomes lactate. So in the process of lactate acid fermentation, pyruvate is converted into the lactate acid. Now in this process, when the lactate acid is formed by pyruvate, then NADH is converted into NAD. That is, two electrons from NADH will also go to lactate acid. Similarly, hydrogen ions will also go to lactate acid. NADH's electrons and hydrogen ions, both will get to lactate acid and NADH will be converted into NAD. And pyruvate will also be converted into lactate acid. For example, in lactate acid fermentation, in bacteria, lactobacillus, which we eat yogurt or curd, in this yogurt, there is lactobacillus. What is lactobacillus? When we do lactate acid fermentation, we convert glucose or carbohydrate into lactate acid. This means that when there is lactate acid fermentation in bacteria, we can use yogurt or other things. The second important thing is in animals. When we exercise, especially in humans, during exercise, our muscles feel that they are pulled. It is a very serious pain. Especially if you start going to the gym in the beginning, or you start exercising and suddenly start running fast, then your muscles become very painful. Why muscles are painful? When we exercise in the gym or we are running or playing, if we do not practice, then why do our muscles start pain? The reason is that when we do heavy exercise, our muscles need energy. This energy oxygen reaches the muscles in the working order due to which the energy will be produced through aerobic respiration. In these conditions, our muscles start an aerobic respiration. In the muscles, lactate acid is produced. Now lactate acid, which is acid, is painful. Later, the lactate acid is converted into glucose. But as long as the lactate acid remains, we were feeling painful. The pain will continue to feel. In the muscles of our animals and bacteria, the lactate acid fermentation occurs. Here is an example of this. The reaction of lactate acid fermentation is pyruvate, which means that when oxygen is not present in the cells, then pyruvate is converted into lactate. And in this, NADH, NADH's electrons and hydrogens will go to the lactate acid. Here you can see that it is written very clearly. Lactate is also written along with lactate acid. These are the two words used. When lactate is a common word used, we will show different reactions. The second type of fermentation is alcoholic fermentation. The word indicates that instead of lactate acid, the pyruvate will be converted into alcohol. This process is called alcoholic fermentation. This type of alcohol is specifically ethanol. When pyruvate is converted into ethanol, then it is called alcoholic fermentation. Again, what will happen during this process? Pyruvate is a three-carbon molecule. The alcohol that needs to be made is two-carbon. This means that one carbon of pyruvate will come out of the carbon dioxide. This means that there will be de-carboxylation and de-carboxylation of pyruvate. One carbon dioxide will come out of the pyruvate. The second important thing will be that NADH will give its electron and hydrogen ions to alcohol and it will be converted into NAD. For example, we eat all the bakery products like cakes and different types of bakery items. All the bakery items are made through alcoholic fermentation. The raw material of the bakery is mixed with yeast and it is kept overnight for a special time. The yeast fermentation will be made through alcoholic fermentation. After baking, when it is cooked in the furnace, then the alcohol evaporates and if you look at the bakery items, you can see the spaces and holes in the bakery items. They are not compact at all. If you look at it, it is a granular form. There are spaces in between. Those spaces show that there was a carbon dioxide and alcohol that evaporated and the space remained. Here we have the reaction of alcoholic fermentation. You can see the reaction of the alcoholic fermentation. The pyruvate is 3-carbon and the ethanol is 2-carbon molecule. Now the alcoholic fermentation will be in two steps. There will be decarboxylation. The carbon dioxide molecule will come out of here. CO2 will come out of here. And we will have acetaldehyde. This will be the decarboxylation step. The second step is that the NADH will be called as a reduction step. As a reduction step, we will get hydrogen ion. And acetaldehyde is converted into ethanol. Why fermentation is there? You have seen that there is no production of ATP or alcohol in the fermentation. So what is the need of fermentation? After simple glycolysis, pyruvate does not remain in the cell. The answer is that if we look at glycolysis more, then glycolysis is being utilized here. When glycerol D-hydre phosphate becomes 1-3-20-phosphoglycerate, reaction number 6. We need NAD on that step. NAD plus NAD positive. Now when glycolysis goes into the cell, all NADs convert into NADH. All the NADs converted into NADH. When NADs are not available, it will be difficult to continue glycolysis. Glycolysis will stop. Glycolysis also means that energy production will stop in the cell. So glycolysis has to continue every time. Now what will happen in this case? These fermentation processes convert NADH into NAD. The actual use of fermentation is regeneration of NAD from NADH.