Enzymes are substance that act as a catalyst to speed up the rate of reaction in biological reaction. It will increase the rate of reaction but enzyme will never being used up. Enzymes are proteins that made of living things. Enzyme act as a catalyst for their own reaction from plants, animal, human and microbes such as bacteria/fungi. For microbes, most of the enzyme work around 40o c and the PH values is not far from PH 7. Different enzyme will have specific PH values and temperature to react in the reaction. For example, When the temperature increase, the rate of reaction also will increase but when the temperature is too high, the enzyme will denatured. Most of the enzyme will denatured above 45o c. When the temperature is too low, enzyme will become inactive. Different types of enzyme will work best with different PH values. To give an example, enzyme in the stomach will work best with the optimum PH 2. How does enzymes act as a catalyst and react in the reaction? There is a condition to start the reaction which is the enzyme molecule must fit with the reactant molecule. After that, the reactant molecule will being break down by the enzyme molecule. This does not need to provide energy by heating. When the decomposition is complete, the product molecule will move away but the enzyme molecule will remain the same, another new reactant molecule will take place and start the reaction again. There are a lot of uses of enzyme such as respiration, processing food and more others. The enzyme will increase the rate of reaction by decreasing the activation energy required for the reaction to occur. Enzyme can produce yeast to help the conversion of sugar/ starch to ethanol. For example, making bread, the yeast and the sugar is contain in the bread dough. In the room temperature, enzymes in the yeast catalyse the reaction, this is called fermentation. The chemical equation for this reaction is C?H??O? (aqueous) ? 2C2H5OH (aqueous) + 2CO2 (gas). The word equation is glucose (aqueous) ? ethanol (aqueous) + Carbon dioxide (gas). Not only making bread, producing alcoholic drink also one of the usage of enzyme, the theory of producing alcoholic drink and making bread is the same. The word equation can show that both of them have the same needs of enzyme, the word equation of producing alcoholic drink is sugar/starch Yeast? ethanol + carbon dioxide. Enzyme really help the human in the daily life a lot. It make human’s life easier. Another example, detergents which is the one have added enzyme in it called biological washing powder. It is very effective in removing stain such as food and blood, food and blood is protein-based substance and enzyme are protein so it can help to remove the stain on the cloth. Enzyme is very important to be used in different way but most important is in our human body. Enzyme can help to control the speed of the chemical reaction that held in our body. If without enzyme, the reaction will remain slow and it is hard to keep us alive. It also can help the cells in out body to communicate with each others and make the cells growth, life and death under the control by enzyme. For example, enzyme in gut helps to break down the larger molecule into a smaller pieces of molecules.Enzyme can work in the same condition where the scientist have found them. For example, AHA enzyme, this is the type of cold-adapted enzymes this type of enzyme can stay in a very low temperature. Extremophiles is a microbes that lives in a very harsh conditions, this type of enzyme will work in the same condition. Different types of enzyme can work in different condition, this will make human’s daily better and more advanced knowledges of science.