A catalyst is the substance that speeds up the rate of reaction by reducing the reaction’s activation energy. Enzymes are the catalysts that help to increase the rate of reaction in many biological and also chemical reactions. Therefore, option (a) is incorrect.
In the chemical reaction, the reactants get converted into products. The rate of formation of products in many reactions depends upon the presence of a suitable catalyst. Therefore, option (b) is incorrect.
A substrate is the substance that binds to the enzyme at a specific site. These substrates undergo a chemical change and they are converted into products. The binding of the substrate to the enzyme do not alter the structure of the enzyme. Therefore, option (c) is incorrect.
When the reaction occurs in the biological system, an enzyme plays a very important role in the completion of the reaction. It is in the biological system that reactant (substrate) attaches to the enzyme at the specific site called active site. Each enzyme is highly specific to a particular type of substrate. In the absence of active site or with altered active site, reaction will not proceed to the completion and the formation of products is hindered. Therefore, option (d) is correct.
Hence, in a chemical reaction, a reactant binds to an enzyme at a region known as (d) active site.