What is the reason behind the rising of bread dough?

Bread dough rises due to the growth of yeast cells in the dough. When yeast cells are added to the dough, they consume the sugar present in it and undergo a process called fermentation. During fermentation, carbon dioxide gas is released as a byproduct. The carbon dioxide gas gets trapped in the dough by the gluten which is formed by the proteins in the dough when they come in contact with water. The entrapment of carbon dioxide in the dough causes it to expand, resulting in the rise of the bread dough. The process of kneading also helps in developing the gluten network in the dough, which further enhances its ability to trap the carbon dioxide gas and contribute to the rise of the bread dough. Therefore, the growth of yeast cells and the entrapment of carbon dioxide gas by gluten are the main reasons behind the rise of bread dough.