One’s “Bread and Butter” means the major occupation which provides him the sustenance for life. “breaking bread” is a community custom which is sharing the food and sitting together. It is thus more than eating but a way to bring the members of a community closer to one another. The importance of bread cannot be overemphasized. Primitive man was a nomad and it was the wheat grass for which womenfolk are credited to have grown, which gave the man a reason to stay put at a place and bring the stability in the life which was almost akin to animals. It provided him with spare time in which to hone his skills and rise above the animals. When he discovered the fire, he learned to cook and roast and thus bread must have been discovered.
Imagine a continuum of breads, ranging from the thinnest flat breads to the fluffiest brioche. Some are amazingly simple: Matzoh, for example, is nothing more than flour and water, baked until crisp. Raised breads, on the other hand, involve the complex interactions between flour and the leaveners that give them their porous, tender quality.
Leaveners come in two main forms: baking powder or soda and yeast.
Baking powder or baking soda is used for faster results as it is based on the chemical reactions of the soda with acidic substances present or released during heating and resulted in the production of carbon dioxide necessary to inflate dough or batter. Baking powder and baking soda are used to leaven baked goods that have a delicate structure, ones that rise quickly as carbon dioxide is produced, such as quick breads like cornbread and biscuits.
Yeast, on the other hand, is a live, single-celled fungus. There are about 160 species of yeast, and many of them live all around us. It is stored in the optimum conditions and activated by availability of sugars present in the milled grains. They release carbon dioxide which makes the bread rise. The reactions are slow in comparison to the baking soda.
Leavening will make the bubbles for sure but some structure is required to contain these bubble and stop them from leaving. This is done by glutton which forms a three dimensional network and trap the produced carbon dioxide. Besides this there is plenty of starch present in the grains. This is attacked by enzymes which break it into the sugars, the food for the yeast to consume and release carbon dioxide and also help absorb the moisture. This is the chemistry behind making of the bread.