What makes a cake rise?

When making a cake you use baking powder or bicarbonate of soda, (or use self-raising flour, which already contains baking powder). Bicarbonate of soda contains carbon dioxide, which can be released as a gas by reacting it with acid or by heating. As the carbon dioxide is much bigger as a gas than it was in the bicarbonate of soda, it expands, makes bubbles in the cake mix and so makes the cake rise.Another way is to beat lots of air into things containing eggs, such as a soufflé. As you cook the beaten eggs the air trapped in the bubbles expands, making the soufflé rise. (The air bubbles contract again as it cools, which is why the soufflé sinks!)