Fungi are a group of heterotrophic eukaryotic organisms that provide a variety of functions. Some, such as yeast, use fermentation to break down carbohydrates into alcohol and release carbon dioxide. This helps bread to rise, and to make alcoholic beverages such as champagne and beer. Mushrooms are another example of fungi which are classified as decomposers--they help to break down organic molecules. In addition to making food, they are also responsible for producing a variety of antibiotics (such as penicillin) and can cause diseases such as yeast infections and athlete's foot.