Fungi can have one cell or many cells. Scientists once believed fungi belonged to the plant kingdom. However, at the cellular level, they have many traits in common with animals, as well as plants. For example, fungi have cell walls like plants, but their cell walls contain a protein called chitin, which is found in animals like beetles but not in plants. Microscopic examples include yeasts such as those that make beer, wine and cheese, as well as the organisms that cause athlete's foot and ringworm. Macroscopic examples include mushrooms and truffles.