A simple plant that is parasitic on other plants and animals. Included in this group are mildews, moulds, mushrooms, toadstools and yeasts. Unlike other plants, they do not contain the green pigment chlorophyll. Most of the world's 100,000 different species of fungus are harmless, or even beneficial, to humans. Yeasts are used in the preparation of food and drinks, and antibiotics are obtained from some fungi. A few, however, can cause fatal disease and illness in humans (see FUNGUS POISONING).