It is easy for scientists to identify the difference between a cow and a lizard, or a lobster and an elephant. Biologists and taxonomists, however, face a more challenging problem when it comes to classifying fungi, protists, and algae. And although these organisms have existed for millions of years, scientists are constantly making new discoveries that raise questions about how they should be categorized. In this book readers will learn about these astoundingly varied life-forms and why their evolutionary development and ecological benefits make them fascinating subjects of biological and biochemical study.

There are about 80,000 described species of fungi. Among them are forms known as mushrooms, molds, yeasts, and rusts. Whereas some fungi exist as plant and animal parasites, others are free-living organisms found in water or soil. Because fungi have membrane bound organelles and nuclei in each cell, they are considered eukaryotic organisms. (Eukaryotic organisms are distinguished from prokaryotic organisms, such as bacteria, which lack distinct organelles). In addition, fungi lack chlorophyll, the green pigment found in plants that allows photosynthesis to take place. Because of this distinction, fungi are classi- fied separately from plants.

Some fungi are beneficial to humans. For example, mushrooms such as morels and truffles are considered great delicacies. Yeasts, which are single celled fungi, aid in the process of creating bread and beer. Likewise, molds are used in the production of certain cheeses, such as Roquefort and Camembert. Fungi are also important ecologically as they help break down organic matter and release essential elements, such as carbon and oxygen, into the atmosphere. Some fungi provide medical benefits and have advanced the fields of cell biology and biochemistry.