Almost every organism you can see without a microscope -- and some microscopic organisms as well -- are examples of eukaryotes. Eukaryotes have many cellular characteristics that distinguish them from prokaryotes like bacteria. For example, all eukaryotes have complex organelles, including a cytoskeleton, a membrane-bound nucleus and other membrane-bound organelles like mitochondria, the Golgi apparatus and chloroplasts. They also have relatively large cells, generally much larger than bacterial cells. All protists, fungi, plants and animals are examples of eukaryotes.
Protists are one-celled eukaryotes. However, like every rule in biology, exceptions exist. Sometimes, various seaweeds are grouped with protists, even though they have many cells. The protists include a wide range of organisms. Some are not particularly closely related. In fact, genetics reveals that protists consist of at least ten groups equivalent to kingdoms. To put this in perspective, all animals, from worms to humans, belong to a single kingdom. Examples of protists include amoebas, parameciums and kelp. All algae, except blue-green algae (now known as cyanobacteria) are eukaryotes.
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.
All of the roughly 250,000 species of plants -- from simple mosses to complex flowering plants -- belong to the eukaryotes. Plant cells have cellulose-bearing cell walls and chloroplasts. Plants use chloroplasts to turn sunlight into fuel to produce oxygen for their cells. Plants produce more oxygen than they use, adding oxygen to the atmosphere.
All animals -- humans, house cats, arthropods, whales and fish -- also belong within the eukaryotes. In a scientific context, animals are sometimes called metazoans or members of the Kingdom Animalia. For people, this is the most familiar group of eukaryotes. Animals have cells with cell membranes, but no rigid cell walls like those of plants, fungi and some protists. As a group, they're generally more mobile and active than other eukaryote groups, though exceptions like corals exist.
- Tree of Life: Eukaryotes; Patrick Keaton et al.
- University of California Museum of Paleontology: Systematics of the Eukaryota
- University of California Museum of Paleontolgy: Introduction to the Plantae
- Elmhurst College: Chemistry 547: Carbohydrates -- Cellulose
- University of California Museum of Paleontology: Introduction to the Metazoa
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