The kingdom of Protista consists of single-celled and multi-celled organisms that have a nucleus. Members of this kingdom are called “protists.” They include well-known one-celled creatures, such as the paramecium, amoeba and single-celled algae. Some of these creatures are very large, like kelp, which we usually think of as seaweed. Plants, fungi and animals probably evolved from protists millions of years ago, which is why it’s fitting that “protista” means “the very first.” Which of these things is a protist?

a. Mycoplasma pneumoniae, a single-celled bacterium without a nucleus that causes pneumonia

b. Euglena spirogyra, a single-celled algae with a nucleus and flagella, or flippers, that help it move around

c. Geotrichum candidum, a complex, multicellular fungus used to make cheese.

d. Apodemus sylvaticus, a complex, multicellular creature known as a wood mouse.