Protista is a biological kingdom proposed by Ernst Haeckel in $${}1866$$ specifically to classify unicellular organisms. This addition expanded the traditional tree of life beyond just the animal and plant kingdoms.

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Ernst Haeckel was a German biologist, philosopher, and physician who expanded upon the two main branches of Linnaeus's tree of life (the animal and plant kingdoms). In $${}1866$$, he proposed the addition of a third kingdom, Protista, for unicellular organisms, and later suggested a fourth kingdom, Monera, for unicellular organisms whose cells lack nuclei, such as bacteria.

Ernst Haeckel

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Microbiology covers the scope and sequence requirements for a single-semester microbiology course for non-majors. The book presents the core concepts of microbiology with a focus on applications for careers in allied health. The pedagogical features of the text make the material interesting and accessible while maintaining the career-application focus and scientific rigor inherent in the subject matter. Microbiology’s art program enhances students’ understanding of concepts through clear and effective illustrations, diagrams, and photographs.

Microbiology is produced through a collaborative publishing agreement between OpenStax and the American Society for Microbiology Press. The book aligns with the curriculum guidelines of the American Society for Microbiology.

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Protista (Kingdom)

Monera is a biological kingdom proposed by Ernst Haeckel to classify unicellular organisms whose cells lack nuclei, such as bacteria. Haeckel introduced this fourth kingdom following his earlier addition of the Protista kingdom to the tree of life.

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