Protozoans are nonphotosynthetic, motile, unicellular eukaryotic organisms that inhabit diverse aquatic and terrestrial environments. While many live independently as free-living organisms, others are parasitic pathogens that cause disease in hosts, or beneficial symbionts that assist their hosts with metabolic functions.

"Animal-Like" Protozoans

Algae are autotrophic protists, existing as either unicellular or multicellular organisms, that play a key ecological role by producing approximately 70% of the oxygen and organic matter in aquatic environments.

"Plant-Like" Algae

Lichens are symbiotic associations between a fungus and a photosynthetic partner, which can be either an alga or a cyanobacterium. They are characteristically slow-growing organisms that can survive for centuries in a variety of habitats.

Lichens

Historically, protists have been informally categorized into three distinct groups based on their characteristics: the animal-like protozoans, the plant-like algae, and the fungus-like protists (such as water molds).

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Types of Parasites

A kingdom made up of single-celled eukaryotes that consume organic matter. Members of this kingdom are not believed to all share a common ancestor, but instead share ancestors with members of the Fungi, Animalia and Chromista kingdoms.

Protozoa (Kingdom)

Protists are a diverse, polyphyletic group of eukaryotic organisms that do not form a single formal taxon. They can be unicellular or multicellular and vary widely in their morphology, reproductive strategies, nutritional acquisition, and methods of locomotion, which may involve contractile vacuoles, cilia, flagella, pellicles, or pseudopodia, though some lack organelles like mitochondria. Their taxonomy is rapidly changing as relationships are reassessed using newer techniques, and they include significant pathogens and parasites.

Protists

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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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Multicellular organisms that can be parasitic or free living, unable to multiply while within humans (in adult form).

Helminths

Organisms that attach or burrow in to the skin for weeks to months long duration.

Ectoparasites

Groups of Protists

*Giardia lamblia* (also known as *G. intestinalis* or *G. duodenalis*) is a widespread flagellated protozoan pathogen within the Fornicata subgroup that lacks mitochondria and causes diarrheal illness (giardiasis). It is transmitted through fecal-contaminated water supplies, where it spreads via environmentally resistant cysts.

*Giardia lamblia*

Plankton are aquatic microorganisms that drift or float in water currents rather than swimming actively.

Plankton

Percolozoa is a phylum of eukaryotic protozoans that are classified as distant relatives of the supergroup Amoebozoa.

Percolozoa

Plasmodium is a genus of apicomplexan parasites that are transmitted through mosquito bites and cause malaria. In host blood cells, Plasmodium can be observed in different developmental stages, including the ring form, the young trophozoite, and the multinucleate schizont.

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