Summary

Protists are a diverse, polyphyletic group of eukaryotic organisms.
Protists may be unicellular or multicellular. They vary in how they get their nutrition, morphology, method of locomotion, and mode of reproduction.
Important structures of protists include contractile vacuoles, cilia, flagella, pellicles, and pseudopodia; some lack organelles such as mitochondria.
Taxonomy of protists is changing rapidly as relationships are reassessed using newer techniques.
The protists include important pathogens and parasites.

Helminth parasites are included within the study of microbiology because they are often identified by looking for microscopic eggs and larvae.
The two major groups of helminth parasites are the roundworms (Nematoda) and the flatworms (Platyhelminthes).
Nematodes are common intestinal parasites often transmitted through undercooked foods, although they are also found in other environments.
Platyhelminths include tapeworms and flukes, which are often transmitted through undercooked meat.

The fungi include diverse saprotrophic eukaryotic organisms with chitin cell walls
Fungi can be unicellular or multicellular; some (like yeast) and fungal spores are microscopic, whereas some are large and conspicuous
Reproductive types are important in distinguishing fungal groups
Medically important species exist in the four fungal groups Zygomycota, Ascomycota, Basidiomycota, and Microsporidia
Members of Zygomycota, Ascomycota, and Basidiomycota produce deadly toxins
Important differences in fungal cells, such as ergosterols in fungal membranes, can be targets for antifungal medications, but similarities between human and fungal cells make it difficult to find targets for medications and these medications often have toxic adverse effects

Algae are a diverse group of photosynthetic eukaryotic protists
Algae may be unicellular or multicellular
Large, multicellular algae are called seaweeds but are not plants and lack plant-like tissues and organs
Although algae have little pathogenicity, they may be associated with toxic algal blooms that can and aquatic wildlife and contaminate seafood with toxins that cause paralysis
Algae are important for producing agar, which is used as a solidifying agent in microbiological media, and carrageenan, which is used as a solidifying agent

Lichens are a symbiotic association between a fungus and an algae or a cyanobacterium
The symbiotic association found in lichens is currently considered to be a controlled parasitism, in which the fungus benefits and the algae or cyanobacterium is harmed
Lichens are slow growing and can live for centuries in a variety of habitats
Lichens are environmentally important, helping to create soil, providing food, and acting as indicators of air pollution