19: "Protists"
- Page ID
- 124002
\( \newcommand{\vecs}[1]{\overset { \scriptstyle \rightharpoonup} {\mathbf{#1}} } \) \( \newcommand{\vecd}[1]{\overset{-\!-\!\rightharpoonup}{\vphantom{a}\smash {#1}}} \)\(\newcommand{\id}{\mathrm{id}}\) \( \newcommand{\Span}{\mathrm{span}}\) \( \newcommand{\kernel}{\mathrm{null}\,}\) \( \newcommand{\range}{\mathrm{range}\,}\) \( \newcommand{\RealPart}{\mathrm{Re}}\) \( \newcommand{\ImaginaryPart}{\mathrm{Im}}\) \( \newcommand{\Argument}{\mathrm{Arg}}\) \( \newcommand{\norm}[1]{\| #1 \|}\) \( \newcommand{\inner}[2]{\langle #1, #2 \rangle}\) \( \newcommand{\Span}{\mathrm{span}}\) \(\newcommand{\id}{\mathrm{id}}\) \( \newcommand{\Span}{\mathrm{span}}\) \( \newcommand{\kernel}{\mathrm{null}\,}\) \( \newcommand{\range}{\mathrm{range}\,}\) \( \newcommand{\RealPart}{\mathrm{Re}}\) \( \newcommand{\ImaginaryPart}{\mathrm{Im}}\) \( \newcommand{\Argument}{\mathrm{Arg}}\) \( \newcommand{\norm}[1]{\| #1 \|}\) \( \newcommand{\inner}[2]{\langle #1, #2 \rangle}\) \( \newcommand{\Span}{\mathrm{span}}\)\(\newcommand{\AA}{\unicode[.8,0]{x212B}}\)
Protists are an artificial group of eukaryotes that are neither animals, fungi, nor plants. They represent the vast diversity of eukaryotic organisms, and thus span the breadth of possibilities with regard to life history traits. They can be heterotrophs or autotrophs, unicellular to massively multicellular (though rarely with any specialized tissue organization), and can be found across ecosystems worldwide. Photosynthesis within protists is the result of multiple separate endosymbiotic events.
- 19.1: Introduction to Protists
- Protists are extremely diverse in terms of their biological and ecological characteristics, partly because they are an artificial assemblage of phylogenetically unrelated groups. Protists display highly varied cell structures, several types of reproductive strategies, virtually every possible type of nutrition, and varied habitats. Most single-celled protists are motile, but these organisms use diverse structures for transportation.
- 19.2: Heterotrophic "Protists"
- Heterotrophic organisms must consume organic matter to obtain energy. Under the umbrella of protists, there are several heterotrophic groups. This chapter will introduce slime molds and oomycetes, as these are groups commonly discussed in botany courses. However, it is important to note that there is a vast diversity of heterotrophic protist lineages not covered here with important and fascinating ecological roles.
- 19.3: Slime Molds
- Slime molds represent several different lineages: the cellular slime molds (Dictyostelids), Protostelids, and plasmodial slime molds (Myxomycetes). These organisms move about as amoebae consuming bacteria until conditions become unfavorable, at which point they form spores. They can be found in damp substrates with ample bacteria and are most frequently found on decaying logs and forest duff.
- 19.4: Oomycota
- Oomycetes, commonly called water molds, are a group of heterotrophic, fungus-like organisms with a filamentous thallus. Unlike fungi, they have diplontic life cycles and cellulose in their cell walls. They are important decomposers in aquatic ecosystems and plant parasites in terrestrial ones.
- 19.5: Photosynthetic "Protists"
- Photosynthetic protists have derived their chloroplasts from multiple endosymbiotic events. Dinoflagellates, brown algae, and diatoms derived their chloroplasts from the secondary endosymbiosis of a red alga. Red algae, green algae, and plants derived their chloroplasts from the primary endosymbiosis of a cyanobacterium.
- 19.6: Dinoflagellates
- Dinoflagellates are a group of morphologically and nutritionally diverse acquatic organisms, from the zooxanthellae that live inside coral polyps to the neurotoxin-releasing microbes that cause red-tides. They have essential roles in marine food webs.
- 19.7: Brown Algae and Diatoms
- Brown algae and diatoms are photosynthetic heterokonts. They both have a diplontic life cycle during some stage of which a cell will have heterokont flagella. They have 4-membraned chloroplasts that contain the pigments chlorophyll a, chlorophyll c, and fucoxanthin. This latter pigment gives the chloroplasts in these groups a golden color. This is about where the similarities end. They have different morphologies, habitats, cell wall composition, and storage carbohydrates.
- 19.8: Red and Green Algae
- Glaucophytes, red algae, and green algae are part of the Archaeplastida. These organisms are descended from the same primary endosymbiosis event. Glaucophytes are thought to be one of the earliest lineages to diverge due to the presence of remnant peptidoglycan between the membranes of its chloroplast-like cyanelles. Glaucophytes and red algae share the same pigments as Cyanobacteria, while green algae share the same pigments as plants.
- 19.9: Chapter Summary
- A brief summary of the chapter concepts.