“Kingdom” Protista - summary
Important general stuff to know about protists:
The Kingdom Protista originated as a dumping ground for all eukaryotic organisms that did not fit the
definitions of plant, animal, or fungi. Most protists are unicellular organisms, but some form colonies with
varying degrees of cell differentiation, and some kinds (such as seaweeds) are arguably multicellular organisms.
As it was, Protista did not stand up to phylogenetic analysis (cladistics). The kingdom Protista was
paraphyletic, since it included the common ancestral eukaryote but only some of its descendents (excluding
plants, animals, and fungi). Though “Protista” may ultimately represent 20+ clades, the terms “protist” is still
used as an informal term for eukaryotic organisms that aren’t plants, animals, or fungi. “Protozoa”, another
informal term, refers to “protists” that have animal-like characteristics. “Algae”, likewise, refers to those with
plant-like features.
Nuclear envelopes and the endomembrane system (ER, golgi, etc.) likely evolved from in-folding of the
plasma membrane (see text).
Mitochondria and chloroplasts evolved from endosymbiotic bacteria that were, respectively, aerobic and
photosynthetic and thus provided benefit for their “host” to keep them around (presumably, rather than
digesting them….). Consult your text for the relevant evidence. Because of this, eukaryotes (including YOU!)
are actually a chimera of prokaryotic ancestors, and thus a real mess for anal-retentive, pedantic cladisticians!
Some important, and/or interesting, and/or commonly used as examples of,.. protists:
The “protozoa”:
Ciliates – Paramecium, Stentor, others. Move and/or feed using cilia. Reproduce asexually by
dividing. Sexual conjugation exchanges/shuffles DNA, but isn’t technically a reproductive process. Consult
your text for details of conjugation in Paramecium.
“Amoeboids” – several groups use pseudopods for movement and/or feeding; such as Amoeba proteus.
Mycetozoa (“Slime molds”) – the “fungus animals”. These fascinating critters blur lines between what
it means to be a single cell versus multicellular; and what it means to be an individual organism (see text).
The algae:
Algae have a wide variety of complex sexual/asexual life cycles; one of which we will study later in plants.
Don’t worry about any life cycle details for now.
Single-celled or colonial algae – includes diatoms, which secrete glass cases around themselves; the
golden algae, and Chlorophyta – the green algae (like Spirogyra and Volvox) which are the nearest protistan
relative of plants. Some are arguably multicellular…depending on where/if one draws that line.
“Seaweeds” – red algae (Rhodophyta); brown algae (Phaeophyta). These are the largest and most
complexly multicellular of all algae. Many have specialized “holdfasts” at one end and air bladders at the other,
for obvious reasons. Some species may grow up to 60 m in length.
Red algae can absorb blue/green wavelengths that penetrate deep water, allowing them to thrive in water
up to 260 m deep. Porphyra is used to wrap sushi.
Brown algae include “kelp”; Laminaria (of Japanese soup fame); and the textbook example of brown
alga, Fucus (careful how you say that, it’s “fyoo-kuss”).