Plantlike Protists

<h1>Text Preview</h1> <p>Protists considered plantlike are autotrophs that carry out photosynthesis. But as we saw with the example of Euglena, this characteristic does not respect taxonomic boundaries. Despite their diversity, plantlike protists are often collectively referred to as algae. Most single-celled plantlike protists live near the surface of oceans, lakes, and other bodies of water. They are a fundamental food source for other organisms sharing their habitat.</p> <p>The dinoflagellates are one such group. They have a variety of shapes reinforced by rigid internal plates made of cellulose. Two flagella lie in crossing grooves. The chloroplasts of dinoflagellates contain reddish pigments, which can tint the water in which these organisms are abundant. The result may be a red tide. Despite their different appearances and lifestyles, dinoflagellates are relatives of ciliates and apicomplexans.</p> <p>The chromists are an important group of diverse but related protists, most of which carry out photosynthesis and have distinctive chloroplasts. Their characteristic pigments often give them a yellow, gold, or brownish color. Diatoms are single-celled protists encased in glassy, symmetrically shaped cell walls. The tiny golden algae and yellow-green algae are also chromists.</p> <p>In contrast to the algae we’ve seen so far, the brown algae, also called phaeophytes, can grow quite large. All of the brown algae are multicellular. Many are forms of seaweed, like kelp. Many brown algae have structures analogous to those of plants, including leaflike blades that serve to capture sunlight for photosynthesis. Keep in mind, though, that neither the brown algae nor any of the other chromists are closely related to plants.</p> <p>Equally distinct from plants, and distinct from all other protists, are the red algae, or rhodophytes. Most red algae are multicellular. Some red algae seaweeds are used by people for food. Red algae have also had an important impact on life science research and biotechnology. They are the source of agar, a substance composed of polysaccharides used in the lab as a growth medium for many types of organisms.</p> <p>The last group of plantlike protists we’ll consider actually are closely related to plants. These are the green algae, or chlorophytes. Biologists believe that the green algae share a common ancestor with plants, so that together they form a single clade. Green algae may in fact be more closely related to plants than they are to any other type of protist. The forms of green algae range from single flagellated cells, through colonies and filaments of individual cells, to multicellular seaweeds. Many green algae have complex life cycles.</p> <p id="TextCopyright">Copyright 2006 The Regents of the University of California and Monterey Institute for Technology and Education</p>