Ch 17 Protists

17. 1 Protists lie at the crossroads between simple and complex organisms Protists are the simplest eukaryotic cells- they have a nucleus and membrane bound organelles. A. What is a protist? Traditionally, Kingdom Protista was defined by exclusion. It was anything that is eukaryotic but isn’t exactly and animal, plant or fungus. Now scientists use evolutionary relationships and Dna evidence to classify protists. B. Protists are important in many ways- photosynthetic protists produce much of the earth’s oxygen, medically important protists include parasites, and many protists have industrial applications.

C. protists have a lengthy evolutionary history- Protists may hold the key to the evolution of all eukaryotes- endosymbiosis theory- Origin of multicellularity- They also shed light on the origin of plants, animals and fungi

17.2 Many protists are photosynthetic Algae- catch all term for any photosynthetic protist that lives in water Algae have chloroplasts and do photosynthesis. They can be single celled, colonial, filamentous or multicellular, but they are not plants because they do not have the reproductive structures that define plants. A. Euglenoids are heterotrophs and autotrophs- Euglenoids are single celled and have an elongated cells. They have a flagellum for movement, eyespots, inhabit fresh water. About 1/3rd are photosynthetic and the rest are heterotrophs. Euglena is a species that can be photosynthetic or heterotrophic depending on its environment.

B. Dinoflagellates are whirling cells Marine protists- have two flagella of different lengths that cause them to move in a circular motion. Major component of plankton- some live within invertebrates and some are predators and parasites. Some result in toxic overgrowth known as “red tide” that can kill fish and harm people

C. Golden algae, diatoms, and brown algae contain yellowish pigments Three groups contain yellow photosynthetic pigments called fucoxanthin in addition to chlorophyll a and B. Golden algae- usually have two flagella, but can be filamentous or colonial, they can act as heterotrophs or autotrophs. Some can be toxic to fish when they overgrow in streams and lakes. Diatoms- Unicellular algae with two part silica cell walls that can occur in many shapes, live in all moist habitats(but most live in the ocean), sensitive to environmental change, fossilize well and the shells form deposits of diatomaceous earth that is used in toothpaste, pool filters, etc.

Brown algae- most complex and largest protest- multicellular- live in marine habitats- includes Sargassum and Kelp. Humans ingest several species of kelp (Asian dishes as well as emulsifiers for ice cream, candy, and chocolate.

D. Red algae live in deep water Red algae are relatively large- somewhat similar to green algae- they can live at deeper depths because they can capture wavelengths of light that persist in deeper water. They are used in agar which we use to culture bacteria, also used in emulsifiers and stabilizers.

Green algae are the most plant-like protist- They have chlorophyll a and b, store starch, and have cellulose cell walls, they have a variety of forms from unicellular to multicellular, they can live in fresh or salt water and have life cycles similar to plants.