Lewis/Life - Review of Key Concepts

Review of Key Concepts - Chapter 23

Kingdom Protista includes many simple eukaryotes. Most are unicellular, but some may be colonial or multicellular. The kingdom includes protozoa, algae, chytrids, water molds, and slime molds. Many protista form plankton, which consists of microscopic organisms that form the bases of food webs.
Protozoa are unicellular protista that move by using cilia, pseudopods, flagella, or amoeboid motion. They have one or two nuclei; if they have two, one may be a macronucleus and one a micronucleus. Holozoic protozoa take in food by phagocytosis, and saprozoic protozoa do so by diffusion, facilitated diffusion, active transport, or pinocytosis. Contractile vacuoles pump out water, and secretory granules contain enzymes. A cyst form enables certain protozoa to survive harsh environmental conditions. All protozoa reproduce asexually, by binary fission, budding, or multiple fission, and may reproduce sexually. Some protozoa form zooplankton.
The protozoa include seven phyla. Phylum Sarcomastigophora includes the flagellated Mastigophora and the Sarcodina, whose amoebae have pseudopods. Labyrinthomorpha are elongated and are either saprozoic or parasitic on algae. Ascetospora live in mollusks, Myxozoa in fish, and Microspora in insects. Apicomplexa have a unique apical complex and mode of reproduction, are nonmotile, and have a complex life cycle. Ciliophora locomote by waving rows of cilia and may reproduce by conjugation. Protozoa cause many diseases.
Algae include cyanobacteria and seven protistan divisions. Protistan algae may be unicellular or multicellular, and they contain a variety of photosynthetic pigments and storage carbohydrates. Algae resemble plants because they photosynthesize, but they lack roots, stems, and leaves. They are probably ancestral to plants. Some algae form phytoplankton.
Algae are classified by habitat, cell structure, number of flagella, thallus form, reproductive mechanism, and life cycle characteristics.
Green algae (Chlorophyta) are very diverse. Many have two flagella, a single haploid nucleus, chlorophyll a and b, a large chloroplast, and a starch-storing pyrenoid.
Euglenoids (Euglenophyta) are elongated, unicellular, and lack cell walls, but they have a supportive flexible layer called a periplast and a storage carbohydrate, paramylon. Stoneworts (Charophyta) have a limestonelike covering and resemble plants. Dinoflagellates (Pyrrhophyta) have two flagella of differing lengths, outer plates, and many pigments. Golden-brown algae, yellow-green algae, and diatoms (Chrysophyta) live in fresh water and have distinctive coverings and pigments. Brown algae (Phaeophyta) are complex, multicellular seaweeds. Their body form includes a holdfast, stemlike stipe, bladder, and blades. Motile cells have a set of flagella. Red algae (Rhodophyta) are multicellular seaweeds with floridean starch and phycobilin pigments.
Chytrids have a flagellum and chitin cell walls. Water molds live in soil or fresh water and may have one cell or many nuclei in a shared cytoplasm. Their cell walls consist of cellulose. Slime molds are single-celled amoebae when food is plentiful, but they aggregate to form large, migrating masses when conditions are harsh. This enables them to move to find food. Slime molds may be acellular or cellular.