Protists Chapter 21

Ch. 28 - Protists Protists Protists: eukaryotic organisms that have a variety of traits Old Classification System hodge-podge group of organisms that share traits A) Animal-like protists B) Plant-like protists C) Fungus-like protists

Ch. 28 - Protists Protist Diversity Protists are more diverse than all other eukaryotes and are no longer classified in a single kingdom Most protists are unicellular, but there are some colonial and multicellular species Protists, the most nutritionally diverse of all eukaryotes, include: Photoautotrophs: which contain chloroplasts Heterotrophs: which absorb organic molecules or ingest larger food particles Mixotrophs: which combine photosynthesis and heterotrophic nutrition

Ch. 28 - Protists Protist Diversity (cont.) habitat freshwater marine species Reproduction and life cycles are also highly varied among protists, with both sexual and asexual species Binary fission cojugation The freshwater ciliate Stentor, a unicellular protozoan (LM) Ceratium tripos, a unicellular marine Dinoflagellate (LM) Delesseria Sanguinea, a multicellular marine red alga Spirogyra, a filamentous freshwater green alga (insert LM)

Ch. 28 – Protists The Evolution of Protists There is now considerable evidence that much of protist diversity has its origins in endosymbiosis The plastid-bearing lineage of protists evolved into red algae and green algae On several occasions during eukaryotic evolution red and green algae underwent secondary endosymbiosis, in which they were ingested

Plastid Dinoflagellates Apicomplexans Red algae Cyanobacterium Secondary endosymbiosis Apicomplexans Red algae Cyanobacterium Primary endosymbiosis Stramenopiles Heterotrophic eukaryote Secondary endosymbiosis Plastid Euglenids Secondary endosymbiosis Green algae Chlorarachniophytes

Ch. 28 - Protists Protist Classification With the recent advancements in molecular biology and genomics, the kingdom Protista has been reshuffled New lineages have been established and organisms have been reclassified based on this data

Fossil Protists Protists were the first eukaryotes. Eukaryotes evolved from prokaryotes. About 300,000 protist species exist today. Click to reveal the first bullet point. Bullet 1: Explain that microscopic fossils of eukaryotic cells, like the one here, have been found in rocks as old as 1.5 billion years. This fossil of Tappania plana indicated to scientists that ancient eukaryotes already had the cytoskeletal structures characteristic of protists today. Click to reveal the second bullet point. Bullet 2: Based on genetic and fossil evidence scientists think that eukaryotes evolved from prokaryotes and are more closely related to present-day Archaea than to Bacteria. Click to reveal the third bullet point. Bullet 3: Point out that most of the major protist groups have remained unicellular, but two have produced organisms that developed true multicellularity. It is from the ancestors of these groups that plants, animals, and fungi arose.

Protist Classification Today Point out that biologists used to group protists into one kingdom, “Protista,” but that this classification has been discarded by most, with scientists constantly revising classifications as they learn more about different groups. The general term “protist” to describe former members of this kingdom, however, has stuck. Use the diagram to explain the most recent classification system for protists decided on by biologists. Review with students that this branching diagram is a cladogram, which shows evolutionary relationships among a group of organisms. Explain that the number of shared branching points in a cladogram can show how closely related two groups are. Click to reveal the label. Read aloud the six major clades, or groups, and have students describe characteristics of the three clades pictured (e.g., presence of cilia, flagella; unicellular, multicellular). Ask: Which protist group is most closely related to Chromalveolata? How do you know? Answer: Foraminifera; they share a branch on the cladogram. Ask: Are Radiolaria more closely related to Excavata or to Choanozoa? How do you know? Answer: Excavata; they are closer together on the cladogram. Branching points

Protists and Other Eukaryotes Plants Fungi Animals Point out that the cladogram shows more than just the relationships among groups of “protists.” Explain that the cladogram also shows the likely relationships between protist groups and other recognized kingdoms: Plants, Animals, and Fungi. Ask for a student volunteer to come to the board to add the labels “Plants,” Animals,” and “Fungi” to the branches they think correspond to those lineages. Click to reveal the three correct labels. Point out that Choanozoa and Animals come off of a single branch, because they share characteristics that indicate they are more closely related to each other than to any other clades. Yet, they are on different sub-branches because they do have several differences from each other. Have students count the number of branching points shared by Animals and Choanozoas and by Animals and Excavates to compare the relationships. (Animals and Choanozoas share five, while Animals and Excavates share only one.) Ask: Which group of “protists” is most closely related to plants? Answer: Rhodophyta Ask: Which group is most closely related to animals? Answer: Choanozoa Ask: From looking at the symbols, what might you infer about why Choanozoa are most similar to animals? Answer: Choanozoa have a structure that allows them to move. Ask: Which protist group is most closely related to fungi? Answer: Amoebozoa

Kingdom Protista Protists can be single- celled or multicellular organisms. All protists are eukaryotes. Groups of Protists: Protozoa (Animal-like) Algae (Plant-like) Fungus-like forms

Examples of Protists Includes: Amoebas Ciliates Flagellates Algae Amoeba, Naegleria fowleri Flagellate, Giardia lamblia Ciliate, Strombidium

Protozoans Protozoans: animal-like protists These protists share characteristics with animals such as: Feed on other organisms Cells lack cell walls Examples: A) Zooflagellates Move around using flagella B) Sarcodines Move using pseudopods (“false feet”) Amoebas C) Ciliates Move using cilia: short hair-like projections D) Sporozoans Do not move on their own Are parasitic Ciliate

Algae Algae: plant-like protists These organisms share characteristics with plants such as: Photosynthetic Cells contain cell walls Examples: A) Phytoplankton algae that live near the surface of the ocean. B) Red, brown or green algae C) Diatoms have silicon in their cell walls) Diatoms

Algae Besides oxygen production, algae are used by humans for many other purposes: A) Food seaweed & kelp are edible (Sushi anyone?) B) Production of agar Gelatin-like substance that has many uses C) Used to make toothpaste “pasty” D) Others?

Fungus-like Protists Like fungi, these are usually decomposers. Absorb nutrient from dead or decaying matter Fungus-like protists do not have chitin in their cell walls like true fungi do. Slime molds Water molds Slime Mold