1. Protists
Chapter 21

2. Ch 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

3. 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

4. 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)

5. 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

6. 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

7. 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

8. 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.

9. 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

10. 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

11. 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

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

13. 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

14. 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

15. 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?

16. 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