Chapter 28
Protists
Teaching Objectives
Protists Are Extremely Diverse
1.Explain why the kingdom Protista is no longer considered a legitimate taxonomic group.
2.Describe the different nutritional strategies of protists.
3.Describe the three ecological categories of protists. Explain why the terms protozoa and algae are not useful as taxonomic categories.
4.Describe the evidence that supports the theory that mitochondria and plastids evolved by serial endosymbiosis. Explain which living organisms are likely relatives of the prokaryotes that gave rise to mitochondria and plastids.
5.Describe the evidence that suggests that mitochondria were acquired before plastids in eukaryotic evolution.
6.Explain the role of secondary endosymbiosis in the evolution of photosynthetic protists.
A Sample of Protistan Diversity
7.Describe the reduced mitochondria of diplomonads. Explain why this group is successful despite this feature.
8.Explain how trypanosomes avoid detection by the human immune system.
9.Explain why Plasmodium continues to pose a great risk to human health despite modern medical advances.
10.Describe the process and significance of conjugation in ciliate life cycles.
11.List three differences between oomycetes and fungi.
12.Describe the life cycle, ecology, and impact on humans of the following stramenopiles:
a.downy mildew
b.diatoms
c.kelp
13.Describe how amoeboid protists move and feed.
14.Explain why foraminiferans and gymnamoebas are not considered to be closely related, although both are amoebas.
15.Compare the life cycles and ecology of plasmodial and cellular slime molds.
16.Explain the problem faced by Dictyostelium aggregates of constraining “cheaters” that never contribute to the stalk of the fruiting body. Discuss how research on this topic may lead to insights into the evolution of multicellularity.
17.Explain the basis for the proposal for a new “plant” kingdom, Viridiplantae.
18.Describe three mechanisms by which large size and complexity have evolved in chlorophytes.
Student Misconceptions
1.Protists are tremendously diverse, varying greatly in size, complexity, habitat, mode of nutrition, and life history features. The variation in protists may overwhelm students. It is possible to help students make sense of this diversity by discussing the novel features that arose within eukaryotes—mitosis, meiotic sex, multicellularity, various specializations—and considering which lineages show particular features.
2.When they think of photosynthesis, students may think primarily or exclusively of land plants. Emphasize to your students that algal protists—seaweeds and phytoplankton—make a significant contribution to Earth’s primary productivity.
3.Students may underestimate the complexity of unicellular protists. Point out to your students that a single-celled Paramecium is far more complex than any of the cells in their own bodies. As the textbook points out, protists include the most elaborate of all cells, cells that carry out the basic functions performed by all of the specialized cells, tissues, and organs of a multicellular organism.
4.Conjugation in ciliates is sexual, resulting in the production of two genetically novel individuals combining the genes of two parents. However, it is not reproduction, because no additional individuals are produced. The unusual life cycles of ciliates can be used to clarify for students the distinction between sex and reproduction.
5.Research addressing the problem faced by Dictyostelium aggregates of constraining “cheaters” that never contribute to the stalk of the fruiting body has led to insights into the evolution of multicellularity. Excellent time-lapse photographs of these fascinating protists can be used to introduce your students to the problem faced by all multicellular organisms—that of constraining “cheating” lineages or reducing their effect on the multicellular body.
Chapter Guide to Teaching Resources
Overview: A world in a drop of water
Concept 28.1Protists are an extremely diverse assortment ofeukaryotes
Transparency
Figure 28.3Diversity of plastids produced by secondary endosymbiosis
Student Media Resource
Activity: Tentative phylogeny of eukaryotes
Concept 28.2Diplomonads and parabasalids have modified mitochondria
Transparency
Figure 28.4A tentative phylogeny of eukaryotes
Concept 28.3Euglenozoans have flagella with a unique internal structure
Transparencies
Figure 28.6Euglenozoan flagellum
Figure 28.8Euglena, a euglenid commonly found in pond water
Instructor and Student Media Resources
Video: Euglena
Video: Euglena motion
Concept 28.4Alveolates have sacs beneath the plasma membrane
Transparencies
Figure 28.11The two-host life cycle of Plasmodium, the apicomplexan that causes malaria
Figure 28.12Structure and function in the ciliate Paramecium caudatum
Instructor and Student Media Resources
Video: Dinoflagellate
Video: Stentor
Video: Stentor ciliate movement
Video: Vorticella cilia
Video: Vorticella detail
Video: Vorticella habitat
Video: Paramecium vacuole
Video: Paramecium cilia
Concept 28.5Stramenopiles have “hairy” and smooth flagella
Transparencies
Figure 28.14The life cycle of a water mold (layer 1)
Figure 28.14The life cycle of a water mold (layer 2)
Figure 28.14The life cycle of a water mold (layer 3)
Figure 28.21The life cycle of Laminaria: An example of alternation of generations
Instructor and Student Media Resources
Video: Water mold oogonium
Video: Water mold zoospores
Video: Diatoms moving
Video: Various diatoms
Concept 28.6Cercozoans and radiolarians have threadlike pseudopodia
Concept 28.7Amoebozoans have lobe-shaped pseudopodia
Transparencies
Figure 28.26The life cycle of a plasmodial slime mold
Figure 28.27The life cycle of Dictyostelium, a cellular slime mold
Instructor and Student Media Resources
Video: Amoeba
Video: Amoeba pseudopodia
Video: Plasmodial slime mold streaming
Video: Plasmodial slime mold
Concept 28.8Red algae and green algae are the closest relatives of land plants
Transparency
Figure 28.31The life cycle of Chlamydomonas, a unicellular chlorophyte
Instructor and Student Media Resources
Video: Chlamydomonas
Video: Volvox colony
Video: Volvox daughter
Video: Volvox flagella
Investigation: What kinds of protists do various habitats support?
Review
Transparency
Table 28.1A sample of protist diversity
For additional resources such as digital images and lecture outlines, go totheCampbell Media Manager or the Instructor Resources section of
Key Terms
alternation of generations
amoeba
apicomplexan
blade
brown alga
cellular slime mold
ciliate
conjugation
diatom
dinoflagellate
diplomonad
euglenid
food vacuole
foraminiferan (foram)
golden alga
green alga
heteromorphic
holdfast
isomorphic
kinetoplastid
mixotroph
oomycete
parabasalid
plasmodial slime mold
plasmodium
protist
pseudopodium
radiolarian
red alga
secondary endosymbiosis
sporozoite
stipe
test
thallus
Word Roots
con- 5 with, together (conjugation: in ciliates, the transfer of micronuclei between two cells that are temporarily joined)
hetero- 5 different; -morph 5 form (heteromorphic: a condition in the life cycle of all modern plants in which the sporophyte and gametophyte generations differ in morphology)
iso- 5 same (isomorphic: alternating generations in which the sporophytes and gametophytes look alike, although they differ in chromosome number)
-phyte 5 plant (gametophyte: the multicellular haploid form in organisms undergoing alternation of generations)
pseudo- 5 false; -podium 5 foot (pseudopodium: a cellular extension of amoeboid cells used in moving and feeding)
thallos- 5 sprout (thallus: a seaweed body that is plantlike but lacks true roots, stems, and leaves)##Instructor’s Guide for Campbell/Reece Biology, Seventh EditionChapter 28Protists##Instructor’s Guide for Campbell/Reece Biology, Seventh EditionChapter 28Protists##Instructor’s Guide for Campbell/Reece Biology, Seventh Edition