Chapter 21: Protist Evolution and Diversity

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1 Chapter 21: Protist Evolution and Diversity AP Curriculum Alignment Big Idea 1, which includes the concept that mutually beneficial associations among ancient bacteria gave rise to eukaryotic cells, is reinforced in Chapter 21. Of course the eukaryotic cells that were produced by this association are what we loosely call protists and the theory of serial endosymbiosis should be connected here to protists. Chapter 21 indicates that our classification system, even with the three domains, does not correctly depict the phylogeny of protists and so this system has been restructured based on new molecular information. This information supports the information in Big Idea 1 that phylogenetic trees and cladograms are dynamic. The organisms that were once placed in the kingdom Protista are now divided among the subgroups of the supergroups that make up the domain Eukarya. Big Idea 2 explains that both biotic and abiotic factors affect the activities of cells, organisms, populations, communities, and ecosystems. Many organisms described in Chapter 21 have the ability to undergo sexual or asexual reproduction. During times of environmental stress, the sexual mode of reproduction is favored as it provides the opportunity for new combinations of genotypes. The microorganisms described in Chapter 21 also comprise the plankton that make up the base of many food webs. The effect of global warming on disease causing microorganisms is presented in this chapter. Big Idea 4 stresses the interactions between systems and the resulting complex properties. Chapter 21 includes several disease conditions that can increase in intensity as global climate change increases the average annual temperature. Synergistic effects of global climate change and disease are explored in this chapter. ALIGNMENT OF CONTENT TO THE CURRICULUM FRAMEWORK Big Idea 1: The process of evolution drives the diversity and unity of life. Enduring understanding (EU) 1.B: Organisms are linked by lines of descent from common ancestry. Essential knowledge (EK) 1.B.2: Phylogenetic trees and cladograms are graphical representations (models) of evolutionary history that can be tested. d. Phylogenetic trees and cladograms are dynamic (i.e., phylogenetic trees and cladograms are constantly being revised), based on the biological data used, new mathematical and computational ideas, and current and emerging knowledge. Big Idea 2: Biological systems utilize free energy and molecular building blocks to grow, to reproduce, and to maintain dynamic homeostasis. Enduring understanding (EU) 2.D: Growth and dynamic homeostasis of a biological system are influenced by changes in the system s environment. Essential knowledge (EK) 2.D.1: All biological systems from cells and organisms to populations, communities and ecosystems are affected by complex biotic and abiotic interactions involving exchange of matter and free energy. a. Cell activities are affected by interactions with biotic and abiotic factors. Mader, Biology, 12 th Edition, Chapter

2 b. Organism activities are affected by interactions with biotic and abiotic factors. c. The stability of populations, communities and ecosystems ism affected by interactions with biotic and abiotic factors. No specific example is required for teaching the above concepts. Teachers are free to choose an example that best fosters student understanding. Essential knowledge (EK) 2.D.2: Homeostatic mechanisms reflect both common ancestry and divergence due to adaptation in different environments. c. Homeostatic control systems in species of microbes, plants and animals support common ancestry. To foster student understanding of this concept, instructors can choose an illustrative example such as the comparison of: Excretory systems in flatworms, earthworms and vertebrates Osmoregulation in bacteria, fish and protists Osmoregulation in aquatic and terrestrial plants Circulatory systems in fish, amphibians and mammals Thermoregulation in aquatic and terrestrial animals (countercurrent exchange mechanisms) Big Idea 4: Biological systems interact, and these systems and their interactions possess complex properties. Essential knowledge 4.B.4: Distribution of local and global ecosystems changes over time. a. Human impact accelerates change at local and global levels. To foster student understanding of this concept, instructors can choose an illustrative example such as: Logging, slash and burn agriculture, urbanization, monocropping, infrastructure development (dams, transmission lines, roads), and global climate change threaten ecosystems and life on Earth. Concepts covered in Chapter 21 also align to the learning objectives that provide a foundation for the course, an inquiry-based laboratory experience, class activities, and AP exam questions. Each learning objective (LO) merges required content with one or more of the seven science practices (SP), and one activity or lab can encompass several learning objectives. The learning objectives and science practices from the Curriculum Framework that pertain to protist evolution and diversity are shown in the table below. Note that other learning objectives may apply as well. LO 1.18 The student is able to evaluate evidence provided by a data set in conjunction with a phylogenetic tree or a simple cladogram to determine evolutionary history and speciation. LO 2.22 The student is able to refine scientific models and questions about the effect of complex biotic and abiotic interactions on all biological systems, from cells and organisms to populations, communities and ecosystems. 316 Mader, Biology, 12 th Edition, Chapter 21

3 LO 2.23 The student is able to design a plan for collecting data to show that all biological systems (cells, organisms, populations, communities and ecosystems) are affected by complex biotic and abiotic interactions. LO 2.24 The student is able to analyze data to identify possible patterns and relationships between a biotic or abiotic factor and a biological system (cells, organisms, populations, communities or ecosystems). LO 4.21 The student is able to predict consequences of human actions on both local and global ecosystems. Key Concepts Summary Classifying single-celled eukaryotes The theory of serial endosymbiosis ties the evolution of protists and prokaryotes. The old Kingdom Protista was polyphyletic, meaning it was of mixed ancestry and needed to be restructured using molecular evidence. Diversity of the Supergroups The Supergroup Archaeplastids include land plants and other photosynthetic organisms, such as green and red algae, that have plastids derived from endosymbiotic cyanobacteria o Both land plants and green algae have chlorophylls a and b, a cell wall that contains cellulose, and food reserves made of starch that all indicate a close relationship o Green algae are subdivided into two groups, the chlorophytes and the charophytes. o Charophytes are thought to be the green algae group most closely related to land plants. o Both chlorophytes and charophytes contain examples of colonial forms and forms that undergo varying reproductive strategies when they are environmental under stress conditions o Red algae are used commercially in laboratory and food products The Supergroup Chromalveolata include two large subgroups: the stramenopiles and the alveolates. o The stramenopiles include the brown algae, diatoms, golden brown algae, and water molds. o Brown algae have chlorophylls a and c in their chloroplasts and an accessory carotenoid pigment that gives them their characteristic brown color. o Alveolates have alveoli (small air sacs) lying just beneath their plasma membranes that are thought to lend support to the cell surface or aid in membrane transport and are all single cellular. o Alveolates include dinoflagellates (important in aquatic food webs), zoozanthellae (form a symbiotic relationship with coral), and apicomplexans Mader, Biology, 12 th Edition, Chapter

4 (parasites responsible for such diseases as malaria) Supergroup Excavata have atypical mitochondria and distinctive flagella and/or deep (excavated) oral grooves. o One group of excavata, the euglenids, can be mixotrophic, some are photoautotrophic, and others are heterotrophic. o Parabasalids and diplomonads are single-celled, flagellated excavates that are endosymbionts of animals. o Trypanosoma brucei, an excavata, is the cause of African sleeping sickness and is carried by the tsetse fly,glossina. Supergroup Amoebozoa members move by pseudopods. o Amoeboids feed by phagocytosis, digestion occurs within a food vacuole. o Plasmodial slime molds exist as a plasmodium, a diploid, multinucleated, cytoplasmic mass enveloped by a slime sheath. o Unfavorable environmental conditions stimulate spore production in both plasmodial and cellular slime molds. Supergroup Opisthokonta contains animals, fungi, and choanoflagellates Supergroup Rhizaria consist of the foraminiferans and the radiolarians, organisms with fine, threadlike pseudopods. o Each geological period has a distinctive form of foraminiferan; thus, foraminiferans can be used as index fossils to date sedimentary rock. Key Terms accessory pigments alveolates amoeboids amoebozoans brown algae cellular slime molds charophytes chlorophytes choanoflagellates cillates colony conjugation cysts diatoms dinoflagellates endosymbiosis euglenids excavates filaments foraminiferans golden brown algae green algae kinetoplastids mixotrophic monophyletic opisthokonts parabasalids plankton plasmodial slime molds protists pseudopods radiolarians red algae redtides rhizarians sporangium stramenopiles supergroup test water molds 318 Mader, Biology, 12 th Edition, Chapter 21

5 Teaching Strategies Class time: Three 45-minute periods Day 1: Lecture on Supergroups 30 minutes Begin Activity 1, supergroup flipbook 15 minutes Day 2: Complete Activity 1 and have students present their work 40 minutes Review of microscope techniques 5 minutes Day 3: Activity 2, supergroup identification 25 minutes Quiz on Supergroups 20 minutes Suggested Approaches There has not been a consensus among scientists as to the acceptance of the number and names of all the supergroups associated with the domain Eukarya. The fluidity of this section needs to be stressed to students. The information about the individual organisms in Chapter 21 is very detailed. The teacher may wish to pick several very important microorganisms for students to examine in detail. Rather than having students memorize the new vocabulary here, have them use the vocabulary while constructing a flip book. Very few of these terms will show up on the AP exam. Student Misconceptions and Pitfalls Most students have not considered the supergroups with subgroups approach to categorizing the organisms in the domain Eukarya and will most likely be confused at first. Avoid the use of old terminology, such as protist or protozoan, when introducing this material. Instead use microbe or microorganism when explaining the single-celled organisms in the domain Eukarya. Mader, Biology, 12 th Edition, Chapter

6 Suggested Activities Activity 1: Supergroup Flipbook Students should make a flip book about the supergroups and subgroups and the major characteristics that are shared by each. Table 21.1 is a great starting point. Students can make either paper or electronic flipbooks. Activity 2: Identification of Supergroups in a Mixed Culture From a biological supply house, order a mixed culture of protists. Have students draw or use their cell phones to document the organisms and then have students place each organism into one of the Supergroups. 320 Mader, Biology, 12 th Edition, Chapter 21

7 Student Edition Chapter Review Answers Answers to Assess Questions 1. d; 2. b; 3. c; 4. a; 5. a; 6. b; 7. b; 8. c; 9. b; 10. c; 11. d; 12. a; 13. b; 14. d; 15. a Answers to Applying the Big Ideas Questions 1. Protists are a diverse group of organisms and represent the oldest branch of eukaryotes in the tree of life. As lineages stretch back in time, we can be less and less certain about how they are related to each other. Use Figure 21.1 on Page 376 to complete parts (a) and (b). a) Describe TWO kinds of data that could be collected by scientists to provide a direct answer to the question, how could scientists determine that land plants and charophytes share a common ancestor and are suited to be in the Archaeplastida supergroup? b) Explain how the data you suggested in part (a) would provide a direct answer to the question. Essential Knowledge Science Practice Learning Objective 1.B.2: Phylogenetic trees and cladograms are graphical representations (models) of evolutionary history that can be tested. 5.3: The student can evaluate the evidence provided by data sets in relation to a particular scientific question. 1.18: The student is able to evaluate evidence provided by a data set in conjunction with a phylogenetic tree or a simple cladogram to determine evolutionary history and speciation. 4 points maximum. Description of the appropriate kind of data and the appropriately linked explanation of its selection may include: Descriptions of data Explanations (1 point each) (1 point each) DNA evidence - Compare similarities in DNA and protein sequences. Current DNA sequencing data suggests that among green algae, the stoneworts (charophytes) are most closely related to land plants. This would have them be closer on a cladogram to one another than they would be to red algae, even though they are all in the same supergroup. Information like this is useful in determining lineages. Mader, Biology, 12 th Edition, Chapter

8 Morphological evidence - Compare morphological similarities of living and fossil species. Statistical evidence - Computer programs have sophisticated ways of measuring and representing relatedness among organisms. Confirm that organisms of these two species contain plastids, a defining feature of this supergroup, and there is evidence for being related and sharing an ancestor that was the first with plastids derived from endosymbiotic bacteria. If the program indicates that the two species are closely related, this could be used as evidence to back up the claim that they share a common ancestor. 2. In protists and bacteria, internal and external signals regulate a variety of physiological responses that synchronize with environmental cycles and cues. Describe the mechanisms that regulate the timing and coordination of physiological events associated with fruiting body formation in slime molds and certain types of bacteria. Essential Knowledge Science Practice Learning Objective 2.E.2: Timing and coordination of physiological events are regulated by multiple mechanisms. 7.2: The student can connect concepts in and across domain(s) to generalize or extrapolate in and/or across enduring understanding and/or big ideas. 2.37: The student is able to connect concepts that describe mechanisms that regulate the timing and coordination of physiological events. 3 points maximum. Description of mechanisms of regulation may include (1 point each): Slime molds were once classified as fungi, which also form fruiting bodies, but slime molds lack cell walls and as well as different motility considerations. Slime molds produce spores by meiosis; the spores germinate to form gametes. Spores release either a haploid flagellated cell or an amoeboid cell. Eventually, two of the haploid cells fuse to form a zygote that feeds and grows, producing a multi-nucleated plasmodium once again. When conditions are unfavorable, a plasmodium develops many sporangia (reproductive structures that produce spores). An aggregate of sporangia is called a fruiting body. The spores produced by a plasmodial slime mold sporangium can survive until moisture is sufficient for them to germinate. 322 Mader, Biology, 12 th Edition, Chapter 21

9 As unfavorable conditions develop, slime mold cells release a chemical that causes them to aggregate into a pseudoplasmodium that is temporary and eventually gives rise to a fruiting body, in which sporangia produce spores. When favorable conditions return, the spores germinate, releasing haploid amoeboid cells, and the asexual cycle begins again. 3. Scientists claim that a variety of phenotypic responses to a single environmental factor (such as interactions with other species) can result from different genotypes within the population. Support this claim by describing at least TWO pieces of evidence involving protists. Essential Knowledge Science Practice Learning Objective 4.C.3: The level of variation in a population affects population dynamics. 6.1: The student can justify claims with evidence. 4.25: The student is able to use evidence to justify a claim that a variety of phenotypic responses to a single environmental factor can result from different genotypes within the population. 2 points maximum. Description of the appropriate evidence may include: In the nineteenth century, the people of Ireland were largely made up of the impoverished whose diet relied heavily on the cheap and hearty potato. The introduction of the potato blight protist (Phytophthora infestans, a water mold) devastated potato crops (and as a result, the people depending on those crops) because the crops had very little genetic diversity and were closely related. After some of the potato plants die, there are none left to reproduce. The vineyards of France in the 1870 s were ravaged by Plasmopara viticola. Species and populations with little genetic diversity are at risk for extinction. A large proportion of plankton is made up of protists, and, along with diatoms, plankton are at the base of the food chain in aquatic systems; however, an imbalance in population density of protists (e.g., algal bloom, red tide of dinoflagellates) can lead to contamination of aquatic ecosystems. Answers to Applying the Science Practices Questions Think Critically 1. The diameter is approximately m. 2. The algae cells are within the plant cells. Mader, Biology, 12 th Edition, Chapter

10 Additional Questions for AP Practice 1. Refine the model below to indicate the affect that global climate change has on cells and organisms to populations, communities and ecosystems that come in contact with the lethal Naegleria fowleri. 2. Using what you ve learned in this chapter, discuss the synergistic effects of human actions on climate change and protist-borne diseases. 3. What new evidence was used to construct the supergroups? A) fossil records B) sediments on the ocean floor C) absence of mitochondria in some groups D) DNA sequence evidence 324 Mader, Biology, 12 th Edition, Chapter 21

11 Answers to Additional Questions for AP Practice 1. Answer will vary and may include: as the summer became hotter, more people went to the freshwater lakes and stirred up the sediment at the bottom that contained the disease causing amoeba so more peop0le became infected. As the temperature heated up, the disease causing amoeba became more active and so an increased number of humans became infected. 2. Answers can include predictions of increased disease to contamination of water supply due to catastrophic weather events, reduced food supply due to drought followed by increased human infections, urban populations increase from immigration from drought areas causing epidemics, insects that carry disease increase in population causing increased disease in humans. 3. The correct answer is D. Mader, Biology, 12 th Edition, Chapter

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