1. Protist Classification–the Saga Continues
Read the title aloud to students.

2. Learning Objectives Explain what a protist is.
Describe how protists are related to other eukaryotes.
Click to reveal each learning objective in turn.
Read each objective aloud or ask a student volunteer to do so.
To activate prior knowledge, write these words on the board: eukaryotic, unicellular, multicellular, photosynthetic, heterotrophic, motile, immotile. Ask students to identify what kingdoms include organisms with each of these characteristics. Students will probably assign each characteristic to an animal, a plant, or a fungus. Then explain that these characteristics can apply to different members of a group called protists.
Emphasize that, by the end of the presentation, students should be able to explain what protists are and how this group of organisms is related to other groups of eukaryotes.
Distribute the lesson worksheet and instruct students to use it throughout the presentation to organize their note taking about protists. Encourage students to sketch a large Frayer model that fills the page so that they have ample space. For the quadrant “Facts and Characteristics,” instruct students to focus on noting information about the relationship between protists and other groups of eukaryotes.

3. What Are Protists? Photosynthetic Motile Unicellular Multicellular
Freshwater
Marine
Terrestrial
Shelled
Describe several representatives of the protist group, clicking to reveal each photo in turn:
Click to reveal first photo.
1. Photosynthetic, motile, unicellular Euglena are common freshwater protists.
Click to reveal second photo.
2. The shells of diatoms, microscopic marine protists, are intricately patterned.
Click to reveal third photo.
3. A group of unicellular protists called slime molds aggregate into colonies like this one at a certain stage of their life cycle.
Click to reveal fourth photo.
4. Plantlike giant kelp play a critical role in some marine ecosystems, including as anchors for sleeping sea otters.
Ask students to come up with a definition or description of protists based on this small number of representatives.
Click to reveal two groups of adjectives.
Ask students whether the term belongs in their definition of protists.
Guide students to realize that a definition for protists is not easy.

4. Challenges of Protist Classification
Protists are eukaryotes; not members of the plant, animal, or fungi kingdoms.
Some protists are more like members of other kingdoms.
Ask: Many protists are unicellular, but all protists are eukaryotes. What can you infer about the structure of unicellular protists?
Answer: They have membrane-bound organelles including a nucleus.
Ask: What can you infer about the relative sizes of unicellular protists and prokaryotes?
Answer: Unicellular protists are much larger than prokaryotes.
Explain that, for a long time, scientists used “protists” as almost a junk category, assigning a eukaryote there if it didn’t seem to fit anywhere else. Over time, however, as they studied different groups of protists more closely, they found that many of these organisms are far more closely related to members of other eukaryotic kingdoms than they are to other “protists.”
Click to reveal the second bullet point.
Emphasize that the problem with this is that, by definition, members of a kingdom should be more like one another than like members of other kingdoms. For a time scientists tried sorting protists into three taxonomic groups: plantlike protists, animal-like protists, and fungus-like protists. But this simple solution began to fail as biologists learned that many protists do not fit into any of these groups. And many of the animal-like and fungus-like protists are so similar that they belong in a single group, not split into two. Emphasize that these classification difficulties pose a protists dilemma for scientists.

5. 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

6. 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

7. 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.

8. Protist Ancestors
Some ancestors of today’s protists gave rise to plants, animals, and fungi.
Explain that all eukaryotes evolved from prokaryotes. Make sure students understand that animals, plants, and fungi evolved independently from the ancestors of today’s protists.
Misconception Alert: Some students might think protists are simple organisms, more like prokaryotes than eukaryotes, because most are single-celled. Make sure students understand that protists are more complex than prokaryotes.
Ask for a student volunteer to come to the board to circle the part of the cladogram that represents the common ancestor of all eukaryotes.
Click to reveal the circled portion and label.
Ask: If the diagram were to show prokaryote ancestors, from where would they branch off?
Answer: from a point below the common ancestor shown
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.
Ask: Did plants, animals, and fungi arise from the protist species that are alive today?
Answer: No, they evolved from ancestors of today’s protists.
Common eukaryote ancestor

9. Overview: The “Protist” Dilemma
Remind students that a dilemma is a choice between undesirable alternatives.
Ask: What is the protist “dilemma”?
Answer: There is no clear set of characteristics that can be used to classify an organism as a protist.
Ask: Why does placing all protists into one kingdom present a dilemma?
Answer: Many protists are more closely related to members of other kingdoms than they are
to other protists.
Ask: Why don’t biologists place protists into other kingdoms?
Answer: Many protists do not fit into other kingdoms.
Ask: What is the relationship between today’s protists and other groups of eukaryotes?
Answer: They share a common eukaryote ancestor.

10. Protist Structure and Function
Read title aloud to students.

11. Learning Objectives
Describe the various methods of protist locomotion.
Describe how protists reproduce.
Click to reveal each learning objective in turn.
Read each objective aloud or ask a volunteer to do so.
Ask students to recall the ways prokaryotes move and reproduce.
Answer: They move in different ways, such as using flagella and gliding. Some do not move. They reproduce in different ways, such as simple cell division, conjugation, and spore formation.
Tell students that protists move and reproduce in many of the same ways as prokaryotes and, like prokaryotes, protists are diverse in how they carry out these functions.

12. Protists Motion: Amoeboid Movement
Move by changing shape
Use cytoplasmic projections called pseudopods
Tell students that the name for this kind of motion comes from the protists known as amoebas, shown here. An amoeba moves by first extending a pseudopod away from its body. The organism’s cytoplasm then streams into the pseudopod.
Explain that amoebas also use pseudopods to surround and ingest prey. In this set of photos, the prey is a cluster of green algal cells.
Ask for a volunteer to go to the screen to point to a pseudopod.
Click to reveal the label and leader lines.
Point out that amoeboid motion is powered by a protein in the cytoskeleton called actin. Actin is also found in the muscle cells of animals, where it plays an important role in muscle contraction.
Pseudopod

13. Protist Motion: Cilia
Motion by cilia is like oars propelling a large rowboat forward.
Cilia
Explain that cilia (singular: cilium) are short and numerous, and they move somewhat like oars on a boat. Point out that cilia are evenly spaced and beat in a regular, efficient pattern.
Tell students that protists that move by way of cilia are called “ciliates.”

14. Protist Motion: Flagella
Motion by some flagella is like the back-and-forth movement of a single long oar at the back of a boat, propelling it forward.
Flagellum
Explain that flagella (singular: flagellum) are relatively long and usually number only one or two per cell. Some flagella spin like tiny propellers, but most produce a wavelike motion from base to tip, whipping back and forth in a pattern that propels the organism through water.
Tell students that protists that move using flagella are called “flagellates.”
Point out that both cilia and flagella are supported by microtubules and have similar internal structures. The microtubules use energy from ATP to slide against one another. Each stroke of a cilium or flagellum involves thousands of chemical reactions.
Ask students to make an inference about the kinds of environments that ciliates and flagellates live in.
Ask: Based on their structure and type of locomotion, in what kind of environments would you expect to find ciliates and flagellates?
Answer: aquatic environments
Be sure students understand that, for tiny organisms such as these, an aquatic environment could be large like a pond or even as small as a few drops of water or moist soil or in the fluids of another organism’s body!

15. Protist Motion: Passive
Nonmotile
Form reproductive structures called spores that can enter the cells of other organisms and live as parasites.
Explain that some of the most important protists are nonmotile, that is, they cannot move under their own power. But being nonmotile does not mean they stay in one place. One example of a nonmotile protist is Plasmodium (left), which is carried by mosquitoes and causes malaria. Another example is Cryptosporidium (right), which is spread through contaminated water and causes intestinal disease. Protists such as these form reproductive structures called spores that can enter the cells of other organisms and live as parasites.
Cryptosporidium – spread through contaminated water, causes intestinal disease
Plasmodium – carried by mosquitos, causes malaria

16. Protists Reproduction: Cell Division
Amoebas and many other protists produce new individuals through mitosis.
Distribute the lesson worksheet and instruct students to make a three-circle Venn diagram to compare forms of reproduction and nonreproductive sexual processes in protists: Cell Division, Conjugation, Alternation of Generations.
Explain that amoebas reproduce by mitosis; that is, they duplicate their genetic material and then simply divide into two genetically identical cells. Most other protists have phases in their life cycle in which they also produce new individuals by mitosis.
Ask students to consider what advantages and disadvantages of this form of reproduction are. Guide them to conclude that mitosis enables protists to reproduce rapidly, especially under ideal conditions, but that it produces cells that are genetically identical to the parent cell, and thus limits the development of genetic diversity.

17. Protist Reproduction: Conjugation
Micronucleus
Micronucleus
undergoes meiosis.
Remaining micronucleus
undergoes mitosis.
Explain that paramecia and most ciliates also reproduce asexually by mitotic cell division. However, under stress, such as during a change in environmental conditions, paramecia can remake themselves through conjugation—a process in which two organisms exchange genetic material.
Ask: Why would an exchange of genetic information be beneficial under stressful conditions?
Sample Answer: Exchanging genetic material increases genetic diversity, which could allow for new combinations of traits potentially favorable to new environmental conditions.
Explain that paramecium has two types of nuclei: a macronucleus and one or more smaller micronuclei. The micronucleus is a bit like a reference library where books don’t circulate—it holds a “reserve copy” of every gene in the cell. The macronucleus is more like a lending library—it has multiple copies of the genes the cell uses in its day-to-day activities.
Have a volunteer go to the board to write on the labels for macronucleus and micronucleus on the far left portion of the diagram.
Click to reveal the correct answers.
First, two paramecia attach to each other, as shown at far left.
The diploid micronuclei of each paramecium undergo meiosis.
Click to reveal the label for meiosis.
Ask: Are the four micronuclei in each cell haploid or diploid?
Answer: haploid
3. In each cell, three of the haploid micronuclei disintegrate.
Click to reveal the label for disintegration.
4. The remaining micronucleus in each cell undergoes mitosis.
Click to reveal the label for mitosis.
Ask: Is the remaining micronucleus haploid or diploid? Will its daughter cells following mitosis be haploid or diploid?
Answer: haploid; haploid
Macronucleus
Three micronuclei
disintegrate.

18. Protist Reproduction: Conjugation, cont.
Cells exchange
one micronucleus.
New macronucleus
forms from
micronucleus.
Click to reveal callout for cells exchanging micronucleus.
5. The two cells exchange one haploid micronucleus from each pair.
Click to reveal callout for micronuclei fusing and macronucleus disintegrating.
6. In each cell, the micronuclei fuse to form a single diploid micronucleus, and the macronuclei disintegrate.
Click to reveal callout for new macronucleus forming from micronucleus.
7. Each cell forms a new macronucleus from its micronucleus.
Ask: Is the final macronucleus haploid or diploid? How do you know?
Answer: Diploid; the macronucleus formed from a micronucleus formed through joining of two haploid nuclei.
Click to reveal the diploid label at far right.
Ask: How is conjugation similar to mitosis?
Answer: A cell that has the same number of chromosomes as the parent cell results—in this case a diploid cell.
Ask: How is conjugation similar to meiosis and fertilization?
Answer: The end result is a diploid cell with recombined genes.
Ask: What is the advantage of conjugation for a paramecium species?
Answer: Conjugation provides new combinations of genes.
Be sure to emphasize that conjugation is NOT a type of reproduction because no new individuals are formed. It is, however, a sexual process, using meiosis to produce new combinations of genetic information. In a large population, conjugation helps produce and maintain genetic diversity, the raw material for evolution.
Micronuclei fuse;
macronucleus
disintegrates.
Diploid

19. Alternation of Generations: Overview
Fertilization
Sexual
reproduction
Meiosis
Asexual
reproduction
Explain that many protists have complex sexual life cycles in which they alternate between a diploid and a haploid phase, a process known as alternation of generations. An example is the life cycle of a type of protist known as a water mold. Water molds, or oomycetes, thrive on dead and decaying organic matter in water or as parasites of plants on land.
Ask for a volunteer to go the board to label the portions of the cycles in the diagram where you would expect to find haploid calls and where you would expect to find diploid cells.
Click to reveal the key at bottom left which identifies haploid and diploid color-coding.
Tell students that in the next two slides they will look more closely at each cycle.

20. Alternation of Generations: Asexual Stage
Flagellated spores
Spores undergo mitosis.
Sporangium 2N
Explain that water molds grow into long branching filaments consisting of many cells formed by mitotic cell division. Water molds—and many other protists—reproduce asexually by producing spores in a structure called a sporangium.
Click to reveal the sporangium and the label.
Point out that in water molds the spores are flagellated.
Click to reveal the label, leader line, and circle for spores.
Explain that spores are disbursed through moisture, and when conditions are favorable, spores undergo mitosis.
Click to reveal mitosis label.
Ask for a volunteer to label in the blank space whether the structure that develops from the spore is 1N or 2N.
Click to reveal the correct answer.
Ask: How does the organism developing from the spore grow?
Answer: through mitosis

21. Alternation of Generations: Sexual Stage
Male nuclei
Fertilization
Egg cell
Male reproductive
structure
Zygotes
Meiosis 2N
Female reproductive
structure
Explain using the diagram that water molds also reproduce sexually by undergoing meiosis and forming male and female structures. These structures produce haploid nuclei that fuse during fertilization, forming a zygote that begins a new life cycle.
Ask: Are the egg cells and male reproductive cells 1N or 2N?
Answer: 1N
Ask for a volunteer to label in the blank space whether each zygote that forms is 1N or 2N.
Click to reveal the correct answer.
Ask: How does the organism developing from the zygote grow?
Answer: through mitosis
Ask: Which form of reproduction results in a greater variety of offspring?
Answer: sexual reproduction

22. Overview: Locomotion and Reproduction1. 2. 3. 4.
Reproduction
Many protists undergo
to produce genetically identical offspring.
In alternation of generations, an organism goes through a
and an stage.
Amoeboid movement
mitosis
Passive movement
Use of cilia
sexual
Use of flagella
asexual
Ask for volunteers to go to the board and list four methods of protist locomotion.
(Answers: amoeboid movement, passive movement, use of cilia, use of flagella)
Click to reveal answers.
Ask for other volunteers to answer verbally with the terms that correctly complete the sentences about protist reproduction.
(Answers: mitosis; sexual, asexual)
Click to reveal answers
Ask: What do paramecia exchange during conjugation?
Answer: haploid nuclei
Ask: Why is conjugation not considered a form of reproduction, even though genetic material is exchanged?
Answer: No new individuals are formed.

23. The Ecology of Protists
Read the title aloud to students.

24. Learning Objectives
Describe the ecological significance of photosynthetic protists.
Describe how heterotrophic protists obtain food.
Identify the symbiotic relationships that involve protists.
Click to reveal each learning objective in turn.
Read each objective aloud or ask a volunteer to do so.
Distribute the lesson worksheet and instruct students to use the worksheet to build a cluster diagram to summarize and organize information from the presentation about the ecological roles of protists. Suggest to students that the first layer of bubbles out from the center (“Ecological Roles”) identify the major categories of ecological (feeding) roles discussed in the presentation, which they will find in the slide headers.

25. Photosynthetic Protists
Ask: What cell structure would you expect photosynthetic protists to have in common with plants?
Answer: chloroplasts
Explain that photosynthetic protists play major roles in maintaining the health and well-being of many organisms and ecosystems. The position of photosynthetic protists at the base of the food chain makes much of the diversity of aquatic life possible.
Click to reveal first photo.
1. Supporting Coral Reefs: Coral reefs provide food and shelter to many marine species. Protists known as zooxanthellae provide most of the coral’s energy needs by photosynthesis. By nourishing coral animals, these algae help maintain the health and equilibrium of the coral ecosystem. Coralline red algae also help to provide calcium carbonate to stabilize growing coral reefs.
Click to reveal second photo.
2. Feeding Fish and Whales: About half of the photosynthesis that takes place on Earth is carried out by phytoplankton, which provide a direct source of nourishment for organisms as diverse as shrimp and baleen whales. And they are an indirect source of nourishment for humans, who feed on fish species like tuna, which feed on fish that ultimately feed on photosynthetic protists.
Click to reveal third photo.
3. Providing Shelter: The largest known protist is giant kelp, a brown alga that can grow to more than 60 meters in length. Kelp forests provide shelter for many marine species, and the kelp itself is a source of food for sea urchins. Another brown alga, called sargassum, forms huge floating mats many kilometers long in an area of the Atlantic Ocean near Bermuda known as the Sargasso Sea.
Click to reveal fourth photo.
4. Recycling Wastes: Many protists grow rapidly in regions where sewage is discharged, where they play a vital role in recycling waste materials. When the amount of waste is excessive, however, populations of protists like euglena can grow to enormous numbers and create an algal bloom. Algal blooms can disrupt ecosystem homeostasis. In another example, blooms of marine protists called dinoflagellates create what is known as a red tide. The toxins produced by these protists can poison fish and shellfish, and disrupt human health as well.
Ask: Which of these examples is disruptive to ecosystem homeostasis?
Answer: Red tides result in toxins that can poison fish and shellfish.

26. Heterotrophic Protists: Paramecium
Macronucleus
Oral groove
Gullet
Contractile
vacuole
Ask: What is the difference between autotrophs and heterotrophs?
Answer: Autotrophs make their own food, and heterotrophs must ingest other organisms for food.
Explain that many protists are heterotrophs. Some heterotrophic protists engulf and digest their food, while others live by absorbing molecules from the environment.
Remind students that amoebas can capture and digest their food, surrounding a cell or particle with their pseudopods and then taking it inside themselves to form a food vacuole, a small cavity in the cytoplasm that temporarily stores food. Once inside the cell, the material is digested rapidly, and the nutrients are passed along to the rest of the cell.
Explain that paramecium and other ciliates use their cilia to sweep food particles into the gullet, an indentation in one side of the organism. The particles are trapped in the gullet and forced into food vacuoles that form at its base. The food vacuoles pinch off into the cytoplasm and eventually fuse with lysosomes, which contain digestive enzymes. Waste materials are emptied into the environment when the food vacuole fuses with a region of the cell membrane called the anal pore.
As you identify each structure, click to reveal the labels.
Ask students to identify the function of each structure.
Ask for a volunteer to circle the portion of the diagram where food vacuoles form.
Click to reveal the circle at the base of the gullet.
Cilia
Micronucleus
Food vacuoles

27. Heterotrophic Protists: Slime Mold Life Cycle
Flagellated cell
Spore
Meiosis
Fertilization
Zygote
Mature
sporangium
Amoebas
Feeding
plasmodium
Use the diagram to explain the slime mild life cycle. Explain that slime molds feed on decaying matter in places that are damp and rich in organic matter—on the floor of a forest or a backyard compost pile, for example. They play key roles in recycling nutrients.
At one stage in their life cycle, shown here, slime molds exist as a collection of individual amoeba-like cells. Eventually these aggregate to form a large structure known as a plasmodium, which may continue to move. The feeding-plasmodium stage in the slime-mold life cycle is a collection of many amoeba-like organisms—in some species, these organisms are contained within a single cell membrane.
The plasmodium eventually develops sporangia, in which meiosis produces haploid spores that grow into amoeba-like or flagellated cells. The flagellated cells then fuse to produce diploid zygotes that repeat the cycle.
Have volunteers go to the board to point out or label the spores and the zygotes.
Click to reveal the correct labels.
Ask: Are the spores 1N or 2N?
Answer: 1N
Ask: Is the zygote 1N or 2N?
Answer: 2N
Ask: Which stage(s) include cells that have flagella?
Answer: the haploid flagellated cells
Ask: Which stage(s) include cells that use pseudopods for movement?
Answer: the haploid amoebas and the large group of amoeba-like organisms that make up
a plasmodium
Ask: Which stage(s) include cells that cannot move on their own?
Answer: spores
Explain that some protists survive by absorbing molecules that other organisms have released to the environment. Water molds, for example, which look like white fuzz, grow on dead or decaying plants and animals, absorbing food molecules through their cellulose cell walls and cell membranes.
Young
sporangium
Mature
plasmodium

28. Symbiotic Protists: Mutualists
Trichonympha
Termites
Have students recall the definition of symbiosis and give examples they have studied in previous lessons. Then review the types of symbiosis: mutualism (both species benefit), commensalism (one species benefits and the other is neither harmed nor helped), and parasitism (one species is helped by harming the other).
Use this figure to discuss the mutualistic relationship of termites and Trichonympha. Trichonympha is a flagellated protist that lives within the digestive system of various species of termites and makes it possible for the insects to digest wood. Termites themselves do not have enzymes to break down the cellulose in wood. Trichonympha and other organisms in the termite’s gut manufacture an enzyme called cellulase that breaks the chemical bonds in cellulose, making it possible for termites to digest wood.
Ask: Why is the relationship shown here a good example of mutualism.
Answer: Termites benefit because Trichonympha breaks down the cellulose in wood, which allows termites to gain nutrients from it. Trichonympha gets a safe home inside the termite and a steady supply of wood to eat.
Ask: What would happen to a termite if its Trichonympha colony died?
Answer: The termite would also die because of its inability to break down cellulose for food.

29. Symbiotic Protists: Parasites
Explain that parasitic protists are responsible for some of the world’s deadliest diseases, including several kinds of debilitating intestinal diseases, African sleeping sickness, and malaria. Waterborne protists are found in streams, lakes, and oceans. Most cause little harm to humans, but some of these microorganisms are parasites that cause serious problems.
Point out that water supplies contaminated by animal or human feces can spread protist parasites, causing serious and sometimes deadly outbreaks of intestinal disease.
Click to reveal the photo of Giardia.
Explain that the flagellated protist Giardia shown at top left causes severe diarrhea and digestive system problems. Even crystal-clear streams may be contaminated with Giardia, which produces tough cysts that can be killed only by boiling water thoroughly or by adding iodine to the water.
Explain that flagellated protists of the genus Trypanosoma cause African sleeping sickness. Trypanosomes are spread from person to person by the bite of the tsetse fly. They destroy blood cells and infect other tissues in the body, including nerve cells. Severe damage to the nervous system causes some individuals to lose consciousness and lapse into a deep and sometimes fatal sleep, from which the disease gets its name.

30. Symbiotic Protists: Parasites
Describe for students the two species shown on the slide:
1. Entamoeba causes a disease known as amebic dysentery. The amoebas live in the intestines, where they absorb food from the host. They also attack the wall of the intestine itself, shown here, destroying parts of it and causing severe bleeding.
2. Cryptosporidium is resistant to the chlorine compounds often used to sanitize drinking water and therefore poses a special threat to public water systems. In 2008, an outbreak in Utah sickened more than 2,000 people.
Lead a short discussion about some of the protists that parasitize humans. Tell students that the protists shown here and on the previous slide are intestinal pathogens, and are passed out of the body in feces. In places where sanitation is poor, the protists may contaminate water supplies and food. Students might be surprised to learn that Giardia and Cryptosporidium are commonly reported in the United States. They are primarily spread via recreational waters, such as lakes, swimming pools, and water parks. Many cases of Giardia are also transmitted directly from person to person.
Ask: How could the waterborne spread of parasitic protists be prevented?
Sample Answer: treatment of water supplies and asking people who have intestinal illnesses not to use recreational waters
Cryptosporidium
Entamoeba

31. Symbiotic Protists: Plasmodium Life Cycle2 3 1
Explain that malaria is one of the world’s most serious infectious diseases. More than 1 million people die from malaria every year, many of them children. Malaria is caused by Plasmodium, a spore-forming parasitic protist carried by the female Anopheles mosquito.
Click to reveal numbered steps as you use the diagram to describe the life cycle of plasmodium.
A female Anopheles mosquito bites a human infected with malaria and picks up Plasmodium gametes.
Fertilization occurs in the mosquito’s digestive tract, and Plasmodium sporozoites develop.
The infected mosquito bites another human, transmitting the sporozoites through its saliva to the human bloodstream.
Inside the human body, the sporozoites infect liver cells, develop into merozoites, and then infect red blood cells.
Infected red blood cells burst, causing malaria symptoms in the human host. Some of the released merozoites form gametes.
Ask: Are sporozoites haploid or diploid? How do you know?
Answer: Diploid; they form through fertilization.
Ask: How many hosts does Plasmodium need to complete its life cycle?
Answer: two 4
Blood cell
Merozoites 5

32. Ecology of Protists Overview1 2 3 4 5
Use the image on this slide to review the major content from this presentation:
Ask: Which two of these organisms engages in mutualistic symbiotic relationships with other organisms?
Answer: 4 (giant kelp) and 2 (Trichonympha)
Ask: Which of these organisms causes intestinal disease?
Answer: 5 (Giardia)
Ask: How does organism 3 obtain nutrients?
Answer: A slime mold’s feeding stage is made up of amoeba-like cells that engulf food particles from decaying matter.
Ask: How does organism 1 obtain nutrients?
Answer: Paramecium is heterotrophic, using its cilia to sweep food particles into its gullet.
Ask: Contrast how a water mold and a paramecium obtain food.
Answer: Water mold absorbs molecules; a paramecium sweeps food into its gullet using cilia.