CHAPTER OUTLINE
29.1 Protists
Protists are eukaryotes. For the most part, protists are unicellular and microscopic. Protists are any eukaryotic organism that is not a plant, animal or fungus and are most likely related to the first eukaryotic cell to have evolved.
Biology of Protists
Protists can be unicellular, colonial, or multicellular. They are structurally diverse. The variability of protists also extends to their lifestyles and modes of reproduction. Most carry out asexual reproduction with sexual spores or cysts as an option if environmental conditions are unfavorable. Some protists are nonmotile, others use flagella, cilia, or psuedopods for locomotion. Protozoan is a common term for a heterotrophic, usually motile, unicellular protist.
Diversity of Protists
In this chapter, we will group the protists into six groups according to some of their major shared characteristics: photosynthetic protists, flagellates, ciliates, amoeboids, sporozoans, and water molds and slime molds.
Photosynthetic Protists
Algae are photosynthetic eukaryotes that can be unicellular or form colonies or filaments. Some types are multicellular seaweeds. In aqueous environments, small algae are often a component of suspended, photosynthesizing organisms termed phytoplankton. Algae contain chloroplasts and perform photosynthesis.  Algae generally have a rigid cell wall, sometimes made of cellulose. Green algae are believed to be closely related to the first plants. Diatoms are the most numerous unicellular algae in the oceans and are important primary producers at the base of marine food chains. Diatoms have a wide variety of elaborate shells made of silica. Dinoflagellates are best known for the red tide they cause when they greatly increase in number. One species in red tides produces a very potent toxin. Red algae are multicellular and produce a number of useful gelling agents. The brown algae are the conspicuous multicellular seaweeds that dominate rocky shores along cold and temperate coasts.
Flagellates
Flagellates are heterotrophic protists that propel themselves using one or more flagella. Most are symbiotic, and many are parasitic. Euglenoids are freshwater unicellular organisms that typify the problem of classifying protists. Many have chloroplasts, but some do not.  
Ciliates
Ciliates are the largest group of protozoans. All of them have cilia, hairlike   structures that rhythmically beat, moving the cell forward or in reverse. Paramecium is the most widely known ciliate. 
Amoeboids
Amoeboids move by pseudopods, processes that form when cytoplasm streams forward in a particular direction. They usually live in aquatic environments.   Foraminiferans and radiolarians are related amoeboid groups that have an   external skeleton.
Sporozoans
Sporozoans produce spores and are either intercellular or extracellular parasites.
Water Molds and Slime Molds
Water molds and slime molds are classified as protists.
Water Molds
Most water molds are saprotrophs, meaning that they feed on dead organic matter. They usually live in water.
Slime Molds
Slime molds feed on dead plant material in forests and woodlands. 
Cellular Slime Molds
Cellular slime molds can exist as individual amoeboid cells. They are common in soil, where they feed on bacteria and yeasts.
Protozoal Diseases of Humans
A relatively few protists cause human diseases.
Malaria
The most widespread and dangerous sporozoan disease is malaria. It can be caused by several sporozoan parasites in the genus Plasmodium, which have a complex life cycle that involves transmission by a mosquito vector. 
Other Sporozoan Diseases
Toxoplasma gondii is commonly transmitted by cat feces and can be harmful to a developing fetus.  Cryptosporidium parvum is common in surface waters and in    the feces of animals and birds, it usually causes self-limiting gastroenteritis.
Diseases Caused by Flagellates
African sleeping sickness, Chagas disease, giardiasis, and vaginitis are all    caused by flagellates.
Diseases Caused by Amoeboids
Amoebic dysentery, corneal inflammations and serious infections are caused by   amoeboids and more rarely, an amoeboid protest can invade and attack the    human nervous system, nearly always resulting in death.
29.2 Fungi
Fungi are a structurally diverse group of eukaryotes that are strict heterotrophs. Most fungi are saprotrophs, which decompose dead plants, animals, and microbes. 
Biology of Fungi
The body of a fungus is composed of a mass of individual filaments called hyphae;   collectively, the mass of filaments is called a mycelium. The cell walls of fungal cells    contain chitin, not cellulose. The energy reserve of fungi is not starch, but glycogen.   Fungi are nonmotile and most do not have flagella. Fungi produce windblown spores,   haploid reproductive cells, during both asexual and sexual reproduction. 
Diversity of Fungi
Fungi are traditionally classified based on their mode of sexual reproduction.
Chytrid Fungi
The chytrid fungi may have been the first type of fungi to evolve. They are unique among the fungi because they are aquatic and they produce flagellated reproductive cells.
Zygospore Fungi
The zygospore fungi are mainly saprotrophs. A sporangium is a capsule that   produces spores. Rhizopus stolonifer, the common bread mold, reproduces    sexually, the ends of + and – hyphae join, haploid nuclei fuse, and a thick-walled zygospore results. 
Sac Fungi
The sac fungi are named for their characteristic cuplike sexual reproductive structure called an ascocarp. Many sac fungi reproduce by producing chains of sexual spores called conidia. Cup fungi, morels and truffles have conspicuous   ascocarps. The original source of penicillin and other species of Penicillium that are necessary to the production of blue cheeses are examples of sac fungi. 
Yeasts
The term yeasts is generally applied to unicellular fungi, and many of   these organisms are sac fungi. Brewer’s yeast is representative of budding yeasts.
Club Fungi
Club fungi are named for their characteristic sexual reproductive structure called a basidium. Mushrooms and shelf or bracket fungi are basidiocarps. Some are posisonous, others produce a hallucinogenic chemical. Smuts and rusts are club fungi that parasitize cereal crops. 
Symbiotic Relationships of Fungi
Fungi commonly form symbiotic relationships with other organisms.
Lichens
Lichens are associations between fungi and cyanobacteria or green algae.     Lichens are efficient at acquiring nutrients and moisture, and therefore can    survive in poor soils as well as on rocks. The body of a lichen has three layers and the fungus forms a thin, tough upper layer and a loosely packed lower layer.
Mycorrhizae
Mycorrhizae are mutualistic relationships between soil fungi and the roots of   most plants, helping them grow more successfully in dry or poor soils. AM fungi are a recently recognized group whose name stands for arbuscular mycorrhial   fungi. Arbuscules are branching invaginations the fungus makes when it invades plant roots.
Fungal Diseases of Humans
Fungi tend to cause disease mainly in people who immune system isn’t working properly. Mycoses, fungal diseases of humans, vary in levels of seriousness.
Superficial Mycoses
Most superficial mycoses are confined to the outer layers of the skin, hair, or nails. Fungi called dermatophytes cause infections of the skin called tineas.    Athlete’s foot, ringworm, yeast infections, and thrush are all examples.
Systemic Mycoses
Systemic mycoses refer to fungal infections affecting the internal organs, mainly   the lungs. Histoplasmosis, valley fever, and “sick building syndrome” are all    examples.
Antifungal Drugs
The similarities between fungal cells and human cells make it a challenge to design antimicrobials against fungi that do not also harm humans. Fungal skin infections can be treated with a topical medication, but systemic fungal infections must have medication taken into the body, resulting in a problem with side effects.

 

1.   Which of the following is correct regarding the phylogenetic nature of kingdom Protista?
a.   Scientists have placed all of the known protist species into at least one of the major monophyletic clades.
b.   All members of the kingdom share characteristics that are unique to Protists.
c.   The kingdom as a whole is paraphyletic.
d.   All of the above are correct.

The correct answer is c—
A.  Answer a is incorrect. The majority of protists have not yet been classified within single, monophyletic clades.

The correct answer is c—
B. Answer b is incorrect. The kingdom is an artificial construct, in reality the members are defined by a lack of common characteristics with other kingdoms rather than many shared characteristics.

The correct answer is c—The kingdom as a whole is paraphyletic.
C. Answer c is correct. See Figure 29.1.

The correct answer is c—
D. Answer d is incorrect. Answer c is correct.

2.   Which of the following events is believed to have occurred first in eukaryotic evolution?
a.   Secondary endosymbiosis of chloroplasts
b.   Endosymbiosis of a cyanobacteria
c.   Endosymbiosis of an energy-producing bacteria
d.   Infolding of the plasma membrane

The correct answer is d—
A. Answer a is incorrect. Refer to Figure 29.4.

The correct answer is d—
B. Answer b is incorrect. Refer to Figure 29.4.

The correct answer is d—
C. Answer c is incorrect. Refer to Figure 29.4.

The correct answer is d—Infolding of the plasma membrane
D. Answer d is correct. Refer to Figure 29.4.

3.   Which of the following would be a key identifying characteristic of an organelle that has undergone secondary endosymbiosis?
a.   A single plasma membrane
b.   A set of two plasma membranes
c.   Four plasma membranes
d.   None of the above

The correct answer is c—
A. Answer a is incorrect. Refer to Figure 29.5.

The correct answer is c—
B. Answer b is incorrect. Refer to Figure 29.5.

The correct answer is c—Four plasma membranes
C. Answer c is correct. Consider chloroplast endosymbiosis. In the primary endosymbiotic event, the single-membraned bacteria are engulfed by the eukaryotic membrane, resulting in two membranes. If this organism now enters another eukaryotic cell by endosymbiosis, there will be two membranes around the original chloroplast, plus the cell membrane of the eukaryote that engulfed it in the primary endosymbiotic event (three membranes). However, the membrane of the second engulfing endosymbiont envelops the entire cell with its own membrane. This leaves the secondary endosymbiont with four membranes around the chloroplast.

The correct answer is c—
D. Answer d is incorrect. Refer to Figure 29.5.

4.   The evolution of which of the following provides for higher levels of genetic recombination and variation?
a.   Schizogony
b.   Sexual reproduction
c.   Asexual reproduction
d.   Budding

The correct answer is b—
A. Answer a is incorrect. Schizogony does not provide for high levels of variation.

The correct answer is b—Sexual reproduction
B. Answer b is correct. Combined with fertilization, sexual reproduction provides for a high level of genetic recombination.

The correct answer is b—
C. Answer c is incorrect. A sexual reproduction does not provide for high levels of variation.

The correct answer is b—
D. Answer d is incorrect. Budding does not provide for high levels of variation.

5.   A protist that lacks mitochondria would most likely be classified with the ________.
a.   Rhodophyta
b.   Parabasalida
c.   Euglenozoa
d.   Stramenophila

The correct answer is b—
A. Answer a is incorrect. Rhodophyta possess mitochondria.

The correct answer is b—Parabasalids
B. Answer b is correct. The lack of mitochondria is a characteristic of the parabasalida and the diplomonads.

The correct answer is b—
C. Answer c is incorrect. The Euglenozoa possess mitochondria.

The correct answer is b—
D. Answer d is incorrect. The Stramenophila possess mitochondria.

6.   Which of the following statements best describes the term kinetoplastid?
a.   An organism with a single mitochondrion in each cell
b.   A form of locomotion in the Alveolata
c.   A form of asexual reproduction in the euglenoids
d.   A Golgi-like organelle found in the Alveolata

The correct answer is a—An organism with a single mitochondrion in each cell
A. Answer a is correct. Typanosomes are a form of kinetoplastid.

The correct answer is a—
B. Answer b is incorrect. This term does not apply to the alveolates.

The correct answer is a—
C. Answer c is incorrect. The term is not associated with reproduction.

The correct answer is a—
D. Answer d is incorrect. The name of the Golgi-like organelles in the Alveolata is alveoli.

7.   A species that is photosynthetic, with fine hairs on the flagella, would be classified with which of the following groups?
a.   Chlorophyta
b.   Euglenozoa
c.   Alveolata
d.   Stramenophila

The correct answer is d—
A. Answer a is incorrect. Although photosynthetic, the Chlorophyta lack the fine hairs.

The correct answer is d—
B. Answer b is incorrect. Although some Euglenazoa are photosynthetic, they lack the fine hairs.

The correct answer is d—
C. Answer c is incorrect. Although some Alveolata are photosynthetic, they lack the fine hairs.

The correct answer is d—Stramenophila
D. Answer d is correct. Although fine hairs are not present in all members of this group, it is one of the defining characteristics.

8.   The organism that causes red tide is a(n) _______ and belongs to the clade __________.
a.   apicomplexan; Alveolata
b.   kinetoplastid;  Euglenozoa
c.   dinoflagellate; Alveolata
d.   brown algae; Stramenopila

The correct answer is c—
A. Answer a is incorrect. Apicomplexans are animal parasites.

The correct answer is c—
B. Answer b is incorrect. Red tide is not caused by a member of the Euglenozoa.

The correct answer is c—dinoflagellate; Alveolata
C. Answer c is correct. Red tide is caused by toxins from a dinoflagellate.

The correct answer is c—
D. Answer d is incorrect. Red tide is not caused by a member of the Stramenophila.

9. What characteristic separates the Rhodophyta and the Chlorophyta?
1. Method of locomotion
2. Lack of mitochondria
3. Method of reproduction
4. Form of photosynthetic pigments

 

The correct answers are a and d—
A. Rhodophyta have lost their flagella while some Chlorophyta (e.g. Chlamydomonas) retain flagella.

 

The correct answers are a and d—
B. Both Rhodophyta and Chlorophyta have mitochondria

The correct answers are a and d—
C. Both multicellular Chlorophyta and Rhodophyta have alternation of generations.

The correct answers are a and d—
D. Rhodophyta have photosynthetic pigments not found in Chlorophyta. They include phycoerythrin, phycocyanin, and allophycocyanin.

 

10. Which of the following lines represents a monophyletic group?
a.   Euglenoids
b.   Amoebas
c.   Forams
d.   Slime molds

The correct answer is a—Euglenoids
A. Answer a is correct. Euglenoids are the only monophyletic group on the list.

The correct answer is a—
B. Answer b is incorrect. Amoeba have a paraphyletic origin.

The correct answer is a—
C. Answer c is incorrect. The forams are paraphyletic.

The correct answer is a—
D. Answer d is incorrect. The slime molds are a paraphyletic group.

11. The disease malaria is caused by a species of the genus________, which belongs to the _______.
a.   Giardia; diplomonads
b.   Plasmodium; apicomplexans
c.   Paramecium; ciliates
d.   Trypanosoma; kinetoplastids

The correct answer is b—
A. Answer a is incorrect. Malaria is not caused by a member of this genus or clade.

The correct answer is b—Plasmodium; apicomplexans
B. Answer b is correct.

The correct answer is b—
C. Answer c is incorrect. Malaria is not caused by a member of this genus or clade.

The correct answer is b—
D. Answer d is incorrect. Malaria is not caused by a member of this genus or clade.

12. In the following below, which multicellular eukaryotic kingdom is NOT linked to its correct protistan ancestor?
a.   Viridiplantae—Chlorophyta
b.   Fungi—Oomycetes
c.   Animals—Choanoflagellates
d.   All of the above are linked correctly.

The correct answer is b—
A. Answer a is incorrect. The origin or the plants is rooted in the Chlorophyta.

The correct answer is b—Fungi—Oomycetes
B. Answer b is correct. At one time scientists believed that this was true. Recent evidence has suggested that this is not the origin of the fungi.

The correct answer is b—
C. Answer c is incorrect. The origin of the animals is rooted in the Choanoflagellates.

The correct answer is b—
D. Answer d is incorrect. One of the above is linked incorrectly.

13. One of the earliest examples of multicellularity occurs in the ________.
a.   euglenoids
b.   amoebas
c.   red algae
d.   cellular slime molds

The correct answer is d—
A. Answer a is incorrect. Euglenoids are not multicellular.

The correct answer is d—
B. Answer b is incorrect. Amoebas are not multicellular.

The correct answer is d—
C. Answer c is incorrect. Although multicellular, the red algae are not the earliest example.

The correct answer is d—cellular slime molds
D. Answer d is correct.

14. The origin of which of the following does NOT represent an endosymbiotic event?
a.   Mitochondria
b.   Chloroplasts
c.   Nucleus
d.   All of the above are endosymbiotic events

The correct answer is c—
A. Answer a is incorrect. The origin of mitochondria is due to endosymbiosis with an aerobic bacterium.

The correct answer is c—
B. Answer b is incorrect. The origin of chloroplasts is due to endosymbiosis with a photosynthetic bacterium.

The correct answer is c—Nucleus
C. Answer c is correct. The nucleus originated due to an infolding of the plasma membrane, not endosymbiosis.

The correct answer is c—
D. Answer d is incorrect. One of the above did not originate by endosymbiosis.

15. In Paramecium, removal of which of the following organelles would inhibit sexual reproduction?
a.   The alveoli
b.   The micronucleus
c.   The macronucleus
d.   The cytoproct

The correct answer is b—
A. Answer a is incorrect. This organelle is not associated with reproduction.

The correct answer is b—The micronucleus
B. Answer b is correct. Micronuclei are involved in conjugation and sexual reproduction.

The correct answer is b—
C. Answer c is incorrect. The macronucleus is formed as a result of sexual reproduction, not as a necessary structure for it.

The correct answer is b—
D. Answer d is incorrect. The cytoproct is an exocytoic vesicle and is not involved in reproduction.

Challenge Questions

1.   Many species of diplomonads and parabasilida lack mitochondria, yet remain aerobic. In chapter 9 you were introduced to the mitochondria as the site of aerobic respiration. If these species retained their aerobic capabilities, what must have happened to the metabolic pathways?

Answer—Remember that many species of bacteria are aerobic, although they do not have mitochondria. Therefore, possessing mitochondria is not a necessity. For the aerobic diplomonads and parabasilida that lack mitochondria, the metabolic pathways must have been moved into the cytoplasm or onto other internal membranes of the cell.

2.   Review the diversity of photosynthetic pigments in the Protista. Can photosynthesis be used as a basis of classification? Explain your answer.

Answer—Photosynthesis as a metabolic process represents a clear case of convergent evolution, with many different species trying out a variety of photosynthetic pigments (see the brown and red algae as an example). Therefore, being photosynthetic is not a good characteristic for classification because photosynthetic pathways have diverged since the original cyanobacteria were endosymbiosed. However, the use of specific photosynthetic pigments is often used as a characteristic for classification since similar pigments are usually encoded by similar genes, which suggests an evolutionary link.

3.   Most scientists will agree that the protist kingdom is a mess. Some scientists believe that these organisms should be placed within the multicellular eukaryotic kingdoms (plants, fungi, and animals). Do you think that this approach is practical? Support your answer.

Answer—Answers may vary. The biggest obstacle occurs with the Protista that are neither animal-like, plantlike, or funguslike. An example is the euglenoids, which can obviously be placed in both the plants and animals. Supporters of moving the protistans into the other kingdoms will state that the origins of the three multicellular kingdoms are obviously rooted in the protists. Many evolutionary biologists believe that the concept of kingdoms is no longer useful in constructing evolutionary hypotheses and that it is best to focus on cladistic approaches unconstrained by traditional kingdom names.

4.   You are viewing a previously unidentified alga under a high-powered microscope. The chloroplast appears to have four membranes surrounding it. Which group of algae would you predict is most closely related to your new species? Why?

Answer—The most likely group is the brown algae where secondary endosymbiosis resulted in the four membranes around the chloroplast. Refer to figure 29.5 for a more detailed explanation.