1. Chapter 20 The Protists
(Sections ) 1

2. 20.5 The Alveolates
Dinoflagellates, ciliates, and apicomplexans are single-celled alveolates, with tiny sacs (alveoli) beneath the plasma membrane
Most dinoflagellates and ciliates are aquatic and free-living, but all apicomplexans are parasites
alveolate
Member of a protist lineage having small sacs beneath the plasma membrane; dinoflagellate, ciliate, or apicomplexan

3. Dinoflagellates
Dinoflagellates are whirling aquatic heterotrophs and autotrophs with cellulose plates
Photosynthetic dinoflagellates supply reef-building corals with sugars and oxygen
Some dinoflagellates are bioluminescent
dinoflagellate
Single-celled, aquatic protist with cellulose plates and two flagella; may be heterotrophic or photosynthetic

4. Dinoflagellate Bioluminescence
Figure 20.6 Dinoflagellate bioluminescence. A tropical dinoflagellate (inset) emits light when disturbed, as by the motion of an oar. The flash of light may benefit the cell by warding off predators.

5. Ciliates
Ciliates are aquatic predators and parasites with many cilia, used in locomotion and feeding
Two types of nuclei:
Macronucleus controls daily activities
Smaller micronuclei function in sexual reproduction
ciliate
Single-celled, heterotrophic protist with many cilia

6. Predatory Ciliates
Most ciliates are aquatic predators that feed on bacteria, algae, and one another
Didinium, a barrel-shaped ciliate with tufts of cilia, engulfing a Paramecium covered with cilia

7. Predatory Ciliates prey prey disappearing into predator’s oral opening
Figure 20.7 Freshwater ciliates. A Didinium, a barrel-shaped ciliate with tufts of cilia, catching and engulfing a Paramecium covered with cilia. B Body plan of Paramecium. Mitochondria are present but not shown.
predator A
Fig. 20.7a, p. 315

8. Body Plan of Paramecium

9. Body Plan of Paramecium
food vacuole
gullet
cilia
empty contractile vacuole
Figure 20.7 Freshwater ciliates. A Didinium, a barrel-shaped ciliate with tufts of cilia, catching and engulfing a Paramecium covered with cilia. B Body plan of Paramecium. Mitochondria are present but not shown.
filled contractile vacuole
macronucleus
micronucleus
Fig. 20.7b, p. 315

10. ANIMATION: Ciliate conjugation
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11. ANIMATION: Paramecium Body Plan
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12. Apicomplexans Apicomplexans are parasitic protists
A complex of microtubules at their apical (top) end allows them to pierce and enter a host cell
apicomplexan
Single-celled parasite that lives inside animal cells
Life cycle often involves more than one host species

13. Key Concepts Single-Celled Lineages
Most protist lineages are entirely single-celled
They include flagellated protozoans, shelled cells called foraminiferans and radiolarians, and the alveolates (ciliates, dinoflagellates, and apicomplexans)

14. 20.6 Malaria and the Night-Feeding Mosquitoes
Malaria is a leading cause of human death, killing more than 1.3 million people every year
Plasmodium, a single-celled apicomplexan, causes malaria
Mosquitoes carry Plasmodium from one human host to another

15. Malaria
Ongoing Plasmodium infection can lead to convulsions, coma, and eventual death
Malaria has been a potent selective force on humans in Africa because the allele that produces sickle-cell anemia also provides protection against malaria
Natural selection also acts on Plasmodium, which has become resistant to several antimalarial drugs

16. Life Cycle of Plasmodium
1. Infected mosquito bites a human
Sporozoites enter blood, which carries them to the liver
2. Sporozoites reproduce asexually in liver cells, mature into merozoites
Merozoites leave the liver and infect red blood cells.
3. Some merozoites reproduce asexually in red blood cells

17. Life Cycle of Plasmodium (cont.)
4. Some merozoites differentiate into gametocytes
5. Female mosquito sucks blood from the infected person
Gametocytes in blood enter her gut and mature into gametes, which fuse to form zygotes
6. Meiosis of zygotes produces cells that develop into sporozoites
Sporozoites migrate to the mosquito’s salivary glands

18. Life Cycle of Plasmodium

19. sporozoites in salivary glands
Life Cycle of Plasmodium
Infected mosquito bites a human. Sporozoites enter blood, which carries them to the liver. 1
Sporozoites reproduce asexually in liver cells, mature into merozoites. Merozoites leave the liver and infect red blood cells. 2
zygote
gametocytes in gut
gametocytes 4 5
asexual blood cycle 3
Merozoites reproduce asexually in some red blood cells. 3 6 1
sporozoites
merozoites
In other red blood cells, merozoites differentiate into gametocytes. 4
sporozoites in salivary glands
mosquito takes up gametocytes or injects sporozoites 2
A female mosquito bites and sucks blood from the infected person. Gametocytes in blood enter her gut and mature into gametes, which fuse to form zygotes. 5
liver stage
Figure 20.8 Life cycle of one of the Plasmodium species that cause malaria.
Meiosis of zygotes produces cells that develop into sporozoites. The sporozoites migrate to the mosquito’s salivary glands. 6
Fig. 20.8, p. 316

20. Life Cycle of Plasmodium5
zygote
gametocytes in gut 6
gametocytes 4
asexual blood cycle 3 1
sporozoites 2
liver stage
sporozoites in salivary glands
merozoites
mosquito takes up gametocytes or injects sporozoites
Figure 13.18: Animated!
Life cycle of the apicomplexan that causes malaria. (1) Infected mosquito bites a human. Sporozoites enter the blood, which carries them to the liver. (2) Sporozoites reproduce asexually in liver cells, then mature into merozoites. Merozoites leave the liver and enter the bloodstream, where they infect red blood cells. (3) Inside some red blood cells, merozoites reproduce asexually. These cells burst and release more merozoites into the bloodstream. (4) Inside other red blood cells, merozoites develop into male and female gametocytes. (5) A female mosquito bites and sucks blood from the infected person. Gametocytes in red blood cells enter her gut and mature into gametes, which fuse to form zygotes. (6) The zygotes develop into sporozoites that migrate to the mosquito’s salivary glands.
Stepped Art
Fig , p. 255

21. ANIMATION: Apicomplexan life cycle
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22. 20.7 Stramenopiles
Stramenopiles include heterotrophic water molds, single- celled diatoms, and multicelled brown algae
Stramenopiles are defined mainly by genetic similarities, rather than visible traits

23. Water Molds
Water molds are decomposers and parasites that grow as a mesh of absorptive filaments
Some parasitic species are important plant pathogens: Phytophthora destroy crops and forests
water mold
Protist that grows as nutrient-absorbing filaments

24. Water Molds
Some water molds grow as fuzzy white patches on fish in fish farms and aquariums

25. Diatoms Diatoms are silica-shelled photosynthetic cells
Some cells live individually and others form chains – they are particularly abundant in cool waters
diatom
Single-celled photosynthetic protist with brown accessory pigments in its chloroplasts and a two-part silica shell

26. Living Diatom
Chloroplasts with a brown accessory pigment (fucoxanthin) are visible through the glassy silica shell
Figure 20.9 A Living diatom. Chloroplasts are visible through the glassy silica shell. See also Figure 20.2C. B Diatomaceous earth is shells of ancient diatoms. It kills crawling insects by scratching their surface so they lose water, dry out, and die.

27. Diatomaceous Earth
Deposits of ancient diatom shells are mined as diatomaceous earth
It kills crawling insects by scratching their surface so they lose water, dry out, and die
Figure 20.9 A Living diatom. Chloroplasts are visible through the glassy silica shell. See also Figure 20.2C. B Diatomaceous earth is shells of ancient diatoms. It kills crawling insects by scratching their surface so they lose water, dry out, and die.

28. Brown Algae
Brown algae, ranging in size from microscopic strands and giant kelps, contain the brown pigment fucoxanthin
Brown algae are the source of algins, used as thickeners and emulsifiers
brown alga
Multicelled marine protist with a brown accessory pigment in its chloroplasts

29. Kelp “Forest”
Giants kelps are the largest protists, reaching 30 meters (100 feet) tall
Figure Kelp ‘forest.’ These brown algae are the largest protists.

30. Key Concepts Brown Algae and Relatives
Brown algae are an entirely multicellular group of protists
They are members of the same lineage as single-celled photosynthetic cells called diatoms, and filamentous heterotrophs called water molds

31. 20.8 Red Algae and Green Algae
Red algae and green algae belong to the same lineage as land plants
red alga
Photosynthetic protist that deposits cellulose in cell walls, stores sugars as starch, and has chloroplasts containing chlorophyll a and red pigments called phycobilins
green alga
Photosynthetic protist that deposits cellulose in cell walls, stores sugars as starch, and has chloroplasts containing chlorophylls a and b

32. Red Algae Do It Deeper Most red algae are multicelled and marine
Accessory pigments called phycobilins allow them to capture light even in deep waters
Red algae are commercially important as the source of agar, carrageenan, and dry sheets (nori) used for wrapping sushi

33. A Red Alga: Porphyra
Like many multicelled algae, the Porphyra life cycle is an alternation of generations
It alternates between haploid bodies (gametophytes) and diploid multicelled bodies (sporophytes)

34. Key Terms alternation of generations
Of land plants and some protists, a life cycle in which haploid and diploid multicelled bodies form
gametophyte
Gamete-producing haploid body that forms in the life cycle of land plants and some protists
sporophyte
Spore-forming haploid body that forms in the life cycle of land plants and some protists

35. 6 Steps in Porphyra Life Cycle
1. The diploid gametophyte is sheetlike
2. Gametes form at its edges
3. Fertilization produces a diploid zygote
4. The zygote develops into a diploid sporophyte
5. Haploid spores form by meiosis on the sporophyte body, and are released
6. Spores germinate and develop into a new gametophyte

36. Life Cycle of Porphyra

37. Life Cycle of Porphyra sporophyte (2n) zygote Diploid stage4
sporophyte (2n)
zygote 3 5
Diploid stage
Fertilization
Meiosis
Haploid stage
germinating spore (n) 2
male gametes
female gametes 6
Figure Life cycle of a multicellular red alga (Porphyra). 1
gametophyte (n) 1
The haploid gametophyte is sheetlike. 2
Gametes form at its edges. 3
Fertilization produces a diploid zygote. 4
The zygote develops into a diploid sporophyte.
Haploid spores form by meiosis on the sporophyte body, and are released. 5
Spores germinate and develop into a new gametophyte. 6
Fig , p. 318

38. Life Cycle of Porphyra sporophyte (2n) zygote Diploid stage4
Life Cycle of Porphyra
Fertilization
zygote 2 3
Diploid stage
Meiosis
germinating spore (n) 5 6
gametophyte (n) 1
male gametes
female gametes
Haploid stage
Figure Life cycle of a multicellular red alga (Porphyra).
Stepped Art
Fig , p. 318

39. ANIMATION: Red alga life cycle
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40. Green Algae
Green algae are the closest relatives of land plants – they may be single cells, colonial, or multicelled
Like land plants, some of the multicelled algae have an alternation of generations: a diploid, spore-producing sporophyte and a haploid gamete-producing gametophyte

41. Some Green Algae
Chlamydomonas is a single- celled species that uses two flagella to swim
Volvox colonies have many flagellated cells – with new colonies (bright green spheres) inside each parent colony
Figure A sampling of green algal diversity.

42. More Green Algae
Multicellular sea lettuce (Ulva) cling to rocks along marine coasts
Freshwater charophytes (Chara) are the closest relatives of land plants
Figure A sampling of green algal diversity.

43. Evolutionary Connections to Land Plants
Red algae, green algae, and land plants all have a cell wall made of cellulose, store sugars as starch, and have chloroplasts
Charophyte algae (Chara) are the closest relatives of land plants: Unlike most other green algae, Chara cells divide by cell plate formation, and have plasmodesmata cytoplasmic connections

44. Key Concepts Red Algae, Green Algae
Red algae and green algae are single-celled and multicelled aquatic producers
Red algae have pigments that allow them to live in deep waters
Green algae are the closest relatives of land plants and have the same pigments as them

45. ANIMATION: Green Alga Life Cycle
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46. 20.9 Amoebozoans
Amoebozoans include heterotrophic free-living amoebas and slime molds
Many are solitary, but some display communal behavior and cell differentiation that hint at complexities to come in animals
amoebozoan
Shape-shifting heterotrophic protist with no pellicle or cell wall; an amoeba or slime mold

47. Solitary Amoebas Amoebas live as single cells
Most amoebas are predators in freshwater habitats – others live in the gut of humans and other animals
amoeba
Single-celled protist that extends pseudopods to move and to capture prey

48. Amoeba proteus Amoeba proteus is a predator in freshwater habitats
The cell has no fixed shape; it feeds or shifts position by extending lobes of cytoplasm (pseudopods)
Figure An amoeba. The cell has no fixed shape. It feeds or shifts position by extending lobes of cytoplasm (pseudopods).

49. Slime Molds Slime molds are “social amoebas”
Animal signaling mechanisms may have started in amoebozoan ancestors
There are two types, common on the floor of temperate forests:
Plasmodial slime molds
Cellular slime molds

50. Plasmodial Slime Molds
The plasmodial slime molds feed as a large multinucleated mass—a plasmodium—that oozes along the forest floor and over logs, devouring bacteria
When food runs low, the mass forms spore-bearing structures
plasmodial slime mold
Protist that feeds as a multinucleated mass
Forms a spore-bearing structure when environmental conditions become unfavorable

51. Plasmodial Slime Mold (Physarum)
Plasmodium and spore-bearing fruiting bodies
Figure Plasmodial slime mold (Physarum). A These protists feed as a large multinucleated mass—a plasmodium —that oozes along the forest floor and over logs, devouring bacteria. B When food runs low, the mass forms spore-bearing structures.

52. Cellular Slime Molds
Cellular slime molds live mostly as individual cells
When food is scarce, cells aggregate into a mobile, multicelled “slug” that seeks a suitable spot, differentiates into a fruiting body, and disperses spores
cellular slime mold
Amoeba-like protist that feeds as a single predatory cell; joins with others to form a multicellular spore-bearing structure when conditions are unfavorable

53. Life Cycle of a Cellular Slime Mold
Life cycle of Dictyostelium discoideum
Germination of spores releases amoeboid cells that restart the life cycle

54. Life Cycle of a Cellular Slime Mold
Spores give rise to amoeboid cells. 5
A fruiting
body forms
with resting
spores atop
a stalk. 4
Cells feed and multiply by mitosis. 1
Mature fruiting body
When food
is scarce, cells aggregate. 2
Figure Life cycle of Dictyostelium discoideum, a cellular slime mold.
The cells form a slug. It may start to develop as a fruiting body right away, or migrate about. In the slug, cells become prestalk (red) and prespore (tan) cells. 3
Migrating slug
stage
Fig , p. 321

55. Life Cycle of a Cellular Slime Mold
Spores give rise to amoeboid cells. 5 4
Mature fruiting body
A fruiting
body forms
with resting
spores atop
a stalk.
Cells feed and multiply by mitosis. 1
The cells form a slug. It may start to develop as a fruiting body right away, or migrate about. In the slug, cells become prestalk (red) and prespore (tan) cells.
Migrating slug
stage 3
When food
is scarce, cells aggregate. 2
Figure Life cycle of Dictyostelium discoideum, a cellular slime mold.
Stepped Art
Fig , p. 321

56. Animation: Cellular Slime Mold Life Cycle

57. Key Concepts Amoebozoans
A lineage of unwalled heterotrophic protists that includes the amoebas and slime molds is the protist group most closely related to the fungi and animals.
Members of this lineage live in aquatic habitats or on the forest floor

58. Harmful Algal Blooms (revisited)
Keeping harmful algal toxins out of the human food supply requires constant vigilance
Nutrients in water (fertilizers, farm waste, sewage) can cause runaway algal growth

59. ANIMATION: Amoeboid Motion
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