1. Chapter 28
Protists

2. Overview: A World in a Drop of Water Even a low-power microscope
Can reveal an astonishing menagerie of organisms in a drop of pond water
Figure 28.1
50 m

3. Protists are more diverse than all other eukaryotes
Concept 28.1: Protists are an extremely diverse assortment of eukaryotes
Protists are more diverse than all other eukaryotes
And are no longer classified in a single kingdom
Most protists are unicellular
And some are colonial or multicellular

4. Protists, the most nutritionally diverse of all eukaryotes, include
Parade #11
Protists, the most nutritionally diverse of all eukaryotes, include
Photoautotrophs, which contain chloroplasts
Heterotrophs, which absorb organic molecules or ingest larger food particles
Mixotrophs, which combine photosynthesis and heterotrophic nutrition

5. Protist habitats are also diverse in habitat
And including freshwater and marine species
Figure 28.2a–d
100 m
4 cm
500 m
The freshwater ciliate Stentor, a unicellular protozoan (LM)
Ceratium tripos, a unicellular marine dinoflagellate (LM)
Delesseria sanguinea, a multicellular marine red alga
Spirogyra, a filamentous freshwater green alga (inset LM)
(a)
(b)
(c)
(d)

6. Reproduction and life cycles
Are also highly varied among protists, with both sexual and asexual species

7. A sample of protist diversity
Table 28.1

8. Endosymbiosis in Eukaryotic Evolution
There is now considerable evidence
12. That much of protist diversity has its origins in endosymbiosis

9. The plastid-bearing lineage of protists
13.
The plastid-bearing lineage of protists
Evolved into red algae and green algae
On several occasions during eukaryotic evolution
Red algae and green algae underwent secondary endosymbiosis, in which they themselves were ingested

10. Diversity of plastids produced by secondary endosymbiosis
13.
Diversity of plastids produced by secondary endosymbiosis
Cyanobacterium
Heterotrophic
eukaryote
Primary
endosymbiosis
Red algae
Green algae
Secondary
Plastid
Dinoflagellates
Apicomplexans
Ciliates
Stramenopiles
Euglenids
Chlorarachniophytes
Alveolates
Figure 28.3

11. These amazing organisms
Belong to the diverse kingdoms of mostly single-celled eukaryotes informally known as protists
14. Advances in eukaryotic systematics
Have caused the classification of protists to change significantly

12. Plasmodial slime molds
Concept 28.2: Diplomonads and parabasalids have modified mitochondria
A tentative phylogeny of eukaryotes
Divides eukaryotes into many clades
Rhodophyta
Chlorophyta
Diplomonadida
Euglenozoa
Animalia
Parabasala
Plantae
Cercozoa
Radiolaria
Fungi
Alveolata
Stramenopila
Amoebozoa
(Opisthokonta)
(Viridiplantae)
Fungi
Plants
Euglenids
Ciliates
Parabasalids
Dinoflagellates
Oomycetes
Diatoms
Golden algae
Brown algae
Radiolarians
Entamoebas
Metazoans
Red algae
Diplomonads
Kinetoplastids
Apicomplexans
Foraminiferans
Gymnamoebas
Chlorophytes
Chlorarachniophytes
Cellular slime molds
Choanoflagellates
Charophyceans
Plasmodial slime molds
Figure 28.4
Ancestral eukaryote

13. Diplomonads and parabasalids
Are adapted to anaerobic environments
Lack plastids
Have mitochondria that lack DNA, an electron transport chain, or citric-acid cycle enzymes

14. (a) Giardia intestinalis, a diplomonad (colorized SEM)
Diplomonads
Diplomonads
Have two nuclei and multiple flagella
Figure 28.5a
5 µm
(a) Giardia intestinalis, a diplomonad (colorized SEM)

15. (b) Trichomonas vaginalis, a parabasalid (colorized SEM)
Parabasalids
Parabasalids include trichomonads
Which move by means of flagella and an undulating part of the plasma membrane
Flagella
Undulating membrane
5 µm
Figure 28.5b
(b) Trichomonas vaginalis, a parabasalid (colorized SEM)

16. Euglenozoa is a diverse clade that includes
Concept 28.3: Euglenozoans have flagella with a unique internal structure
Euglenozoa is a diverse clade that includes
Predatory heterotrophs, photosynthetic autotrophs, and pathogenic parasites

17. The main feature that distinguishes protists in this clade
Is the presence of a spiral or crystalline rod of unknown function inside their flagella
Flagella
0.2 µm
Crystalline rod
Ring of microtubules
Figure 28.6

18. Kinetoplastids Kinetoplastids
Have a single, large mitochondrion that contains an organized mass of DNA called a kinetoplast
Include free-living consumers of bacteria in freshwater, marine, and moist terrestrial ecosystems

19. The parasitic kinetoplastid Trypanosoma
Causes sleeping sickness in humans
Figure 28.7
9 m

20. Euglenids
Euglenids
Have one or two flagella that emerge from a pocket at one end of the cell
Store the glucose polymer paramylon
Figure 28.8
Long flagellum
Short flagellum
Nucleus
Plasma membrane
Paramylon granule
Chloroplast
Contractile vacuole
Light detector: swelling near the
base of the long flagellum; detects
light that is not blocked by the
eyespot; as a result, Euglena moves
toward light of appropriate
intensity, an important adaptation
that enhances photosynthesis
Eyespot: pigmented
organelle that functions
as a light shield, allowing
light from only a certain
direction to strike the
light detector
Pellicle: protein bands beneath
the plasma membrane that
provide strength and flexibility
(Euglena lacks a cell wall)
Euglena (LM)
5 µm

21. Concept 28.4: Alveolates have sacs beneath the plasma membrane
Members of the clade Alveolata
Have membrane-bounded sacs (alveoli) just under the plasma membrane
Figure 28.9
Flagellum
Alveoli
0.2 µm

22. Dinoflagellates Dinoflagellates
Are a diverse group of aquatic photoautotrophs and heterotrophs
Are abundant components of both marine and freshwater phytoplankton

23. Each has a characteristic shape
That in many species is reinforced by internal plates of cellulose
Two flagella
Make them spin as they move through the water
Figure 28.10
3 µm
Flagella

24. Rapid growth of some dinoflagellates
Is responsible for causing “red tides,” which can be toxic to humans

25. Apicomplexans Apicomplexans
Are parasites of animals and some cause serious human diseases
Are so named because one end, the apex, contains a complex of organelles specialized for penetrating host cells and tissues
Have a nonphotosynthetic plastid, the apicoplast

26. Most apicomplexans have intricate life cycles
With both sexual and asexual stages that often require two or more different host species for completion
An infected Anopheles
mosquito bites a person,
injecting Plasmodium
sporozoites in its saliva. 1
The sporozoites enter the person’s
liver cells. After several days, the sporozoites
undergo multiple divisions and become
merozoites, which use their apical complex
to penetrate red blood cells (see TEM below). 2
Figure 28.11
Inside mosquito
Inside human
Sporozoites
(n)
Oocyst
MEIOSIS
Liver
Liver cell
Merozoite
Red blood
cells
Gametocytes
FERTILIZATION
Gametes
Zygote
(2n)
Key
Haploid (n)
Diploid (2n)
cell
Apex
0.5 µm
An oocyst develops
from the zygote in the wall
of the mosquito’s gut. The
oocyst releases thousands
of sporozoites, which
migrate to the mosquito’s
salivary gland. 7
The merozoites divide asexually inside the
red blood cells. At intervals of 48 or 72 hours
(depending on the species), large numbers of
merozoites break out of the blood cells, causing
periodic chills and fever. Some of the merozoites
infect new red blood cells. 3
Gametes form from gametocytes.
Fertilization occurs in the mosquito’s
digestive tract, and a zygote forms.
The zygote is the only diploid stage
in the life cycle. 6
Another Anopheles mosquito
bites the infected person and picks
up Plasmodium gametocytes along
with blood. 5
Some merozoites
form gametocytes. 4

27. Ciliates, a large varied group of protists
Are named for their use of cilia to move and feed
Have large macronuclei and small micronuclei

28. Conjugation is separate from reproduction
The micronuclei
Function during conjugation, a sexual process that produces genetic variation
Conjugation is separate from reproduction
Which generally occurs by binary fission

29. FEEDING, WASTE REMOVAL, AND WATER BALANCE
Exploring structure and function in a ciliate
50 µm
FEEDING, WASTE REMOVAL, AND WATER BALANCE
Paramecium, like other freshwater protists, constantly takes in water
by osmosis from the hypotonic environment. Bladderlike contractile vacuoles accumulate excess water from radial canals and periodically expel it through the plasma membrane.
Contractile Vacuole
Paramecium feeds mainly on bacteria. Rows of cilia along a funnel-shaped oral groove move food into the cell mouth, where the food is engulfed into food vacuoles by phagocytosis.
Oral groove
Cell mouth
Food vacuoles combine with lysosomes. As the food is digested, the vacuoles follow a looping path through the cell.
Thousands of cilia cover the surface of Paramecium.
Micronucleus
Macronucleus
The undigested contents of food vacuoles are released when the vacuoles fuse with a specialized region of the plasma membrane that functions as an anal pore.
Figure 28.12

30. CONJUGATION AND REPRODUCTION8 7 2
MICRONUCLEAR FUSION
Diploid micronucleus
Haploid micronucleus
MEIOSIS
Compatible mates
Key
Conjugation
Reproduction
Macronucleus
Two cells of compatible
mating strains align side
by side and partially fuse. 1
Meiosis of micronuclei produces four haploid micronuclei in each cell. 2 3
Three micronuclei in each cell disintegrate. The remaining micro- nucleus in each cell divides by mitosis.
The cells swap one micronucleus. 4
The original macro- nucleus disintegrates. Four micronuclei become macronuclei, while the other four remain micronuclei. 8
The cells separate. 5
Micronuclei fuse, forming a diploid micronucleus. 6
Two rounds of cytokinesis partition one macronucleus and one micronucleus into each of four daughter cells. 9
Three rounds of mitosis without cytokinesis produce eight micronuclei. 7

31. Concept 28.5: Stramenopiles have “hairy” and smooth flagella
The clade Stramenopila
Includes several groups of heterotrophs as well as certain groups of algae

32. Most stramenopiles
Have a “hairy” flagellum paired with a “smooth” flagellum
Smooth
flagellum
Hairy
5 µm
Figure 28.13

33. Oomycetes (Water Molds and Their Relatives)
Include water molds, white rusts, and downy mildews
Were once considered fungi based on morphological studies

34. Most oomycetes Are decomposers or parasites
Have filaments (hyphae) that facilitate nutrient uptake

35. germinate, growing into
The life cycle of a water mold
Encysted zoospores
land on a substrate and
germinate, growing into
a tufted body of hyphae. 1
Several days later,
the hyphae begin to
form sexual structures. 2
Meiosis produces
eggs within oogonia
(singular, oogonium). 3
On separate branches of the
same or different individuals, meiosis
produces several haploid sperm nuclei
contained within antheridial hyphae. 4
Figure 28.14
Cyst
Zoospore
(2n)
ASEXUAL
REPRODUCTION
Zoosporangium
Germ tube
Zygote
germination
FERTILIZATION
SEXUAL
Zygotes
(oospores)
MEIOSIS
Oogonium
Egg nucleus
(n)
Antheridial
hypha with
sperm nuclei
Key
Haploid (n)
Diploid (2n)
Each zoospor-
angium produces
about 30
biflagellated
zoospores
asexually. 9
The ends
of hyphae
form tubular
zoosporangia. 8
The zygotes germinate
and form hyphae, and the
cycle is completed. 7
Antheridial hyphae grow like
hooks around the oogonium and
deposit their nuclei through
fertilization tubes that lead to the
eggs. Following fertilization, the
zygotes (oospores) may develop
resistant walls but are also
protected within the wall of the
oogonium. 5
A dormant period
follows, during which the
oogonium wall usually
disintegrates. 6

36. The ecological impact of oomycetes can be significant
Phytophthora infestans causes late blight of potatoes

37. Diatoms are unicellular algae
With a unique two-part, glass-like wall of hydrated silica
Figure 28.15
3 µm

38. Diatoms are a major component of phytoplankton
And are highly diverse
Figure 28.16
50 µm

39. Accumulations of fossilized diatom walls
Compose much of the sediments known as diatomaceous earth

40. Golden algae, or chrysophytes
Are named for their color, which results from their yellow and brown carotenoids
The cells of golden algae
Are typically biflagellated, with both flagella attached near one end of the cell

41. Most golden algae are unicellular
But some are colonial
Figure 28.17
25 µm

42. Brown algae, or phaeophytes
Are the largest and most complex algae
Are all multicellular, and most are marine

43. Brown algae
Include many of the species commonly called seaweeds
Seaweeds
Have the most complex multicellular anatomy of all algae
Figure 28.18
Blade
Stipe
Holdfast

44. Kelps, or giant seaweeds
Live in deep parts of the ocean
Figure 28.19

45. Human Uses of Seaweeds Many seaweeds
Are important commodities for humans
Are harvested for food
Figure 28.20a–c
(a) The seaweed is
grown on nets in
shallow coastal
waters.
(b) A worker spreads
the harvested sea-
weed on bamboo
screens to dry.
(c) Paper-thin, glossy sheets
of nori make a mineral-rich wrap
for rice, seafood, and vegetables
in sushi.

46. Alternation of Generations
A variety of life cycles
Have evolved among the multicellular algae
The most complex life cycles include an alternation of generations
The alternation of multicellular haploid and diploid forms

47. The life cycle of the brown alga Laminaria
Figure 28.21
Sporophyte
(2n)
Zoospores
Female
Gametophytes
(n)
MEIOSIS
FERTILIZATION
Developing
sporophyte
Zygote
Mature female
gametophyte
Egg
Sperm
Male
Sporangia
Key
Haploid (n)
Diploid (2n)
The sporophytes of this seaweed
are usually found in water just below
the line of the lowest tides, attached
to rocks by branching holdfasts. 1
In early spring, at the end of
the main growing season, cells on
the surface of the blade develop
into sporangia. 2
Sporangia produce
zoospores by meiosis. 3
The zoospores are all
structurally alike, but
about half of them develop
into male gametophytes
and half into female
gametophytes. The
gametophytes look
nothing like the sporo-
phytes, being short,
branched filaments that
grow on the surface of
subtidal rocks. 4
The zygotes
grow into new
sporophytes,
starting life
attached to
the remains of
the female
gametophyte. 7
Male gametophytes release
sperm, and female gametophytes
produce eggs, which remain
attached to the female gameto-
phyte. Eggs secrete a chemical
signal that attracts sperm of the
same species, thereby increasing
the probability of fertilization in
the ocean. 5
Sperm fertilize
the eggs. 6

48. Concept 28.6: Cercozoans and radiolarians have threadlike pseudopodia
A newly recognized clade, Cercozoa
Contains a diversity of species that are among the organisms referred to as amoebas
Amoebas were formerly defined as protists
That move and feed by means of pseudopodia
Cercozoans are distinguished from most other amoebas
By their threadlike pseudopodia

49. Foraminiferans (Forams)
Foraminiferans, or forams
Are named for their porous, generally multichambered shells, called tests
Figure 28.22
20 µm

50. Pseudopodia extend through the pores in the test
Foram tests in marine sediments
Form an extensive fossil record

51. Radiolarians are marine protists
Whose tests are fused into one delicate piece, which is generally made of silica
That phagocytose microorganisms with their pseudopodia

52. The pseudopodia of radiolarians, known as axopodia
Radiate from the central body
Figure 28.23
200 µm
Axopodia

53. Concept 28.7: Amoebozoans have lobe-shaped pseudopodia Amoebozoans
Are amoeba that have lobe-shaped, rather than threadlike, pseudopodia
Include gymnamoebas, entamoebas, and slime molds

54. Gymnamoebas Gymnamoebas
Are common unicellular amoebozoans in soil as well as freshwater and marine environments

55. Most gymnamoebas are heterotrophic
And actively seek and consume bacteria and other protists
Figure 28.24
Pseudopodia
40 µm

56. Entamoeba histolytica
Entamoebas
Entamoebas
Are parasites of vertebrates and some invertebrates
Entamoeba histolytica
Causes amebic dysentery in humans

57. Slime molds, or mycetozoans
Were once thought to be fungi
Molecular systematics
Places slime molds in the clade Amoebozoa

58. Plasmodial Slime Molds
Many species of plasmodial slime molds
Are brightly pigmented, usually yellow or orange
Figure 28.25
4 cm

59. At one point in the life cycle
They form a mass called a plasmodium
The plasmodium erects
stalked fruiting bodies (sporangia)
when conditions become harsh. 3
The feeding stage
is a multinucleate
plasmodium that lives
on organic refuse. 1
The plasmodium
takes a weblike form. 2
Figure 28.26
Feeding
plasmodium
Mature
(preparing to fruit)
Young
sporangium
Spores
(n)
Germinating
spore
Amoeboid cells
Zygote
(2n)
1 mm
Key
Haploid (n)
Diploid (2n)
MEIOSIS
SYNGAMY
Stalk
Flagellated cells
The cells unite
in pairs (flagellated
with flagellated
and amoeboid with
amoeboid), forming
diploid zygotes. 7
These cells are
either amoeboid or
flagellated; the two
forms readily convert
from one to the other. 6
The resistant spores disperse
through the air to new locations
and germinate, becoming active
haploid cells when conditions
are favorable. 5
Within the bulbous
tips of the sporangia,
meiosis produces haploid
spores. 4

60. The plasmodium
Is undivided by membranes and contains many diploid nuclei
Extends pseudopodia through decomposing material, engulfing food by phagocytosis

61. Cellular slime molds form multicellular aggregates
In which the cells remain separated by their membranes

62. The life cycle of Dictyostelium, a cellular slime mold
In a favorable
environment, amoebas
emerge from the spore
coats and begin feeding. 9
In the feeding
stage of the life
cycle, solitary haploid
amoebas engulf bacteria. 1
During sexual repro-
duction, two haploid
amoebas fuse and
form a zygote. 2
The zygote
becomes a giant
cell (not shown)
by consuming
haploid amoebas.
After developing a
resistant wall, the
giant cell undergoes
meiosis followed by
several mitotic
divisions. 3
Spores
(n)
Emerging
amoeba
Solitary amoebas
(feeding stage)
ASEXUAL
REPRODUCTION
Fruiting
bodies
Aggregated
amoebas
Migrating
aggregate
SYNGAMY
MEIOSIS
SEXUAL
Zygote
(2n)
Amoebas
600 µm
200 µm
Key
Haploid (n)
Diploid (2n)
Figure 28.27
Spores
are released. 8
Other
cells crawl
up the stalk
and develop
into spores. 7
The resistant
wall ruptures,
releasing new
haploid amoebas. 4
When food is depleted,
hundreds of amoebas
congregate in response to a
chemical attractant and form
a sluglike aggregate (photo
below left). Aggregate
formation is the beginning
of asexual reproduction. 5
The aggregate migrates for a
while and then stops. Some of the
cells dry up after forming a stalk that
supports an asexual fruiting body. 6

63. Dictyostelium discoideum
Has become an experimental model for studying the evolution of multicellularity

64. Concept 28.8: Red algae and green algae are the closest relatives of land plants
Over a billion years ago, a heterotrophic protist acquired a cyanobacterial endosymbiont
And the photosynthetic descendants of this ancient protist evolved into red algae and green algae

65. Red algae are reddish in color
Due to an accessory pigment call phycoerythrin, which masks the green of chlorophyll

66. Red algae Are usually multicellular; the largest are seaweeds
Are the most abundant large algae in coastal waters of the tropics
Figure 28.28a–c
(a) Bonnemaisonia hamifera. This red alga has a filamentous form.
Dulse (Palmaria palmata). This edible
species has a “leafy” form.
(b)
A coralline alga. The cell walls of
coralline algae are hardened by calcium
carbonate. Some coralline algae are
members of the biological communities
around coral reefs.
(c)

67. Green Algae Green algae Are named for their grass-green chloroplasts
Are divided into two main groups: chlorophytes and charophyceans
Are closely related to land plants

68. Most chlorophytes Other chlorophytes
Live in fresh water, although many are marine
Other chlorophytes
Live in damp soil, as symbionts in lichens, or in snow
Figure 28.29

69. Chlorophytes include Unicellular, colonial, and multicellular forms
Volvox, a colonial freshwater chlorophyte. The colony is a hollow
ball whose wall is composed of hundreds or thousands of
biflagellated cells (see inset LM) embedded in a gelatinous
matrix. The cells are usually connected by strands of cytoplasm;
if isolated, these cells cannot reproduce. The large colonies seen
here will eventually release the small “daughter” colonies within
them (LM).
(a)
Caulerpa, an inter-
tidal chlorophyte.
The branched fila-
ments lack cross-walls
and thus are multi-
nucleate. In effect,
the thallus is one
huge “supercell.”
(b)
Ulva, or sea lettuce. This edible seaweed has a multicellular
thallus differentiated into leaflike blades and a rootlike holdfast
that anchors the alga against turbulent waves and tides.
(c)
20 µm
50 µm
Figure 28.30a–c

70. Most chlorophytes have complex life cycles
With both sexual and asexual reproductive stages
These daughter cells develop flagella
and cell walls and then emerge as
swimming zoospores from the wall of
the parent cell that had enclosed them.
The zoospores grow into mature haploid
cells, completing the asexual life cycle. 7
In Chlamydomonas,
mature cells are haploid and
contain a single cup-shaped
chloroplast (see TEM at left). 1
In response to a
shortage of nutrients, drying
of the pond, or some other
stress, cells develop into gametes. 2
Gametes of opposite
mating types (designated
+ and –) pair off and
cling together. Fusion of
the gametes (syngamy)
forms a diploid zygote. 3
Figure 28.31
Flagella
Cell wall
Nucleus
Regions
of single
chloroplast
Zoospores
ASEXUAL
REPRODUCTION
Mature cell
(n)
SYNGAMY
SEXUAL
Zygote
(2n)
MEIOSIS
1 µm
Key
Haploid (n)
Diploid (2n)  +
The zygote secretes a durable coat that
protects the cell against
harsh conditions. 4
When a mature cell repro-
duces asexually, it resorbs its
flagella and then undergoes two
rounds of mitosis, forming four
cells (more in some species). 6
After a dormant period, meiosis
produces four haploid individuals (two
of each mating type) that emerge from
the coat and develop into mature cells. 5