1. Chapter 28 Protists

2. A World in a Drop of Water Even a low-power microscope
menagerie of organisms in a drop of pond water
Figure 28.1
50 m

3. Diverse kingdoms of mostly single-celled eukaryotes informally known as protists
Classification of protists

4. More diverse than all other eukaryotes
no longer classified in a single kingdom
Most unicellular
some are colonial or multicellular

5. Most nutritionally diverse of all eukaryotes
Photoautotrophs, (w/ chloroplasts)
Heterotrophs, (absorb organic molecules or ingest larger food particles)
Mixotrophs, (combine photosynthesis and heterotrophic nutrition)

6. Diverse habitats including freshwater and marine 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)

7. Reproduction and life cycles
highly varied (both sexual and asexual)

8. Protist diversity
Table 28.1

9. Endosymbiosis
Protist diversity has its origins in endosymbiosis

10. Probably undigested prey or internal parasites
Figure 26.13
Cytoplasm
DNA
Plasma
membrane
Ancestral
prokaryote
Infolding of
plasma membrane
Endoplasmic
reticulum
Nuclear envelope
Nucleus
Engulfing
of aerobic
heterotrophic
Cell with nucleus
and endomembrane
system
Mitochondrion
eukaryote
Plastid
Engulfing of
photosynthetic
prokaryote in
some cells
Photosynthetic

11. Plastid-bearing lineage of protists evolved into red algae and green algae

12. Plasmodial slime molds
Tentative phylogeny of eukaryotes
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. e.g. Parasitic Trypanosoma
Euglenozoans
e.g. Parasitic Trypanosoma
Causes sleeping sickness in humans
Figure 28.7
9 m

14. Photosynthetic/ heterotrophic
Euglenids
1 or 2 flagella
Photosynthetic/ heterotrophic
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

15. Dinoflagellates
Component of marine and freshwater phytoplankton
Also, Toxic “red tides”

16. Plasmodium – causes malaria
2 different hosts
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
mosquito
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

17. FEEDING, WASTE REMOVAL, AND WATER BALANCE
Ciliates
e.g. Paramecium
FEEDING, WASTE REMOVAL, AND WATER BALANCE
50 µm
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

18. 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

19. Oomycetes (Water Molds)
Once considered fungi
Decomposers or parasites
Have filaments (hyphae)nutrient uptake

20. germinate, growing into
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

21. The oomycetes Phytophthora infestans causes late blight of potatoes

22. Diatoms Unicellular algae Unique two-part, glass-like wall of silica
Figure 28.15
3 µm

23. Diatoms  major component of phytoplankton
Figure 28.16
50 µm

24. Fossilized diatom walls diatomaceous earth

25. Brown Algae or phaeophytes Largest and most complex algae
Multicellular, marine
‘Seaweeds’
Figure 28.18
Blade
Stipe
Holdfast

26. Kelps, or giant seaweeds
Deep water
Figure 28.19

27. Harvested for food, other purposes
Human Uses of Seaweeds
Harvested for food, other purposes
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.

28. Alternation of Generations *
Alternation of multicellular haploid and diploid forms

29. 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

30. Foraminiferans (Forams)
Multichambered shells, called tests
Figure 28.22
20 µm

31. Foram tests in marine sediments form an extensive fossil record

32. The pseudopodia of radiolarians radiate from the central body
Figure 28.23
200 µm
Axopodia

33. Amoebozoans
Most heterotrophic and actively seek and consume bacteria and other protists
Figure 28.24
Pseudopodia
40 µm

34. Plasmodial Slime ‘Molds’
brightly pigmented
decomposers
Figure 28.25
4 cm

35. Life cycle Figure 28.26 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

36. Red algae and green algae, closest relatives of land plants
Over a billion years ago, a heterotrophic protist acquired a cyanobacterial endosymbiont
 photosynthetic descendants evolved into red algae and green algae

37. Usually multicellular; largest are seaweeds
Red Algae
Usually multicellular; largest are seaweeds
Red pigment absorbs blue light
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)

38. Green Algae (chlorophytes)
Named f/ grass-green chloroplasts
Closely related to land plants
 similar pigments, etc.

39. Chlorophytes
Most fresh water, some marine, in damp soil, as symbionts in lichens, or in snow
Figure 28.29

40. Chlorophytes 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

41. Chlorophytes life cycles
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