1. Chapter 28
Protists

2. Protist is the informal name of the kingdom of mostly unicellular eukaryotes
Advances in eukaryotic systematics have caused the classification of protists to change significantly
Protists constitute a paraphyletic group, and Protista is no longer valid as a kingdom

3. Concept 28.1: Diversity of Single-celled Organisms
Protists are eukaryotes and thus have organelles and complexity than prokaryotes
Most are unicellular, but some are colonial and multicellular species

4. Protist habitats are also diverse in habitat
Protists, the most structurally and nutritionally diverse of all eukaryotes, include
Photoautotrophs, which contain chloroplasts
Heterotrophs, which absorb or ingest food particles
Mixotrophs, which combine photosynthesis and heterotrophy
Protist habitats are also diverse in habitat
Reproduction and life cycles include sexual and asexual species

5. Endosymbiosis in Eukaryotic Evolution
There is now considerable evidence that much protist diversity has its origins in endosymbiosis
Endosymbiosis is the process in which a unicellular organism engulfs another cell, which becomes an endosymbiont and then organelle in the host cell
Mitochondria evolved by endosymbiosis of an aerobic prokaryote
Plastids evolved by endosymbiosis of a photosynthetic cyanobacterium

7. Our understanding of the relationships among protist groups continues to change rapidly
One hypothesis divides all eukaryotes (including protists) into five supergroups

8. Concept 28.2: Excavates include protists with modified mitochondria and protists with unique flagella
The clade Excavata is characterized by its cytoskeleton
Some members have a feeding groove
This controversial group includes the diplomonads, parabasalids, and euglenozoans

9. (a) Giardia intestinalis, a diplomonad (colorized SEM)
Diplomonads
Have two nuclei and multiple flagella
Derive energy anaerobically, for example, by glycolysis
Figure 28.5a
5 µm
(a) Giardia intestinalis, a diplomonad (colorized SEM)

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

11. Euglenozoa is a diverse clade that includes
Predatory heterotrophs, photosynthetic autotrophs, and pathogenic parasites
The main feature that distinguishes protists in this clade
Is the presence of a spiral or crystalline rod of unknown function inside their flagella
This clade includes the kinetoplastids and euglenids
Flagella
0.2 µm
Crystalline rod
Ring of microtubules
Figure 28.6

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

13. Euglenids, Euglena
Have one or two flagella that emerge from a pocket at one end of the cell
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

14. Concept 28.3 Chromalveolates
Some data suggest that the clade Chromalveolata is monophyletic and originated by a secondary endosymbiosis event
The proposed endosymbiont is a red alga
This clade is controversial and includes the alveolates and the stramenopiles

15. Members of the clade Alveolata have membrane-bounded sacs (alveoli) just under the plasma membrane
The function of the alveoli is unknown
Alveolata includes the dinoflagellates, apicomplexans, and ciliates

16. Dinoflagellates
Are a diverse group of aquatic photoautotrophs and heterotrophs
Are abundant components of both marine and freshwater phytoplankton
Two flagella make
them spin as they
move through the
water
Figure 28.10
3 µm
Flagella

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

18. Apicomplexans, Plasmodium
The apicomplexan Plasmodium is the parasite that causes malaria
Plasmodium requires both mosquitoes and humans to complete its life cycle
Approximately 2 million people die each year from malaria
Efforts are ongoing to develop vaccines that target this pathogen

20. Ciliates, a large varied group of protists, Paramecium
Are named for their use of cilia and have a large macronuclei and small micronuclei

21. Stramenopiles Most stramenopiles
Includes several groups of heterotrophs as well as certain groups of algae
Most stramenopiles
Have a “hairy” flagellum paired with a “smooth” flagellum
Smooth
flagellum
Hairy
5 µm
Figure 28.13

22. Diatoms are unicellular algae
With a unique two-part, glass-like wall of hydrated silica
Accumulations of fossilized diatom walls compose much of the sediments known as diatomaceous earth
Figure 28.15
3 µm

23. The cells of golden algae
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
Most golden algae are unicellular
But some are colonial
Figure 28.17
25 µm

24. Brown algae, or phaeophytes
Are the largest and most complex algae
Are all multicellular, and most are marine
Include many of the species commonly called seaweeds
Figure 28.18
Blade
Stipe
Holdfast

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

26. Oomycetes include water molds, white rusts, and downy mildews
They were once considered fungi based on morphological studies
Most oomycetes
are decomposers
or parasites
Their ecological
impact can be
great, as in potato
blight caused by Phytophthora infestans

28. Concept 28.4: Rhizarians
DNA evidence supports Rhizaria as a monophyletic clade
Amoebas move and feed by pseudopodia; some but not all belong to the clade Rhizaria
Rhizarians include forams and radiolarians

29. Radiolarians are marine protists
Whose tests are fused into one delicate piece, which is generally made of silica
That phagocytose microorganisms with their pseudopodia
The pseudopodia of radiolarians, known as axopodia
Radiate from
the central body
Figure 28.23
200 µm
Axopodia

30. Concept 28.5 Archaeplastida
Over a billion years ago, a heterotrophic protist acquired a cyanobacterial endosymbiont
The photosynthetic descendants of this ancient protist evolved into red algae and green algae
Archaeplastida is a supergroup used by some scientists and includes red algae, green algae, and land plants

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

32. 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.

33. Green algae Are named for their grass-green chloroplasts
Are divided into two main groups: chlorophytes and charophyceans (chapter 29)
Are closely related to land plants

34. 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

35. 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

36. Concept 28.6: Unikonts
The supergroup Unikonta includes animals, fungi, and some protists
This group includes two clades: the amoebozoans and the opisthokonts (animals, fungi, and related protists)
The root of the eukaryotic tree remains controversial

37. Amoebozoans
Are amoebas that have lobe-shaped, rather than threadlike, pseudopodia
Include gymnamoebas, entamoebas, and slime molds

38. Concept 28.7: Protists play key roles in ecological communities
Protists are found in diverse aquatic environments
Protists often play the role of symbiont or producer

39. Symbiotic Protists Some protist symbionts benefit their hosts
Dinoflagellates nourish coral polyps that build reefs
Wood-digesting protists digest cellulose in the gut of termites

40. Some protists are parasitic
Plasmodium causes malaria
Pfiesteria shumwayae is a dinoflagellate that causes fish kills
Phytophthora ramorum causes sudden oak death

41. Photosynthetic Protists
Many protists are important producers that obtain energy from the sun
In aquatic environments, photosynthetic protists and prokaryotes are the main producers
In aquatic environments, photosynthetic protists are limited by nutrients
These populations can explode when limiting nutrients are added

42. Prokaryotic producers
Figure 28.27
Other consumers
Herbivorous plankton
Carnivorous plankton
Figure Protists: key producers in aquatic communities.
Protistan producers
Prokaryotic producers

43. Figure 28.UN06
Figure 28.UN06 Summary table, Concepts 28.2–28.6