3. 17.1 Eukaryotic organelles
probably arose by endosymbiosis
Protists (kingdom Protista) are
eukaryotes
Endosymbiotic theory - at least
mitochondria and chloroplasts are derived
from independent prokaryotic cells
17-3
5. 17.2 Protists are a diverse group
Protists vary in size from microscopic to
macroscopic exceeding 200 m in length
Most protists are unicellular, but they have attained a
high level of complexity
Asexual reproduction by mitosis is the norm in
protists
Sexual reproduction generally occurs only in a hostile
environment
They are of enormous ecological importance
They are a major component of plankton
Organisms suspended in the water and are food for animals
Protists have symbiotic relationships from parasitism to
mutualism 17-5
7. APPLYING THE CONCEPTS—HOW SCIENCE PROGRESSES
17.3 How can the
protists be classified?
Lumping all the single-celled eukaryotes
(protists) into a single kingdom is artificial
Does not represent evolutionary history
17-7
10. 17.4 Protozoans called
flagellates move by flagella
Zooflagellates - thousands of species of mostly
unicellular, heterotrophic protozoans that move with
a flagellum
Many zooflagellates are symbiotic and some are parasitic
Euglenoids include about 1,000 species of small
(10–500 μm) freshwater unicellular organisms
One-third of all genera have chloroplasts; the rest do not
Those that lack chloroplasts ingest or absorb their food
Some do both
Euglena deces, an inhabitant of freshwater ditches and ponds
can undergo photosynthesis as well as to ingest food
17-10
12. 17.5 Protozoans called
amoeboids move by pseudopods
Pseudopods - extensions that form when
cytoplasm streams in a particular direction
May be zooplankton, microscopic suspended organisms
that feed on other organisms
Feed by phagocytosis, surrounding prey with
pseudopods and digesting it in a food vacuole
Foraminiferans and Radiolarians have shells
called tests
Intriguing and beautiful
In foraminiferans the test is often multichambered
Deposits of foraminiferans formed the White Cliffs of
Dover 17-12
16. 17.6 Protozoans called
ciliates move by cilia
Ciliates - approximately 8,000 species of unicellular
protists
Range from 10 to 3,000 μm in size
The most structurally complex and specialized of all
protozoans
The majority are free-living
Several parasitic, sessile, and colonial forms exist
When a paramecium feeds, food particles are swept
down a gullet into food vacuoles
Asexual reproduction
Ciliates divide by transverse binary fission
Sexual reproduction involves conjugation
17-16
20. 17.7 Protozoans called
sporozoans are not motile
Sporozoans - nearly 3,900 species
nonmotile, parasitic, spore-forming
Many sporozoans have multiple hosts
One million people die each year from malaria
Widespread disease caused by four types of
sporozoan parasites in the genus Plasmodium
17-20
21. Figure 17.7 Life cycle of Plasmodium vivax, the cause of one type
of malaria
17-21
23. 17.8 The diversity of protists
includes slime
molds and water molds
The Plasmodial Slime Molds
Exist as a plasmodium, a diploid, multinucleated,
cytoplasmic mass
Enveloped by a slimy sheath creeping along, phagocytizing
decaying plant material
During droughts, plasmodium develops many
sporangia, spore producing reproductive structures
An aggregate of sporangia is called a fruiting body
17-23
24. Cellular Slime Molds
Exist as individual amoeboid cells and are too
small to be seen
Common in soil, feeding on bacteria and yeasts
As the food supply runs out cells release a
chemical that causes them to aggregate into a
pseudoplasmodium
Eventually gives rise to a fruiting body
17-24
26. Water Molds
Water Molds
Usually live in water, where they form furry growths
when they parasitize fishes or insects and
decompose remains
Water molds have a filamentous body as do fungi, but
their cell walls are largely composed of cellulose
17-26
29. 17.9 The diatoms and dinoflagellates
are significant algae in the oceans
Diatoms (approximately 11,000 species) are
free-living photosynthetic cells in aquatic and
marine environments
Most numerous unicellular algae in the oceans and
freshwater environments
Significant part of the phytoplankton, photosynthetic
organisms suspended in the water
Serve as an important source of food and oxygen for
heterotrophs
Diatom Structure
Often compared to a hat box
Cell wall has two halves, or valves, with the larger
valve acting as a “lid” that fits over the smaller valve
17-29
30. Figure 17.9A Cyclotella, a diatom. Diatoms live in “glass houses”
because the outer visible valve, which fits over the smaller inner
valve, contains silica
17-30
31. Dinoflagellates
Dinoflagellates (about 4,000 species) are usually
bounded by protective cellulose plates impregnated
with silicates
Typically, the organism has two flagella:
One in a longitudinal groove with its distal end free
One in a transverse groove that encircles the organism
Important source of food for small animals in the ocean
Some are symbionts in the bodies of invertebrates
Corals usually contain large numbers of zooxanthellae
Some undergo a population explosion and cause “red
tides”
17-31
32. Figure 17.9B Gonyaulax, a dinoflagellate. This dinoflagellate is
responsible for the poisonous “red tide” that sometimes occurs
along the coasts
17-32
33. 17.10 Red algae and brown
algae are multicellular
Red algae (>5,000 multicellular species) living primarily in
warm seawater
Some grow attached to rocks in the intertidal zone
Others can grow at depths exceeding 200 m
economically important
Produce agar, a gelatin-like product made primarily from the algae
Gelidium and Gracilaria, used commercially and in the laboratory
Brown algae (>1,500 species of seaweeds)
Range from small forms with simple filaments to large, multicellular
forms that may reach 100 m in length
Majority of brown algae, like Fucus, live in cold ocean waters
Multicellular forms of green, red, and brown algae are called
seaweeds, a common term for any large, complex alga
17-33
36. 17.11 Green algae are
ancestral to plants
Green algae (Approximately 7,500 species)
Not always green
Some have an orange, red, or rust color
Inhabit a variety of environments
Oceans, freshwater, snowbanks, bark of trees, backs of turtles
Lichen-symbiotic algal relationship with fungi
Filaments - end-to-end chains of cells that form after cell
division in only one plane
In some algae, the filaments are branched, and in others the
filaments are unbranched
Asexual Reproduction
Chlamydomonas produces 16 daughter cells still within the
parent cell
Sexual reproduction
Spirogyra undergoes conjugation, temporary union, during
which cells exchange genetic material 17-36
42. APPLYING THE CONCEPTS—HOW SCIENCE PROGRESSES
17.12 Life cycles among the
algae have many variations
Asexual Reproduction
When environment is favorable to growth, asexual reproduction is a frequent
mode of reproduction among protists
Offspring are identical to parent
Sexual Reproduction
More likely to occur among protists when the environment is changing and is
unfavorable to growth
May produce individuals more likely to survive extreme environments
Haploid life cycle
The zygote divides by meiosis to form haploid spores that develop into haploid
individuals
Alternation of generations
Diploid sporophyte produces haploid spores
Spore develops into a haploid gametophyte that produces gametes
Gametes fuse to form a diploid zygote that develops into sporophyte
Diploid life cycle
Diploid individual produces haploid gametes by meiosis
Gametes fuse to form a diploid zygote 17-42
46. Connecting the Concepts:
Chapter 17
Protists we study today are not expected to include the
direct ancestors to fungi, plants, and animals
They may be related to the other eukaryotic groups by way of
common ancestors that have not been discovered in the fossil
record
May represent an adaptive radiation experienced by the first
eukaryotic cell
Mutualism is a powerful force that shaped the eukaryotic
cell and also shapes all sorts of relationships in the living
world
All possible forms of reproduction and nutrition are present
among the protists
Each of the other eukaryotic groups specializes in a particular type
of reproduction and a particular method of acquiring needed
nutrients
17-46