Protists
Chapter 29
Protists
Protists are the most diverse of the four
eukaryotic kingdoms
-Unicellular, colonial and multicellular groups
The kingdom Protista is paraphyletic and
grouped for convenience
The 15 major protist phyla are grouped into
seven major monophyletic groups
-However, 60 lineages cannot be placed with
confidence 2
Protists
3
Protists
4
Eukaryotic Origins
Eukaryotic cells differ from prokaryotes by the
presence of a cytoskeleton and organelles
Appearance of eukaryotes in microfossils
occurred about 1.5 BYA
5
Eukaryotic Origins
The nucleus and
endoplasmic reticulum
arose from infoldings
of prokaryotic cell
membrane
6
Eukaryotic Origins
Many organelles evolved via endosymbiosis
between an ancestral eukaryote and a
bacterial cell
-Mitochondria – Aerobic bacteria
Organisms that host chloroplasts are not
monophyletic
-Red and green algae engulfed
cyanobacteria
-Brown algae engulfed red algae
-Secondary endosymbiosis 7
8
9
Eukaryotic Origins
Over time, most organellar genes moved into
the nucleus
-Therefore, these organelles cannot be
grown in pure culture
Mitosis and cytokinesis did not evolve in
eukaryotes all at once
-Intermediate mechanisms survive today
-Fungal nuclear membranes do not dissolve
10
General Biology of the Protists
Cell surface
-Plasma membrane
-Extracellular material (ECM), in some
-Diatoms – Silica shells
Cysts
-Dormant cell with resistant outer covering
-Used for disease transmission
11
General Biology of the Protists
Locomotion
-Flagella
-Cilia
-Pseudopodia (“false feet”)
-Lobopods – Large, blunt
-Filopods – Thin, branching
-Axopods – Thin, long
12
General Biology of the Protists
Nutrition
-Phototrophs
-Heterotrophs
-Phagotrophs – Particulate food matter
-Osmotrophs – Soluble food matter
-Mixotrophs are both phototrophic and
heterotrophic
13
General Biology of the Protists
Asexual reproduction
-Typical mode of reproduction
-Some species have an unusual mitosis
-Binary fission = Equal cells
-Budding = Progeny cell smaller
-Schizogony = Multiple fission
Sexual reproduction
-Union of haploid gametes which are
produced by meiosis 14
Diplomonads and Parabasalids
Are closely related to the early, now extinct
eukaryotic cell
-Flagellated
-Lack
mitochondria
-May have lost their mitochondria,
rather than never acquired them 15
Diplomonads and Parabasalids
Diplomonads
-Have two nuclei
-Giardia intestinalis
Parabasalids
-Have undulating
membranes
-Trichomonas vaginalis
16
Euglenozoa
Euglenoids were among the earliest
eukaryotes to possess mitochondria
-1/3rd have chloroplasts
-All have a
flexible pellicle
-None have
sexual
reproduction
17
Euglenozoa
Euglena
-Two anterior (and unequal) flagella
-Contractile vacuoles – Collect excess water
-Stigma – Movement towards light
-Numerous small chloroplasts
-The concept of a single Euglena genus is
now being debated
18
Euglenozoa
19
Euglenozoa
Kinetoplastids
-Unique, single mitochondrion with DNA
maxicircles and minicircles (RNA editing)
-Trypanosomes cause human diseases
-African sleeping sickness – Tsetse fly
-Leishmaniasis – Sand fly
-Difficult to control because organisms
repeatedly change their protective coat
20
Euglenozoa
21
Alveolata
Alveolata have flattened vesicles called
alveoli
-These function like Golgi bodies below the
cell membrane
22
Alveolata
Dinoflagellates
-Unicellular with two unequal flagella
-Live in aquatic environments
-Most are
photosynthetic
-Do not appear
to be directly
related to any
other phylum 23
Alveolata
Dinoflagellates
-Reproduction is primarily asexual
-DNA is not complexed with histones
-About 20 species produce powerful toxins
that harm vertebrates
-“Blooms” are responsible for red tide
24
Alveolata
Apicomplexans
-Spore-forming animal parasites
-Apical complex is a
unique arrangement
of organelles at one
end of the cell
-Enables the cell
to invade its
host 25
Alveolata
Plasmodium
-An apicomplexan that causes malaria
-Eradication of malaria
1. Elimination of mosquito vectors
2. Development of drugs
3. Development of vaccines
-Organism has a very complex life cycle 26
27
Alveolata
Other apicomplexans
-Gregarines
-Found in the intestines
of arthropods, annelids
and mollusks
-Toxoplasma gondii
-Causes infections in
humans with
immunosuppression 28
Alveolata
Ciliates
-Feature large numbers of cilia arranged in
longtitudinal rows or spirals around the cell
-Have two types of vacuoles
-Food vacuoles = Digestion of food
-Contractile vacuoles = Regulation of
water balance
29
30
Alveolata
Ciliates
-Have two types of nuclei
-Macronucleus = Divides by mitosis
-Responsible for physiological functions
-Micronucleus = Divides by meiosis
-Involved in conjugation
-Fusion of two cells of different
mating types
31
32
Stramenopila
Stramenopiles have very fine hairs on their
flagella
-A few species have lost their hairs during
evolution
33
Stramenopila
Brown algae
-Kelps
-Grow in relatively shallow
waters throughout the world
-Life cycle involves alternation
of generations
-Sporophyte = Multicellular and diploid
-Gametophyte = Multicellular and haploid
34
35
Stramenopila
Diatoms (Phylum Chrysophyta)
-Unicellular organisms
-Have unique double shells made of silica
-Some move using raphes
-Two long grooves lined with vibrating
fibrils
36
Stramenopila
37
Stramenopila
Oomycetes (“water molds”)
-Were once considered fungi
-Motile zoospores with two unequal flagella
-Undergo sexual reproduction
-Either parasites or saprobes
-Phytophthora infestans
-Irish potato famine (1845-1847)
38
Rhodophyta
Rhodophyta, or red algae, range from
microscopic to very large sizes
-Lack flagella and centrioles
-Have accessory photosynthetic pigments
within phycobilisomes
-Origin has been a source of controversy
-Tentatively, treated as a sister clade of
Chlorophyta (green algae)
39
Rhodophyta
40
Choanoflagellida
Choanoflagellates are most like the common
ancestor of all animals
-Single emergent flagellum, surrounded by
funnel-shaped contractile collar
-Use collar to feed on bacteria
-Have a surface tyrosine kinase receptor
found in sponges
41
Choanoflagellida
42
Protists Without a Clade
Amoebas are paraphyletic
-Rhizopoda (True amoebas)
-Move by means of cytoplasmic
projections called pseudopods
-Actinopoda (Radiolarians)
-Glassy exoskeletons made of silica
-Needlelike pseudopods
43
Protists Without a Clade
44
Protists Without a Clade
Foraminifera are heterotrophic marine protists
-Have pore-studded shells called tests,
through which thin podia emerge
-Use podia for swimming and feeding
-Have complex life cycles with haploid and
diploid generations
-Limestones are rich in forams
-White cliffs of Dover
45
Protists Without a Clade
46
Protists Without a Clade
Slime molds
-Were once considered fungi
-Include two lineages
1. Plasmodial slime molds
2. Cellular slime molds
47
Protists Without a Clade
1. Plasmodial slime molds
-Stream along as a plasmodium, a
nonwalled, multinucleate mass of cytoplasm
-Ingests bacteria and other organic material
-When food or moisture is scarce, organism
forms sporangia, where spores are produced
48
Protists Without a Clade
49
Protists Without a Clade
2. Cellular slime molds
-Individual organisms behave as separate
amoebas
-Move through soil ingesting bacteria
-When food is scarce, organisms aggregate
to form a slug
-Slug differentiates into a sorocarp
50
Protists Without a Clade
51