Biology, Seventh Edition
Solomon • Berg • Martin
Chapter 24
Protists
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Biology, Seventh Edition
CHAPTER 24 Protists
• Kingdom Protista
• “Simple” eukaryotes
• Mostly unicellular
• Some form colonies
• Some are coenocytic
–Multiple nuclei in one mass of
cytoplasm
• A few are multicellular
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Biology, Seventh Edition
CHAPTER 24 Protists
• Most protists live in aquatic
environments
• Sixty major groups of protists
• Important in the biosphere
• Food for other organisms
• Photosynthetic protists supply
oxygen
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Biology, Seventh Edition
CHAPTER 24 Protists
• Locomotion
•
•
•
•
Pseudopodia
Flagella
Cilia
A few are nonmotile
• Modes of nutrition
• Autotrophs
• Heterotrophs
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CHAPTER 24 Protists
Chlamydomonas
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Biology, Seventh Edition
CHAPTER 24 Protists
• Interactions with other organisms
•
•
•
•
Free-living
Mutualism
Commensalism
Parasitism
• Habitats
• Most live in the ocean or freshwater
ponds, lakes, and streams
• Parasites live in host’s bodily fluids
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Biology, Seventh Edition
CHAPTER 24 Protists
• Modes of reproduction
• Many protists reproduce both
sexually and asexually
–Syngamy (union of gametes)
• Some protists are solely asexual
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CHAPTER 24 Protists
• Endosymbiont theory
• Certain organelles arose from
symbiosis with prokaryotes
• Mitochondria arose from aerobic
eubacteria
• Chloroplasts arose from
cyanobacteria
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CHAPTER 24 Protists
Primary and
secondary
endosymbiosis
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Biology, Seventh Edition
CHAPTER 24 Protists
• Classifying eukaryotes
• Ultrastructure
–Fine details of cell structure
• Molecular data
–Ribosomal RNA
–Nuclear genes
• The protist kingdom is probably
paraphyletic
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Biology, Seventh Edition
CHAPTER 24 Protists
Eight monophyletic groups of eukaryotes
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CHAPTER 24 Protists
• Zooflagellates
• Mostly unicellular heterotrophs
• Move using flagella
• Now separated into several
monophyletic groups
–Excavates
–Discicristates
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Biology, Seventh Edition
CHAPTER 24 Protists
• Excavates live in oxygen-free
environments
• Diplomonads
–No mitochondria
–No Golgi complex
–One or two nuclei
–Up to eight flagella
• Giardia is a parasite
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CHAPTER 24 Protists
Giardia
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CHAPTER 24 Protists
• Discicristates have disc-shaped
mitochondrial cristae
• Euglenoids
–About 1/3 are photosynthetic
–Inhabit freshwater ponds and
puddles
• Trypanosoma causes African
sleeping sickness
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CHAPTER 24 Protists
Euglena gracilis
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Biology, Seventh Edition
CHAPTER 24 Protists
• Alveolates have flattened
vesicles under the plasma
membrane
• Ciliates
–Move by hairlike cilia
–Micronuclei for sexual reproduction
–Macronuclei control metabolism
–Reproduce sexually by conjugation
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CHAPTER 24 Protists
Paramecium, a ciliate
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CHAPTER 24 Protists
• Alveolates
• Dinoflagellates
–Mostly unicellular with two flagella
–Mostly photosynthetic
• Apicomplexans
–Parasitic
–Spore-forming
–Plasmodium causes malaria
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Dinoflagellates
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CHAPTER 24 Protists
Biology, Seventh Edition
CHAPTER 24 Protists
• Heterokonts are motile with two
different kind of flagella
• Water molds
–Mycelium absorbs organic material
–Reproduce asexually with
biflagellate zoospores
–Reproduce sexually with oospores
–Phytophthora causes plant
diseases
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Mycelium around a dead insect
Saprolegnia
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CHAPTER 24 Protists
Biology, Seventh Edition
CHAPTER 24 Protists
• Heterokonts
• Diatoms
–Mostly unicellular with shells
containing silica
–Some diatoms are part of plankton
• Golden algae
–Mostly unicellular, biflagellate algae
–Both freshwater and marine
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Diatoms
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CHAPTER 24 Protists
Biology, Seventh Edition
CHAPTER 24 Protists
• Heterokonts
• Brown algae
–Multicellular seaweed
–Ecologically important in cooler
ocean waters
–Kelps have leaflike blades, stemlike
stipes, anchoring holdfasts, gasfilled bladders
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CHAPTER 24 Protists
Brown algae
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CHAPTER 24 Protists
• Cercozoa are amoeboid cells
that often have hard outer
shells, called tests, through
which cytoplasmic projections
extend
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Biology, Seventh Edition
CHAPTER 24 Protists
• Cercozoa
• Foraminferans
–Many-chambered tests with pores
–Cytoplasmic extensions to move
and obtain food
• Actinopods
–Mostly marine plankton
–Axopods to obtain food
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CHAPTER 24 Protists
An actinipod
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CHAPTER 24 Protists
• Plants have chloroplasts
bounded by inner and outer
membranes
• Land plants, red algae, and
green algae are monophyletic
• Red algae and green algae are
in kingdom Protista
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Biology, Seventh Edition
CHAPTER 24 Protists
• Red algae are mostly
multicellular seaweeds
• Ecologically important in warm
tropical waters
• Red algae with calcium
carbonate in their cell walls are
important for reef building
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CHAPTER 24 Protists
Red algae
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CHAPTER 24 Protists
• Green algae are diverse in size,
structural complexity, and
reproduction
• May be the ancestors of land
plants
• Multicellular forms do not have
cells differentiated into tissues,
unlike plants
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Biology, Seventh Edition
CHAPTER 24 Protists
Green algae
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Biology, Seventh Edition
CHAPTER 24 Protists
• Amoebas move and obtain food
using cytoplasmic extensions
called pseudopodia
• Capture and engulf food by
surrounding it and forming a
vacuole around it
• Entamoeba histolytica causes
amoebic dysentery
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Biology, Seventh Edition
CHAPTER 24 Protists
• Plasmoidal slime mold
• Feeding stage is a multinucleate
plasmodium that extends up to
one foot in diameter
• In the reproductive stage, stalks
called sporangia produce haploid
spores
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Biology, Seventh Edition
CHAPTER 24 Protists
Plasmoidal slime mold
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Biology, Seventh Edition
CHAPTER 24 Protists
• Cellular slime molds
• Feeding stage is individual
amoeboid cells
• During moisture or food shortage,
they aggregate into a migrating
pseudoplasmodium
• Forms stalked fruiting body
containing spores
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CHAPTER 24 Protists
Cellular slime mold
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