What is a Protist?
How are
Protists related
to other
eukaryotes?
Does everyone agree how to classify
protists?
• No, at present, biologists
do not agree how to
classify protists
• The amount of diversity
among the protists, is
much greater than within
or between the other
three eukaryotic
kingdoms
The Protist Dilemma
• Protists are grouped
together solely because
they are not fungi, plants
or animals
• Furthermore, many
protists are more closely
related to members of
other eukaryotic kingdoms
than they are to other
protists.
Current Protist classification
• It has been proposed that the protista
kingdom be divided into six groups or clades
• Today, while we still use the term Protist, this
is not a single kingdom, but a collection of
organisms in six clades
What is a Protist?
• A protist is a eukaryote
(has a nucleus)
• A protist is any
eukaryote that is not a
plant, animal or fungus
Evolution of Protista
Endosymbiont Hypothesis
Are all protists unicellular?
• No, although most are unicellular, some protists
are colonial, and some like the giant kelp are
multicellular.
Unicellular
Colonial
Multicellular
How do Protists Move?
Some move with flagella
• Long whip-like
projections
• One to two per cell
• Examples
– Trypanosoma
– Euglena
Trypanosoma
Euglena
 Two flagella
 No cell wall
 Chloroplasts
How do Protists move?
Some move with cilia
Cilia can be used for
feeding and
movement
Cilia are short and
used like oars on a
boat
Example
 Paramecium
Ciliates - Paramecium
Lysosomes
Trichocysts
Oral groove
Gullet
Anal pore
Contractile vacuole
Micronucleus
Macronucleus
Go to
Section:
Food vacuoles
Cilia
Some do not move
 Those that do not
move produce spores
and live as parasites
 Plasmodium causes
malaria
 Cryptosporidium
spreads through
contaminated drinking
water and caused
intestinal disease
Excavates: feeding groove, flagella
• Diplomonads
– Giardia is an intestinal parasite that causes
cramping and diarrhea
• Discicristates
– Euglena is free living and can use its chloroplast
for photosynthesis or can live as a heterotroph
– Trypansoma causes African sleeping sickness;
carried by tsetse flies
Euglena
Chloroplast
Carbohydrate
storage bodies
Gullet
Pellicle
Flagella
Go to
Section:
Eyespot
Nucleus
Contractile
vacuole
Chromalveolates: very diverse group; most are
photosynthetic
• Phaeophytes = multicellular brown algae
• Chrysophytes = unicellular golden algae
• Diatoms = unicellular algae with intricate silicon
dioxide (silica) shells
• Ciliates = paramecium are not photosynthetic
• Dinoflagellates = half are photosynthetic, half are
heterotrophs; some are luminescent
• Apicomplexans = parasitic Plasmodium
Brown algae
Phaeophytes
• Photosynthetic
• Chlorophylls a and c
• Brown accessory
pigment fucoxanthin
• Multicellular
• Giant kelp, Fucus
Photosynthetic protists
• Chrysophytes
 “Golden plants”
 Gold-colored
chloroplasts
 Cell walls contain pectin
instead of cellulose
 Store food as oil rather
than starch
 Can form thread like
colonies
Photosynthetic protists
Diatoms
 Glass like cell walls
 Cell walls contain silicon
(Si)
 Cell walls like petri dish
Photosynthetic
protists
Dinoflagellates
 Luminescent
 “Fire plants”
 Half photosynthetic
 Half heterotrophs
 Two flagella
Apicomplexan
• Plasmodium
• Mosquito
borne
parasites like
the species
that causes
malaria
Cercozoa, Foraminiferan, Radiolarian
• Have pseudopods
• Many produce
protective shells
Heliozoan
Foraminiferans
Rhodophytes
Red Algae
• Chlorophyll a
• Red accessory pigment
– phycobilin
• Absorbs blue light
• Grows very deep
• Multicellular
• Nori
Ecology of photosynthetic protists
• Base of the food
chain
• Half of the
photosynthesis on
earth is carried
out by
phytoplankton
Ecology of photosynthetic protists
• Algal blooms
 Caused by too much pollution
or nutrients
 Deplete water of oxygen
 Kill fish and invertebrates
 Dinoflagellates cause “red
tides”
 Red tides produce toxins which
can be taken in by shellfish.
Eating these shellfish can cause
illness, paralysis and death
Green algae
• Phylum Chlorophyta
• Same chlorophyll and cell wall composition as
green plants
• Chlorophyll a and b
• Store food as starch
• Found in fresh and salt water and on land
• Unicellular, colonial and multicellular
• Now classified with plants
Unicellular
green algae
• Chlamydomonas
 Lives in ponds, ditches and
wet soil
 Egg shaped
 Two flagella
 Large, cup-shaped
chloroplast
Colonial
green algae
• Spirogyra
 Filamentous
 Forms threadlike
colonies
 Spiral chloroplasts
• Volvox
 Hollow spheres
 500 – 50,000 identical
cells
 Some cell specialization
Human uses of algae
• Oxygen
• Food (nori; thickening agent (carrageenan) in ice
cream, egg nog, chocolate, salad dressing)
• Industry (plastics, waxes, paints, lubricants)
• Science labs (agar)
• Alternation of generation – alternating
between diploid and haploid organisms
• Diploid – having two copies of each
chromosome
• Haploid – having one copy of each
chromosome
• Gametophyte – haploid gamete producing
organism
• Sporophyte – diploid spore producing
organism
Heterotrophic protists
• Amoebozoa = Amoebas use pseudopods for
movement and feeding
• Ciliates = Paramecia use cilia to move food to gullet;
food vacuoles and lysosomes digest the food; waste
is released through the anal pore
• Slime Molds and Water Molds absorb food
through their cell walls from dead or decaying
matter; decomposers
Section 20-2
An Amoeba
Contractile vacuole
Pseudopods
Nucleus
Food vacuole
Go to
Section:
Slime molds
Slime molds
Water molds
• Cells are multinucleate
• Cell walls of cellulose
• White fuzz on dead fish in
water
• Plant parasites on land
Cause potato blight responsible for
potato famine
Reproduction in
water molds
• Can produce
sexually and
asexually
• Motile
(swimming)
spores
• Antheridium
produces
sperm
• Oogonium
produces eggs
Mutualistic relationships
• Zooxanthellae – live
inside coral and provide
food through
photosynthesis
• Trychonympha – live
in the gut of termites
and digest cellulose