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Protista
A World in a Drop of Water
A World in a Drop of Water
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Even a low-power microscope
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Can reveal an astonishing menagerie of
organisms in a drop of pond water
Figure 28.1
50 m
The Diversity of Protists
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Morphological Diversity
Organelles
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Divide a Large Cell into Compartments
Structures for Support and Protection
Nutrition
 Photoautotrophs
 Heterotrophs
 Mixotrophs
Habitat
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Fresh water
Marine
Reprodution
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Sexual and Asexual
Variation in Life Cycles
Endosymbiosis in Eukaryotic
Evolution
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considerable evidence
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plastid-bearing protists
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Evolved into red algae and green algae
Red algae and green algae
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protist diversity has its origins in endosymbiosis
underwent secondary endosymbiosis
they were ingested
Diversity of plastids produced by secondary
endosymbiosis
The Endosymbiosis
Theory
Symbiosis occurs when
individuals of two different
species live in physical contact
 Endosymbiosis occurs when an
organism of one species lives
inside an organism of another
species.
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Supporting Data
1.
2.
3.
4.
Mitochondria and chloroplasts are
about the size of an average
bacterium.
Both organelles replicate by fission, as
do bacteria, and have their own
ribosomes to manufacture their own
proteins.
Mitochondria and chloroplasts have
genes that code for the enzymes
needed to replicate and transcribe
their own genomes.
Both organelles have double
membranes, consistent with the
engulfing mechanism.
Impacts on Human Health
and Welfare
The most spectacular crop
failure in history, the Irish
potato famine, was caused by a
protist: Phytophthora infestans.
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Malaria
Malaria, the world's most
chronic public health problem, is
caused by Plasmodium
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Other Human Health Problems Caused
by Protists
Ecological Importance of
Protists
Protists represent just 10% of
the total number of named
eukaryotic species and have
relatively low diversity but are
extraordinarily abundant.

Primary Producers.
Species that produce chemical energy by
photosynthesis
Diatoms
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rank
among the leading primary producers in the
oceans
abundant
Production
of organic molecules in the world’s
oceans
responsible for almost half of the total
carbon that is fixed on Earth.
Protists Play a Key Role in Aquatic
Food Chains
Bacteria and photosynthetic
protists are primary producers
in the aquatic food chain
A food chain describes
nutritional relationships among
organisms.
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Plankton and Phytoplankton
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Plankton
Small
organisms that live near the surface of
oceans or lakes
drift
along or swim only short distances
Phytoplankton
photosynthetic
species of plankton
organic compounds producedare the basis of
food chains in freshwater and marine
environments
Protists Act as Carbon Sinks
Play key role in the global
carbon cycle
 Could help reduce global
warming
 Carbon sink
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a
long-lived carbon reservoir.
Themes in the Diversification of
Protists
Several general evolutionary
themes tie together the
diversity of eukaryotes.
The key to understanding the
protists is to recognize that a
series of important innovations
occurred, often repeatedly, as
eukaryotes diversified.
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Morphological
Diversity
Metabolism inside the
eukaryotic cell can outstrip the
cell's transport and exchange
capabilities because as cells get
larger, the surface area/volume
ratio decreases.
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Organelles Divide a
Large Cell into
Compartments
Eukaryotes solve the problem
of size by dividing their cell
volume into compartments
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The Evolution of
Multicellularity
Eukaryotic cells have many internal
compartments with distinct, specialized
functions.

 After ingesting a bacterium, for example, a Paramecium
surrounds it with an internal membrane, forming a compartment
called a food vacuole.
When the food has been digested and nutrients have diffused
out of the food vacuole, the vacuole merges with the plasma
membrane at the anal pore and expels waste molecules
The cytoskeleton supports and organizes the interior of the
cell, including the organelles
The Evolution of Multicellularity
Differentiation
of cell types is a
crucial criterion for defining
multicellularity.
In
contrast, colonial growth defines
groups of cells that all perform the
same function
Structures for Support
and Protection
Protists have a complex
intracellular structure
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many have a rigid internal
skeleton or a hard external
structure that provides support
or protection, or both
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shell
 test
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Ingestive Feeding
Some protists are large
enough to surround and ingest
other protists through
engulfment by long, fingerlike
projections called pseudopodia
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Species that feed by beating
their cilia to create water
currents often attach
themselves to a substrate and
collect food by sweeping
particles into their mouths
Organisms that filter food out
of water in this way are called
filter feeders, or suspension
feeders.
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Absorptive Feeding
Absorptive feeding occurs
when nutrients are taken up
directly from the environment.
Decomposers feed on dead
organic matter, or detritus.
Parasites live inside other
organisms and absorb their
nutrition directly from the
environment inside their host,
causing damage to the host
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Photosynthesis
A wide variety of protists are
photosynthetic. The major
photosynthetic groups of
protists are distinguished by
the pigments they contain and
many live symbiotically with
animals or other protists.
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Key Lineages of Protists
Excavata
 Excavata - Diplomonadida
 Excavata - Parabasalida
Discicristata
 Discicristata - Euglenida
Alveolata
 Alveolata - Ciliata
 Alveolata - Dinoflagellata
 Alveolata - Apicomplexa
Key Lineages of Protists
Stramenopila (Heterokonta)
 Stramenopila - Oomycota
 Stramenopila - Diatoms
 Stramenopila - Phaeophyta (Brown Algae)
Cercozoa
 Cercozoa - Foraminifera
Plantae
 Rhodophyta (Red Algae)
Amoebozoa
 Myxogastrida (Plasmodial Slime Molds)
Evaluating Molecular Phylogenies
Current phylogenetic tree based on
sequence data
 Eight major lineages of eukaryotes
 Paraphyletic

they
do not constitute all the
descendants of a single common
ancestor
Excavata
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Are adapted to anaerobic environments
Lack plastids
Mitochondria that lack
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Diplomonads (e.g., Giardia)
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DNA
an electron transport chain
citric-acid cycle enzymes
two nuclei
lack a cell wall
reproduce asexually
Parabasalids (e.g., Trichomonas)
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lack a cell wall
reproduce asexually (some also reproduce sexually)
feed by engulfing
Diplomonads
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Diplomonads
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Have two nuclei and multiple flagella
Figure 28.5a
(a) Giardia intestinalis, a diplomonad (colorized SEM)
5 µm
Parabasalids
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Parabasalids include trichomonads
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Which move by means of flagella and an
undulating part of the plasma membrane
Flagella
Undulating membrane
5 µm
Figure 28.5b (b) Trichomonas vaginalis, a parabasalid (colorized SEM)
Discicristata

Euglenids
lack an external wall
 reproduce asexually
 most ingest bacteria or other small cells
 have flagella with a unique internal
structure
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Clade includes
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predatory heterotrophs
photosynthetic autotrophs
pathogenic parasites
Kinetoplastids
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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
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Kinetoplastid
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The parasitic kinetoplastid Trypanosoma
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Causes sleeping sickness in humans
Figure 28.7
9 m
Alveolata
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Ciliates
micronucleus and macronucleus
 reproduce asexually or by conjugation
use cilia for locomotion
spiral or crystalline rod of unknown function
inside their flagella
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Dinoflagellates
About half are photosynthetic
asexual and sexual reproduction occur.
Cells
from sexual reproduction may form
tough cysts that allow them to remain
dormant
Alveolata
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Apicomplexans
Are parasites of animals and some cause
serious human diseases
 apex, contains a complex of organelles
specialized for penetrating host cells and
tissues
 Have apicoplast
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a nonphotosynthetic plastid, the
Alveolates
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Members of the clade Alveolata
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Have membrane-bounded sacs (alveoli)
just under the plasma membrane
0.2 µm
Figure 28.9
Flagellum
Alveoli
Dinoflagellates
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Each has a characteristic shape
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That in many species is reinforced by internal
plates of cellulose
Two flagella
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Make them spin as they move through the water
Flagella
Figure 28.10
Red Tides
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Rapid growth of some dinoflagellates
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Is responsible for causing “red tides,”
which can be toxic to humans
Apicomplexa
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Parasitic
Apical complex at one end
specialized
for penetrating cells
Membrane-bounded sacs (alveoli)
just under the plasma membrane
 Reproduce
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sexually
asexually