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30 Cards in this Set

  • Front
  • Back
T or F?
Eukarya are the third domain on the tree of life?
• The Eukarya, the third domain on the tree of
life, range from single-celled organisms the
size of bacteria to sequoia trees and blue whales.
The largest and most morphologically complex
organisms on the tree of life—algae, plants,
fungi, and animals—are eukaryotes.
T or F?
Protists are a diverse group of organisms that includes all eukaryotes.
•Protists are a diverse group of organisms that
includes all eukaryotes except the green plants,
fungi, and animals (Figure 28.1).
Why Do Biologists Study Protists?
• Biologists study protists because:
–they are intrinsically interesting
–they are so important medically and ecologically
–they are critical to understanding the evolution of plants,
fungi, and animals
• Impacts on Human Health and Welfare
–The most spectacular crop failure in history, the Irish
potato famine, was caused by a protist: Phytophthora
–Malaria, the world's most chronic public health problem,
is caused by Plasmodium (Figure 28.2).
–A number of other human health problems are also caused
by protists (Table 28.1). For example: toxic algal blooms.
A harmful algal bloom occurs when...?
• A harmful algal bloom occurs
when toxin-producing protists reach
high densities in a particular area.
Algal blooms of dinoflagellates are
known as red tides (Figure 28.3).
What are the 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.
•Species that produce chemical energy by
photosynthesis are called primary producers.
Diatoms, for example, are photosynthetic protists
rank among the leading primary producers in the
oceans because they are so abundant. Production of
organic molecules in the world’s oceans, in turn, is
responsible for almost half of the total carbon that
fixed on Earth.
T or F?
Protists do not play a key role in aquatic food chains.
• Bacteria and photosynthetic protists are primary
producers in the aquatic food chain (Figure 28.4). A
food chain describes nutritional relationships among
•Plankton are small organisms that live near the
surface of oceans or lakes and drift along or swim only
short distances. The organic compounds that are
produced by phytoplankton—photosynthetic species
of plankton—are the basis of food chains in freshwater
and marine environments.
How Could Protists Help
Reduce Global Warming?
• The movement of carbon atoms from carbon dioxide
molecules in the atmosphere to organisms in the soil or
the ocean and then back to the atmosphere is called the
global carbon cycle.
•Protists in the oceans play a key role in the global
carbon cycle and act as carbon sinks that could help
reduce global warming (Figure 28.5). A carbon sink is
a long-lived carbon reservoir.
How Do Biologists Study Protists?
• Although protists have been the focus of intense
study, they are so diverse that it has been difficult to
find any overall patterns in their evolution and
•Recently, researchers have made dramatic progress in
understanding protistan diversity by combining data on
the morphology of key groups and phylogenetic
analyses of DNA sequence data.
• Morphology
–Many protists have a characteristic overall form
with synapomorphies—shared, derived traits that
are used to distinguish major monophyletic groups
(Figure 28.6; Table 28.2).
•Evaluating Molecular Phylogenies
–The current phylogenetic tree based on sequence
data has identified eight major lineages of
eukaryotes and confirms that the lineages grouped
under the name protist are paraphyletic—they do
not constitute all the descendants of a single
common ancestor (Figure 28.7).
T or F?
The first eukaryotes were probably single-celled
organisms with a cytoskeleton and a nucleus but no
cell wall.
What is the endosymbiosis theory?
•The endosymbiosis theory proposes that
mitochondria originated when a bacterial cell took up
residence inside a eukaryote about 2 billion years ago
(Figure 28.9). The endosymbiosis theory also
contends that chloroplasts originated in an analogous
When does symbiosis occur?
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.
Describe Data Support the Endosymbiosis Theory.
Observations consistent with the endosymbiosis theory
include the following:
1. Mitochondria and chloroplasts are about the size of
an average bacterium.
2. Both organelles replicate by fission, as do bacteria,
and have their own ribosomes to manufacture their
own proteins.
3. Both organelles have double membranes,
consistent with the engulfing mechanism.
4. Mitochondria and chloroplasts have genes that
code for the enzymes needed to replicate and
transcribe their own genomes.
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:
•Organelles Divide a Large Cell into Compartments
•The Evolution of Multicellularity
•Structures for Support and Protection
T or F?
Organelles divide a small cell into compartments.
• 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.
•Eukaryotes solve the problem of size by dividing their cell
volume into compartments (Figure 28.12).
•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
–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.
Where do biologists draw the line between the
loose aggregations of cells called a colony and the
more highly structured arrangements of cells that
create a body and typify multicellular organisms?
–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 (Figure
What are the structures for support and protection in protists?
• All protists have a complex intracellular
•Many have a rigid internal skeleton or a hard
external structure called a shell or a test
–provides support or protection, or both (Figure
How Do Protists Find Food?
• The large cell size and evolution of the cytoskeleton has
enabled a unique feeding strategy that allows protists to eat
bacteria, archaea, or other protists, rather than just absorbing
organic compounds or photosynthesizing.
•Ingestive Feeding- Some protists are large enough to surround
and ingest other protists through engulfment by long, fingerlike
projections called pseudopodia (Figure 28.15a).
•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 (Figure 28.15b).
Organisms that filter food out of water in this way are called
filter feeders, or suspension feeders.
How Do Protists Find Food?
• 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 (Figure 28.16).
•Photosynthesis- A wide variety of protists are photosynthetic.
The major photosynthetic groups of protists are distinguished
by the pigments they contain (Figure 28.17), and many live
symbiotically with animals or other protists.
•Ingestive, absorptive, and photosynthetic lifestyles occur in
protists and many other eukaryotic lineages, and all three can
occur within a single clade.
How Do Protists Move?
• Cell crawling is a sliding movement accomplished
by streaming of pseudopodia (Figure 28.20a).
•The other major mode of locomotion involves
flagella (Figure 28.20b) or cilia (Figure 28.20c).
–Flagella and cilia have identical structures; but flagella are
long and are usually found alone or in pairs, whereas cilia
are short and numerous.
How Do Protists Reproduce?
• Sexual reproduction evolved in protists
• Produces offspring that are genetically
different from their parents, as opposed to
asexual reproduction in which the offspring are
genetically identical to the parent.
•Most protists undergo asexual reproduction
routinely. Many protists undergo sexual
reproduction only intermittently.
T or F?
There is no variation in life cycles for protists.
• A life cycle describes the sequence of events that
occurs as individuals grow, mature, and reproduce.
•Every aspect of a life cycle is variable among protists
(Figure 28.21).
•Alternation of generations (Figure 28.22) is a
phenomenon in which the haploid and diploid phases
of the life cycle are multicellular. The multicellular
haploid form is called a gametophyte, and the diploid
form is a sporophyte.
Describe Excavata.
• Diplomonads have two nuclei, lack a cell
wall, and reproduce asexually (e.g., Giardia)
(Figure 28.23).
•Parabasalids lack a cell wall, reproduce
asexually (some also reproduce sexually),
and feed by engulfing (e.g., Trichomonas)
(Figure 28.24).
Describe Discicristata.
• Euglenids lack an external wall and
reproduce asexually; most ingest
bacteria or other small cells, although
some are photosynthetic (Figure
Describe Alveolata.
• Ciliates have a micronucleus and a macronucleus,
can reproduce asexually or by conjugation, and use
cilia for locomotion (Figure 28.26).
•Most dinoflagellates are unicellular. Some species are
capable of bioluminescence—they emit light via an
enzyme-catalyzed reaction. About half the species are
photosynthetic. Both asexual and sexual reproduction
occur. Cells from sexual reproduction may form tough
cysts that allow them to remain dormant (Figure
•Apicomplexa are parasitic, have an apical complex at
one end, and reproduce sexually or asexually (Figure
Describe Stramenopila (Heterokonta).
• Oomycetes resemble fungi, and many have long
branching filaments called hyphae (Figure 28.29).
They are extremely important decomposers in aquatic
•Diatoms are supported by silicon-rich, glassy shells
and are photosynthetic (Figure 28.30). They are the
most important producer of carbon compounds in the
•Phaeophyta (brown algae) are photosynthetic and
sessile—permanently fixed to a substrate—although
their reproductive cells may be motile—capable of
locomotion (Figure 28.31). They form forests that are
important habitats.
• Foraminifera have multiple nuclei and feed
by engulfment with pseudopodia. Their tests
are usually made of organic material (Figure
28.32). Dead forams often form extensive
sedimentary deposits when they settle out of
the water, producing layers that eventually
solidify into chalk, limestone, or marble.
Describe Plantae.
•Glaucophyte algae
•Rhodophyta (red algae) have cell walls
composed of cellulose and other polymers and
have no flagella (Figure 28.33).
–Almost all red algae are photosynthetic.
–Some species contribute to reef building.
•Green Algae
•Land Plants
Describe Amoebozoa.
•Lobose Amoebae
•Cellular Slime Molds
•Myxogastrida (plasmodial slime molds)
have a huge supercell with many nuclei.
–They are important decomposers in forest
ecosystems (Figure 28.34).