28. Protists Flashcards
Key concepts
28.1 Most eukaryotes are single-celled organisms
28.2 Excavates include protists with modified mitochondria and protists with unique flagella
28.3 SAR is a highly diverse group of protists defined by DNA similarities
28.4 Red algae and green algae are the closest relatives of plants
28.5 Unikonts include protists that are closely related to fungi and animals
28.6 Protists play key roles in ecological communities
protists
an informal term applied to any eukaryote that is not a plant, animal or fungus. Most protists are unicellular, though some are colonial or multicellular
mixotroph
an organism that is capable of both photosynthesis and heterotrophy
endosymbiosis
a relationship between two species in which one organism lives inside the cell or cells of another organism
algae
a general term for any species of photosynthesis protist, including both unicellular and multicellular forms. Algal species are included in three eukaryote supergroups (Excavata, SAR and Archaeplastida)
secondary endosymbiosis
a process in eukaryotic evolution in which a heterotrophic eukaryotic cell engulfed a photosynthetic eukaryotic cell, which survived in a symbiotic relationship inside the heterotrophic cell.
Supergroups of eukaryotes
- Excavata
- SAR
- Archaeplastida
-Unikonta
Excavata
- have unique cytoskeletal features
- some species have an excavated feeding groove on one side of the cell body
diplomonad
a protist that has modified mitochondria, two equal- sized nuclei and multiple flagella
parabasilid
a protist such as trichomonad, with modified mitochondria
euglenozoan
a member of a diverse clade of flagellated protists that includes predatory heterotrophs, photosynthetic autotrophs and pathogenic parasites
kinetoplastid
a protist such as a trypanosome, that has a single large mitochondrion that houses and organized mass of DNA
euglenid
a protist such as a euglena or its relatives characterized by an anterior pocket from which one or two flagella emerge
SAR
- contains a large, extremely diverse collection of protists from three major subgroups: stramenopiles, alveolates and rhizarians
stramenopiles
one of three major subgroups for which the SAR eukaryotic supergroup is named. This clade arose by secondary endosymbiosis and includes diatoms and brown algae
diatoms
photosynthetic protist in the stramenopile clade; diatoms have a unique glass-like wall made of silicon dioxide embedded in an organic matrix
brown alga
a multicellular, photosynthetic protist with a characteristic brown or olive color that results from carotenoids in its plastids. Most brown algae are marine and some have a plantlike body
holdfast
a rootlike structure that anchors a seaweed
stipe
a stemlike structure of a seaweed
blade
- a leaflike structure of a seaweed that provides most of the surface area for photosynthesis
- the flattened portion of a typical leaf
alternation of generations
a life cycle in which there is both a multicellular diploid form, the sporophyte and a multicellular haploid form, the gametophyte; characteristic of plants and some algae
heteromorphic
referring to a condition in the life cycle of plants and certain algae in which the sporophyte and gametophyte generations differ in morphology
isomorphic
referring to alternating generations in plants and certain algae in which the sporophytes and gametophytes look alike, although they differ in chromosome number
alveolates
one of the three major subgroups for which the SAR eukaryotic supergroup is named. This clade arose by secondary endosymbiosis, and its members have membrane-enclosed sacs (alveoli) located just under the plasma membrane
dinoflagellate
a member of a group of mostly unicellular photosynthetic algae with two flagella situated in perpendicular grooves in cellulose plates covering the cell
apicomplexan
a group of alveolate protists, this clade includes many species that parasitize animals. Some apicomplexans cause human disease
ciliates
a type of protist that moves by means of cilia
conjugation
- in prokaryotes the direct transfer of DNA between two cells that are members of different species, conjugation results in horizontal gene transfer
- in ciliates, a sexual process in which two cells exchange haploid micronuclei but do not reproduce
rhizarians
one of the three major subgroups for which the SAR eukaryotic supergroup is named. Many species in this clade are amoebas characterized by threadlike pseudopodia
amoeba
a protist characterized by the presence of pseudopodia
pseudopodium
cellular extension of amoeboid cells used in moving and feeding
radiolarian
a protist usually marine with a shell generally made of silica and pseudopodia that radiate from the central body
foraminiferan
and aquatic protist that secretes a hardened shell containing calcium carbonate and extends pseudopodia through pores in the shell
test
in foram protists a porous shell that consists of a single piece of organic material hardened with calcium carbonate
cercozoan
an amoeboid or flagellated protist that feeds with threadlike pseudopodia
archaeplastida
- one of the supergroups
- a monophyletic group which includes red algae, green algae and plants descended from an ancient protistan ancestor that engulfed a cyanobacterium
red alga
photosynthetic protist named for its color which results from a red pigment that masks the green of chlorophyll. Most red algae are multicellular and marine
green alga
a photosynthetic protist named for green chloroplasts that are similar in structure and pigment composition to the chloroplasts of plants. Green algae are a paraphyletic group; some members are more closely related to plants than they are to other green algae
unikonta
- one of the four supergroups
- consists amoebozoans and opisthokonts
amoebozoan
- a protist in a clade that includes many species with lobe or tube shaped pseudopodia
opisthokont
a member of an extremely diverse clade of eukaryotes that includes fungi, animals, and several closely related groups of protists
producers
an organism that produces organic compounds from CO2 by harnessing light energy or by oxidizing inorganic chemicals
consumers
an organism that feeds on producers other consumers or nonliving organic material
Concept 28.1 Summary
-Domain Eukarya includes many groups of protists, along with plants, animals, and fungi. Unlike prokaryotes, protists and other eukaryotes have a nucleus and other membrane-enclosed organelles, as well as a cytoskeleton that enables them to have asymmetric forms and to change shape as they feed, move, or grow.
-Protists are structurally and functionally diverse and have a wide variety of life cycles. Most are unicellular. Protists include photoautotrophs, heterotrophs, and mixotrophs.
-Current evidence indicates that eukaryotes originated by endosymbiosis when an archaeal host (or a host closely related to the archaea) engulfed an alpha proteobacterium that would evolve into an organelle found in all eukaryotes, the mitochondrion.
-Plastids are thought to be descendants of cyanobacteria that were engulfed by early eukaryotic cells. The plastid-bearing lineage eventually evolved into red algae and green algae. Other protist groups evolved from secondary endosymbiotic events in which red algae or green algae were themselves engulfed.
-In one hypothesis, eukaryotes are grouped into four supergroups: Excavata, SAR, Archaeplastida, and Unikonta.
Concept 28.2, 28.3, 28.4, 28.5, summary
page 617
What do a carnivorous dinoflagellate, a parasitic apicomplexan, and a ciliate have in common?
All three have sacs known as alveoli just beneath their plasma membranes.
Which example below is a characteristic shared by diplomonads and parabasalids?
Both lack plastids.
All of the following are genera of protists that parasitize humans EXCEPT:
Chlamydomonas
Which of these groups includes photosynthetic unicellular organisms with flagella and contractile vacuoles?
Euglenids
The term mixotroph indicates that a protist __________.
combines photosynthesis and heterotrophic nutrition
Protists are best described as which of the following?
Eukaryotes that are not plants, animals, or fungi
Organisms are classified as Excavata based on __________.
morphological studies of the cytoskeleton
Which protist group is thought to be most closely related to animals?
Choanoflagellates
Which of these groups includes unicellular organisms that, due to the structure of their cell walls, can withstand pressures equal to the pressure under each leg of a table supporting an elephant?
Diatoms
Which of the following is not a cellular organelle possessed by a protist?
Sporozoite
Which protists were once categorized as fungi due to their multinucleate filaments that resemble hyphae?
Oomycetes
The holdfast of brown algae functions in
anchoring the algae
Which of these groups includes species that produce a substance that is toxic to humans?
Dinoflagellates
Molecular data suggest that plastids originated as __________ engulfed by a heterotrophic eukaryote.
cyanobacteria
Parasites of the genus Trypanosoma evade immune responses through what defense?
Frequently changing their surface proteins
What is one way in which a cellular slime mold differs from a plasmodial slime mold?
A cellular slime mold is multicellular.
Which of these groups is characterized by cells that have more than one nucleus?
Ciliates
Which of the following is not a structure used for locomotion in protists?
Cilia
Flagella
Pseudopodia
Undulating membrane
Which of the following does not take place during the process of conjugation?
Reproduction
Why have protists been “mixed in” with plants, animals, and fungi under the hypothesis that groups eukaryotes into five supergroups?
Many protists are more closely related to plants, animals, or fungi than they are to each other and recent evidence makes it clear that the former kingdom Protista was paraphyletic.
Which of the following is one of the main weaknesses of the proposed classification scheme in which all eukaryotes are divided into five supergroups?
It shows all five supergroups diverging simultaneously from a common ancestor.
Green algae are divided into two main groups, the charophytes and the __________.
chlorophytes
Apicomplexans are currently assigned to the chromalveolates because
the apicoplast, a modified plastid, appears to be of red algal origin
Which of these groups includes parasitic unicellular organisms with a complex of organelles specialized for penetrating host cells and tissues?
Apicomplexans
Although
engulfed a photosynthetic red alga in a secondary endosymbiosis event
_________ is a protist that causes late blight of potatoes and was responsible for the Irish potato famine of the 19th century.
Phytophthora infestans
Which of the following is the best description of protists’ contribution to photosynthesis?
About 30% of the world’s photosynthesis is performed by protists.
The term algae refers to _
several diverse groups of photosynthetic protists
Which organisms are capable of producing a “red tide”?
Dinoflagellates
Which of the following is not a group included in the protists?
Ciliates
Brown algae
Diatoms
Forams
