4. Protists Flashcards
T/F
Many important parasites such as Plasmodium, Trypanosoma, and Giardia are Protists
true
Protists are only parasites
false
They can be mutualists (eg. termite gut symbionts) and commensals (eg. opalinids in frogs)
(they can also be parasites, like giardia)
Are protists a Kingdom?
No, not anymore- they’re clearly not monophyletic as a Kingdom
In 1969 Robert Whittaker proposed a 5-kingdom system, which listed Protists as a Kingdom
Now, protists are treated as an UNRANKED, paraphyletic grouping of eukaryotes that are not plants, animals, or fungi
Give the 2 main reasons why Kingdom Protista was given up
- It was clearly not monophyletic
- the degree of molecular divergence between many protist clades is similar to that b/w other recognized kingdoms –> these differences warrant recognition at or above kingdom level (= SUPERGROUP)
What level of organization are “supergroups”?
between domain and kingdom
In a phylogram, what do the lengths of branches represent?
The lengths of branches reflect degree of molecular divergence
(phylograms are the circular “trees”)
T/F
Sequencing of new protist groups has altered composition of previous clades and added many more possible supergroup-level clades
true
T/F
The phylum-level taxonomy within the protists is generally agreed upon
false
depending on the classification scheme, can be from 6 to more than 50 phyla recognized!
Sometimes ‘groupings of convenience’ are used to classify protists. Sometimes these match clades, but not always. Give 3 of these groupings
- general morphology
- modes of movement
- nutrition
How many species of protists are there?
- known vs predicted
known: ~74,000
predicted: 140,000 to 1.6 million!
Are there more named species of protists or of Placozoa?
Protists
The majority of protists are __cellular or ______
unicellular or colonial
Give 2 examples of protists that are truly multicellular
most red algae (Rhodophyta)
some green algae (Chlorophyta)
What is the most common mode of reproduction in protists?
asexual reproduction
List and describe 3 ways in which protists can reproduce asexually
- binary fission: cell’s nucelus duplicates, cell splits into 2 cells
- multiple fission: nucleus undergoes several divisions before dividing into multiple daughter cells (each of which has a single nucleus)
- Plasmotomy: a single-celled, multinucleate individual splits into 2 + multinucleate daughter cells
T/F
Many protists engage in strange types of sexual reproduction
true
(even though asexual rep is most common)
Some protists can engage in both sexual and asexual reproduction in their life cycle. Give an example
Opalinid (symbionts of amphibians)
How big are most protists
Most are 100-200 micrometers long!
- some smaller & some bigger
Small size is a common feature of protists
Many protists have rigid skeletal structures. These can be “autogenic” or “allogenic”. Define each
Autogenic= skeletal structure can be created by the protist’s own metabolic activity
- eg. cellulose plates, carbonate/ silicate shells
Allogenic= skeletal structure is made of other materials (eg mineral fragments) that are glued together by the protist
- e.g. tests of some amoebae
T/F
Diversification through endosymbiosis is seen in protists, but rarely in animals
true
Describe the famous example of diversification through endosymbiosis in protists
The ancestral eukaryotic cell was the product of an ancient endosymbiotic event involving the capture of an aerobic proteobacterium by a ‘pre-eukaryotic’ cell that had a membrane-bound nucleus
What is the difference between primary and secondary endosymbioses?
Primary= capture of free-living prokaryotes by (pre)eukaryotes
Secondary= capture of a eukaryotic cell by a eukaryotic cell
difference= whether a prokaryote or eukaryote was grabbed
A famous example of endosymbiosis:
cyanobacterium –> photosynthetic ____
plastid
Some protists still posses the nucleus/ genome of their eukaryotic algal ____
endosymbionts
T/F
protists with ancient endosymbionts can retain multiple cell membranes (some from the endosymbionts)
true
T/F
protists are always sessile
false
can be sessile, sedentary, or very mobile
sessile=
glued to one spot and cannot depart from it
sedentary=
tend to stay in one place but can move if necessary
planktonic protists are mobile; how to they move?
most just float (not much control over their lateral direction but can adjust height)
- some can actively crawl or swim w/ structures
What are pseudopodia in protists?
= temporary cytoplasm-filled extensions of the cell used for locomotion and prey-capture
Which group of protists are pseudopodia most common in?
Amoebozoa
List and describe the 2 main types of pseudopodia
- lobopodia: blunt, relatively thick extensions
- axopodia: thin, rigid rods supported by microtubules
The cytoplasm in the cell of pseudopods can take 2 forms:
1
2
- thick and gel-like ectoplasm
- fluid endoplasm
T/F
Some protists move by beating one or more flagella
true
A clade of protists “Ciliata” is defined in part on the abundance of _____ that can sometimes entirely cover the cell membrane like a coat of fur
cilia
eg. paramecium
How do photoautotrophic protists get their nutrients?
ie algae
use sunlight, water, and carbon dioxide to make their own carbohydrates
How do heterotrophic protists get their nutrients?
Feed on other organisms (living or dead)
How do mixotrophic protists get their nutrients?
They can both feed on other organisms or use sunlight/water/ CO2 (depending on conditions)
Are Euglena mixotrophic or heterotrophic protists?
Describe what this means
Mixotrophic!
Means they can both feed on other organisms or use sunlight/water/ CO2 (depending on conditions). Can switch day vs night
T/F
In protists, some of the same structures used for locomotion are also used for feeding
true!
e.g. pseudopodia can engulf prey
Explain how most protists feed
cilia move water & particles towards the cytostome (acts as a mouth).
Solid food particles are surrounded by a vacuole (membrane-bound compartment) & then digested. This is called phagocytosis
Pinocytosis=
“cell drinking”
some protists use this method to feed; take in dissolved material via very small vesicles that open at the cell membranes surface
List and describe the 2 main types of vacuoles
- food vacuole: for digestion of solid particles
- ## contractile vacuole: i.e. water expulsion vesicles
