4. Protists

Question 1

T/F

Many important parasites such as Plasmodium, Trypanosoma, and Giardia are Protists

Answer 1

true

Question 2

Protists are only parasites

Answer 2

false

They can be mutualists (eg. termite gut symbionts) and commensals (eg. opalinids in frogs)

(they can also be parasites, like giardia)

Question 3

Are protists a Kingdom?

Answer 3

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

Question 4

Give the 2 main reasons why Kingdom Protista was given up

Answer 4

1. It was clearly not monophyletic
2. 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)

Question 5

What level of organization are “supergroups”?

Answer 5

between domain and kingdom

Question 6

In a phylogram, what do the lengths of branches represent?

Answer 6

The lengths of branches reflect degree of molecular divergence

(phylograms are the circular “trees”)

Question 7

T/F

Sequencing of new protist groups has altered composition of previous clades and added many more possible supergroup-level clades

Answer 7

true

Question 8

T/F

The phylum-level taxonomy within the protists is generally agreed upon

Answer 8

false

depending on the classification scheme, can be from 6 to more than 50 phyla recognized!

Question 9

Sometimes ‘groupings of convenience’ are used to classify protists. Sometimes these match clades, but not always. Give 3 of these groupings

Answer 9

• general morphology
• modes of movement
• nutrition

Question 10

How many species of protists are there?
- known vs predicted

Answer 10

known: ~74,000
predicted: 140,000 to 1.6 million!

Question 11

Are there more named species of protists or of Placozoa?

Answer 11

Protists

Question 12

The majority of protists are __cellular or ______

Answer 12

unicellular or colonial

Question 13

Give 2 examples of protists that are truly multicellular

Answer 13

most red algae (Rhodophyta)

some green algae (Chlorophyta)

Question 14

What is the most common mode of reproduction in protists?

Answer 14

asexual reproduction

Question 15

List and describe 3 ways in which protists can reproduce asexually

Answer 15

1. binary fission: cell’s nucelus duplicates, cell splits into 2 cells
2. multiple fission: nucleus undergoes several divisions before dividing into multiple daughter cells (each of which has a single nucleus)
3. Plasmotomy: a single-celled, multinucleate individual splits into 2 + multinucleate daughter cells

Question 16

T/F

Many protists engage in strange types of sexual reproduction

Answer 16

true

(even though asexual rep is most common)

Question 17

Some protists can engage in both sexual and asexual reproduction in their life cycle. Give an example

Answer 17

Opalinid (symbionts of amphibians)

Question 18

How big are most protists

Answer 18

Most are 100-200 micrometers long!
- some smaller & some bigger

Small size is a common feature of protists

Question 19

Many protists have rigid skeletal structures. These can be “autogenic” or “allogenic”. Define each

Answer 19

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

Question 20

T/F

Diversification through endosymbiosis is seen in protists, but rarely in animals

Answer 20

true

Question 21

Describe the famous example of diversification through endosymbiosis in protists

Answer 21

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

Question 22

What is the difference between primary and secondary endosymbioses?

Answer 22

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

Question 23

A famous example of endosymbiosis:

cyanobacterium –> photosynthetic ____

Answer 23

plastid

Question 24

Some protists still posses the nucleus/ genome of their eukaryotic algal ____

Answer 24

endosymbionts

Question 25

T/F protists with ancient endosymbionts can retain multiple cell membranes (some from the endosymbionts)

Answer 25

true

Question 26

T/F protists are always sessile

Answer 26

false can be sessile, sedentary, or very mobile

Question 27

sessile=

Answer 27

glued to one spot and cannot depart from it

Question 28

sedentary=

Answer 28

tend to stay in one place but can move if necessary

Question 29

planktonic protists are mobile; how to they move?

Answer 29

most just float (not much control over their lateral direction but can adjust height) - some can actively crawl or swim w/ structures

Question 30

What are pseudopodia in protists?

Answer 30

= temporary cytoplasm-filled extensions of the cell used for locomotion and prey-capture

Question 31

Which group of protists are pseudopodia most common in?

Answer 31

Amoebozoa

Question 32

List and describe the 2 main types of pseudopodia

Answer 32

- lobopodia: blunt, relatively thick extensions - axopodia: thin, rigid rods supported by microtubules

Question 33

The cytoplasm in the cell of pseudopods can take 2 forms: 1 2

Answer 33

1. thick and gel-like ectoplasm 2. fluid endoplasm

Question 34

T/F Some protists move by beating one or more flagella

Answer 34

true

Question 35

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

Answer 35

cilia eg. paramecium

Question 36

How do photoautotrophic protists get their nutrients?

Answer 36

ie algae use sunlight, water, and carbon dioxide to make their own carbohydrates

Question 37

How do heterotrophic protists get their nutrients?

Answer 37

Feed on other organisms (living or dead)

Question 38

How do mixotrophic protists get their nutrients?

Answer 38

They can both feed on other organisms or use sunlight/water/ CO2 (depending on conditions)

Question 39

Are Euglena mixotrophic or heterotrophic protists? Describe what this means

Answer 39

Mixotrophic! Means they can both feed on other organisms or use sunlight/water/ CO2 (depending on conditions). Can switch day vs night

Question 40

T/F In protists, some of the same structures used for locomotion are also used for feeding

Answer 40

true! e.g. pseudopodia can engulf prey

Question 41

Explain how most protists feed

Answer 41

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

Question 42

Pinocytosis=

Answer 42

"cell drinking" some protists use this method to feed; take in dissolved material via very small vesicles that open at the cell membranes surface

Question 43

List and describe the 2 main types of vacuoles

Answer 43

1. food vacuole: for digestion of solid particles 2. contractile vacuole: i.e. water expulsion vesicles - accumulate and expel excess water

Question 44

Contractile vacuoles are more prominent in freshwater protists. Explain why

Answer 44

Because solute concentrations in their cytoplasm is often higher than in the surrounding water (marine protists are more likely to be isosmotic with sea water)