Protists: Origins, Diversity, Ecology

Question 1

Protista

Answer 1

The name of the former Kingdom that comprised mostly unicellular eukaryotes
Evolutionary relationships of protists remain unclear

Question 2

Is the term protist still used?

Answer 2

yes - it is still used to refer to eukaryotes that are neither plants, animals, nor fungi

Question 3

Protists

Answer 3

Eukaryotes and thus have organelles and are more complex than prokaryotes
Protists exhibit more structural and functional diversity than any other group of eukaryotes
The most nutritionally diverse of all eukaryotes

Question 4

Are most Eukaryotes are single-celled or multicellular organisms?

Answer 4

Single-celled

Question 5

What is the difference between biological functions in unicellular vs. multicellular organisms?

Answer 5

In multicellular organisms, some biological activity is relegated to specific tissue types
In unicellular, processes are carried out in subcellular organelles

Question 6

Photoautotrophs

Answer 6

Contain chloroplasts - plant-like

Question 7

Heterotrophs

Answer 7

Absorb organic molecules or ingest larger food particles
Animal-like (ingestive) or Fungi-like (absorptive)

Question 8

Mixotrophs

Answer 8

Combine photosynthesis and heterotrophic nutrition

Question 9

Where does much of the diversity in protists originate from?

Answer 9

Endosymbiosis

Question 10

Endosymbiosis

Answer 10

The process in which a unicellular organism engulfs another cell, which becomes an endosymbiont and then organelle in the host cell

Question 11

When does secondary endosymbiosis occur?

Answer 11

When algae is ingested in food vacuoles

Question 12

Chlorarachniophytes

Answer 12

Engulfed cell becomes a plastid which has a vestigial nucleus (nucleomorph), sequence of which resembles that of green alga
Plastids have 4 membranes
- inner from inner and outer membranes of ancient cyanobacterium
- 3rd from engulfed alga’s plasma membrane
- outer from heterotrophic eukaryote’s food vacuole

Question 13

What are the four supergroups of Eukaryotes?

Answer 13

Excavata, Archaeplastida, SAR, and Unikonta

Question 14

What was different about the old phylogeny?

Answer 14

It had 5 supergroups of eukaryotes - the 5th was Rhizaria
Our understanding of the relationships among protist groups continues to change rapidly

Question 15

What types of protists are included in Excavates?

Answer 15

Protists with modified mitochondria and protists with unique flagella

Question 16

What do diplomonads and parabasalids share?

Answer 16

These two groups lack plastids, have modified mitochondria, and most live in anaerobic environments

Question 17

Diplomonads

Answer 17

-Have modified mitochondria called mitosomes
-Derive energy from anaerobic biochemical pathways
-Have two equal-sized nuclei and multiple flagella
-Are often parasites

Question 18

Parabasalids

Answer 18

Have reduced mitochondria called hydrogenosomes that generate some energy anaerobically

Question 19

Euglenozoa

Answer 19

A diverse clade that includes predatory heterotrophs, photosynthetic autotrophs, and pathogenic parasites

Question 20

What is the main distinguishing feature of Euglenozoa?

Answer 20

A spiral or crystalline rod of unknown function inside their flagella

Question 21

Kinetoplastids

Answer 21

Have a single mitochondrion with an organized mass of DNA called a kinetoplast

Question 22

Trypanosomes

Answer 22

• Use “bait-and-switch” defense, aka “antigenic variation”
• 1/3 genome devoted to producing surface proteins
• Switches between 1000’s of protein variants
• Blunts the adaptive immune response

Question 23

Euglenids

Answer 23

Have one or two flagella that emerge from a pocket at one end of the cell
- Can also crawl using a shape changing mechanism called “metaboly”

Question 24

Are Euglenids usually photosynthetic, heterotrophic, or mixotrophic?

Answer 24

They can be all three
- Many are photosynthetic, but can also be heterotrophic
- use light detector to get to the right light intensity
- Some are mixotrophic
- photosynthetic in the daylight and heterotrophic at
night

Question 24

What is SAR defined by?

Answer 24

It is a highly diverse group of protists defined by DNA similarities

Question 24

Stramenopiles

Answer 24

Includes important phototrophs as well as several clades of heterotrophs - Most have a "hairy" flagellum paired with a "smooth" flagellum - Stramenopiles include diatoms, golden algae, brown algae, and oomycetes

Question 25

Diatoms

Answer 25

Unicellular algae with a unique two-part, glass-like wall of hydrated silica - usually reproduce asexually, and occasionally sexually - major component of phytoplankton and are highly diverse

Question 26

Diatomaceous earth

Answer 26

Much of this sediment is composed of fossilized diatom walls - after a diatom population has bloomed, many dead individuals fall to the ocean floor undecomposed

Question 27

Biological carbon pump

Answer 27

-During the carbon cycle, CO2 is naturally removed from the atmosphere -Over thousands of years, a fraction of it is sequestered in the oceans for prolonged periods of time -Dead phytoplankton and other organisms act as CO2 vessels, driving this pump as they sink towards the bottom of the ocean

Question 28

Ocean gardening: Iron Hypothesis

Answer 28

John Martin - "Fertilizing the oceans with iron would increase carbon sequestration and could potentially be used to mitigate some of the effects of global warming" Famous for joking - "Give me half a tanker of iron, and I will give you the next ice age"

Question 29

What are the main problems with climate engineering (geoengineering) by iron fertilization?

Answer 29

- Sediment traps indicate that small amounts reached ocean floor - it's a slow process - May lead to anoxia in deep ocean (dead zone) - Each ocean likely to respond differently - Other unintentional unforeseen consequences

Question 30

What are the two different groups of diatoms?

Answer 30

Pennates, pen-shaped, and centric, like a cylinder

Question 31

What is amnesic shellfish poisoning caused by?

Answer 31

Neurotoxins - Short-term memory loss - Seizures - Death Bioaccumulates in shellfish and fish that feed on toxic phytoplankton

Question 32

Brown algae

Answer 32

The largest and most complex algae - all are multicellular - most are marine - includes many species commonly called "seaweeds" - have the most complex multicellular anatomy of all algae

Question 33

What is the structure of brown algae?

Answer 33

The algal body is plantlike but lacks true roots, stems, and leaves and is called a thallus - base is called the holdfast - middle stem-like piece is called the stipe - leaf-like top is called blades

Question 34

Alteration of generations

Answer 34

Possesses multicellular haploid and diploid life stages

Question 35

What does alteration of generations look like in brown algae?

Answer 35

- The diploid sporophyte found just below low tide mark - Cells on blades develop into sporangia - Releases haploid flagellated spores called zoospores - Half turn into male gametophytes and half turn into female gametophytes - Males release sperm, fertilize attached eggs - Zygote develops into new sporophyte

Question 36

What is the defining characteristics of Alveolates?

Answer 36

They have membrane-enclosed sacs (alveoli) just under the plasma membrane

Question 37

Dinoflagellates

Answer 37

- Armored cellulose plates - Flagellum lies in groove - Spinning motion examples - Alexandrium catenella - Causative organism of Paralytic Shellfish Poisoning Dinophysis sp. - Causative organism of Diarrhetic Shellfish Poisoning

Question 38

Deadly Red Tide at Carlsbad Aquafarm

Answer 38

Anoxic conditions decimated the fish and shellfish in the lagoon. The decomposing biomass, biotoxins, carbon dioxide, ammonia, hydrogen sulfide, sulfur dioxide, methane and other noxious gases bubbled up to the surface

Question 39

CINAPS

Answer 39

Stands for Center of Integrated Networked Aquatic PlatformS - Investigate formation, propagation and prediction of HAB's

Question 40

Why do blooming dinoflagellates produce toxins?

Answer 40

- Energetically expensive to synthesize toxins - Lab studies suggest that the toxins can inhibit or kill other phytoplankton - may represent a form of inter-specific competition - Metabolic pathways responsible for toxin production still under investigation

Question 41

What are the impacts of HAB on ecosystem health?

Answer 41

2-degree effects - Loss of tourism - Loss of food sources - Ecosystem damage - monitoring - accumulation

Question 42

What kind of relationship do corals and zooxanthellae have?

Answer 42

A symbiotic relationship - Coral bleaching occurs when zooxanthellae exit the coral

Question 43

Apicomplexans

Answer 43

Parasites of animals and some cause serious human diseases (e.g., malaria, toxoplasmosis, etc.) - one end, the apex, contains a complex of organelles specialized for penetrating a host - have a non-photosynthetic plastids, the apicoplast, perhaps of red algal origin - most have sexual and asexual stages that require two or more different host species for completion

Question 44

What are the steps to the infection cycle of merozoite in humans when infected by a mosquito?

Answer 44

1. Anopheles mosquito bites 2. Injects sporozoites 3. Sporozoites enter hepatocytes 4. Divides into merozoites 5. Merozoites penetrate RBC's 6. Merozoites divide every 48-72 hours 7. Break out of RBC's - cause symptoms 8. Merozoites infect other RBC's / form gametocytes 9. Another mosquito bites and picks up gametocytes 10. Male gametocytes produce several slender male gametes 11. Fertilization occurs in mosquito digestive tract to form a zygote 12. Oocyst develops from zygote in gut wall 13. Oocyst releases thousands of sporozoites 14. Sporozoites migrate to mosquito's salivary gland 15. Cycle repeated

Question 45

Why isn't there a malaria vaccine?

Answer 45

Potential targets - sporozoites in "pre-erythrocytic" or "hepatic phase" - phase is brief and may escape immune response - merozoites in "erythrocytic phase" to prevent invasion or multiplication - gametocytes - might reduce spread of infection but would offer no therapeutic effect to the patient Problems - large genome - 5000+ genes - complex life cycle, often resides within cells, escapes immune detection - very high rate of mutagenesis - evolution of antibiotic-resistant strains and changes in surface proteins (antigens) - affects the poorest countries so little financial incentive for pharma to develop vaccines

Question 46

Apicoplast

Answer 46

Non-photosynthetic plastid - vital for parasite survival - Apicoplast's algal origin may provide a target for drugs

Question 47

Ciliates

Answer 47

- Use cilia to feed and move - Distinctive feature is two types of nuclei - Tiny micronuclei and larger macronuclei Genetic variation through conjugation - Two ciliates exchange haploid micronuclei - Resulting two micronuclei fuse, undergo mitosis, and produce new macronucleus - Binary fission yields four daughter cells

Question 48

What is defining about Rhizarians?

Answer 48

They are a diverse group of protists defined by DNA similarities

Question 49

Radiolarians

Answer 49

- marine protists - have tests fused into one delicate piece, usually made of silica - use their pseudopodia to engulf microorganisms through phagocytosis - the pseudopodia radiate from the central body

Question 50

Foraminiferans

Answer 50

Also known as forams, named for porous, generally multi-chambered shells, called tests - consists of a single piece of organic materia hardened with calcium carbonate - pseudopodia extend through the pores in the test and function in swimming, feeding and test formation - can be up to one cm in diameter - foram tests in marine sediments form an extensive fossil record

Question 51

Cercozoans

Answer 51

Include most amoeboid and flagellated protists that feed with threadlike pseudopodia - most are heterotrophs and often predatory - common in marine, freshwater, and soil ecosystems

Question 52

The chromatophore

Answer 52

This structure evolved from a different cyanobacterium than the plastids of other photosynthetic eukaryotes - evidence that endosymbiosis occurred more than once

Question 53

What is archaeplastida?

Answer 53

Red and green algae, the closest relatives of plants - a super group used by some scientists and includes red algae, green algae, and land plants

Question 54

What evolved into red and green algae?

Answer 54

A heterotrophic protist that acquired a cyanobacterial endosymbiont

Question 55

Did plants descend from red or green algae?

Answer 55

Green algae

Question 56

Red Algae

Answer 56

Color is due to an accessory pigment called phycoerythrin - greenish red in color in shallow waters to almost black in deep water - accessory pigments allow them to absorb blue and green light, which penetrate relatively far into the water - presence of phycoerythrin masks the green of chlorophyll - usually multicellular; largest are seaweeds - abundant in coastal waters of the tropics

Question 57

Green Algae

Answer 57

Named for their grass-green chloroplasts Two main groups - Chlorophytes - include unicellular, colonial, and multicellular forms - Charophytes

Question 58

Chlorophytes

Answer 58

Majority of chlorophytes live in freshwater, although some are marine or terrestrial - E.g., Watermelon snow (Chlamydomonas nivalis) - contains a bright red carotenoid pigment in addition to chlorophyll - thrives in melting ice - indicator of melting - accelerates thawing

Question 59

How did chlorophytes evolve to become larger and more complex?

Answer 59

1. By forming colonies of individual cells, or as filamentous masses - colony is a hollow ball whose wall is composed of hundreds or thousands of biflagellated cells embedded in a gelatinous matrix - cells are usually connected by strands of cytoplasm - large colonies eventually release the small "daughter" colonies within them 2. By forming true multicellular bodies by cell division and differentiation - Edible chlorophyte has a multicellular thallus differentiated into leaf-like blades and a root-like holdfast 3. By the repeated division of nuclei with no cytoplasmic division - branched filaments lack cross-walls - are multinucleate - thallus is one huge "supercell"