Protists: Origins, Diversity, Ecology Flashcards
Protista
The name of the former Kingdom that comprised mostly unicellular eukaryotes
Evolutionary relationships of protists remain unclear
Is the term protist still used?
yes - it is still used to refer to eukaryotes that are neither plants, animals, nor fungi
Protists
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
Are most Eukaryotes are single-celled or multicellular organisms?
Single-celled
What is the difference between biological functions in unicellular vs. multicellular organisms?
In multicellular organisms, some biological activity is relegated to specific tissue types
In unicellular, processes are carried out in subcellular organelles
Photoautotrophs
Contain chloroplasts - plant-like
Heterotrophs
Absorb organic molecules or ingest larger food particles
Animal-like (ingestive) or Fungi-like (absorptive)
Mixotrophs
Combine photosynthesis and heterotrophic nutrition
Where does much of the diversity in protists originate from?
Endosymbiosis
Endosymbiosis
The process in which a unicellular organism engulfs another cell, which becomes an endosymbiont and then organelle in the host cell
When does secondary endosymbiosis occur?
When algae is ingested in food vacuoles
Chlorarachniophytes
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
What are the four supergroups of Eukaryotes?
Excavata, Archaeplastida, SAR, and Unikonta
What was different about the old phylogeny?
It had 5 supergroups of eukaryotes - the 5th was Rhizaria
Our understanding of the relationships among protist groups continues to change rapidly
What types of protists are included in Excavates?
Protists with modified mitochondria and protists with unique flagella
What do diplomonads and parabasalids share?
These two groups lack plastids, have modified mitochondria, and most live in anaerobic environments
Diplomonads
-Have modified mitochondria called mitosomes
-Derive energy from anaerobic biochemical pathways
-Have two equal-sized nuclei and multiple flagella
-Are often parasites
Parabasalids
Have reduced mitochondria called hydrogenosomes that generate some energy anaerobically
Euglenozoa
A diverse clade that includes predatory heterotrophs, photosynthetic autotrophs, and pathogenic parasites
What is the main distinguishing feature of Euglenozoa?
A spiral or crystalline rod of unknown function inside their flagella
Kinetoplastids
Have a single mitochondrion with an organized mass of DNA called a kinetoplast
Trypanosomes
- 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
Euglenids
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”
Are Euglenids usually photosynthetic, heterotrophic, or mixotrophic?
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
What is SAR defined by?
It is a highly diverse group of protists defined by DNA similarities
Stramenopiles
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
Diatoms
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
Diatomaceous earth
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
Biological carbon pump
-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
Ocean gardening: Iron Hypothesis
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”
What are the main problems with climate engineering (geoengineering) by iron fertilization?
- 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
What are the two different groups of diatoms?
Pennates, pen-shaped, and centric, like a cylinder
What is amnesic shellfish poisoning caused by?
Neurotoxins
- Short-term memory loss
- Seizures
- Death
Bioaccumulates in shellfish and fish that feed on toxic phytoplankton
Brown algae
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
What is the structure of brown algae?
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
Alteration of generations
Possesses multicellular haploid and diploid life stages
What does alteration of generations look like in brown algae?
- 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
What is the defining characteristics of Alveolates?
They have membrane-enclosed sacs (alveoli) just under the plasma membrane
Dinoflagellates
- 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
Deadly Red Tide at Carlsbad Aquafarm
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
CINAPS
Stands for Center of Integrated Networked Aquatic PlatformS
- Investigate formation, propagation and prediction of HAB’s
Why do blooming dinoflagellates produce toxins?
- 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
What are the impacts of HAB on ecosystem health?
2-degree effects
- Loss of tourism
- Loss of food sources
- Ecosystem damage
- monitoring
- accumulation
What kind of relationship do corals and zooxanthellae have?
A symbiotic relationship
- Coral bleaching occurs when zooxanthellae exit the coral
Apicomplexans
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
What are the steps to the infection cycle of merozoite in humans when infected by a mosquito?
- Anopheles mosquito bites
- Injects sporozoites
- Sporozoites enter hepatocytes
- Divides into merozoites
- Merozoites penetrate RBC’s
- Merozoites divide every 48-72 hours
- Break out of RBC’s - cause symptoms
- Merozoites infect other RBC’s / form gametocytes
- Another mosquito bites and picks up gametocytes
- Male gametocytes produce several slender male gametes
- Fertilization occurs in mosquito digestive tract to form a zygote
- Oocyst develops from zygote in gut wall
- Oocyst releases thousands of sporozoites
- Sporozoites migrate to mosquito’s salivary gland
- Cycle repeated
Why isn’t there a malaria vaccine?
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
Apicoplast
Non-photosynthetic plastid
- vital for parasite survival
- Apicoplast’s algal origin may provide a target for drugs
Ciliates
- 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
What is defining about Rhizarians?
They are a diverse group of protists defined by DNA similarities
Radiolarians
- 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
Foraminiferans
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
Cercozoans
Include most amoeboid and flagellated protists that feed with threadlike pseudopodia - most are heterotrophs and often predatory
- common in marine, freshwater, and soil ecosystems
The chromatophore
This structure evolved from a different cyanobacterium than the plastids of other photosynthetic eukaryotes
- evidence that endosymbiosis occurred more than once
What is archaeplastida?
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
What evolved into red and green algae?
A heterotrophic protist that acquired a cyanobacterial endosymbiont
Did plants descend from red or green algae?
Green algae
Red Algae
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
Green Algae
Named for their grass-green chloroplasts
Two main groups
- Chlorophytes
- include unicellular, colonial, and multicellular forms
- Charophytes
Chlorophytes
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
How did chlorophytes evolve to become larger and more complex?
- 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
- colony is a hollow ball whose wall is composed of
- 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 - By the repeated division of nuclei with no cytoplasmic division
- branched filaments lack cross-walls - are
multinucleate
- thallus is one huge “supercell”
