SAR Supergroup

What does SAR stand for?

Stramenopiles, Alveolates, and Rhizarians

What do SAR organisms share in common?

They are highly diverse protists, many of which are photosynthetic or predatory, and mostly aerobic

What is the defining characteristic of Stramenopiles?

They have one “hairy” flagellum and one smooth flagellum

What are the main groups of Stramenopiles?

Diatoms and Brown Algae

What are diatoms?

Unicellular algae with a two-part, glass-like wall made of hydrated silica

How do diatoms reproduce?

Usually asexually, sometimes sexually

What ecological role do diatoms play?

They are a major component of phytoplankton and contribute to carbon fixation

What is “diatomaceous earth”?

sediments composed of fossilized diatom walls

How do diatoms affect the carbon cycle?

When they die, many sink to the ocean floor, carrying carbon dioxide with them — part of the biological carbon pump

What is the “Iron Hypothesis”?

The idea that adding iron to oceans could stimulate phytoplankton growth and increase carbon sequestration to reduce global warming

What are potential problems with ocean iron fertilization?

It could cause anoxic zones, uneven ocean responses, and unintended ecological side effects

What are the two shapes of diatoms?

Pennate (pen-shaped) and Centric (cylindrical)

What is Pseudo-nitzschia and why is it important?

A toxic diatom that produces domoic acid, a neurotoxin that causes amnesic shellfish poisoning

What is brown algae?

The largest and most complex algae; all are multicellular and mostly marine

What is the structure of brown algae?

• tallus - plantlike body lacking true roots or stems

• blade, stipe, and holdfast resemble plant organs

What is “alternation of generations”?

A life cycle with multicellular diploid (sporophyte) and haploid (gametophyte) stages

How does reproduction occur in brown algae?

• Sporophyte (2n) produces zoospores by meiosis

• Zoospores grow into male/female gametophytes

• Gametes fuse → zygote → new sporophyte

What defines Alveolates?

Presence of membrane-bound sacs (alveoli) just beneath the plasma membrane

What are the main groups of Alveolates?

Dinoflagellates, Apicomplexans, and Ciliates

What is the structure of a Dinoflagellate?

Covered with cellulose plates; have two flagella in perpendicular grooves, causing a spinning motion

What are “red tides”?

Blooms of toxic dinoflagellates that discolor water and can be deadly to marine life

Why do some dinoflagellates glow?

Bioluminescence from luciferin/luciferase reactions triggered by movement

What causes Harmful Algal Blooms (HABs)?

Nutrient runoff, pollution, and global warming — though improved detection also plays a role

Why do blooming dinoflagellates produce toxins?

Likely as chemical defense or competition suppression against other phytoplankton

What are the ecological impacts of HABs?

Ecosystem damage, fish kills, shellfish poisoning, economic loss (tourism, fisheries)

What is the relationship between corals and dinoflagellates?

Corals host symbiotic photosynthetic dinoflagellates (zooxanthellae); loss of them causes coral bleaching

What are Apicomplexans?

Animal parasites with a specialized apical complex for host penetration

What human diseases are caused by Apicomplexans?

Malaria (Plasmodium) and Toxoplasmosis (Toxoplasma gondii)

What organelle do Apicomplexans possess that hints at algal ancestry?

The apicoplast — a non-photosynthetic plastid from red algae

Why is it difficult to make a malaria vaccine?

Plasmodium has a complex life cycle, hides inside cells, has a large genome (5000+ genes), and rapidly mutates surface proteins

What are the main phases of the Plasmodium life cycle?

1. Sporozoite enters human via mosquito bite

2. Invades liver cells (pre-erythrocytic phase)

3. Forms merozoites → infect RBCs

4. Reproduces → cells lyse, causing fever

5. Some become gametocytes → taken by new mosquito

6. In mosquito gut → fertilization → oocyst → new sporozoites

Why is the apicoplast a target for malaria drugs?

It’s essential for parasite survival and distinct from human cell components

How do ciliates move and feed?

Using cilia for movement and directing food into the cell mouth

What is unique about ciliate nuclei?

They have two types of nuclei — a macronucleus (cell functions) and micronuclei (sexual processes)

How do ciliates reproduce sexually?

By conjugation, where two cells exchange haploid micronuclei, fuse them, and form new macronuclei

What defines Rhizarians?

Mostly amoeboid protists that move and feed with threadlike pseudopodia

What are the main groups of Rhizarians?

Radiolarians, Foraminiferans, and Cercozoans

What do Radiolarians look like?

Intricate silica skeletons (tests) fused into one piece

How do Radiolarians feed?

Capture microorganisms using pseudopodia radiating from the central body

What are Foraminiferans (forams)?

Protists with porous calcium carbonate shells (tests) and pseudopodia extending through pores

How big can Forams get?

Up to 1 cm in diameter — unusually large for single-celled organisms

Why are Forams important to geology?

Their fossilized tests form an extensive marine sediment record, used in climate studies

SAR Summary: Stramenopiles - Key Trait

Hairy + smooth flagella

SAR Summary: Stramenopiles - Example

Diatoms, Brown Algae

SAR Summary: Stramenopiles - Role

Photosynthesis, Carbon cycling

SAR Summary: Alveolates - Key Trait

Alveoli under plasma membrane

SAR Summary: Alveolates - Example

Dinoflagellates, Apicomplexans, Ciliates

SAR Summary: Alveolates - Role

Symbiosis, Parasitism

SAR Summary: Rhizarians - Key Trait

Threadlike pseudopodia

SAR Summary: Rhizarians - Example

Radiolarians, Forams

SAR Summary: Rhizarians - Role

Predation, Fossil record