Lecture 24 - Protists

BIOLI 1551

Protists

Primary unicellular eukaryotes

Polyphyletic

A group containing members from different ancestors

Eukarya

Most protists are single-celled organisms and belong to what domain?

Protists

Group that exhibits more structural and functional diversity than any other group of eukaryotes

Protists are the most nutritionally diverse of all eukaryotes

Some protists are photoautotrophs with chloroplasts, some heterotrophs (absorb organic molecules/ingesting food particles), some are mixotrophs and can do both

Endosymbiosis - process in which unicellular organisms engulf another cell that evolve into organelles

What accounts for the vast diversity of protists?

Alpha Proteobacteria

Mitochondria derived from eukaryotes engulfing what type of organism?

Photosynthetic cyanobacterium

What type of organism was engulfed by heterotrophic eukaryotes to evolve into plastids?

Gave rise to red and green algae - process is known as serial endosymbiosis

Secondary Endosymbiosis

When red and green algae were ingested by heterotrophic eukaryote and became endosymbionts themselves

Excavata

“SAR” Clade

Archaeplastida

Unikonta

4 supergroups for organizing protists

Modified mitochondria and protists with unique flagella

Excavates include protists with…

Proposed clade from the study of the cytoskeleton

Diplomonads, parasalids, euglenozoans

Three monophyletic groups in excavata…

Plastids and have modified mitochondria, found in anaerobic environments

Diplomonads and parabasalids lack ______

Predatory heterotrophs, photosynthetic autotrophs, and pathogenic parastes

Euglenozoans are a diverse clade that includes…

Euglenids

Most _____ are autotrophic in sunlight but can become heterotrophic in dark.

Stramenopiles, Alveolates, Rhizarians…

“SAR” clade that may have originated by secondary endosymbiosis

Diatoms - unicellular algae abundant in both freshwater and marine phytoplankton

Type of Stramenopile (includes some of the most important photosynthetic organisms on the planet)

Diatomaceous earth

Accumulation of fossilized diatoms, good filtering medium

Brown algae

Largest and most complex protists known, multicellular & typically a marine species

Example: Kelp/seaweeds

Alveolates

Have membrane-closed sacs (alveoli) under plasma membrane:

Dinoflagellates

Type of alveolate… foundation of most marine and many freshwater food chains.

Cause “red tides”

Ciliates

Diverse group of protists, named for their use of cilia and feed (example: paramecium and stentor)

Archaeplastids

Red and green algae, land plants make up _____ what super group?

Cyanobacterium

Archaeplastids derived from ancient protists engulfing a ______.

Phycoerythrin

Red algae get their red color from _____. there are more than 6,000 known species

Green algae

Named for their grass-green chloroplasts. Closets relatives to plants.

Charophytes (most closely related to land plants) and chlorophytes (mostly found in fresh water but also in marine and terrestrial areas - example Volvox, Ulva, Caulerpa)

Green algae is divided into what two groups?

Unikonts

Supergroup that is closely related to fungi and animals

Amoebozoans, opisthokonts

Two major clades of Unikonts

Opisthokonts

Extremely diverse group of eukaryotes that include animals, fungi, and several closely related groups of protists.

Nucleariids & choanoflagellates

Protists within the opisthokonts that are closely related to fungi / animals (2 answers)

Amoebozoans

Amoebas with love/tube shaped pseudopodia

Includes slime molds, tubulinids, and entamoebas

Slime mold

Mycetozoan, produce fruiting bodies that aid in spore dispersal (resemblance to fungi is due to convergence)

Tubulinids

Large and varied group of free-living (nonparasitic) amoebozoans

Most common in soil/freshwater and marine environments

Most heterotrophic

Entamoebas

Mostly parasitic species

Example: E. histolytica

Aquatic environments/anywhere there is water, attach to the rocks, sand, or silt

Where do most protists live?

Many protist form symbiotic relationship with other species.

Example: Coral and protists or Termites and wood-digesting protists in their gut

Parasites

Pathogenic protists that survive by attacking host

Producers

In aquatic communities, main ____ are photosynthetic protists and prokaryotes.

• 30% of world’s photosynthesis by aquatic protists

• 20% from photosynthetic prokaryotes

• 50% from land plants