Chapter 28 (Protists)

Protists

A diverse group of mostly unicellular eukaryotes that do not fit into the animal, plant, or fungi kingdoms. They are more likely related to plants, animals, etc more, than they are to each other. Most are unicellular, the organisms in most eukaryotic lineages are protists.

Endosymbiosis

A relationship between two species in which one organism lives inside the cell of another organism (the host)

Eukaryotic supergroups

A large group of organisms that share a common ancestor and share a unique characteristic (Each supergroup has smaller groups within it)

Excavata

Have an “excavated” feeding groove on one side of the body

Includes:

Diplomonads

Parabasalids

Euglenozoans

Diplomonad

Two nuclei + multiple flagella (unique cell structure)

Lacks mitochondria

Causes giardiasis

Giardia Infection (disease)

Intestinal infection marked by stomach cramps, bloating, nausea, and diarrhea

Spread through contaminated water

Also called (Backpackers Nightmare) A part of the Diplomonad protists

Parabasalid Protist

Parabasal organ (similar to the Golgi apparatus)

Also have reduced mitochondria (hydrogenosomes)

Characteristic undulating membrane + multiple flagella

Causes trichomoniasis

Trichomonas

One of the most common STD’s worldwide

Often asymptomatic → spreads silently

Part of the Parabasalid Protist

Euglenozoans

• Flagellated protists that include predatory heterotrophs, photosynthetic autotrophs, and pathogenic parasites

• A rod with either a spiral or a crystalline structure inside the flagella

Kinetoplastids

Kinetoplastids have a single large mitochondrion that contains an organized mass of DNA called a kinetoplast

Include species that feed on prokaryotes in freshwater

Euglenids

Has a pocket at one end where flagella emerge

Some are mixotrophs phs

Photosynthesis and Heterotrophic - Phagocytosis

Eyespot

Light detector

Trypanosoma

Transmitted by tsetse flies in Africa

Causes African sleeping sickness

Constantly changes surface proteins → evades immune defense

Deadly if untreated

Part of the Euglenozoan

Chagas Disease

From the euglenozoan group

Transmitted by bloodsucking insects and can lead to congestive heart failure

Early symptoms include fever, body aches, and eye swelling

“Bait and Switch”

1. They are coated with millions

of copies of a single protein

2. When the host’s immune

system recognizes the

protein to attack

3. New generations of the

parasite switches to another

surface protein with a

different molecular structure

4. These “frequent changes” in

The surface proteins prevent

the host from developing

proper immunity

SAR: Stramenopiles

“Straw hair” in Latin

Numerous fine, hairlike flagella

Paired with a shorter smooth, non-hairy flagellum

Includes some of the most important photosynthetic organisms on the planet

-Diatoms

-Brown Algae

-Oomycetes

Diatoms

Stramenopiles with intricate silica (glass) cell walls

A major component of phytoplankton in oceans and lakes

Photosynthetic → produce 20% of the global oxygen supply

Base of aquatic food webs

Brown Algae: Underwater Forests

Includes the largest protists (multicellular)

Form kelp forestss → biodiversity hotspots

Used in Food industry

Holdfast

A rootlike structure; anchors down algae

Stipe

A stemlike structure

Blades

Leaflike structure

No tissues or organs in any of the three

Sporophytes

diploid individual; produces spores

The spores are haploid and move by flagella

Zoospores divide by mitosis and develop into male and female gametophytes

Part of the brown algae group

Gametophytes

Produces gametes

Hetermorphic

Sporophytes and gametophytes are structurally different

Isomorphic

Structurally the same

Oomycetes

Stramenopiles that look like fungi (filamentous)

Previously classified as one (“egg-fungus”)

Cell walls made of cellulose

Decomposers of plant pathogens

Phytophthora infestans (disease)

Caused the Irish Potato Famine

Millions starved, mass migration, 1840’s

Example of protists shaping human history

Turns the stalks and stems of potato and tomato plants into black slime

Part of the ommyocytes

Alveolates

Characterized by alveoli (membrane-bound sacs just under their plasma membranes)

-Dinoflagellates

-Apicomplexans

-Ciliates

Dinoflagellates

Reinforced by cellulose plates

Have two flagella

One of them causes them to spin and one causes them to move through the water

Some produce bioluminescence → glowing beaches

Others cause harmful algal blooms (“red tides”) Kills fish and shellfish poision

Sea Sparkle and Red Tides

Apicomplexans

Alveolates are specialized as parasites

• Almost all are parasites in animals

• Virtually all animal species examined so

far attacked by them

Plasmodium → malaria parasite

• Requires two hosts: humans +

mosquitoes (both asexual and sexual)

Mosquito’s partner in Crime

Ciliates

Alveolates covered in rows of cilia

• Example: Paramecium

• Use cilia for movement and feeding

• Ciliary beating – gradual, slow, and

controlled movement of cilia

• “The wave” in the stadium

• Most are predators (of bacteria or other

protists)

• Have two nuclei:

• Macronucleus = daily cell function

• Micronucleus = sexual reproduction

(conjugation)

• Show surprising complexity for

single-celled organisms.

: Tiny Powerhouses

Rhizarians

A diverse group, mostly amoeboid protists with thin pseudopodia, builds protective shells

Major roles: Ocean sediments, nutrient cycling, symbiosis

Thin and thread-like pseudopodia

Radiolarians, Foraminiferans, Cercosozoans

Radiolarians

Glassy Skeletons

Intricate silica skeletons; often symmetrical

Skeletons often appear like glass art under microscope

Pseudopodia radiate outward for feeding

Dead skeletons sink —> form siliceous ooze on ocean floor

Formaminiferans

Formen = little hole

Calcium carbonate shells

Pseudopodia extend through pores for feeding

Fossilized shells from limestone deposists ex: white cliffs Dover

Used to study past climates

Cercozoans

Hidden Diversity

Mostly aquatic and soil-dweling amoeboid and flagellated protists

Many are parasites of plants, animals, or other protists. Important for nutrient cycling soil in ecosystems.

Paulinella chromatophore

Part of the Cercozoans

• They are autotrophs so that they can generate energy themselves, through the secondary endosymbiosis of cyanobacteria. Peptidoglycan unique feature

Archaeplastida

-Red algae, green algae, land plants

All descended from a protist that engulfed a cyanobacterium (primary endosymbiosis)

A heterotrophic protist acquired a cyanobacterial endosymbiont

FOUNDATION OF PLANT EVOLUTION

Red Algae

Deep Water Specialists

Also known as rhodophytes (rhodes = red)

Contain pigment phycoerythrin - that masks the green color of chlorophyll

Shallow water species have less phycoerythrin.

Absorb the blue and green lights

Mostly mutlicellular

Red algae (reproduction)

Can reproduce sexually and asexually

They have no flagellated gametes (fertilization depends on water currents)

Economic uses: nori, agar, carrageenan

Also perform alternative generation (above)

Green Algae

Plant Relatives (closest relatives to land plants)

Share the same chloroplast structure and cell wall composition with plants. Some scientists want them to be in a new plant kingdom (Viridiplantae, Viridis = green)

Charophytes

Part of green algae

Most related to plants

• Charophytes are the protists most closely related to land plants 

  • Share structural proteins in cell walls and enzymes with plants 

• Some form protective zygotes→ adaptation toward land 

• Bridge group linking algae to plants

Chlamydomonas

Unicellular, bi-flagellated, model organism

Part of green algae and Chlorophytes

Volvox

colonial form, shows early steps toward multicellularity

Green algae, Chlorophytes

Ulva

Multicellular, simple leaf-like body (edible). Have blades and holdfast

Chlorophytes

Chloros = green

Most of them live in water

Exhibit wide diversity: unicellular, colonial, multicellular

showcase diversity from unicellular to multicellular 

Amoebozoans Overview

Amoebas move and feed using pseudopodia (extentions of cytoplasm)

Thick and lobe shaped pseudopodia

Found in soil, freshwater, and marine habitats

Include free-living and parasitic species

Slime Molds

Part of Unikonta and Amoebozoans

Behavior without brains

Once classified as fungi (due to apperance)

Unikonta

Animals, Fungi, some protists

There are two major clades of unikonts

• Amoebozoans

• Opisthokonts

Plasmodial Slime Molds

Multinucleated

Large but not multicellular

Single mass of cytoplasm that contain many nuclei

Feed on decaying organic matter (phagocytosis)

Move slowly by streaming cytoplasm

Can grow surprisingly large, visible to the naked eye

Extended pseudophodia through moist soil, leaf mulch, or rotting logs

Cellular Slime Molds

Exist as individual amoeboid cells when food is abundant

When food is scarce, cells aggregate into multi-cellular-like structure

Act cooperatively to form a spore-producing body (fruiting body)

Entamoebas

Parasites of Humans

Most amoebozoans are free-living

Parasitic amoebozoans that infect humans and other animals

Infect all classes of vertebrate animals and some invertebrates

Entamoeba histolytica

Causes amoebic dysentery —> diarrhea, abdominal pain, potentially fatal

Can be consumed be fecal-contaminated food/water

Invade the large intestines

Still a leading cause of death from parasitic infections

Opisthokonts

Our close relatives

Animals, fungi, related protists

Defined by a single posterior flagellum in some cells

Differentiates them from other eukaryotes that typically have one or more anterior flagella

• Protis relative include choanoflagellates → closest relatives of animals 

• Bridges protist to the multicellular kingdoms 

Pfiesteria

The killer algae

Dinoflagellate associated with massive fish kills in estuaries

Produces toxins that stun fish, then feed on them

Nicknamed the “cell from hell”

Mixotricha paradoxa

A walking zoo of symbiosis

Protist found in termite guts

Doesn’t move with its own cilia —> covered in thousands of symbiotic bacteria that act like cilia

Lives in mutualism with termites, digesting cellulose

Brain-eating amoeba (naegleria fowleri)

Rare but terrifying

Can get it from drinking it up your nose

Vampyrella

The vampire amoeba

Bright ornage amoeba that pierces algal cell walls

sucks out the content os algal cell (literally eats them alive)