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Domain and Kingdom?

Domain: Eukarya
Kingdom: "Protista"


What's special protists?

Not monophyletic. It is paraphyletic (common ancestor and some but not all groups). Kingdom "Protista" is a catch all for eukaryotic cells that do not fall under plants, animals, or fungi.


History of Eukaryotes

Nuclear envelope, mitochondria, endoplasmic reticulum, and other membrane bound structures are present. Oldest unicellular eukaryote is 1.8 billion years old. Red algae is the oldest multicellular specimen at 1.2 billion years old.


About the Kingdom:

Most eukaryotic lineages are protists. Most unicellular, some colonial, and some multicellular. No chemoautotroph or photoheterotroph eukaryotes. Only photoautotrophs, heterotrophs, and mixotrophs (hetero and photoatuo pathways, usually only one used at a time though). Free-living and parasitic heterotrophs.


Photosynthetic protists are called what?
Heterotrophic protists are called what?



Endosymbiont Theory

Multicellularity evolved multiple times. Mitochondria come from Alpha subgroup of Proteobacteria. Chloroplast as a cyanobacteria to form endosymbiosis with eukaryote. Mitochondria and chloroplast formely small independent prokaryotes that began living as symbionts within larger cells. Discovered in 1910 when chloroplast division was seen to have been similar to that of binary fission.


Steps for Endosymbiosis to Occur

1. Prokaryote lost cell wall in order to grow larger and develop infoldings of cell membrane to increase surface area to volume ratio.
2. Infolding of cell membrane.
3. Pinching off of membrane leads to an internal membrane structure.
4. Proteobacterium enters newly formed eukaryote as prey or parasite and avoids digestion and over time becomes mitochondria producing ATP for the cell.
5. Some eukaryotes go on to acquire endosymbiosis in the form of cyanobacteria to have chloroplasts.


On the phylogenetic tree of life:

mitochondria at the base of all eukaryotes as derived trait. Chloroplasts occur at the base of Archaeplastida for "Protista".


Evidence for Endosymbiotic Theory

Mitochondria and chloroplast inner membrane is similar to membrane structure of gram negative bacteria. Cell division of mitochondria and chloroplast looks a lot like binary fission. Transcribe and translate their own DNA. DNA structure is circular just like bacteria.


Supergroups of Kingdom "Protista":

SAR Clade


Excavata Supergroup contains:

Diplomonad Clade
Parabasalid Clade
Euglenozoan Clade

-All possess an excavated feeding groove


Euglenozoan Clade

Heterotrophs, autotrophs, mixotrophs, and parasites. Crystalline rod cross section of flagella. Rod is crystalline or spiral in flagella.

2 Phyla in this Clade: Euglenids and Kinetoplastids


Euglenid Phylum

Mixotrophs. 2 flagella running parallel to one another. One long and one short. Pellice (protein band that provides strength and flexibility) present. Allows for scrunch up and burst off movement.


Kinetoplastid Phylum

Large mitochondria contains kinetoplasts (organized mass of DNA). All are heterotrophic (marine, freshwater, and terrestrial). Parasites present in this phylum: Trypanosoma (resposible for African Sleeping Sickness). Has a "bait and switch" immune defense - after a few generations can completely switch its surface proteins.


Diplomonad Clade

"Double cell". Two nuclei in each cell. Reduced mitochondra called MITOSOMES. Makes them incapable of electron transport and oxygen use. Obligate anaerobes. Multiple flagella. Many are parasites, such as giardia.


Parabasalid Clade

Reduced mitochondria called HYDROGENOSOMES. Even less capable of carrying out cellular respiration. Very limited anaerobic functions. H2 gas as a byproduct. Exist as a symbiont with host or as a parasite. Trichomonas vaginalis is an STD and an example of a parasite. Trychonypha campanula and bacter are a symbiont within termites that allow them to ingest wood.


SAR Clade Sugergroup contains:

Stramenophile Clade
Alveolate Clade
Rhizaria Clade

- No one unique synapomorphy (shared derived trait) for this supergroup.


Stramenophile Clade

"Straw hair". Two flagella. One very hairy flagella and one smooth flagella.
Three Subgroups: Diatoms, Brown Algae, and Golden Algae


Diatom Subgroup

Unicellular algae. Frostule- "glass house". Silica. Bilaterally symmetrical. Most abundant photosynthetic organisms on the planet. 70% of all marine plankton. 1/2 of all carbon fixation the ocean is responsible for.


Brown Algae Subgroup

Many seaweeds and all kelps included in this subgroup. Polyphyletic group, multicellular algae. Holdfast anchors in place. Pnuematocyst - a float packet to help keep boyant.


Golden Algae Subgroup

Marine/ fresh water. Possess carotenoid pigments (yellow, brown, red, orange colors). Unicellular, often found in colonial constructs. Protective cysts allow them to coil and drain water to remain dormant for up to decades in presence of little water. Photosynthetic and mixotrophic.


Divergence of Photosynthetic Ability in Protists

1. Primary Endosymbiosis- heterotrophic eukaryote engulfs cyanobacteria.
2. Red algae and green algae diverge as red algae possess red pigment.
3. Secondary Endosymbiosis- heterotrophic eukaryote engulfs red algae.
4. Engulfed red algae leads to divergence into dinoflagellates and stramenophiles.
5. Secondary Endosymbiosis occurs twice. Green algae engulfed by heterotroph.
6.Engulfed green algae diverges into euglenids and chlorarichinophyes.
Plastid Evolution- Primary endosymbiosis with cyanobacterium led to a plastid-bearing lineage of protists called Archaeplastida.
SAR and Excavata supergroups engulfed archaeplastida and obtaine chloroplast through secondary emdosymbiosis.


Alveolate Clade

Possess alveoli ( membrane encolsed sacs under plasma membrane) that allow for ventilation and gas exchange.


Alveolate Clade Includes:

Dinoflagellate Subgroup
Apicomplexan Subgroup
Ciliate Subgroup


Dinoflagellate Subgroup

"Armor" of cellulose plates with two flagella which fit nicely into the grooves of the armor. Responsible for red tides when environmental conditions are favorable for blooms. Population grows exponentially and is toxic, thus leading to massive die offs. Pfisteria uses pdungle (sp?) to penetrate fish for parasitic action. Autotrophic and heterotrophic species.


Apicomplexan Subgroup

Nearly all in this subgroup are animal parasites. Possess an apex- specialized to penetrate into cells/tissues. Sexual and asexual life stage. Each stage requires a different host. Plasmodium responsible for malaria (and in this group). Malaria leading cause of death via protist parasite.



Paramecium is an example. Named for their cilia which are used to move and feed. Almost all are heterotrophic, free-living predators. Possess two types of nuclei: macronucleus & micronucleus (at least one, sometimes many of these). Contractile vacuole present and responsible for maintenance of osmotic equilibrium. Unicellular. Possess oral groove which functions as mouth, but isn't technically one. Conjugation of ciliates via oral groove increases genetic diversity (looks like kissing) in addition to sexual reproduction.


Process of Conjugation of Ciliates

Diploid micronucleus undergoes meiosis to produce four haploid cells. Three of these haploid cells then disintegrate and the remaining micronuclues undergoes mitosis. The two ciliates swap nuclei and go their seperate ways with a copy of their own original micronucleus and a copy of the micronucleus of the other ciliate.


Rhizarian Clade

All unicellular. Thread-like psuedopods. Most are amoebas.


Rhizarian Clade Includes:

Radiolarian Subgroup
Foraminiferan Subgroup
Cercozoan Subgroup


Radiolarian Subgroup

All marine, all unicellular. Glass exoskeletons (made of silica). Thin, stiff pseudopods --> reinforced with microtubules (allows them to stick out). Use the microtubule extensions for gas exchange and to stay afloat.


Foraminiferan Subgroup

Marine or freshwater. "Foramen"- little hole. "Ferre"- to bear. Possess a test (porouse shell made of calcium carbonate). Pseudopods extend through the little holes. Fossilize very well, most we know about this subgroup comes from fossils. Not sure of their exact prevalence in modern day.


Cercozoan Subgroup

Marine, freshwater, and soil native. Consumer of bacteria. Heterotrophic and free-living.



Developed independently multiple times. Evolutionary advantage to being multicellular indicated. Brown algae, Archaeplastida Supergroup, Fungi, Animals, and Plants are all multicellular.

Selective Pressures for Multicellularity:
- predator avoidance
- obtaining resources
- feeding advantage


Why Not One Cell

Diffusion is only effective over a short distance. Nutrient dispersal and waste removal difficult in large unicellular body.


Simple Multicellularity

Cell adhesion, few specialized cell types, and only a small penalty for cell death.


Volvox Cells as an Example of Simple Multicellularity

Germ cells are potentially immortal, nonmotile, and specialized for growth and reproduction. They are located within the internal structure of a volvox. Soma cells are small, specialized for motility, and programmed to die after a few days. They are located along the outside of a volvox.


Complex Multicellularity

Three Synapomorphs:

3-dimensional. Bulk Flow- movement of molecules through organisms faster than diffusion.
1. Cell adhesion (In plants, pectin. In animals, cadherin)
2. Specialized cellular communication. Signaling molecules need to move from cell to cell. (Plants have plasmodesmata. Animals have gap junctions).
3. Cell and tissue differentiation (stem cells, blood cells, and neuron cells in humans).


Supergroup Archaeplastida

Ancestor acquired cyanobacteria via endosymbiosis.


Supergroup Archaeplastida Includes:

Red Algae Clade
Green Algae Clade
Land Plant Clade


Red Algae Clade

Marine, multicellular. Edible. Phycoerythin-red pigment. Do not use red or orange part of electromagnetic spectrum, depend more on shorter light wavelengths of violet, blue, and green. Shorter wavelengths of light penetrate further into water column and red algae can lives at depths as great as 260 meters.


Clade Green Algae Includes:

Chlorophyte Subgroup
Charophyte Subgroup


Chlorophyte Subgroup

Freshwater and marine. Chlorophyll dependent.


Charophyte Subgroup

Not covered in this chapter. Included with plants.