Eukaryotes and Protista
Lecture:
Life on earth, the first cells, began around three and a half billion years ago. These first cells were the Prokaryotes. It was not until 1.8 billion years ago that the first eukaryotes evolved due to endosymbiosis. This means that it took 1.7 billion years for the first eukaryotes to evolve.
The Endosymbiont Theory explains how simple prokaryotes evolved in to eukariotic cells that contain double membrane organelles.
Endosymbiosis explains how an Archaea prokaryote engulfed a bacterial prokaryote which continued to live inside the other prokaryote becoming an organelle. Because the two cells were now living in symbiosis it is referred to all endo-symbiosis.
Once Eukaryotes evolved the endosymbiosis did not stop. There is evidence of eukaryotes engulfing other eukaryotes creating other forms of endosymbiosis. We can see this with some protists. There are protists that have a vestigial nucleous, we called it a nucleomorph. These protists also have plastids that contain four membranes. The DNA of the plastids show a relation to red algae.
Student Practice:
Open your books and work on the Scientific Skills Exercise on Page 485. Answer the 3 questions.
Lecture:
Eukarya has been divided into 4 supergroups. These groups were created based on morphological and molecular data.
Group 1
Excavata
-This group has an "excavated" groove on one side of the body. There are three clades in this group.
-Diplomonads and Parabasalids both have modified mitochondria
-Euglenozoans have a strange flagella that is different than any other organisms flagella
-Important Excavata
-The Diplomod parasite known as Giardia. Giardia comes from drinking contaminated water
Group 2
SAR Clade
-This group is named after the 3 large clades within the group.
-Stramenopiles are some of the most important photosynthetic organisms on earth like the Diatom
-Alveolates have both photosynthetic members and parasitic members that caused pathogens like plasmodium which causes malaria
-Rhizarians are an amoeba group that have pseudopodia
-Important SAR's
-Stramenopiles - Diatoms and Brown Algae
-Alveolates - Dinoflagellates, Apicomplexans, and Ciliates
-Rhizarians - Forams and Cercozoans
Group 3
Archaeplastida
- This group includes most of the multicellular photosynthetic organisms
-Red Algae
-Chlorophytes - The green algae
-Charophytes - Freshwater green algae
-Land Plants
Group 4
Unikonta
-This group includes most of the multicellular heterotrophs and decomposers.
-Amoebozoans - Divided into two groups
-Gymnamoebas
-Slime Molds
-Optisthokonts - Divided into four groups
-Nucleariids
-Fungi
-Choanoflagellates - (Probably the origin of multicellular animals)
-Animals
Protists is an informal group. The name will have to be changed soon. There are three types of Protists, Animal like protists, plant like protists, and fungi like protists. They are broken into these groups based on how they eat. The animal like protists are heterotrophic, the plant like protists are autotrophic, and the fungi like protists are decomposers.
The group protista was meant to be a group of all single celled eukaryotes but there are some that are multiicellular, like algae.
Group Work:
A side note on what is Algae
-Is not a plant! No leaves, stems, or roots
-A single cellular (Seaweeds are multicellular) organism in the domain of Eukarya
-Algae is a "plant like" protist
-There is no exact definition for what algae is. Many scientist disagree on the classification.
-Some definitions are:
-Any photosynthetic organism that is not a plant
-Anything that has chlorophyll and its reproductive organs are not covered
(These two definitions include photosynthetic bacteria)
-Any photosynthetic protist (This means that algae are only Eukaryotic protists)
(This is the definition that we will use for this class)