Bio test 7

Four supergroups that evolved from the early heterotrophic and photosynthetic eukaryotes

1. Excavata

2. SAR

3. Archaeplastida

4. Unikonta

Endosymbiosis

• A symbiotic relationship in which one organism lives inside the body or cell of another organism

• Much of eukaryotic diversity can be traced back to this

What were the earliest eukaryotic cells like

• Unicellular

• Structurally more complex cell than prokaryotes

Initial diversification in eukaryotes

• Diverse eukaryotes were present by 1.8 billion years ago

• Early eukaryotes had a nucleus, a membrane, and a cytoskeleton

What does the term algae refer to

All photosynthetic protists

What novel biological features evolved during the early diversification of eukaryotes

• Complex multicellularity

• Sexual life cycles

• Eukaryotic photosynthesis

When did large multicellular eukaryotes appear in the fossil record

• Ediacaran period

• About 635-541 years ago

What does it mean that a eukaryote is a “combination” organism

Some of their genes and cell characteristics are derived from archaea, and others from bacteria

Endosymbiont theory

Suggests that mitochondria and plastids evolved from bacteria living inside larger cells

Endosymbiont

The cell that lives inside a host cell

Serial endosymbiosis hypothesis

Suggests that mitochondria and plastids evolved sequentially

• Mitochondria arose initially and plastids evolved later

SImilarities between mitochondria/plastids and bacteria that support their endosymbiont origins

• Similar splitting for cell replication

• Similar ribosome structure

• DNA forms a circular chromosome lacking histones

Excavata

• Simpler protists

• Includes parasites and photosynthetic species

SAR

• Made up of Stramenopiles, Alveolates, and Rhizarians

Stramenopiles

Include important photosynthetic organisms

• such as diatoms

Alveolates

Includes photosynthetic and important parasitic species

• such as the cause for malaria

Rhizarians

Include many species of amoebas with threadlike pseudopodia

Diatoms

• Microscopic, single-celled algae found in nearly all aquatic habitats

• In the group Stramenopiles

• Look like glass seashells

Archaeplastida

• Precursors to plants

• Most are photosynthetic

• Species of red algae, green algae, and plants

Unikonta

Includes amoebas, animals, fungi, and non-amoeba protists

Excavata

• Named for the excavated feeding groove found on one side of the cell body

• Includes diplomonads, parabasalids, and euglenozoans

• Most are found in anaerobic environments

Diplomonads

• Derive energy from anaerobic biochemical pathways

• Are often parasites (Giardia for example)

• Move using flagella

Parabasalids

Generate some energy anaerobically and release hydrogen gas as a by-product

Euglenozoa

A diverse clade that includes predatory heterotrophs, photosynthetic autotrophs, and parasites

• Their distinguishing feature is a rod with a spiral inside each flgellum