Protists and Protist Diversity

Domain Eukarya

• Organisms with membrane-bound organelles and a nucleus.

• This domain includes protists, plants, fungi, and animals.

Eukaryotic

• Protists are ___, meaning they have a nucleus and organelles (e.g., mitochondria, chloroplasts).

Endosymbiotic Theory

Proposes that mitochondria originated as free-living Alpha-proteobacteria that were internalized by a pre-eukaryotic host cell, leading to the formation of the modern eukaryotic cell

Key Events in Endosymbiosis

• Ancestral prokaryote engulfed a bacterium (likely an alpha-proteobacterium) that became the mitochondrion.

  • This allowed the host to use oxygen for energy (aerobic respiration).

• Later, some eukaryotic cells engulfed cyanobacteria, which evolved into chloroplasts in plants and algae.

No, because protists are a paraphyletic group (some protists are more closely related to PAF than other protists)

Are Plants, Animals, and Fungi a Sister Taxon to Protists? Why or why not

Multicellularity evolved independently multiple times in eukaryotes

Did Complex Multicellularity Arise Once or Multiple Times in Eukaryotes?

Six independent origins of complex multicellularity

• Animals

• Plants

• Fungi (twice: once in mushrooms, once in molds like chytrids)

• Brown Algae (e.g., kelp)

• Red Algae

• Green Algae (which led to land plants)