1. Chapter 25: The Origin and Diversification of Eukaryotes
AP Biology, Period 2
April 20, 2016

2. Eukaryotes arose by endosymbiosis more than 1.8 billion years ago
Concept 25.1
Eukaryotes arose by endosymbiosis more than 1.8 billion years ago Pg

3. Early evolution of eukaryotes: 3 major stagesPg
Bya = billion years ago
(1) Initial Diversification
(2) Appearance of Novel Features
(3) Rise of Large Eukaryotes

4. Eukaryotes contain a mixture of archaeal and bacterial genes and cellular characteristics.
Pg. 484

5. A hypothesis for the origin of eukaryotes
Endosymbiont theory: mitochondria and plasmids, including chloroplasts, originated as prokaryotic cells engulfed by host cells. The engulfed cell and its host cell then evolved into a single organism.
Page 484
Endosymbiont theory

6. Diversity of plastids produced by endosymbiosis
Other groups of protists evolved from secondary endosymbiosis events.
Pg. 486
Secondary endosymbiosis

7. Concept 25.2 Multicellularity has originated several times in eukaryotesPg

8. Multicellular colonies
The first multicellular eukaryotes were colonies, collections of cells that are connected to one another but show little or no cellular differentiation.

9. Independent origins of complex multicellularity
Complex multicellular eukaryotes -- those with differentiated cell types -- arose independently in a variety of eukaryotic groups (including plants, fungi, animals, and several lineages of algae).
Genomic analyses suggest that a transition to multicellularity from unicellular ancestors can result primarily from changes in how existing genes are used.

10. Concept 25.3
Four “supergroups” of eukaryotes have been proposed based on morphological and molecular data Pg

11. The “supergroups” Each is a monophyletic clade
Contains great diversity
Most are unicellular

12. Excavata
Excavates have unique cytoskeletal features, and some species have an “excavated” feeding groove on one side of the cell body.
Include parasites as well as many predatory and photosynthetic species.

13. The “SAR” Clade
Contains large, extremely diverse collection of protists from three major subgroups.

14. Archaeplastida
This monophyletic group, which includes red algae, green algae, and land plants, descended from an ancient protist ancestor that engulfed a cyanobacterium.

15. Unikonta
This clade, which is supported by studies of myosin proteins and DNA, consists of amoebozoans and opisthokonts.
One current hypothesis states that unikonts may have been the first group of eukaryotes to diverge from other eukaryotes.*
The opisthokonts are a broad group of eukaryotes, including both the animal and fungus kingdoms, together with the eukaryotic microorganisms that are sometimes grouped in the paraphyletic phylum Choanozoa
*more evidence required; root of eukaryotic tree remains unknown

16. Concept 25.4 Single-celled organisms play key roles in ecological communities and affect human health Pg

17. Protists: key producers in aquatic communities
Photosynthetic protists are among the most important producers in aquatic communities.
Climate change has decreased the growth of marine producers, which could have far- reaching effects on marine ecosystems.

18. Symbiotic protists
Protists form a wide range of mutualistic and parasitic relationships that affect their symbiotic partners and many other members of the community. Some can pose major challenges to human health.
Plasmodium, the apicomplexan that causes malaria.

19. Questions?