Outline: -Characteristics of eukaryotes -Protists -Fungi -Plants -Animals

Evolution of the nuclear envelope Fig 20_1 -The nuclear envelope may have evolved gradually from the cell membrane -As cells got bigger folded cell membranes allowed better access to external environment -Eukaryote DNA is more similar in structure to archea than bacteria (introns)

Endosymbiotic theory: Mitochondria and Chloroplasts are derived from once free-living bacteria Fig 20_2 -Mitochondria were free living aerobic bacteria -Chloroplasts were free living photosynthetic bacteria (cyanobacteria) -Each became incorporated into a eukaryotic cell, formed a symbiotic relationship, can no longer live outside of cells

Evidence that mitochondria were once free living bacteria -Mitochondria are similar in size to bacteria -Have their own DNA, circular without introns -Use ribosomes that are similar to bacterial ribosomes for translation of RNA to proteins -Divide by simple fusion -Have a double layered membrane

Evidence that chloroplasts were once free living bacteria -Posses circular DNA -Use prokaryotic machinery -Photosynthesis occurs using the 3 systems found in prokaryotes

The protists are the most basal eukaryotes -Every eukaryrote that is not a plant, animal, of fungus is a protist (negative definition) -Phylogeny not well resolved -Evolved mitochondria and chloroplasts -Evolved sex -Evolved multicellularity

Sex evolved in protists What is sex? - Fusion of haploid gametes to form a diploid individual. Sex combines genomes from 2 parents What is the advantage of sex? - Greatly increases genetic diversity of a population, which improves adaptive ability of a population. In asexual populations diversity can only arise by mutation What selection pressures lead to the evolution of sex? - Stress

Protists have independently evolved multicellularity several times Fig 20_8 Phylogeny of protists - 5 major groups are not shown because their phylogenetic position is uncertain

Ancestors of plants Pg 385 Fig 20_16 Fig 20_17 -Red algae live in deeper marine environments -Green algae are direct ancestors of plants, most are marine, few exceptions -Exhibit alternating life cycle

Ancestors of animals Pg 387 Fig 20_19 -Choanoflagellates are the ancestors of animals -Single celled heterotrophs -Filter feed bacteria from water -May be colonial, resemble sponges -Genetically closest group to animals

Is this organism multicellular? My brothers dog Nada

Is this organism multicellular? A sponge

Is this organism multicellular? Stromatolites in Shark Bay Aus.

The road to multicellularity - cooperation in dictyostelium discoideum Fig 20_24

Multicellularity What is the advantage of being multicellular? -Cell sizes are limited by surface to volume dynamics and physical-structural issues -Cells can specialize What is multicellularity? -Multiple cells that are permanently associated with integrated activities Colonial organisms -Permanently associated cells with no coordinated activities Aggregates -Single cells that group together