The Evolution of Cellular Life Grade 10 Biology Spring 2011

 What are the differences between prokaryotes and eukaryotes?

 Distinguish between the two groups of prokaryotes  Describe the evolution of eukaryotes  Recognize an evolutionary advance first seen in protists  Summarize how mass extinctions have affected the evolution of life on Earth

 Fossil: the preserved mineralized remains (bone, tooth, shell) or imprint of an organism that lived long ago ◦ Oldest fossil from prokaryotes, 2.5 billion years old

 Cyanobacteria: photosynthetic protists ◦ Among first prokaryotes, marine

 Before cyanobacteria oxygen was scarce  As cyanobacteria photosynthesized, released oxygen gas into oceans  After hundreds of millions of years the oxygen began to escape into the air  Today oxygen makes up 21% of Earth’s atmosphere

 Eubacteria  Ex. E.Coli  Prokaryotes that contain a chemical called peptidoglycan in their cell walls  Often cause disease and decay  Archaebacteria  Ex. Sulfolobus  Prokaryotes that lack peptidoglycan in their cell walls and have unique lipids in their cell membranes  Are found living in extreme environments

 About 1.5 million years ago, the first eukaryotes appeared

 Endosymbiosis: mitochondria are the descendants of symbiotic, aerobic (oxygen- requiring) eubacteria and chloroplasts are the descendents of symbiotic, photosynthetic eubacteria

 Steps of endosymbiosis: ◦ Bacteria entered large cells either as parasites or undigested prey ◦ Instead of being digested, bacteria began to live inside host cell where performed cellular respiration (mitochondria) or photosynthesis (chloroplast)

 Ideas to support endosymbiosis: ◦ Size and structure  Mitochondria and chloroplasts about the same size as bacteria  Both have two membranes (outer membrane thought to be derived from endoplasmic reticulum of host cell)

 Ideas to support endosymbiosis: ◦ Genetic material  Both have circular DNA similar to chromosomes in bacteria  Both contain genes that are different from those found in nucleus of host cell

 Ideas to support endosymbiosis ◦ Ribosomes  Moitochondria and chloroplast ribosomes have a size and structure similar to the size and structure of bacterial ribosomes

 Ideas to support endosymbiosis: ◦ Reproduction  Like bacteria both reproduce by simple fission  Replication takes place independently of cell cycle of host cell

 6 Kingdoms ◦ Eubacteria ◦ Archaebacteria ◦ Fungi ◦ Plants ◦ Animals

 Eubacteria and Archaebacteria ◦ Single celled protists  Protists ◦ Eukaryotic ◦ Large varied group that includes both multicellular and unicellular organisms  Fungi, Plants, Animals ◦ Eukaryotic, multicellular

 Unicelluar body plan ◦ Very sucessful ◦ Half the biomass ◦ Single cell must carry out all of the activities of an organism

 Multicellular ◦ Distinct types of cells in one body can have specialized functions ◦ Almost all organisms large enough to be seen by the naked eye are multicellular

 Most animal phyla probably originated during a relatively short time ◦ 10 to 100 million years ago, during the late Precambrian and early Cambrian periods ◦ Cambrian explosion  Trilobites: marine arthropods that became extinct about 250 million years ago

 Sudden change occurred at end of Ordovician period  About 440 million years ago a large percentage of organisms on Earth suddenly became extinct

 Extinction: death of all members of a species ◦ First of five major mass extinctions that have occurred on earth  Mass extinction: is an episode during which large numbers of species become extinct

 Permian period mass extinction: 245 million years ago ◦ About 96% of all species of animals living at the time became extinct ◦ Worldwide geological and weather changers are likely factors

 Some scientist think another mass extinction is happening today ◦ Earth’s ecosystem’s are being destroyed by humans