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