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Earth History and Macroevolution– The fossil record is:

• The sequence in which fossils appear in rock strata • An archive of macroevolution

– Geologists have established a geologic time scale reflecting a consistent sequence of geologic periods.

– Separated into four broad divisions:• Precambrian• Paleozoic• Mesozoic• Cenozoic

Earth History and Macroevolution

Carbon-14 in shell

Time (thousands of years)

Radioactive decayof carbon-14

How carbon-14dating isused to

determinethe vintage

of a fossilizedclam shell

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Earth History and MacroevolutionFossils and radiometric dating

Major Episodes in the History of LifeEarth was formed about 4.6 billion years ago.

Prokaryotes

• Evolved by 3.5 billion years ago

• Began oxygen production about 2.7 billion years ago

• Lived alone for almost 2 billion yearsPrecambrian

Common ancestor toall present-day life

Origin ofEarth

Earth cool enoughfor crust to solidify

Oldest prokaryotic fossils

Atmospheric oxygenbegins to appear dueto photosyntheticprokaryotes

Millions of years ago4,500 4,000 3,500 3,000 2,500

Major Episodes in the History of Life

Paleozoic MesozoicCenozoic

Bacteria

Archaea

Plants

Fungi

Animals

Pro

karyote

sE

ukaryo

tes

Pro

tists

Oldest eukaryoticfossils

Origin ofmulticellularorganisms

Oldestanimalfossils

Plants andsymbiotic fungicolonize land

Extinction ofdinosaurs

First humans

Millions of years ago

Cambrianexplosion

2,000 1,500 1,000 500 0

Major Episodes in the History of Life

–What if we use a clock analogy to tick down all of the major events in the history of life on Earth?

Humans

Origin of solarsystem and Earth

1 4

0

2 3

Present

AnimalsColoniz

of landation

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Inorganic compounds

Abiotic synthesisof organic monomers

Abiotic synthesisof polymers

Formationof pre-cells

Self-replicatingmolecules

Membrane-enclosed compartment

Complementarychain

Polymer

Organic monomers

The Origin of Life

Four-Stage Hypothesis for the Origin of Life

Prokaryotes

Bacteria

Archaea

Prokaryotes

Eukarya

Protists

Plants

Fungi

Animals

The Two Major Categories of Cells● The countless cells on earth fall into two categories:

Prokaryotic cells — Bacteria and ArchaeaEukaryotic cells — Eukarya

protists, plants, fungi, and animals

● All cells have several basic features.1. They are all bound by a thin plasma membrane.2. All cells have DNA. 3. All cells have ribosomes.

Cytoplasm-the entire contents of a cell

Prokaryotic Cells

Plasma membrane(encloses cytoplasm)

Cell wall (providesRigidity)

Capsule (stickycoating)

Prokaryotic flagellum(for propulsion)

Ribosomes (synthesize proteins)

Nucleoid (contains DNA)

Pili (attachment structures)

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● ProkaryotesAre smaller than eukaryotic cellsLack internal structures surrounded by membranesLack a nucleusHave a rigid cell wall

Colorized SEM

Prokaryotes•Are ecologically significant, recycling carbon and other vital chemical elements back and forth between organic matter, the soil, and atmosphere•Cause about half of all human diseases•Are more typically benign or beneficial

Prokaryotic Cells

– Prokaryotes come in several shapes:• Spherical (cocci)• Rod-shaped (bacilli)• Spiral

Prokaryotic Cells

SHAPES OF PROKARYOTIC CELLS

Spherical (cocci) Rod-shaped (bacilli) Spiral

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– Most prokaryotes can reproduce by binary fission and at very high rates if conditions are favorable.

– Some prokaryotes• Form endospores, thick-coated, protective cells that are

produced within the cells when they are exposed to unfavorable conditions

• Can survive very harsh conditions for extended periods, even centuries

Prokaryotic Cells

Endospore

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MODES OF NUTRITION

Light Chemical

ChemoautotrophsPhotoautotrophs

Photoheterotrophs Chemoheterotrophs

Energy source

Elodea, an aquatic plant

Rhodopseudomonas Little Owl (Athene noctua)

Bacteria from a hot spring

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Prokaryotic Cells

Prokaryotic Cells– By comparing diverse prokaryotes at the molecular

level, biologists have identified two major branches of prokaryotic evolution: • Bacteria • Archaea (more closely related to eukaryotes)

Bacteria

ArchaeaProkaryotes

EukaryaProtistsPlants

Fungi

Animals

– Bacteria and other organisms that cause disease are called pathogens.

– Most pathogenic bacteria produce poisons.• Exotoxins are poisonous proteins secreted by

bacterial cells.• Endotoxins are not cell secretions but instead

chemical components of the outer membrane of certain bacteria.

Bacteria That Cause Disease

BioterrorismHumans have a long and ugly history of using organisms as weapons.

Prokaryotes and Chemical Recycling– Prokaryotes play essential roles in

• Chemical cycles in the environment

• The breakdown of organic wastes and dead organisms

Prokaryotes and Bioremediation– Bioremediation is the use of organisms to remove

pollutants from• Water

• Air

• Soil

Liquid wastes Outflow

Rotatingspray arm

Rock bed coatedwith aerobicprokaryotes andfungi

– Protists• Are eukaryotic

• Evolved from prokaryotic ancestors

• Are ancestral to all other eukaryotes, which are– Plants

– Fungi

– Animals

Protists

Bacteria

ArchaeaProkaryotes

Eukarya

Protists

Plants

Fungi

Animals

Figure 15.UN08

The Origin of Eukaryotic Cells– Eukaryotic cells evolved by

• The infolding of the plasma membrane and

(a) Origin of the endomembrane system

Plasmamembrane

Ancestralprokaryote

DNA

Cytoplasm

Endoplasmicreticulum

Membraneinfolding

Nucleus

Nuclearenvelope

Cell with nucleus andendomembrane system

The Origin of Eukaryotic Cells

(b) Origin of mitochondria and chloroplasts

Photosyntheticeukaryotic cell

Photosyntheticprokaryote

Aerobicheterotrophic

prokaryote

Endosymbiosis (Some cells)

Mitochondrion

Chloroplast

– Eukaryotic cells evolved by

• Endosymbiosis – a free-living bacterium, came to reside inside a host cell, producing mitochondria and chloroplasts

– The classification of protists remains a work in progress.

– The four major categories of protists, grouped by lifestyle, are

• Protozoans

• Slime molds

• Unicellular algae

• Seaweeds

The Diversity of Protists

The Origin of Multicellular LifeMulticellular organisms have interdependent, specialized cells that perform different functions, such as: feeding, waste disposal, gas exchange, protection

(all are dependent on each other)

Unicellularprotist

Colony

Locomotorcells

Food-synthesizingcells

Early multicellular organismwith specialized, interdependent cells

Later organism withgametes and somatic cells

Somaticcells

Gamete