major episodes in the history of life€¦ · major episodes in the history of life • earth was...

MAJOR EPISODES IN THE HISTORY OF LIFE• Earth was formed about 4.6 billion years ago. • Prokaryotes

– evolved by about 3.5 billion years ago, – began oxygen production about 2.7 billion years

ago, – lived alone for more than a billion years, and – continue in great abundance today.

– Eukaryotes • Single-celled eukaryotes first evolved about 2.1 billion years ago. • Multicellular eukaryotes first evolved at least 1.2 billion years ago.

© 2013 Pearson Education, Inc.

Figure 15.1a

Precambrian

Ancestor to  all present-day life

Origin of  Earth

Earth’s crust  solidifies

Oldest  prokaryotic fossils

Atmospheric  oxygen begins  to appear

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

Figure 15.1b

Millions of years ago2,000 1,500 1,000

Precambrian

Oldest eukaryotic  fossils

Origin of  multicellular organisms

Oldest animal fossils

Figure 15.1c

Millions of years ago

1,000 500 0

Precambrian Paleozoic CenozoicMeso-  zoic

Bacteria

Archaea

PlantsFungi

AnimalsCambrian explosion

Oldest animal fossils

Plants colonize land

Extinction of  dinosaurs

First humans

Protists

Prokaryotes

Eukaryotes

• All the major phyla of animals evolved by the end of the Cambrian explosion, which – began about 540 million years ago and – lasted about 10 million years.

• Plants and fungi – first colonized land about 500 million years ago and – were followed by amphibians that evolved from fish.

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?

MAJOR EPISODES IN THE HISTORY OF LIFE


Figure 15.2

Humans

Origin of solar system and Earth

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Figure 15.2a

Origin of solar system and Earth

1 4

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Figure 15.2b

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THE ORIGIN OF LIFE

• We may never know for sure how life on Earth began.


Resolving the Biogenesis Paradox

• All life today arises by the reproduction of preexisting life, or biogenesis. • If this is true, how could the first organisms arise? • From the time of the ancient Greeks until well into the 1800s, it was commonly

believed that life regularly arises from nonliving matter, an idea called spontaneous generation.


• Today, most biologists think it is possible that life on early Earth evolved from simple cells produced by

– chemical and – physical processes.

Resolving the Biogenesis Paradox


Figure 15.3

A Four-Stage Hypothesis for the Origin of Life

• According to one hypothesis, the first organisms were products of chemical evolution in four stages.


Stage 1: Abiotic Synthesis of Organic Monomers

• The first stage in the origin of life was the first to be extensively studied in the laboratory.


The Process of Science:  Can Biological Monomers Form Spontaneously?• Observation: Modern biological macromolecules are all composed of elements

that were present in abundance on early Earth. • Question: Could biological molecules arise spontaneously under conditions like

those on early Earth?


• Hypothesis: A closed system designed to simulate early Earth conditions could

produce biologically important organic molecules from inorganic ingredients. • Prediction: Organic molecules would form and accumulate.

The Process of Science:  Can Biological Monomers Form Spontaneously?


• Experiment: An apparatus was built to mimic the early Earth atmosphere and included

– hydrogen gas (H2), methane (CH4), ammonia (NH3), and water vapor (H2O),

– sparks that were discharged into the chamber to mimic the prevalent lightning of early Earth, and

– a condenser that cooled the atmosphere, causing water and dissolved compounds to “rain” into the miniature “sea.”



Figure 15.4

Miller and Urey’s experiment

“Sea”

H2O

Sample for chemical analysis

Cooled water containing organic molecules

Cold water

Condenser

Electrode

“Atmosphere”Water vapor

CH4

NH3 H2

• Results: After the apparatus had run for a week, an abundance of organic molecules essential for life had collected in the “sea,” including amino acids, the monomers of proteins.

• These laboratory experiments – have been repeated and extended by other

scientists and – support the idea that organic molecules could have

arisen abiotically on early Earth.



Stage 2: Abiotic Synthesis of Polymers

• Researchers have brought about the polymerization of monomers to form polymers, such as proteins and nucleic acids, by dripping solutions of organic monomers onto – hot sand, – clay, or – rock.


Stage 3: Formation of Pre-Cells

• A key step in the origin of life was the isolation of a collection of abiotically created molecules within a membrane.

• Laboratory experiments demonstrate that pre-cells could have formed spontaneously from abiotically produced organic compounds.


• Such pre-cells produced in the laboratory display some lifelike properties. They – have a selectively permeable surface, – can grow by absorbing molecules from their

surroundings, and – swell or shrink when placed in solutions of different

salt concentrations.

Stage 3: Formation of Pre-Cells


Stage 4: Origin of Self-Replicating Molecules

• Life is defined partly by the process of inheritance, which is based on self-replicating molecules.

• One hypothesis is that the first genes were short strands of RNA that replicated themselves

– without the assistance of proteins, – perhaps using RNAs that can act as enzymes,

called ribozymes.


Figure 15.5-1

RNA monomers

Figure 15.5-2

RNA monomers

Formation of  short RNA polymers:  simple “genes”

Figure 15.5-3

RNA monomers


Assembly of a complementary  RNA chain

Figure 15.5-4

Original “gene”

RNA monomers


Assembly of a complementary  RNA chain

The complementary  chain serves as a template of the original “gene.”

From Chemical Evolution to Darwinian Evolution

• Over millions of years – natural selection favored the most efficient pre-cells

and – the first prokaryotic cells evolved.


PROKARYOTES

• Prokaryotes lived and evolved all alone on Earth for about 2 billion years.


Vox Bacteria Video

They’re Everywhere!

• Prokaryotes – are found wherever there is life, – have a collective biomass that is at least ten times

that of all eukaryotes, – thrive in habitats too cold, too hot, too salty, too

acidic, or too alkaline for any eukaryote, – cause about half of all human diseases, and – are more commonly benign or beneficial.


Figure 15.6

• Compared to eukaryotes, prokaryotes are – much more abundant and – typically much smaller.



Figure 15.7

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• Prokaryotes living in soil and at the bottom of lakes, rivers, and oceans help to decompose dead organisms and other organic waste material, returning vital chemical elements to the environment.



The Structure and Function of Prokaryotes

• Prokaryotic cells – lack a membrane-enclosed nucleus, – lack other membrane-enclosed organelles, – typically have cell walls exterior to their plasma

membranes, but – display an enormous range of diversity.


Figure 4.4

Plasma membrane

Cell wall

Capsule

Prokaryotic flagellum

Ribosomes

Nucleoid

Pili

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Figure 4.5

CytoskeletonRibosomes Centriole

Lysosome

Nucleus

Plasma membrane

Mitochondrion

Rough endoplasmic reticulum (ER)

Golgi apparatus

Smooth endoplasmic reticulum (ER)

Idealized animal cell

Idealized plant cell

CytoskeletonMitochondrion

Nucleus

Rough endoplasmic reticulum (ER)

Ribosomes

Smooth endoplasmic

reticulum (ER)

Golgi apparatus

Plasma membrane

Channels between cells

Not in most plant cells

Central vacuoleCell wallChloroplast

Not in animal cells

• The three most common shapes of prokaryotes are 1. spherical (cocci), 2. rod-shaped (bacilli), and 3. spiral or curved.

Prokaryotic Forms


Figure 15.8

SHAPES OF PROKARYOTIC CELLSSpherical (cocci) Rod-shaped (bacilli) Spiral

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Figure 15.8a

Spherical (cocci)

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Figure 15.8b

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Rod-shaped (bacilli)

Figure 15.8c

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Spiral

• All prokaryotes are unicellular. • Some species

– exist as groups of two or more cells, – exhibit a simple division of labor among specialized

cell types, or – are very large, dwarfing most eukaryotic cells.

Prokaryotic Forms


Figure 15.9

(a) Actinomycete

(b) Cyanobacteria (c) Giant bacteriumC

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SEM

LM LM

• About half of all prokaryotes are mobile, and many of these travel using one or more flagella.

Prokaryotic Forms


• In many natural environments, prokaryotes attach to surfaces in a highly organized colony called a biofilm, which – may consist of one or several species of

prokaryotes, – may include protists and fungi, – can show a division of labor and defense against

invaders, and can form on almost any type of surface, including

– rocks, – metal, – plastic, and – organic material including teeth.

Figure 15.10

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

• Some prokaryotes form endospores, which are – thick-coated, protective cells – produced when the prokaryote is exposed to

unfavorable conditions.

Prokaryotic Reproduction


Figure 15.11

Endospore

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Prokaryotic Nutrition

• Biologists use the phrase “mode of nutrition” to describe how organisms obtain energy and carbon. – Energy

– Phototrophs obtain energy from light. – Chemotrophs obtain energy from environmental

chemicals.



– Carbon – Autotrophs obtain carbon from carbon dioxide

(CO2). – Heterotrophs obtain carbon from at least one

organic nutrient—the sugar glucose, for instance.


• We can group all organisms according to the four major modes of nutrition if we combine the – energy source (phototroph versus chemotroph) and – carbon source (autotroph versus heterotroph).



• Dominant among multicellular organisms are – photoautotrophs and – chemoheterotrophs.

• The other two modes are used only by certain prokaryotes.



Figure 15.12

MODES OF NUTRITION

Light ChemicalChemoautotrophsPhotoautotrophs

Photoheterotrophs Chemoheterotrophs

Energy source

Elodea, an aquatic plant

Rhodopseudomonas Kingfisher with prey

Bacteria from a hot spring

Org

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Car

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Figure 15.12a

A photoautotroph: Elodea, an  aquatic plant

Figure 15.12b

A chemoautotroph: Bacteria  from a hot spring

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Figure 15.12c

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A photoheterotroph:  Rhodopseudomonas

Figure 15.12d

A chemoheterotroph: Kingfisher with prey

The Two Main Branches of Prokaryotic Evolution: Bacteria and Archaea• By comparing diverse prokaryotes at the molecular level, biologists have

identified two major branches of prokaryotic evolution: 1. bacteria and 2. archaea (more closely related to eukaryotes).


The Two Main Branches of Prokaryotic Evolution: Bacteria and Archaea• Thus, life is organized into three domains:

1. Bacteria, 2. Archaea, and 3. Eukarya.


• Some archaea are “extremophiles.” – Halophiles thrive in salty environments. – Thermophiles inhabit very hot water. – Methanogens

– inhabit the bottoms of lakes and swamps and – aid digestion in cattle and deer.

The Two Main Branches of Prokaryotic Evolution: Bacteria and Archaea


Figure 15.13

(a) Salt-loving archaea (b) Heat-loving archaea

Bacteria and Disease  Bacteria That Cause Disease• Bacteria and other organisms that cause disease are called pathogens. • Most pathogenic bacteria produce poisons.

– Exotoxins are proteins bacterial cells secrete into their environment.

– Endotoxins are – not cell secretions but instead – chemical components of the outer membrane of

certain bacteria.


Figure 15.14

Haemophilus influenzae

Cells of nasal lining

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• The best defenses against bacterial disease are – sanitation, – antibiotics, and – education.

Bacteria That Cause Disease


• Lyme disease is – caused by bacteria carried by ticks and – treated with antibiotics, if detected early.

Bacteria That Cause Disease


Figure 15.15

“Bull’s-eye” rash

Tick that carries  the Lyme disease  bacterium

Spirochete that causes Lyme disease

SEM

The Ecological Impact of Prokaryotes

• Pathogenic bacteria are in the minority among prokaryotes. • Far more common are species that are essential to our well-being, either

directly or indirectly.


• Prokaryotes play essential roles in – chemical cycles in the environment and – the breakdown of organic wastes and dead

organisms.

Prokaryotes and Bioremediation

• Bioremediation is the use of organisms to remove pollutants from – water, – air, and – soil.

• A familiar example is the use of prokaryotic decomposers in sewage treatment.


Figure 15.17

Liquid wastes Outflow

Rotating arm spraying  liquid wastes

Rock bed coated with aerobic prokaryotes and fungi

• Certain bacteria – can decompose petroleum and – are useful in cleaning up oil spills.

Prokaryotes and Bioremediation


Figure 15.18

PROTISTS

• Protists are – eukaryotes that are not fungi, animals, or plants, – mostly unicellular, and – ancestral to all other eukaryotes.


The Origin of Eukaryotic Cells

• Eukaryotic cells evolved by – the infolding of the plasma membrane of a

prokaryotic cell to form the endomembrane system and

– a process known as endosymbiosis.


The Origin of Eukaryotic Cells

• Symbiosis is a more general association between organisms of two or more species.

• Endosymbiosis – refers to one species living inside another host

species and – is the process by which eukaryotes gained

mitochondria and chloroplasts.


Figure 15.19

(a) Origin of the endomembrane system (b) Origin of mitochondria and chloroplasts

Plasma membraneDNA

Cytoplasm

Endoplasmic  reticulum

Nucleus

Nuclear envelope

Ancestral prokaryote

Membrane  infolding

Cell with nucleus and  endomembrane system

Photosynthetic  eukaryotic cell

Photosynthetic  prokaryote

Aerobic  heterotrophic  prokaryote

Endosymbiosis

Mitochondrion

Chloroplast

Figure 15.19a

(a) Origin of the endomembrane system

Plasma membraneDNA

Cytoplasm

Endoplasmic  reticulum

Nucleus

Nuclear envelope

Ancestral prokaryote

Membrane  infolding

Cell with nucleus and  endomembrane system

Figure 15.19b

(b) Origin of mitochondria and chloroplasts

Photosynthetic  eukaryotic cell

Photosynthetic  prokaryote

Aerobic  heterotrophic  prokaryote

Endosymbiosis

Mitochondrion

Chloroplast

The Diversity of Protists

• The group called protists – consists of multiple clades but – remains a convenient term to refer to eukaryotes

that are not plants, animals, or fungi.


• Protists obtain their nutrition in a variety of ways. – Algae are autotrophs, producing their food by

photosynthesis.



– Other protists are heterotrophs. – Some protists eat bacteria or other protists. – Other protists are fungus-like and obtain organic

molecules by absorption. – Parasites derive their nutrition from a living host,

which is harmed by the interaction. Parasitic trypanosomes infect blood and cause sleeping sickness.

– Other protists are heterotrophs. – Some protists eat bacteria or other protists. – Other protists are fungus-like and obtain organic

molecules by absorption. – Parasites derive their nutrition from a living host,

which is harmed by the interaction. Parasitic trypanosomes infect blood and cause sleeping sickness.



Figure 15.20

(a) An autotroph: Caulerpa, a multicellular alga

(b) A heterotroph: parasitic  trypanosome

(c) A mixotroph: Euglena

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• Protist habitats are diverse and include – oceans, lakes, and ponds, – damp soil and leaf litter, and – the bodies of host organisms with which they share

mutually beneficial relationships, such as – unicellular algae and reef-building coral animals,

and – cellulose-digesting protists and termites.



Figure 15.21

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Protozoans

• Protists that live primarily by ingesting food are called protozoans.


Figure 15.22

A foram

A flagellate: Giardia

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Another flagellate: Trichomonas An amoeba

Red  blood  cell

Apical complex

TEM

An apicomplexan A ciliate

Cilia

Cell  “mouth”

• Protozoans with flagella are called flagellates and – are typically free-living, but – some are nasty parasites.

Protozoans


Figure 15.22a

A flagellate: Giardia

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• Amoebas are characterized by – great flexibility in their body shape and – the absence of permanent organelles for

locomotion. • Most species move and feed by means of pseudopodia (singular,

pseudopodium), temporary extensions of the cell.

Protozoans


Figure 15.22c

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An amoeba

• Other protozoans with pseudopodia include the forams, which have shells.

Protozoans


• Apicomplexans are – named for a structure at their apex (tip) that is

specialized for penetrating host cells and tissues, – all parasitic, and – able to cause serious human diseases, such as

malaria caused by Plasmodium.

Protozoans


Figure 15.22e

Red  blood  cell

Apical complex

TEM

An apicomplexan

• Another apicomplexan is Toxoplasma, – occurring in the digestive tracts of millions of people

in the United States but – held in check by the immune system.

• A woman newly infected with Toxoplasma during pregnancy can pass the parasite to her unborn child, who may suffer nervous system damage.

Protozoans


• Ciliates are protozoans that – are named for their use of hair-like structures called

cilia to move and sweep food into their mouths, – are mostly free-living (nonparasitic), such as the

freshwater ciliate Paramecium, and – include heterotrophs and mixotrophs.

Protozoans


Figure 15.22f

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A ciliate

Cilia

Cell  “mouth”

Slime Molds

• Slime molds – resemble fungi in appearance and lifestyle due to

convergence, but – are more closely related to amoebas.

• The two main groups of these protists are – plasmodial slime molds and – cellular slime molds.


• Plasmodial slime molds – are named for the feeding stage in their life cycle,

an amoeboid mass called a plasmodium, – are decomposers on forest floors, and – can be large.

Slime Molds


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Figure 15.23

A plasmodial slime mold

• Cellular slime molds have an interesting and complex life cycle of successive stages: – a feeding stage of solitary amoeboid cells, – a swarming stage as a slug-like colony that can

move and function as a single unit, and – a stage during which they generate a stalk-like

multicellular reproductive structure.

Slime Molds


Figure 15.24

Life stages of a cellular slime mold

Slug-like colony

Amoeboid  cells

Reproductive  structure

LM1

2

3

Unicellular and Colonial Algae

• Algae are – photosynthetic protists whose chloroplasts support

food chains in – freshwater and – marine ecosystems.

• Many unicellular algae are components of plankton, the communities of mostly microscopic organisms that drift or swim weakly in aquatic environments.


• Unicellular algae include – dinoflagellates, with

– two beating flagella and – external plates made of cellulose,

– diatoms, with glassy cell walls containing silica, and

– green algae.



• Green algae are – unicellular in most freshwater lakes and ponds, – sometimes flagellated, such as Chlamydomonas,

and – sometimes colonial, forming a hollow ball of

flagellated cells as seen in Volvox.



Figure 15.25

(a) A dinoflagellate, with its wall of  protective plates

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SEM

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(b) A sample of diverse diatoms, which have glassy walls

(c) Chlamydomonas, a unicellular green alga with a pair of flagella

(d) Volvox, a colonial green alga

Figure 15.25a

(a) A dinoflagellate, with its wall of  protective plates

SEM

Figure 15.25b

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(b) A sample of diverse diatoms, which have glassy walls

Figure 15.25c

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(c) Chlamydomonas, a unicellular green alga with a pair of flagella

Figure 15.25d

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(d) Volvox, a colonial green alga

Seaweeds

• Seaweeds – are large, multicellular marine algae, – grow on or near rocky shores, – are only similar to plants because of convergent

evolution, – are most closely related to unicellular algae, and – are often edible.


• Seaweeds are classified into three different groups, based partly on the types of pigments present in their chloroplasts: 1. green algae, 2. red algae, and 3. brown algae (including kelp).

Seaweeds


Figure 15.26

Brown algaeRed algaeGreen algae

Evolution Connection:  The Origin of Multicellular Life• Multicellular organisms have

– specialized cells that are dependent on each other and perform different functions, such as

– feeding, – waste disposal, – gas exchange, and – protection.


• Colonial protists likely formed the evolutionary links between – unicellular and – multicellular organisms.

• The colonial green alga Volvox demonstrates one level of specialization and cooperation.

Evolution Connection:  The Origin of Multicellular Life


Figure 15.27-1

Unicellular protist

An ancestral colony may have formed when a cell divided and  remained  attached to  its offspring.

Figure 15.27-2

Unicellular protist

Locomotor cells

Food-  synthesizing cells

Cells in the colony may have become specialized and  interdependent.


Figure 15.27-3

Unicellular protist

Locomotor cells

Food-  synthesizing cells Somatic

cells

Gamete

Additional specialization may have led to sex cells (gametes) and  nonreproductive  cells (somatic cells).

Cells in the colony may have become specialized and  interdependent.


Figure 15.UN01

Bacteria

Archaea

Prokaryotes

Eukarya

Protists

Plants

Fungi

Animals

Figure 15.UN02

Bacteria

Archaea

Prokaryotes

Eukarya

Protists

Plants

Fungi

Animals

Figure 15.UN03

Major episode Millions of years ago

All major animal phyla establishedPlants and fungi colonize land

Origin of Earth

First multicellular organismsOldest eukaryotic fossilsAccumulation of O2 in atmosphereOldest prokaryotic fossils

5005301,2001,8002,4003,5004,600

Figure 15.UN04Inorganic compounds

Abiotic synthesis of organic monomers

Abiotic synthesis of polymers

Formation of  pre-cells

Self-replicating molecules

Membrane-enclosed compartment

Complementary chain

Polymer

Organic monomers2

1

3

4

Figure 15.UN05

Spherical Rod-shaped Spiral

Figure 15.UN06

Nutritional Mode Energy Source Carbon Source

Photoautotroph

Chemoautotroph

Photoheterotroph

Chemoheterotroph

Sunlight

Inorganic chemicals

Sunlight

Organic compounds

CO2

Organic compounds

Figure 15.UN07

Bacteria

Archaea

Prokaryotes

Eukarya

Protists

Plants

Fungi

Animals

Figure 15.UN08

Bacteria

Archaea

Prokaryotes

Eukarya

Protists

Plants

Fungi

Animals

major episodes in the history of life€¦ · major episodes in the history of life • earth was...

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