biology · of short stretches of their own sequence or other short ... powerpoint® lecture...

Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

PowerPoint® Lecture Presentations for

Biology

Eighth Edition

Neil Campbell and Jane Reece

Lectures by Chris Romero, updated by Erin Barley with contributions from Joan Sharp

BIG IDEA I The process of evolution drives

the diversity and unity of life. Enduring Understanding 1.D

The origin of living systems is explained by natural processes.

Essential Knowledge 1.D.1

There are several hypotheses about the natural origin

of life on Earth, each with supporting scientific evidence.


Essential Knowledge 1.D.1: There are several hypotheses about the natural origin of life on Earth, each with supporting scientific evidence.

• Learning Objectives:

– (1.27) The student is able to describe a scientific hypothesis

about the origin of life of Earth.

– (1.28) The student is able to evaluate scientific questions

based on hypotheses about the origin of life on Earth.

– (1.29) The student is able to describe the reasons for revisions

of scientific hypotheses of the origin of life on Earth.

– (1.30) The student is able to evaluate scientific hypotheses

about the origin of life on Earth.

– (1.31) The student is able to evaluate the accuracy and

legitimacy of data to answer scientific questions about the origin

of life on Earth.


Overview: Lost Worlds

• Fossils in all parts of the world tell a similar, surprising story:

past organisms were very different from those now alive.

• The sweeping changes in life on Earth revealed by fossils

illustrate macroevolution, the pattern of evolution over large

time scales.

• Specific examples of macroevolutionary change include the

origin of key biochemical processes such as

photosynthesis, the emergence of the first terrestrial

vertebrates, and the long-term impact of a mass

extinction on the diversity of life.

• Taken together, such changes provide a grand view of

the evolutionary history of life on Earth.


Early Earth Conditions

• Conditions on early Earth made the origin of life possible. There is scientific

evidence that Earth and the other planets of the solar system formed about 4.6

billion years ago.

• The earliest evidence of life on Earth comes from fossils of microorganisms

that are about 3.5 billion years old.

• The current theory about how life arose indicates that chemical and physical

processes on early Earth may have produced simple cells in a sequence of

four main stages:

1. Primitive Earth provided inorganic precursors from which small organic molecules

were abiotically synthesized due to the presence of available free energy and the

absence of a significant quantity of oxygen.

2. These molecules served as monomers for the formation of more complex

molecules, such as nucleic acids and nucleic nucleotides.

3. All these molecules were packaged into protobionts, membrane-containing

droplets, whose internal chemistry differed from that of the external environment.

4. The joining of these monomers produced polymers with the ability to replicate,

store and transfer information – which made inheritance possible.


Synthesis of Organic Compounds on Early Earth http://highered.mcgraw-hill.com/sites/9834092339/student_view0/chapter26/animation_-_miller-urey_experiment.html

• There is scientific evidence that Earth and the other planets of the solar

system formed about 4.6 billion years ago.

• The first atmosphere was probably thick with water vapor; along with

various compounds released by volcanic eruptions, including nitrogen

and oxides, carbon dioxide, methane, ammonia, hydrogen, and

hydrogen sulfide.

• As Earth cooled, the water vapor condensed into the oceans, and

much of the hydrogen quickly escaped into space.

• In the 1920s, Russian and British chemists Oparin and Haldane

hypothesized that Earth’s early atmosphere was a reducing (electron-

adding) environment, in which organic compounds could have formed

from simple molecules.

• They suggested that the early oceans were a solution of organic

molecules, a “primitive soup” from which life arose.

http://highered.mcgraw-hill.com/sites/9834092339/student_view0/chapter26/animation_-_miller-urey_experiment.html








Abiotic Synthesis of Macromolecules

• The presence of small organic molecules, such as amino acids, is not

sufficient for the emergence of life as we know it.

• Every cell has an assortment of macromolecules – including enzymes and

other proteins and nucleic acids that are essential for self-replication.

• Experiments suggest that such molecules could have formed in early

Earth.

• Some models suggest that primitive life developed on biogenic surfaces,

such as clay, that served as templates and catalysts for assembly of

macromolecules.

• By dripping solutions of amino acids into hot sand, clay, or rock,

researchers have been able to produce amino acid polymers. The

polymers formed spontaneously, without the help of enzymes or

ribosomes.

• It is possible that such polymers may have acted as weak catalysts for a

variety of reactions on early Earth.


Protobionts

• The necessary conditions for replication and metabolism

early in life’s history may have been met by protobionts.

• Protobionts are aggregates of abiotically produced

molecules surrounded by a membrane or membrane-like

structure.

– Protobionts may exhibit some properties of life, such

as simple reproduction and metabolism, as well as the

maintenance of an internal chemical environment

different from that of their surroundings.

– Experiments demonstrate that protobionts could have

formed spontaneously from abiotically produced

organic compounds.


Protobionts


Self Replicating RNA and the Dawn of Natural Selection

• According to the RNA World hypothesis, the first genetic

material was most likely RNA, not DNA.

• RNA molecules called ribozymes have been found to

catalyze many different reactions:

– For example, ribozymes can make complementary copies

of short stretches of their own sequence or other short

pieces of RNA.

• Early protobionts with self-replicating, catalytic RNA would

have been more effective at using resources and would

have increased in number through natural selection.

• The early genetic material might have formed an “RNA

world”.


PowerPoint® Lecture Presentations for

Biology

Eighth Edition

Neil Campbell and Jane Reece

Lectures by Chris Romero, updated by Erin Barley with contributions from Joan Sharp

BIG IDEA I The process of evolution drives

the diversity and unity of life. Enduring Understanding 1.D

The origin of living systems is explained by natural processes.

Essential Knowledge 1.D.2

Scientific evidence from many different

disciplines supports models of the origin of life.


Essential Knowledge 1.D.2: Scientific evidence from many different disciplines supports models of the origin of life.

• Learning Objectives:

– (1.32) The student is able to justify the selection of geological,

physical, and chemical data that reveal early Earth conditions.


Geologic evidence provides support for models of the origin of life on Earth.

• The Earth formed approximately 4.6 billion years

ago, and the environment was too hostile for life

until 3.9 billion years ago.

• The earliest fossil evidence for life dates to 3.5

billion years ago.

• Taken together, this evidence provides a plausible

range of dates when the origin of life could have

occurred.


The Fossil Record

• The fossil record is the sequence in which fossils appear in

the layers of sedimentary rock that constitute Earth’s

surface.

– The fossil record reveals changes in the history of life on earth.

Fossils can also document how new groups of organisms

arose from previously existing ones.

– Sedimentary rocks are deposited into layers called strata and

are the richest source of fossils.

– Few individuals have fossilized, and even fewer have been

discovered.

– The fossil record is biased in favor of species that existed for a

long time; were abundant and widespread, and had parts

capable of fossilizing.


How Rocks and Fossils Are Dated

• Sedimentary strata reveal the relative ages of

fossils:

– In relative dating, the order of rock strata is used to

determine the relative age of fossils.

• The absolute ages of fossils can be determined by

radiometric dating

– Radiometiric dating uses the decay of radioactive

isotopes to determine the age of the rocks or fossils.

– It is based on the rate of decay, or half-life of the

isotope (the time required for half the parent isotope to

decay).


Key Events in Life’s History


Key Events in Life’s History

• Key events in life’s history include the origins of

single-celled and multicelled organisms.

– The earliest living organisms were prokaryotes.

– About 2.7 billion years ago, oxygen began to accumulate

in Earth’s atmosphere as a result of photosynthesis.

– Eukaryotes appeared about 2.1 billion years ago.

– Multicellular eukaryotes evolved about 1.2 billion years

ago.

– The colonization of land occurred about 500 million

years ago, when plants, fungi, and animals began to

appear on Earth.


The First Single-Celled Organisms

• The earliest evidence of life (3.5 billion years

ago) comes from fossilized stromatolites.

• These are layered rocks that form when certain

prokaryotes bind thin films of sediment

together.

• Early prokaryotes were Earth’s sole inhabitants

from about 3.5 to 2.1 billion years ago.

• These prokaryotes transformed life on our

planet.


Photosynthesis and the Oxygen Revolution

• Most atmospheric oxygen gas is of biological origin, produced

during the water-splitting steps of photosynthesis.

• When oxygenic photosynthesis first evolved, the free O2

produced probably dissolved in the surrounding water until it

reached a high enough concentration to react with dissolved

iron.

• This would have caused the iron to precipitate as iron oxide,

which accumulated as sediments. Once all of the dissolved

iron had precipitated, additional O2 dissolved in the water until

the seas and lakes became saturated.

• After this, O2 began to “gas out” of the water and enter the

atmosphere.


Photosynthesis and the Oxygen Revolution


Effects of the Oxygen Revolution

• The “oxygen revolution” had an enormous impact on life.

• In certain chemical forms, oxygen attacks chemical bonds

and can inhibit enzymes and damage cells.

• As a result the rising concentrations of atmospheric O2

probably doomed many prokaryotic groups.

• Some species survived in anaerobic habitats, where we

find their descendants living today.

• Among other survivors, diverse adaptations to the

changing atmosphere evolved, including cellular

respiration, which uses O2 in the process of harvesting the

energy stored in organic molecules.


Endosymbiosis and the First Eukaryotes http://highered.mcgraw-hill.com/sites/9834092339/student_view0/chapter4/animation_-_endosymbiosis.html

• The oldest fossils of eukaryotic cells date back

2.1 billion years.

• The hypothesis of endosymbiosis proposes

that mitochondria and plastids (chloroplasts

and related organelles) were formerly small

prokaryotes living within larger host cells

• An endosymbiont is a cell that lives within a

host cell.

http://highered.mcgraw-hill.com/sites/9834092339/student_view0/chapter4/animation_-_endosymbiosis.html






Endosymbiosis Theory


• The endosymbiotic hypothesis proposes that

mitochondria and plastids (chloroplasts) were

formerly small prokaryotes that began living within

larger cells. Evidence for this hypothesis includes:

– Both organelles have enzymes and transport systems

homologous to those found in the plasma membranes of

living prokaryotes.

– Both replicate by a splitting process similar to prokaryotes.

– Both contain a single, circular DNA molecule, not

associated with histone proteins.

– Both have their own ribosomes which translate their DNA

into proteins.

Evidence Supporting the Endosymbiotic Theory


The Origin of Multicellularity

• The evolution of eukaryotic cells allowed for a greater

range of unicellular forms.

• A second wave of diversification occurred when

multicellularity evolved and gave rise to algae, plants,

fungi, and animals.

• Comparisons of DNA sequences date the common

ancestor of multicellular eukaryotes to 1.5 billion years

ago.

• The oldest known fossils of multicellular eukaryotes are of

small algae that lived about 1.2 billion years ago.


The Rise and Fall of Dominant Groups

• Anaerobic prokaryotes originated, flourished, and then

declined as the oxygen content of the atmosphere rose.

• Billions of years later, the first tetrapods emerged from the

sea, giving rise to amphibians that went on to dominate life

on land for 100 millions years – until other tetrapods

(dinosaurs and later, mammals) replaced them as the

dominant terrestrial vertebrates.

• These and other major changes in life on Earth have been

influenced by large-scale processes such as continental

drift, mass extinctions, and adaptive radiations.


Continental Drift

• Continental drift is the movement of Earth’s

continents on great plates that float on the hot,

underlying mantle.

• Plate movements rearrange geography slowly,

but their cumulative effects are dramatic. In

addition to reshaping physical features of our

planet, continental drift has a major impact on

life on Earth.

• Formation of the supercontinent Pangaea

about 250 million years ago had many effects:

– A reduction in shallow water habitat; a colder

and drier climate inland; changes in climate as

continents moved toward and away from the

poles; changes in ocean circulation patterns

leading to global cooling.


The “Big Five” Mass Extinction Events


Consequences of Mass Extinctions


Adaptive Radiations

• Adaptive radiations are periods of evolutionary change in

which groups of organisms form many new species whose

adaptations allow them to fill different ecological niches.

– Large-scale adaptive radiations occurred after each of the big five

mass extinctions, when survivors became adapted to the many

vacant ecological niches.

– Fossil evidence indicates that mammals underwent an adaptive

radiation after the extinction of terrestrial dinosaurs .

– The disappearance of dinosaurs (except birds) allowed for the

expansion of mammals in diversity and size.

– Other notable radiations include photosynthetic prokaryotes, large

predators in the Cambrian, land plants, insects, and tetrapods.


Major Changes in Body Form

• The fossil record tells us what the great changes in the

history of life have been and when they occurred.

• Our understanding of continental drift, mass extinction,

and adaptive radiation provides a picture of how those

changes came about.

• We now must seek to understand the intrinsic

biological mechanisms that underlie changes seen in

the fossil record.

• For this, we focus on genetic mechanisms of change,

paying particular attention to genes that influence

development.


Evolutionary Novelty

• Evolutionary novelty can arise when structures that

originally played one role gradually acquire a different

one.

• Structures that evolve in one context but become co-

opted for another function are referred to as

exaptations.

– For example, it is possible that feathers of modern

birds were co-opted for flight after functioning in

some other capacity, such as thermoregulation.


“Evo-Devo”

• “Evo-devo” is a field of study in which evolutionary

biology and developmental biology converge.

• This field is illuminating how slight genetic divergences

can be magnified into major morphological differences

between species.


Heterochrony

• Heterochrony is an evolutionary change in the rate or

timing of developmental events.

• Change relative rates of growth even slightly can

change the adult form of an organisms substantially,

thus contributing to the potential for evolutionary

change.


Homeotic Genes

• Homeotic genes are master regulatory genes that

determine the location and organization of body parts.

– Hox genes are one class of homeotic genes.

– Changes in Hox genes and in the genes that

regulate them can have a profound effect on

morphology, thus contributing to the potential for

evolutionary change.

Fig. 25-21

Vertebrates (with jaws) with four Hox clusters

Hypothetical early vertebrates (jawless) with two Hox clusters

Hypothetical vertebrate ancestor (invertebrate) with a single Hox cluster

Second Hox duplication

First Hox duplication Duplication of the single Hox complex occurs and

provides genetic material associated with origin of first

vertebrate. Dulpicate set of genes takes on new roles –

such as development of backbone.

Second duplication of Hox complex may have allowed the

development of even greater structural complexity – such

as jaws and limbs.


Fig. 25-22

Hox gene 6 Hox gene 7 Hox gene 8

About 400 mya

Drosophila Artemia

Ubx


Evolution is Not Goal Oriented

• Evolution is like tinkering—it is a process in which new

forms arise by the slight modification of existing forms:

– Most novel biological structures evolve in many stages from previously existing structures.

– Natural selection can only improve a structure in the context of its current utility.


Evidence for the Origin of Life Hypotheses

• Chemical experiments have shown that it is

possible to form complex organic molecules from

inorganic molecules in the absence of life.

• In the 1920s, Russian and British chemists Oparin

and Haldane hypothesized that Earth’s early

atmosphere was a reducing (electron-adding)

environment, in which organic compounds could

have formed from simple molecules.

• They suggested that the early oceans were a

solution of organic molecules, a “primitive soup”

from which life arose.

The Miller-Urey experiment http://bcs.whfreeman.com/thelifewire/content/chp03/0301s.swf

http://bcs.whfreeman.com/thelifewire/content/chp03/0301s.swf


Sidney Fox and Proteinoids

• In the 1960s, Sidney Fox synthesized organic

polymers such as polypeptides by dripping

dilute solutions of organic monomers over hot

sand, clay, or rock.

• This method mimics the condensation of the

Miller-Urey model, but with the idea that rain

falling from the early atmosphere or waves

washing onto hot substrate would be

favorable to the formation of polypeptides

and other organic polymers.

• Once these polymers have formed, they can

form aggregates, which spontaneously form

into proteinoids (protobiont structures similar to

living organisms).


Evidence for the Origin of Life Hypotheses

• Molecular and genetic evidence from extant and

extinct organisms indicates that all organisms on

Earth share a common ancestral origin of life.

– Scientific evidence includes molecular building

blocks that are common to all life forms

(carbohydrates, proteins, lipids, amino acids).

– Scientific evidence includes a common genetic

code (DNA and RNA).

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