bio3.life on earthu

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PreliminaryBiologyTopic3LifeonEarthcopyright2005-2008 keepitsimplesciencewww.keepitsimplescience.com.au

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What is this topic about?To keep it as simple as possible, (K.I.S.S.) this topic involves the study of:1. THE ORIGINS OF LIFE ON EARTH

2. THE HISTORY OF LIFE ON EARTH

3. THE PROCARYOTIC ORGANISMS TODAY

4. THE VARIETY OF LIFE & HOW WE CLASSIFY

but first, an introduction...Biological Evolution Evolution means to undergo a sequence of

changes. The change is NOT random... it fo llows

a sequence or pattern.

There is overwhelming scientifi c evidence that

LIFE ON EARTH HAS CHANGED

over millions of years, and that there is a

definite pattern in the changes... life has

evolved.

In this topic you will study the

FACTS OF EVOLUTION

...what we know about the pattern of changes to

life on Earth over millions of years.

In a later topics you will study the

THEORY OF EVOLUTION

...the scientific theory which attempts to explainhow and why evolution of life occurs.

The Variety of Life

Estimates vary enormously, but there areundoubtably millions of different types (species)of living things on Earth today. This variety isjust a t iny fraction of all the d if ferent types thathave ever lived.

How can we study and understand suchdiversity? Only by developing a system to

classify organisms into groups.

You already know about grouping like-thingstogether:

In this topic you will study the way that sciencedeals with the staggering diversity of life on Earth.

Preliminary Biology Topic 3

LIFE ON EARTH

Plantsaredifferenttoanimals...

dolphinsareexactlyunlikecentipedes...

andjellyfishandmushroomshavenosimilaritiesexcepttheirgeneralshape.


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The EarlyEarth

Technologies

that help usUnderstand Changing

Ideas

Science&

CulturalBeliefs

The Need to Classify&

Criteria used

Dichotomous

Keys

The ClassificationSystem

Changesto the

System?

Technolgiesto Study

Procaryotes

PossibleEnvironments in

Which LifeBegan

The MainSteps

LIFEon

EARTH

Origins of

Life on Earth

History of

Life on Earth

Procaryotic

Organisms

Today

Variety of Life

&

How We Classify

TheArchaea

TheoriesofOrigins of Life

CONCEPT DIAGRAM ( Mind Map ) OF TOPICSome students find that memorising the OUTLINE of a topic helps them learn and remember

the concepts and important facts. As you proceed through the topic,come back to this page regularly to see how each bit fits the whole.

At the end of the notes you wil l find a blank version of th is Mind Map to pract ise on.


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In the Beginning...

We believe the Earth is about 4.6 billion

(= 4,600 million) years old. How do weknow? That will be dealt with later.

The Earth of 4 billion years ago wasvery different to that of today.

How do we know that? Well, we cannotbe 100% sure, but this descriptionmatches with: -

conditions & chemicals on other planets.

the chemicals that erupt from volcanicvents today, and probably always have.

Chemicals First, Then Cells

We think that he atmosphere of the primitive Earth contained exactlythe same elements that the chemicals of life are made from...

mainly carbon, hydrogen, oxygen & nitrogen.

In the 1920s it was suggested by two scientists independently,that maybe the conditions on Earth 4 bil lion years ago:-

firstly caused chemical reactions that made complex organic molecules. then these chemicals somehow came together to form living cells. and once life got s tarted, it evolved into all the species in the

fossil record and alive today.

1. THE ORIGINS OF LIFE ON EARTH

Volcanoesaddmanygasestoatmosphere

StrongU.V.raysfromSun AtmosphereofH2Ovapour,methane,ammonia,carbondioxide,nitrogen,hydrogen.NOfreeoxygen

Spontaneous Generation of Life

Until about 150 years ago, it was

generally believed that life could appearspontaneously... maggots just happened in rotting meat and frogsjust arise from swampy ground.

This concept was finally proven wrongby Louise Pasteurs famous experimentof 1862...

...and by the 1880s the cell theory of lifewas established as a scientificprinciple.

This includes the statement that allcells (life) come(s) from pre-existingcells (life).

So how did the first living thingsget started on the primitive Earth?

Eachflaskcontainsabroth,boileduntilsterilized

Closed flaskremains

sterile... nomicrobesgrow in it.

Open flask growsmicrobes & rots.It was believedthe life came

spontaneouslyfrom contact

with air.

This flask is open to theair, but the gooseneckprevents airborne spores

getting to the broth.It remained sterile, andproved spontaneousgeneration is wrong.

Violentstorms-alotofLightning

Earlyoceans


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Significance of theUrey-Miller Experiment

1. It demonstrates the way Scienceworks, by formulating an hypothesisand then testing it by experiment. In thiscase the hypothesis was put forward byother scientists 30 years before theexperiment was done.

2. Although it didnt prove how life gotstarted on Earth, the experimentalresults support the hypothesis byshowing that life-forming chemicalscould have been produced naturallyunder the conditions of the primitiveEarth.

3. In combination wi th evidence from:

Space Exploration Vulcanology & Earth Chemistry Ancient Rocks & Fossils Study of Primitive Life Alive Today

and other areas of scientific study, theUrey-Miller experiment is just one partof a package of evidence that seemsquite consistent with the idea that lifeformed naturally on the primitive Earthsome 4 billion years ago, and hasevolved into what we see today.

We cannot prove how life arose, but theweight of evidence suggests were on

the right track.


This was one of the most famousexperiments in the history of Biology. Itwas designed in the 1950s to test the first

part of the hypothesis about the origins oflife... that the conditions of the primitiveEarth could naturally produce the complexmolecules necessary for life to start.

The initial experiments resulted in theproduction of sugars and amino acids,and later variations produced thechemical building blocks for cellmembranes, and even for DNA.

THIS SUPPORTS THE FIRST PART OFTHE HYPOTHESIS... the chemicals oflife could have appeared spontaneouslyon the primitive Earth.

OceanFlaskbeganwithpurewater

AtmosphereFlask

HEAT

Vpscrcuae

Electricsparksimulateslightning

Condensercoolsvapoursbacktoliquids

Liquid Trapwas later found to

contain organic

chemicals, such assugars and aminoacids... the basicchemicals of life.

Mixture of gases to simulateprimitive atmosphere.methane(CH4), CO2,

ammonia (NH3), N2, H2

The Urey-Mil ler Experiment

Life From Outer Space?The hypothesis that Urey &Miller tested is not the onlyidea for the origins of life.

It has been suggested that thefirst living things on Earth (orat least the chemicals theyformed from) could have come

from outer space.

This is an interesting

idea, but so far the

weight of evidence

supports the hypothesis

that Earth life arose on

Earth, and not

somewhere else.


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This is one of the key technologies inour search for an understanding of theorigins of life. It is the method thatallows us to measure the age of rocks &fossils.

The atoms of each chemical element arenot all exactly the same. They have thesame number of protons & electrons(thats what makes them that element),but the number of neutrons in the atomcan vary. Such atoms of the sameelement, but with a different number of

neutrons, are called isotopes . Someisotopes are radio-active and give offnuclear radiations... hence radio-isotopes.

Radio-isotopes decay at a predictablerate. That is, the level of radiation diesdown over time in an exactmathematical way.

ThisRadiometricDatingishowweknowtheageoftheEarth,ofdifferentfossilsetc,andcandescribetheentirehistoryoflifeonEarthfairlyprecisely.


TIME

RIAONLV

fromhere

toh

ere

tohere

100

50

25

0

half-lifehalf-life

half-life

The time it takesfor the radiationto drop to half

the previous level

is constant.This is theHalf-life

Technologies That Help Us Understand

By measuring the amount of radiationpresent now, and knowing the half-lifeof the isotope, the age of objects can becalculated.

The most famous example is CarbonDating which uses an isotope ofcarbon (called carbon-14) to find theage of artifacts from human history.

Carbon-14 has a half-life of about 5,700years, so if a bone or

wooden tool ismeasured to haveonly 1/2as muchradiation as it wouldhave had originally,then one half-life hasgone by since that bone or tree died...therefore, it must be 5,700 years o ld.

Carbon-14 is not much use beyondabout 40,000 years, but there are other

isotopes (e.g. potassium and uranium)with half-lives of many millions of years.These can measure the ages of fossilsand rocks which formed millions, oreven bil lions of years ago.

Radiometric Dating

The Electron MicroscopeThis device was mentioned in Topic 2 as having a major impact

on our understanding of cells and cell structures.

Electron microscopes can also allow scientists to studyvery ancient fossil cells in rocks and to make

comparisons with some types of primitive cells whichstill live today. This gives us further clues about how

ancient life-forms li ved and evolved.


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Biochemical Analysis &DNA Technology

Its well known from TV crime dramasthat by analysing traces of DNA from acrime scene, a criminal can be

positively identified.

The technique is also used to identifythe remains of victims of war or naturaldisasters. By comparing DNA samplesfrom a body part with samples from therelatives of missing people, scientistscan positively determine which familythe victim is from.

The same technique can be used to findthe relatedness of different livingthings, and even give estimates of howlong ago 2 related species divided fromeach other, in an evolutionary sense.

For example, DNA studies suggeststrongly that humans and chimpanzeesare closely related; our DNA is 99%identical.

Our ancestors and chimp ancestorsmust have separated only about 5million years ago.

Were prettycertain about

this, even though

the relevantfossils have not

been discovered.

More generally, biochemistry and DNAstudies have shown:

all life forms on Earth are related. Thismeans that all living things todayevolved from one original type.

which types are more closely, or moredistantly, related.

This complements the evidence of thefossil record, to give us a clearer pictureof the exact sequence of evolution.

Fill in the blank spaces.

We believe that the Earth of 4 billionyears ago had an atmospherecontaining gases such as(a).........................., (b)..........................and (c)......................................... but nouncombined (d)............................. Therewere many (e)........................... erupting,and violent storms producing a lot of

(f)..................................(g)......................... radiation f rom the sunwas at high levels.

Under these conditions, it is possiblethat complex (h)..................... chemicalscould form naturally. The (i).....................& ........................ experiment supportedthis hypothesis. The experimentinvolved simulating the conditions ofthe primitive Earth, and after some timeit was found that (j)...............................

and (k)................................ had formed.

Another hypothesis for how li fe beganon Earth is that living cells, or at leastthe chemicals they formed from camefrom (l)...............................................

Radio-metric dating is a techniquewhich measures the (m)...........................from radio-active (n).................................The age of rock or fossil etc can becalculated from the (o)....................-life

of the isotope.

The electron microscope has not onlyhelped our understanding of livingcells, but also helps us discover andstudy ancient (p)....................... in rocks.

DNA technology adds to ourunderstanding of the evolution of lifeby determining how closely(q)........................................ dif ferentorganisms are.

Worksheet 1 Origins of Life


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Multiple Choice

1.

Which of the following was probably NOT a

common gas in the atmosphere on Earth 4

billion years ago?A. Carbon dioxide

B. Oxygen

C. Methane

D. Ammonia

2.

Louise Pasteurs famous gooseneck flask

experiment of 1862 proved that:

A. li fe could begin spontaneously from contact

with air.

B. organic compounds could not have been

produced naturally on the primitive Earth.C. a nutrient broth rots after contact with air.

D. the theory of spontaneous generation was

wrong.

3.

In the Urey-Miller experiment:

A. organic molecules were produced f rom

inorganic.

B. living cells were produced from non-living

chemicals.

C. microsphere membrane structures were

made artificially.

D. complex inorganic molecules were

produced.

4.

The technology that has allowed us to

accurately measure the age of rocks, fossils

and the Earth i tself is:

A. radio-isotope studies.

B. electron microscope.

C. the principle of superposition of fossils.

D. DNA sequencing.

Longer Response QuestionsMark values given are suggestions only, and are

to give you an idea of how detailed an answer is

appropriate. Answer in the spaces provided.

5. (6 marks)Describe the condi tions on Earth 4 billion years

ago, covering:

a) significant physical conditions

b) chemical composition of the atmosphere.

6. (5 marks)Give an outline of the Urey-Miller experiment,

including:

a) the hypothesis it set out to test.

b) a basic description of what was done.

c) the main results.

d) what conclus ion may be drawn from it .

7. (3 marks)

a) Explain how radio-isotopes have contributed

to our understanding of the history of life on

Earth.

b) Identify another recently developed

technology and outline its contribution to our

knowledge of the history of li fe.

Worksheet 2 Practice Questions (Section 1)


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Summary of the Main EventsThe following time-line identifies the major

stages in the evolution of li fe on Earth. The main

evidence for this has come from fossils

preserved in sedimentary rocks. The timessuggested are approximate, but based on radio-

metric studies of the rocks.

Formation ofOrganic Molecules

This probably began as soon as the

Earth was cool enough forthe molecules to existwithout being torn apartagain. The Urey-Millerexperiment (and manyothers since) prove thatsugars, amino acids, lipidsand even the buildingblocks of DNA and RNAcould form spontaneouslyin the chemical condit ionsof the primi tive Earth.

Eventually, by 4 billion years ago, theearly oceans must have become achemical soup , highly concentrated inorganic molecules.

Molecules Formed MembranesIt is thought that the next cruc ial step

was the formation of membranes. In the

watery environment of the oceans,hydrophobic (water-hating ) moleculesnaturally tend to cling together, like oilforming droplets in water. Experimentshave shown that some lipid moleculesin water will, quite naturally, formmicrospheres with other chemicalstrapped inside.

A microsphere is not a liv ing cel l, butscientists believe that structures likethis were the precursors of cells.

2. THE HISTORY OF LIFE ON EARTH

Millionsofyearsago4,500

4,000

3,500

3,000

2,500

1,000

500

0

1,500

2,000

EarthformedOrganicmoleculesformingassuggestedbytheUrey-Millerexperiment?

Moleculesformedmembranes?

Firstlivingthingssomewherehere(?)Throughoutthisimmenseperiodalllifewasbacteria-like,anaerobic(livingwithoutoxygen)andheterotrophic,feedingontheorganicmoleculesoftheenvironment.Firstautotrophs?chemosyntheticbacteria

First Cyanobacteria, usingchlorophyll for photosynthesis

and releasing oxygen

Over this time the Earth went frombeing ANOXIC to OXIC.

Organisms using oxygen forcellularrespiration appeared.

Firstsexualreproduction.Evolutionspeedsup

Animals with hard parts (shells etc)appear. Huge increase in fossils

Fish

Amphibians, InsectsReptiles, MammalsDinosaursBirdsHumans

1

3

4

5

7

8

9

6

2

One lipid molecule

Lipidmoleculesclingtogether,formingamicrosphere

Other chemicalsmay be

trapped inside

First multicellular plants (algae)and animals

(sponges, worms, jellyfish)

First Eucaryotic cells(with membrane-based

organelles)

1

2


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The First Living Cellsmust have been microspheres which

trapped inside themselves a mixture ofchemicals that could attract othermolecules in through the membraneso they became bigger (i.e. feeding &

growing) and also cause copies of theirown molecules to be built... small RNAmolecules can do this.

Eventually thesphere wouldsplit in two,(reproduction!)each part witha share of the

essentialchemicals tomake it all happen over again.

We cant be sure when this happened,but by about 3.8 billion years ago wefind chemical evidence of living cells insome rocks, and by 3 billion years agothere are foss ils of bacteria-like cells, invarious forms... they were evolving intonew types already.

These cells lived without oxygen(anaerobic ) and were probablyfeeding on the soup of organicmolecules still in the oceans.

A Bi ll ion Years of Scavenging

For perhaps 1,000 million years themost advanced organisms on Earthwere bacteria-like cells which livedwithout oxygen, and scavenged theorganic soup of organic molecules inthe oceans.

Probably the production of organicmolecules (food) was still occurringas in the Urey-Miller experiment, but thewhole regime was about to change...

The First Autotrophs

Chemosynthesis & Photosynthesis

About 2.8 bi ll ion years ago, a new typeof bacteria appears in the fossil record.

The fossils appear similar toautotrophic bacteria alive today, whichmake their own food, using energy fromchemicals in the environment. Thisprocess is called Chemosynthesis.(details later)

By 2.3 billion years ago, fossils of cellsrecognisable as cyanobacteria appeared.These are bacterial type cells, but usechlorophyll to trap sunlight, and produceOXYGEN as their waste product.

They grew in shallow seas in s tructures

called stromatolites which we find ascommon fossils in rocks from this time.Living stromatolites still grow in someplaces today.


3

4

5

LivingStromatolitesPhotobyPatBride

WATER+CARBON GLUCOSE+OXYGENDIOXIDE6H2O + 6CO2 C6H12O6 + 6O2

chlorophyll

lightenergy

LivingmatofcellsinthintoplayerColumngrowslikeastalagmite.Newlayersgrowontopofold,deadlayers


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The World Goes Oxic

Up until this time the Earth was anoxic ... completely without anyuncombined molecular oxygen (O2).There were plently of oxygen atoms of

course, but they were all chemicallycombined in water (H2O) and CO2 andvarious other compounds.

But now the cyanobacteria beganmodern style photosythesis inmillions of stromatolites, for mill ions ofyears...

We find huge deposits of evidence for

what happened next... the world wentrusty!

In many parts of the world (includingWestern Australia) we find hugedeposits of Banded Ironstone ; rockcontaining layers of iron oxide (Fe2O3).The iron mineral is very fine grained asif precipitated from a water solution.

The explanation is that, in the anoxicearly conditions a lot of iron wasdissolved in the oceans in the solubleform of Fe2+ ions. As the cyanobacteriabegan releasing vast quantities of O2oxygen, it reacted with the iron formingthe insoluble Fe2O3 iron oxide (which isRUST).

Eventually, after about 200 milion years,all the iron was precipitated, and nowthe oxygen began building up in the

atmosphere... the air became OXIC .

This had four important consequences:-

1. The natural production of organicchemicals by the Urey-Miller processstopped forever. Oxygen is chemicallyactive enough to destroy organic

molecules as fast as they could form.Life could never again start up

the way it once did.

2. The old-type anaerobic bacteria foundoxygen poisonous, so many becameextinct. A few survived in environmentswhere there is no oxygen, and therethey live to this day... you will studythem soon.

3. Atmospheric oxygen alloweddevelopment of an ozone layer. Thisabsorbs UV rays and was vital for thelater development of l ife on land.

4. The oxic environment encouraged anew, more efficient way to use foodenergy... cellu lar respiration. By 2 billionyears ago the famil iar modern cycle wasoperating:

ATP is the energy compound whichpowers all life processes... celldivision, moving, growing etc.


Lightenergy

GLUCOSE+

OXYGEN

CARBONDIOXIDE+

WATER

ATP

PHOTOSYNTHESIS(incyanobacteria)

AEROBICRESPIRATION(inalllivingthings)

6


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The First Eucaryotic Cells

Al l the more advanced li ving th ingson Earth today are characterized bycells containing many organelles whichare built from and/or surrounded by

membranes. Such cells are calledeucaryotic.(This was dealt with in Topic 2)

Prior to about 1.5 billion years ago, alllife on Earth was procaryotic meaningthat the cells lack a true nucleus,mitochondria, chloroplasts, etc. Theliving procaryotes of today are thebacteria and cyanobacteria. Withouttrue organelles to organize their cellfunctions better, the procaryotes haveto remain very tiny, single cells in whichdiffusion distances are small, and theSA/Vol ratio is high.

And thats how li fe on Earth might haveremained forever, except some cells atesome smaller cells, but failed to digestthem. The small cells lived on insidetheir host in a relationship that soon

became mutualism, and after millions ofyears, the ingested cells evolved tobecame organelles of the larger cell.


Larger cell enveloping a smaller cell forfood, but fails to digest it.

Smaller cell becomes mitochondrionwithin the host cell

By a similar process, aphotosynthetic cell is

eaten andbecomes a

chloroplast

EvolvestobecomeanAnimalcell EvolvestobecomeaPlantcell

7 Whats the evidence for this? Both mitochondria & chloroplasts

contain their own DNA, and it isbacteria-like DNA in a loop.These organelles reproduce

independently of the rest of the cellin a mini-version of a cell division.

Mitochondria contain their ownribosomes for making their ownproteins.

Mitochondrial enzymes (which controlcellular respiration) are attached to theinner membrane in a very bacteria-like

way.

This whole idea is known as the Endosymbiotic Hypothesis and is ourbest explanation of where the first cellscame from that later evolved into theplants and animals.(Endo- = inside,

symbiosis = to live together)

Sex Speeds Things Up

So far in the history of life, all the living thingsprobably reproduced by simple cell division.This produces identical daughter cells. (ascovered in Topic 2) The only way a new variationcould occur was by occasional genetic accidents ... mutations. So the evolution ofnew types was very slow.

A li tt le over 1 bi ll ion years ago, some cel lsbegan exchanging bits of DNA with each other.Fossils have been disc overed (using theelectron microscope) of 2 cells joined by a thintube apparently in conjugation , in which the

cells swap DNA fragments in a kind of simplesexual fertilisation of each other.

The result is more genetic variations and moredifferences between individuals. Evolution hadmore opportunities, and sure enough, the fossil

record shows an accelerating increase in new,more complex fo rms appearing.

8

CELLSinCONJUGATION

Small fragments of DNA are passed throughthe tube, increasing the genetic variations

within a population


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Similarly, some eucaryotic,heterotrophs became colonial to evolveinto the first

multicellularanimals, similarto modernsponges. Latercame flatwormsand jellyfish-likecreatures wi thvery simple bodyplans.

About 600 mil lion years ago there came

an explosion of life. We find a hugeincrease in fossil numbers and forms,partly because some types developedshells and other hard body parts thatfossil ized well.


9 The First Multicellular Organismsappeared about 800 mill ion years ago.

It is often an advantage for an organismto be large. A larger organism deterspredators and gathers more of theresources of the environment, so itschance to survive and thrive is better.But, as you know from Topic 2, a singlecell cannot grow too large because theSA/Vol ratio gets less.

The other way to get large is have morecells.

About 800 million years ago someeucaryotic, photosynthetic cells

became colonial . When the cellsdiv ided, they didn t separate, but stayedattached to each other, formingfilaments or flat sheets. These simple,multicellular associations evolved intothe algae group and from one type ofthem, came (eventually) the plants.

Science Clashes With Culture?Darwins Theory of Evolution causedtremendous controversy whenpublished in 1859 because it was notconsistent with the Biblical story of divine creation and many people sawthis as an attack on their religion andtheir culture.

Even today, there are some religiousgroups who reject the entire concept ofthe Evolution of Life because theyinterpret their traditional, cultural or

religious stories of creation veryliterally.

Most mainstream religions however,accept that Science is not trying toattack any belief, culture or tradition,but only to understand and explain thenatural world. Most religiousorganizations now accept the Facts ofEvolution that life on Earth has existedfor bi llions of years, and has undergone

progressive change.

Many Christian churches, for example,accept the scientific evidence for the

age of the Earth, the beginnings andhistory of life, and recognise that thecreation stor ies in Genesis are notliterally true, but are allegories to thepower and benevolence of the Judaic-Christian-Islamic God. The belief is thatevolution happened, but under Godscontrol and supervision, along apathway He ordained.

Thus it i s quitepossible toreconcilereligious beliefand faith withscientificenquiry andknowledge.

Each contr ibutes in its own way tohuman culture, and to each individuals

humanity.


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Fossils have been known and collectedby people for thousands of years. InChina they were considered as DragonBones, while it was supposed by

Europeans up until the 1860s thatfossils represented the many types ofanimal which never made it to NoahsArk and so drowned in the Bibl icalFlood.

The Principle of Superposition wasdeveloped by early Geologists and used tostart putting fossil discoveries into relativetime order, although the actual ages werenot known.

From many studies like this, the fossilsover the entire known span of Earthhistory were arranged in order.

Once this rough order of age for fossilswas established, scientis ts began to seethe pattern... the fossil record shows aclear pattern from few and simpletowards more varied and complex lifeforms.

It was partly this pattern in the fossilrecord that convinced Charles Darwinthat life on Earth had changed andevolved.

The fossils dont just show that life onEarth has changed, but that is haschanged in a sequence, in a directionfrom few & simple to more variety &

more complex .

Until the 20th century, little notice wastaken of the most ancient rocks onEarth, from the Pre-cambrian time.Few fossils could be detected in them,and it seemed that animal life hadsimply appeared in abundance at acertain point in t ime.

Improved technologies changed allthat...

Radio-metric dating of meteorites and

Moon-rock told us the true age of theSolar System and therefore of the Earth.Dating of fossils and the ancient rocksput the sequence of the fossil recordinto a proper time-scale.

Improved microscopic techniques,especially the electron microscope,discovered the cellular fossils in theancient rocks. It was previously thoughtthere were no traces of life in the Pre-

cambrian rocks.

Now with the insights into evolutionprovided by DNA technology, and thebiochemical experiments of Urey &Miller and many others, we canunderstand the fossil record and thehistory of life right back to its originswith some degree of scientificconfidence. We cant know everything,but no longer believe in dragonbones.


ANCIENTTIMES MODERNTIMESLesscomplexity MorecomplexLessvariety GreatervarietyUnlikemodern Moreandmorelikelife-forms modernlife-forms

Rockprofilein1stlocationRockprofilein2ndlocation

Thesefossilscorrelatetoeachother,

sothecorrespondingrocklayers(indifferentplaces)mustbethesameage.od

yo

Changing Ideas About the History of Life


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The age of the Earth is thought to beabout (a).............. billion years. Byabout 4 billion years ago (BYA) it islikely that many (b)..................................compounds had formed from theinorganic chemicals present.

The next step was probably that certainlipid molecules (which are(c).................................... =water hating)may have come together and formed(d)............................................ Thesestructures, in which the lipid layer actslike a (e)........................................., may

have trapped other chemical inside.

If the chemicals inside were able to(f)........................................ themselves,and to attract other molecules inthrough the membrane , then thestructure is alive . This may have firsthappened about (g)...................... BYA.

For the next billion years, all life onEarth was bacteria-like, (h)......................(living without oxygen) andheterotrophic, feeding on the(i).................................. moleculesdissolved in the oceans.

The first (j)............................................(self-feeders) appeared about 2.5 BYA.They were able to make food using theenergy of (k)...........................................from their environment. The first cellsdoing photosynthesis were the(l)................. ................................., which

grew in large structures called(m)............................................. Theyreleased (n)............................. gas whichreacted with disso lved (o).......................This precipitated and formed extensivesediments, which are known as(p)......................... .................................Eventually there was enough oxygenformed to turn the atmosphere frombeing (q)......................., to become oxic.

This was a disaster for many anaerobiccells, which became extinct. They were

replaced by new types which used(r)........................... ...........................(process) to release energy from theirfood in the form of the energy chemical(s)......................

About 1.5 BYA, the first(t)........................ cells (with membrane-based organelles) appeared. The bestexplanation for these is called the (u).............................................................

Hypothesis in which one cell ingestedanother, but failed to(v)....................................... it. Thesmaller cell survived to live within thelarger, eventually becoming anorganelle such as a mitochondrion or(w)...................................Evidence supporting this hypothesis isthat some organelles contain their own(x).................. and .....................................

for making proteins.

Roughly 1 BYA some cells beganswapping bits of DNA in a primitive sortof (y)................................ This increasedthe (z)...................................... variationand so evolution (aa)..............................

About 800 MYA, the first(ab)...................................... organismsappeared. The early forms resembled

(ac)............................(plant) and(ad).................................. (animal).

About 600 MYA there was an explosion in the fossil record, whenmany animals with (ae)..........................body parts appeared.

WHENCOMPLETED,WORKSHEETSBECOMESECTIONSUMMARIES

Worksheet 3 History of Life on Earth


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15


Multiple Choice1. A precursor to the formation of the first

living cells was probably:

A. formation of an oxic environment.

B. formation of chemical systems capable of

photosynthesis.

C. formation of microsphere membrane

structures.

D. polymerisation of natural inorganic

chemicals.

2. The first living cells were probably:

A. aerobic, procaryotic and autotrophic.

B. anaerobic, procaryotic and heterotrophic .

C. anaerobic, eucaryotic & chemosynthetic.

D. anoxic, eucaryotic and heterotrophic.

3. It is thought that the organisms mainlyresponsible for the conversion of the Earth to an

oxic environment were the:

A. Archaea.

B. chemosynthetic autotrophs.

C. early eucaryotic algae.

D. cyanobacteria.

4. The Endosymbiotic Hypothesis is a

proposal for the formation of the first:

A. procaryotic cel ls.

B. photosynthetic cells.

C. eucaryotic cells.D. cells capable of aerobic respiration.

5. The Endosymbiotic Hypothesis is

supported by which of the following pieces of

evidence?

A. Mitochondria have their own DNA.

B. Cells regularly envelop and eat smaller

cells.

C. Fossils of cells in conjugation have been

discovered.

D. Mitochondria can live independantly outside

of their host cell.

6. It is thought that the correct sequence of

certain events in the history of life was:

A. sexual reproduct ion, eucaryotic cel ls,

multicellular.

B. eucaryotic cells, multicellular, sexual

reproduction.

C. eucaryotic cells, sexual reproduction,

multicellular.

D. multicellular, sexual reproduction,

eucaryotic cells.




7. (2 marks)

Identify two major s tages or processes that are

believed to have occurred before the

appearance of the fir st li ving cells on Earth.

8. (5 marks)

One of the most signifi cant events in thehistory of the Earth was the change from an

anoxic to an oxic environment.

a) What does this mean?

b) Identify the organisms, and the process that

caused the change.

c) Explain the signif icance of this change for

the evolution of life.

9. ( 4 marks)

a) What does the Endosymbiotic Hypothesis

attempt to explain?

b) Outline the hypothesis.

c) Give a piece of evidence supporting the

hypothesis.



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16

3. THE PROCARYOTIC ORGANISMS TODAY

Technology to Study ProcaryotesEven with a good light microscope, bacterial cells are so small that

they appear as simple rods, spheres and spiral-shaped cells.

The Electron Microscope

With its superior magnification andresolution, the electron microscope wasthe technology that revealed the finedetails of cell structure. It was theelectron microscope that first gave usthe understanding of eucaryotic andprocaryotic cells as beingfundamentally different.

This understanding led to the

classification of all the procaryoticorganisms into the kingdom Monera,totally different life forms to the eucaryoticplants, animals and fungi.

Within this procaryotic kingdom of life,many different sub-groups wererecognized, but they were all thought tobe essentially alike because of theirprocaryotic structure. New technologieshave changed that view...

Nucleus and other organelles madefrom or bound by membranes

Nuclear region, butno true nucleus

PROCARYOTIC EUCARYOTICCELL CELL

Ribosomes in cytoplasm,but no membrane-bound

organelles

DNA & Protein Sequencing

These allow scientists to determine theprecise sequence of chemical units inDNA molecules and protein chains.

Studies on the different types ofprocaryotic organisms have shown thatthere are some types that are sodifferent from the rest, that theyperhaps should be placed into a new

kingdom, to be called Archaebacteriaor simply Archaea(pronounced ark-ee-a).

Whats different about them?They have:

completely different RNA molecules toall other life.

cell walls which are chemicallydifferent to all other life.

totally different enzymes for releasingenergy from food.

different pathways of metabolism forsome cell processes.

The word archae means ancient ,and it is believed that these verydifferent organisms are modernsurvivors from those primitive cells of 3

billion years ago.

The ArchaeaWhen the cyanobacteria began photosynthesizing in their

stromatolites just over 2 billion years ago, the oxygenthey released firstly caused the oceans to rust, and then

caused the atmosphere to become oxic.

We think many of the older species of anaerobic life couldnot cope with oxygen and died out. Some however,

survived in habitats where there is no oxygen...


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17

The methanogens get their energy fromthe chemical reaction:

carbon + hydrogen methane + waterdioxide

CO2 + 4H2 CH4 + 2H2O

It is their production of methane (CH4)that gives them their name.

As wel l as living in the decomposingsediments under water, somemethanogens live in the gut of animals.Other microbes help digest plant foodsby fermentation, producing CO2 & H2.The methanogens convert these gasesto methane... intestinal gas.


The methanogens are one type of theArchaea group. They cannot to lerateoxygen at all and live in habitats wherethere is none:

in the muddy sediments underswamps, lakes and the seas.

in the digestive systems of manyanimals, especially the ruminants,a group of grazing animals includingcattle.

Their original habitat of 3 billion yearsago was the anoxic oceans with anatmosphere containing the gases theyneed... carbon dioxide and hydrogen.

As the oxygen levels rose many diedout, but the oxygen never reached someplaces such as the mud and sedimentsunder water, where the processes ofdecomposition remove any oxygenimmediately, and produce carbondioxide and hydrogen from thefermentation of dead plant material andother organics which settle into themud.

The Methanogens

The Thermoacidophi lesThermoacidophiles are another group of theArchaea which are probably descended from

ancient types. They love hot, acid condit ions.

(Thermo- = heat, -acido- = acid, -phile = loving.

The thermoacidophiles live today in extreme

habitats which may be quite similar to the

habitats they li ved in bi llions of years ago. Some

are found in the boili ng, acidic waters of

volcanic hot springs, li ke these in New Zealand.

Others have

been

discovered in

the deep ocean,

around volcanic

vents where

they are the

basis of some

weird food

chains that do

NOT depend on photosynthesis.

Thermoacidophiles are autotrophs capable of

making their own food from simple inorganicchemicals like CO2 & H2O.

The energy needed to make food is not fromsunlight, as in photosynthesis, but from theenergy in certain naturally occurring inorganicchemicals... they are chemosynthetic .

The thermoacidophiles depend on hydrogensulfide (H2S) which is abundant in the volcanicsprings they live in. It is H2S which gives thecharacteristic rotten-egg smell of volcanicsprings. It is poisonous to most life-forms (notto mention the boiling temperatures and highlyacidic condit ions) but to these Archaea cells it i s

home-sweet-home, possibly just like thehabitats they inhabited 3 billion years ago on theyoung, volcanically-active Earth.

Some of the deep-sea chemosynthetic typeshave formed mutualistic relationships with gianttube worms, and are the basis of foodproduction in the totally dark ecosystemsthousands of metres deep. The chemosyntheticArchaea cells live inside the tube-worms body.The worm channels H2S from the volcanic ventsto the procaryotes which make food forthemselves and for the worms. An entirecommunity of crabs, starfish and mussels live

on this food supply.

PHOTOMICROGRAPHofMETHANOGENcells


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18

The Ice-Concentration Scenario

Some scientists have doubts that theorganic chemical soup of the oceanscould ever have been concentratedenough in Urey-Miller chemicals forenough chemicals to form microspheres

and eventually li ving cells.

Experiments show that as sea-waterfreezes, the dissolved chemicals can bepushed together into small zones ofvery high concentration.

Some scientists suggest that life beganin pools of water that periodically frozeand re-melted. Each freezing cyclecould have concentrated the chemicalsso that suitable microspheres couldform.

Perhaps life began in a place like this?Certainly, there are plenty of Archaea(and others) which can thrive in theseextreme conditions.


Other Possible Environments in Which Life BeganIt is generally assumed that the first living cells formed in the oceans of theprimitive Earth. However, the Archaea (including many types other than the

methanogens and thermoacidophiles) inhabit a huge range ofextreme environments on Earth today.

Could this mean that it was in one of these extreme environments that life firstbegan? Some scientists have suggested that this could be the case.

The Volcanic Vent Scenario

We believe that the primitive Earth of3-4 billion years ago was a lot hotterthan today, and that volcanic activitywas very widespread.

The presence of the thermoacidophilesin modern hot springs proves that lifecan thrive in such conditions, so maybethats where life actually began.

The Clay Sediments ScenarioSome scientists have pointed to theimpressive catalytic properties of clayminerals called zeolites, which can attractorganic molecules and cause chemicalreactions to occur, includingpolymerisation, an essential reaction to

make the large, complex molecules of life.

They suggest that perhaps the firstliving cells began in zeolite claysediments, where the necessaryreactions of life could get some helpfrom the clay itself. This might havehappened deep in the Earth, and it isinteresting to note that some Archaeatypes are found thriving (although insmall numbers) deep in the rocks of the

crust.


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19


Eucaryotic cells are those which have atrue a)............................... and otherb)............................-bound organelles.Cells lacking these features are calledc)..................................................... Thetechnology which allowed us todiscover this was thed)...................................... .......................

Other new technologies such ase)................................................... have

shown that not all procaryotes are thesame. One type, now called thef)..................................... have significantdif ferences such as g).............................

We think they may be descended fromsome extremely ancient cells fromabout h)................... billion years ago.

One type are calledi)...................................... because theyproduce methane from the gasesj)......................... and k).............................They live in habitats such as in thel)....................................... under waterand in the m).............................. of manyanimals. These organisms aren)................................................. whichmeans they live without oxygen, and infact would be o)........................................by it.

Another type of Archaea are thep)............................................... whichthrive in habitats such asq)..........................................and in thedeep ocean, around r)................................................................

These organisms are s).....................-synthetic. They make food from simpleinorganic chemicals, using energy fromt).................................... (chemical name)

which is common around volcanicvents. The deep-sea variety are vital totheir isolated ecosystems because theyu)...............................................................................................................

Because the Archaea are so ancient,and because they live in such extremev)..................................., it has beensuggested that perhaps life did not

begin in the w)........................................as generally assumed. Alternativeplaces for life to have started includex)............................... vents, in sedimentsof clays called y)................................... oreven in cold places where chemicalscould become z).......................................as the water froze.

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Worksheet 5 Procaryotic Life


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20


Multiple Choice

1.

A cel l like the one shown:

A. may have li ved when the Earthwas anoxic.

B. may have been the first type

to appear on Earth.

C. evolved from procaryotic

ancestors.

D. could be a member of the

Archaea.

2. The realization that the Archaea are very

different to other procaryotes has come mainly

from:

A. use of the electron microscope to study the

cells.

B. study of the extreme habitats in which they

live.

C. discovery of fossil cells f rom 3 billion years

ago.

D. study of their biochemical pathways and

DNA.

3.

You would be unlikely to discover

methanogen cells living in:

A. the in testines of a goat.

B. the soil in your garden.

C. the mud of a swamp.

D. the sediments under the sea floor.

4.

The group known as thermoacidophiles are

best described as:

A. chemosynthetic autotrophs.

B. autotrophic decomposers.

C. photosynthetic heterotrophs.

D. chemosynthetic eucaryotes.




5. ( 4 marks)Distinguish between procaryotic and

eucaryotic cells, naming examples of each.

6. ( 5 marks)

a) Identify the technology which has produced

evidence that the living procaryotes includetwo fundamentally different types of life.

b)

i) Identify a group of organisms belonging to

the Archaea.

ii) Describe the habitat of the group named in

part (i).

iii) Outline simi larities between the current

habitat of these organisms, and the Earth

environment of the past.

7. (3 marks)

It is generally assumed that life began in the

oceans of the early Earth. However, there have

been other suggestions.

Describe one possib le alternative environment

in which li fe may have originated. Give a

reason why this idea is proposed as a serious

hypothesis.



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21

The Need to ClassifyImagine a supermarket without any system for placing products on the shelves.

Baked-beans are under the light bulbs, beside the fresh tomatoes,the ice-cream and the washing detergent. This would be chaos!

Cladistic ClassificationIn recent times, the use of structural criteria is

being improved and extended using information

from new technologies such as the electron

microscope and DNA and biochemical studies.

DNA and pro tein sequencing is ab le to

determine the relatedness of species in an

evolutionary sense. A system based more on

the evolutionary pathways is called a Cladistic

Classification.

The advantage of a cladistic system is that the

groupings are truly family trees that put

organisms together in groups with their true

relatives.

More and more, as fossil discoveries and the

new technologies reveal more details about

evolutionary relationships, the traditional

Morphological classification is being adjusted

and altered to become more Cladistic. Examples

of these changes will be discussed later.

4. THE VARIETY OF LIFE & HOW WE CLASSIFY IT

MORPHOLOGICAL CLASSIFICATIONBIRDisDIFFERENT

Croc&LizardinSAME GROUP

Basedonbodystructure

Croc&BirdinSAME GROUP

CLADISTIC CLASSIFICATION

BasedonFossilsandDNAstudies,whichshowevolutionaryrelationships

LIZARDisDIFFERENT

The Criteria Used to Classify

Morphological Classification

Traditionally, biological classification

uses morphology ... the structure oforganisms bodies and cells to placeeach species into groups with otherswith similar structures. Using structuralcharacteristics has several advantages:

Usually, structural features stay the same

throughout an organisms life, unlike (say)

colour which could change from time to time.

Structural features are often obvious and

easily observed so that classification (at least

at a general level) is quick and easy once youknow the things to look for.

Structural features are often the result of

evolution, so this can automatically lead to the

placing of related species into the same

groups.

However, this doesnt always work.

Example: Based on structural features, the

snakes, lizards & crocodiles are classified

together as Reptiles , while the birds are aseparate group. See more details at right.

Taxonomy

The branch of Biology concerned withputting the living supermarket intoorder is called Taxonomy . Overseveral hundred years a system ofclassifying living things has developedin order to:

bring order to the study of millions of

living organisms. help communication, by agreeing on a unique

name for each species.

show the relationships between organisms,

or between groups, so that the evolutionary

pathways can be more easily interpreted.

Fossils and DNA evidence suggest that

crocodiles and birds are actually more closelyrelated than crocod iles are to snakes & lizards.


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22

The Classification HierarchyA hierarchy means an organisation invo lv ing levels. For example, an army has a

hierarchy of command where a corporal or sergeant commands a section ofsoldiers, a lieutentant commands a platoon of sections, a captain commands a

company of platoons, and so on, upwards. As you go upwards through the levels,you are including more and more soldiers in each higher grouping.

The Biological Hierarchy works the same way:

LevelorTaxon Example1:Human Example2:EasternGreyKangaroo DefiningCriteriaKINGDOM Animals Animals (Eucaryoticcells,nocellwall)PHYLUM Chordates Chordates (Animalswithanotochord)Sub-Phylum: Vertebrates Vertebrates (Chordateswithspinalchordenclosedinavertebral column)CLASS Mammals Mammals (warm-blooded,furry,femaleshavemilkglands)Sub-Class:Metatheria (Marsupials...pouchedmammals)ORDER Primates Diprotodonts (Herbivorousmarsupials)(mammalswithgraspinghands,binocularvision)

Sub-Order: Anthropoids(includeshumans,apes&monkeys)FAMILY Hominids Macropods(big-footmarsupials...includesallkangaroos(apes&humans) &wallabies)GENUS Homo Macropus (includesonlycertainlarge kangaroos)(humans,includingextinctancestors&relatives)SPECIES sapiens giganteus (EasternGreyKangaroo)(modernhumansonly)

At the top of the taxon hierarchy the groups are broad and general and contain many different

types. As you go down the hierarchy the groups become smaller until at the bottom you have

defined one specific organism... the species.

Noticethatextrataxonscanbeaddedbetweenthemainlevels,asneeded,byusingsub- groupsandsuper- groups.

You need to remember that the classification system is an arbitrary,human-made, artificial scheme trying to impose some order

on the complexity and amazing variety of l iving things.

As we learn more, we may change the ru les and adjust the system

to match our improving knowledge.

The Binomial System of Naming

To name any species you use its Genus and species names. So a human is Homo sapiens and the eastern grey kangaroo is Macropus giganteus .

Note: the Genus name must be written with a capital letter, but the species namemust be writ ten in lower case. The name is usually underlined and/or in italics.


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23


Getting Specific: What is a Species?At the top of the classi ficat ion system are the Kingdoms of life,

each containing many thousands of l ife forms.

At the bottom are the individual types, or species. A species refers to asingle type of living thing which reproduces its own kind, over generations.

One species either cannot, or normally does not, interbreed with another species.

Whats in a Name?

Each species has been given a scientific name which is used by all scientists.This ensures that there is no confusion about exactly which organism

is being studied or discussed, when scientists communicate.

The name of each species has 2 parts. We say it is binomial. (bi = 2, nom = name)

These 3 big cats are all closely related and, sure enough, their scientific namesall have the same surname.

Lions and tigers are closely related and

(in a zoo) sometimes inter-breed. Their

babies are called l igers or tigons .

However, in the

wild these

animals never

meet and neverinter-breed.

Therefore, they are considered

separate species.

Horses and donkeys can inter-breed too.Their baby is called a mule.

This would probablynever happen in nature,but more importantly,mules are not fertile andcannot have babies.

Horses and donkeys areconsidered separatespecies because they cannotinter-breed over generations.

Example:We might call this

animal the easterngrey kangaroo , but

scientifically it isMacropus giganteus

The name must

always be underlinedor in italic print.

This red kangaroo isMacropus rufus.

Notice how the firstpart of the name is

the same?Closely related

species have thesame first-name, just

like human family

members having thesame surname.

LeopardPanthera pantheris

LionPanthera leo

TigerPanthera tigris


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24

Classification KeysOne of the important aids to using theclassification system is the dichotomous key.Dichotomous means to divide in two, so itmeans the key always splits into 2 alternativepathways. At each decision point twoalternative criteria allow you to choose the

correct path to take, to eventually classify anorganism into a taxonomic g roup.

The criteria used need to be structural, inkeeping with the whole concept of biologicalclassification.

Dichotomous keys can be in diagram form like aflow chart, or contain a series of pairedstatements.

Paired Statements KeyAt each level is a pair of statements. Decide whichalternative (a or b) applies, then go to the next levelspecified, until the name of a group is given.

Level 1a) Has 2 pairs of wings .............................. level 2b) Has 1 pair of wings............................... Diptera

Level 2a) Front and hind wings have similar texture

and patterns. May be di fferent sizes.......level 3b) Front and hind wings quite different in

thickness and/or texture .........................level 5

Level 3a) Body has distinc t, narrow waist between

thorax and abdomen.................... Hymenopterab) No dist inct waist ............................... level 4

Level 4

a) Wings covered in patternedscales.......................................... Lepidoptera

b) Wings clear, withmany veins.................................... Odonata

Level 5a) Front wings totally hardened forming

protective cover for rear wings.No large mouth parts....................... Coleoptera

b) Front wings only partly hardened. Largemouthparts for grasping or piercingprey ............................................ Hemiptera

insectA insectB

insectC

insectD

insectEinsectF

START

One pair of wings

Diptera Two pairs of wings

Front and hind wingsquite different inthickness and/or

texture.

Wings covered inpatterned scales

Lepidoptera

No distinct waist Body has distinct,narrow waist betweenthorax and abdomen.

Hymenoptera

Front wings onlypartly hardened.

Large mouthparts forgrasping or piercing

prey.

Hemiptera

Front wings totallyhardened formingprotective cover for

rear wings.No large mouth parts

Coleoptera

Wings clear, withmany veins

Odonata

Front and hind wingshave similar texture

and patterns. Maybe different sizes.

Flow-Chart Diagram KeyChoose the correct path at each branch

CheckyouranswersinAnswerSection

Wing partlythickened

Patternedscales

TWO DIFFERENT TYPESOF DICHOTOMOUS KEY

(Both these keys give the same result. Try both)

Usethekeysbelowtoclassifytheseinsectsintogroups(Orders)


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25

The Five Kingdom SchemeIn the 20th century, the electronmicroscope revealed much morestructural detail about cells.

The ultracentrifuge allowed cell parts to beseparated for chemical analysis and the useof radio-isotopes for tracing biochemicalpathways showed up fundamentaldifferences between living things.


ANIMALSEucaryotic,multicellular,heterotrophic,nocellwall

PLANTSEucaryotic,multicellular,autotrophic,withcell-wall

MONERAProcaryoticcells

PROTISTSEucaryotic,single-celled.Includesplant-likeandanimal-liketypessuchassingle-celledalgae&protozoa

FUNGIEucaryotic,multicellular,heterotrophic,withcell-wall

LIVINGTHINGS

Changes to the Classif ication SystemThe biological classification system was developed over 200 years ago. Since thattime an enormous amount of new knowledge has been discovered which has, from

time to time, necessitated changes in the way we classi fy life.

Two Kingdom SchemeWhen the system was invented, all known living thingsseemed to be either plant or animal, so a Two

Kingdom scheme was used. The fungi appeared to be

rather weird plants, and later when bacteria were

discovered, it was decided that they were closer to

plants than animals.

LIVING THINGS

ANIMALS PLANTSIncluding Includesfungi&single-celled bacteria,aswellprotozoa assingle-celledalgaeBy the middle of the 20th century it was realised that

this scheme was really not satisfactory.

Scientists realised:

the enormous difference between

procaryotic and eucaryotic cells.

that the fungi are not just weirdplants... theyre a totally differenttype of organism.

that single-celled organisms arefundamentally different to multicellularlife, regardless of other characteristics.

This new understanding led to adoption

of a new scheme with Five Kingdoms.

More Changes in the Future?

The new technologies of DNA and protein

sequencing have already revealed thefundamental differences between the Archaea

and the other types of p rocaryotes.

Because of this, many scientists are already

using a Six Kingdom Scheme:

ARCHAEA ANIMALS PROTISTS

FUNGI

BACTERIA PLANTS

However, this method is not Cladisticenough for others... it doesnt showclearly enough the evolutionaryrelationships between the major groups.To do so, some scientists are beginningto use another taxon, called Domainwhich is higher than Kingdom .

Perhaps in the future we will use a newscheme something like that shown onthe next page...


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26

The Problems ofClassifying Extinct Species

Our biological classification scheme isused not just for todays living things,but for all the extinct species we knowfrom fossils.

There are problems classifying anorganism from its fossils alone:

modern classification relies on cellstructures at some taxons.In most fossi l impr ints the cell detailshave not been preserved.

the new DNA technologies andbiochemical analysis which are souseful for finding relatedness amongliving organisms, cannot be used onmost fossils because the organicchemicals have not been preserved infossilisation.

For a fossil such as that shown above, there is

no problem classifying it. An expert in fish

anatomy can probably decide on its groupings

all the way down to Genus, and even assign it a

species name.

For other fossils though, especially if they are

very small and very ancient, exact classifi cation

is impossible without DNA samples and well-

preserved cellular impr ints.

Clear cellular imprints are very rare, and DNA

samples do not survive fossil isation, except in a

few rare cases of animals being preserved by

freezing for a few thousand years, but not for

millions of years. The Jurassic Park scenario

of re-building dinosaurs from fossilised DNA

cannot really happen.


This is a life-size sketch of Hallucigenia , a

bizarre animal whose fossils are known from

the famous Burgess Shale deposit in

western Canada.

It lived over 500 million years ago. Although

vaguely related to insects, its 7-part body plan

defies modern classifi cation.

Until the exact details are agreedupon, we will continue to use the

5 (or 6) Kingdom Scheme

The Next Classification Scheme?

Three Domains

Domainsof Life

Sub-DomainsorSuper-Kingdoms

Kingdoms

LIVINGTHINGS

BACTERIA EUCARYOTESRCHAEA

ANIMALS

PROTISTSsingle-celled METACYTESmulticellular

PLANTS FUNGI

Classify

This!


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27

Worksheet 7Fill in the blank spaces.

The branch of Biology which dealswith classification is called

a).........................................

Some reasons for classifying are; to bring some b)..................................

to the chaos. to help c).............................................

by giving uniformity of names. to help the study of life by placingorganisms in groups which havesimilar d)................................ to show how organisms are

e).............................. in an evolutionarysense.

The criteria used to classifyorganisms are usually f )........................features, because these do notusually g)........................... during anorganisms life. Also, structures areusually the result of h)...........................Classification based on structural

features is called ai)..................................... classification,while a Cladistic scheme is basedon j).......................... relationships.Modern technologies, especiallyk).......................... and l)........................sequencing are useful in determining relatedness for Cladistic schemes.

The classification hierarchy has 7main levels, or m).............................

The most general level is Kingdom ,then come n)............................,o)..............................., Order ,p)........................., q).............................and finally r)............................ Extrataxons can be added between themain levels using prefixes(s)................ (below) and t)..................(above).

Classification

To name a species, you use theu).................... and v)...........................names. If 2 species have the same

genus name they must be veryw)............................................................

The definition of a species is basedon x)........................, so i f 2 organismsnaturally produce y)..................... &............................ offspring then theyare the same species.

Classification keys are alwaysz)................................ which means to

split in two.

The classification system is arbitraryand subject to changes. For example,originally a 2 kingdom system wasused because everything wasthought to be either aa)........................or ab)............................... In the 20thcentury, improved knowledgeresulted in a switch to a 5-kingdom

scheme: as well as plants andanimals there were the kingdoms ofac).........................., (which areprocaryotic), ad).............................(single-celled eucaryotes) andae)................................................

It is likely that this will change againin the future, since it is alreadyrecognized that the kingdomMonera should be split into

af)...................... and ag).......................

Dichotomous Key Exercise

Use the information given on page 25about the Five Kingdoms of livingthings to construct a dichotomouskey.WHENCOMPLETED,

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28


Multiple Choice1.

If you were to study an extensive fossil

deposit, and work your way down through the

layers, you might expect the fossils to show a

trend:

A. of increasing complexity.

B. of greater resemblance to modern life.

C. of decreasing diversity.

D. of younger and younger ages.

2.

Of the following taxons which one is the

most general grouping , or least specifi c?

A. Family

B. Phylum

C. Class

D. Genus

3.

A part icular animals sc ienti fi c name is Mus

hirsutus. Which of the following animals is

most c losely related ?

A. Mus rufus

B. Volex hirsutus

C. Hirsutus ascara

D. Hirsutus muscus

4.

In the 5-kingdom classification scheme, if anorganism was described as eucaryotic,

heterotrophic and multicellular , it could

belong to either of TWO groups:

A. plants or prot ists.

B. fungi or monera.

C. animals or monera

D. animals or fungi.

5.

If we were to adopt a SIX kingdom scheme

for classification, the existing kindom that

would have to be split up is the:

A. Protists.B. Fungi.

C. Monera.

D. Plants.

6. The problem with classify ing some extinct

organisms from their fossils is that:

A. we cannot be sure what habi tat they l ived in.

B. their cell structure & DNA are not preserved.

C. only hard parts, such as bones, shells, etc

are preserved.

D. their original body parts have been

petrified.

Longer Response QuestionsMark values given are suggestions on ly, and are


appropriate.

7. (3 marks)

Give 3 reasons to justify the existence of a

biological classification system.

8. (6 marks)

Compare and contrast a Morphological to a

Cladistic classification scheme and give an

advantage of each.

9. (2 marks)

The horse and the donkey both belong thegenus Equus. They can interbreed producing

healthy of fspring known as a mule. Mules are

sterile and cannot produce offspring.

Should the horse and donkey be considered as

members of the same, or separate, species?

Explain your answer.

10. (5 marks)

Use the following list of characteristics to

construct a dichotomous key for the majorplant groups.

Group True Veins? Seeds? SeedLeaves? Structure

Algae No No No n/a

Mosses Yes No No n/a(simple)

Ferns Yes Yes No n/a -

Conifers Yes Yes Yes cones

Angiosperms Yes Yes Yes flowers/frui ts

11. (5 marks)

Discuss, with reference to the 2-kingdom andthe 5-kingdom schemes, the impact of

changes in technology on biological

classification schemes.



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CONCEPT DIAGRAM ( Mind Map ) OF TOPICSome students find that memorising the OUTLINE of a topic

helps them learn and remember the concepts and important facts.

Practise on this blank version.

LIFEon

EARTH


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Answer Sect ion

Worksheet 1a),b)& c) any 3 of carbon dioxide, methane,

ammonia, hydrogen, nitrogen, water vapour.

d) oxygen e) volcanoes

f) lightning g) ultra-violet (UV)

h) organic i) Urey & Miller j) & k) sugars & amino acids (organic molecules)

l) outer space m) radiation

n) isotopes o) half

p) fossils q) related

Worksheet 21. B 2. D 3. A 4. A

5.

a) There would have been a lot of volcanic

activity, constantly adding volcanic gases to the

atmosphere. Violent storms would have been

near continuous, with a lot of ligh tning.. Withoutan ozone layer, there would have been high

levels of UV radiation from the Sun penetrating

to the surface.b) The atmosphere would have contained nooxygen at all, but been made up of gases suchas carbon dioxide, nitrogen, ammonia,methane, hydrogen and water vapour.

6.a) The experiment was designed to test thehypothesis that the conditions of the primitiveEarth could have naturally produced organicmolecules.b) Flasks were set up containing the simpleinorganic chemicals thought to be present onthe primitive Earth. The flasks were heated,irradiated with UV, and electric sparkssimulated lightning..After several weeks, the flask contents wereanalysed chemically.c) the flasks were found to contain organicchemicals including sugars and amino acids.d) Conclusion: the hypothesis is supported.Organic molecules can be produced fromsimple inorganic chemicals under theconditions thought to have existed on Earth 4

BYA.

7.a) Because radio-isotopes decay , theirradiation levels decline in a predictable way.This allows rocks & fossils to be accurately dated . Thus we have an accurate time scalefor the history of the Earth & its l ife.b) DNA sequencing. This can determinesimilarities & differences in the DNA of differentspecies and is a measure of how closely relatedthey are in an evolutionary sense.

Worksheet 3a) 4.6 BYA b) organic

c) hydrophobic d) microspheres

e) membrane

f) copy/duplicate/replicate

g) 3.5 to 4 BYA h) anaerobic

i) organic j) autotrophs

k) chemicals l) cyanobacteriam) stromatolites n) oxygen

o) iron p) banded ironstone

q) anoxic r) cellular respiration

s) ATP t) eucaryotic

u) Endosymbiosis v) digest

w)chloroplast x) DNA & ribosomes

y) sexual reproductionz) genetic

aa) speeded up ab) multicellular

ac) algae ad) sponges

ae) hard

Worksheet 41. C 2. B 3. D 4. C 5. A 6. C

7.1. Production of organic molecules, which arethe building blocks of living cells.2. Formation of microspheres from fatty lipidmolecules. These act like membranes...necessary to form the first cells.

8.a) The change from an environment withoutany free oxygen gas (anoxic), to one with free

oxygen (oxic).b) The cyanobacteria, carrying outphotosynthesis, released the oxygen.c) When the Earth became oxic, many of thepreviously dominant anaerobic organismsbecame extinct, and it opened up opportuniti esfor the evolution of cells us ing aerobic cellularrespiration.

9.a) Explains the evolution of the eucaryotic cellsfrom procaryotic ancestors.b) A larger procaryotic cell ate a smaller one,but failed to digest it . The small cell survived

inside the larger one, and evolved to becomean organelle such as mitochondr ion orchloroplast.c) Mitochondria and chloroplasts con tain theirown DNA and it is bacterial-type. This suggeststhese organelles were once separateprocaryotic cells.


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Worksheet 5a) nucleus b) membrane

c) procaryotic d) electron microscope

e) DNA sequencing / biochemical pathways /

protein sequencing

f) Archaea

g) RNA / cell walls / enzymes

h) 2 to 3 BYA i) methanogensj) & k) carbon d ioxide & hydrogen

l) mud / sediments m) gut / intestines

n) anaerobic o) poisoned / killed

p) thermoacidophiles q) volcanic hot springs

r) volcanic vents s) chemo-

t) hydrogen sulfide u) produce al l the food

v) habitats w) ocean

x) volcanic y) zeolites

z) concentrated

Worksheet 6

1. C 2. D 3. B 4. A

5.Eucaryotic cells have a t rue nucleus andother membrane-bound organelles. Examplesinclude all plants & animals.Procaryotic cells lack organelles, except non-membrane structures such as ribosomes. Theyhave a nuc lear region but no true nucleus.Examples are the bacteria, cyanobacteria andthe Archaea.

6.a) Evidence for this has come from study ofbiochemical pathways, protein, DNA & RNAsequencing, and chemical analysis of cell partssuch as cell walls. This has shown that the mainstream procaryotes (e.g. bacteria) aredistinc tly d ifferent to the Archaea.b) i) Methanogens

ii) Anaerobic muddy sediments underswamps, wetlands, oceans.

iii) Their current habitats may be similar tothose they occupied 3 BYA... i.e. anaerobic,lots of organic molecules available.

7.

Life may have originated in zeolite claysediments. Zeolites have a chemical ability toattract organic molecules and to catalyzechemical reactions such as polymerization,which is essential for life to get started.

Classification Keys Exercise page 24

Insect A = Coleoptera Insect B = Lepidoptera

C = Hymenoptera D = Diptera

E = Odonata F = Hemiptera

Worksheet 7

a) Taxonomy b)order / organization

c) communication d) similar character istics

e) related f) structural

g) change h) evolution

i) Morphological j) evolutionary

k) DNA l) proteinm) taxons n) Phylum

o) Class p) Family

q) Genus r) Species

s) sub- t) super-

u) Genus v) species

w) closely related / similar

x) reproduction y) healthy & fertile

z) dichotomous

aa) & ab) Plant or animal

ac) Monera ad) Protists

ae) Fungi

af) & ag) Bacteria & Archaea

Make a Dichotomous Key ExerciseThere are many correct ways to do this.

Format may be Paired Statements or

Flowchart Diagram . A Good key will use only

structural character ist ics and i t wil l be

unambiguous, and (most importantly) it WILL

WORK when used.

Sample Answer:

1. a) Cells are Procaryotic ..................... Monerab) Cells are Eucaryotic ....................... level 2

2. a) Organism is single-celled ............ Protis t

b) Multicellular .................................... level 3

3. a) Cells have chloroplasts

(photosynthetic)....... Plant

b) Cells lack chloroplasts ...................... level 4

4. a) Cells have a cell wall ...................... Fungi

b) No cell wall .................................... Animal



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Worksheet 81. C 2. B 3. A 4. D 5. C 6. B

7

Classification:

1. brings some order and organization to the

chaos of millions of diff erent species.

2. helps communication by giving everyspecies a unique name agreed by all.

3. places organisms into groups of similar

types, making it easier to understand

evolutionary relationships.

8.

Both classification schemes place organisms

into similar groups, and try to show the

relationships between them.

Morphological systems used cell & bodystructures as their criteria. This has the

advantage of being relatively easy to study and

observe.

Cladistic systems attempt to place organisms

into groups according to their evolutionary

relatedness . This has the advantage of

producing true family trees that help us

understand the history and evolution of life.

9.

They must be considered as separate species.The definition of a species is that 2 organisms

are the same species if they can interbreed and

produce healthy, fertile offspring. Since the

mule is sterile, the conditions of the definition

are NOT met, so horse & donkey are not the

same species.

10. (Many correct answers possible)

1. a) Do NOT have veins........................... level 2

b) Have veins ....................................... level 3

2. a) Have simple leaves ...................... Mosses

b) No leaves ....................................... A lgae

3. a) Produce seeds ................................ level 4

b) Do not produce seeds ...................... Ferns

4. a) Seeds produced in cones ............ Conifers

b) Seeds produced in

flowers/frui ts.......................... Angiosperms

11.

When the classif ication scheme was first

developed it seemed that all life was either

plant or animal, so a 2-kingdom system was

used.

Later technologies, especially the electron

microscope which revealed details of cell

structures led to the realisation that :

there are 2 totally di fferent cell types...

procaryotes & eucaryotes.

the Fungi are not plants, but a totally different

life form.

unicellular organisms are fundamentally

different to multicellular, regardless of being

plant-like or animal-like at the cell level.

The result was a change to the 5-kingdomsystem, recognising Animals, Plants, Fungi,

Protists & Monera as being fundamentally

different.


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